Abstract:Flume experiments were conducted with the combinations of five flow rates (20, 30, 40, 50, and 60 L/min) to clarify the effects of hydraulic characteristics on yellow soil detachment capacity (D_c) under different bulk densities (1.06, 1.15, 1.18, and 1.21 g/cm³) in karst area, and establish the prediction model for D_c. The results showed that both flow rate and bulk density significantly affected D_c. When the bulk density was 1.06 g/cm³, D_c increased with the flow rate as a power function, while D_c increased with the flow rate as a linear function under other higher bulk density conditions. Under the same flow condition, D_c decreased with the increase of bulk density, and the reduction trend was more obvious under the higher flow condition. Power functions could be used to describe the relationships between Dc and shear stress (τ), stream power (ω), unit stream power (P), and unit energy (E), respectively, while τ showed the best predictability (R²=0.96). The erodibility values (K_τ, K_ω, K_P, and K_E) and critical values (τ_C,ω_C, P_C, and E_C) corresponding to hydraulic parameters all presented decreased trend with the increasing bulk density, and these erodibility values were negatively linearly correlated with bulk density. The results will provide theoretical basis for understanding the mechanism of soil erosion in karst area and establishing soil erosion process models.

Abstract:Soil and water loss has become one of the main ecological environmental problems in China. The observation data of natural rainfall, runoff and sediment in the Jiangzi River minor watershed from 2012 to 2019 were used to explore the influence of rainfall types on slope sediment yield and runoff under different crop measures. Random forest algorithm was used to obtain the relationships among rainfall factors, runoff and sediment yield. The results showed that the changes of runoff and soil loss were consistent with the rainfall. The runoff and soil loss under sweet potato were larger, and tea gave the smallest. The rainfall could be classified into three types:Type A was rainfall with low frequency, long duration, heavy rainfall and higher rainfall intensity, Type B with high frequency, short duration, small rainfall and low rainfall intensity, and Type C with lower frequency, longer duration, moderate rainfall, high rainfall intensity. The degree of influence on runoff and sediment yield was type A>type C>type B. Precipitation had the highest degree of influence on runoff. The soil loss was affected by PI, PI₆₀, P and I₃₀, and I₆₀ had a low degree of impact on runoff and sediment production, less than 11%. The runoff depth of each crop measure had a significant and linear correlation with soil loss, and the growth rate of soil loss was sweet potato>mulberry>tea>chestnut>soybean>oil tea. These results provided important theoretical basis for the establishment of slope erosion prediction model, and were of important theoretical value and practical significance for the soil and water conservation work and the construction of ecological civilization in the western Dabie mountains area of Anhui Province.

Abstract:In order to reveal the mechanism of soil erosion process of engineering accumulation during spring thawing period, the accumulation of excavated river engineering in western Liaoning Province was taken as the research object, the erosion process of cinnamon soil engineering accumulation slope during spring thawing period was studied by indoor simulated water discharge scouring test. The results showed that:The runoff of each thawed slope increased with the increase of discharge scouring amount, and under the same discharge scouring amount, the runoff trend was unfreezing slope>thawed 2 h slope>thawed 4 h slope>control; the longer the thawing time, the more obvious the delay effect of slope on runoff and the more serious the slope erosion; under the same discharge scouring amount, the trend of the total sediment yield on the slope surface of the accumulation body was thawed 4 h slope>thawed 2 h slope>unfreezing slope>control. Compared with the control, the average sediment yield of slope affected by freezing and thawing increased by 7.90%~44.76%, respectively. Under different thawing time and water discharge conditions, the runoff, sediment yield, and water discharge of engineering accumulation slope linearly changed. With the increase of discharge scouring amount, runoff and sediment yield linearly increased. Compared with natural soil, engineering accumulation is more prone to soil erosion.

Abstract:To provide reasonable scientific basis and control reference for soil erosion conservation in Pakistan, soil erosion map was made, and the dominant factors of soil erosion was analyzed. Based on the Chinese Soil Loss Equation (CSLE), taking soil erosion sampling survey units and soil erosion factor datasets such as rainfall erosivity factor (R factor), soil erodibility factor (K factor), slope steepness and slope length factor (LS factor), biological measure factor (B factor), engineering-control practices factor (E factor), and tillage practices factor (T factor) as data sources, spatial interpolation and map algebra method were used to make soil erosion maps for water erosion area, the spatial interpolation result was then used as a reference to update the map algebra calculation result with histogram matching to obtain the Pakistan water erosion rate map. The standards for classification and gradation of soil erosion (SL 190—2007) proposed by the Ministry of Water Resources of the People's Republic of China was adopted for qualitative evaluation the wind erosion intensity in Pakistan. Meanwhile, classification decision tree was used to analyze the dominant influence factors of soil erosion. The results showed that the spatial interpolation method has good accuracy of spatial prediction while the map algebra method can express good local variation characteristics. The soil erosion map matched by histogram had the advantages of the two methods. Average value of soil water erosion rate was 972.9 t/(km²·a), and the grade of soil erosion was serious. The wind erosion area was dominated by severe and extremely strong wind erosion. Biological measures factor was the dominant influence factor for soil erosion in most areas, while the R factor and LS factor were the dominant influence factors in agricultural area and mountainous area respectively.

Abstract:Northwestern Sichuan and southern Gansu (NSSG) is located in the source areas of Yellow River and Yangtze River. Quantitative study of soil erosion in this area is of great significance for ecological security of large river source region and sustainable development of local economy. In this study, variously sourced data, combined with a variety of methods were used to quantitatively evaluate the temporal and spatial distribution characteristics and change rules of soil erosion in NSSG from 2000 to 2015 based on USLE. The results showed that:(1) R values representing rainfall erosivity ranged from 65 to 411 (MJ·mm)/(hm²·h·a), and the high values were mainly found in southeast part, and the spatial distribution of high values was consistent with the rainfall pattern. (2) Soil erodibility K ranged from 0.19 to 0.41 (t·hm²·h)/(hm²·MJ·mm), the high values sporadically distributed in space, which was mainly influenced by the physical and chemical properties of zonal soil. (3) The slope length and slope gradient factor LS ranged from 0 to 8.24, the high values were mainly distributed in high mountains of the middle and North parts of research area, while the low values were found more in the northeast and southwest regions with gentle terrain. (4) Factor C of vegetation cover management ranged from 0 to 1, the high values were concentrated in the northwest and southwest parts, where the vegetation cover was relatively low. (5) Based on USLE, the annual erosion amount of NSSG was 3.3×10⁸ t/a, which was generally characterized by mild erosion. (6) From 2000 to 2015, soil erosion in NSSG showed a weakening trend, which was related to the enhancement of vegetation activities under the background of warming.

Abstract:In order to explore the effects of land-use and climate change on the runoff and sediment of the area in Loess Plateau, the Lanhe River basin in the upper reaches of Fenhe River was selected as the study area, where the ecological restoration effect was very significant. Based on the annual precipitation data, the annual runoff data and the annual sediment data of the Lanhe River from 1955 to 2018, the hydrological trend and the abrupt change were studied by Mann-Kendall test, Sliding t-test, and YAMAMOTO Index method. The law of the runoff and sediment change was analyzed by flow and sediment duration curve method, and the contribution of land-use and climate change to the runoff and sediment variation was quantitatively researched by double accumulation curve method. The results indicated that:From 1955 to 2018, precipitation had insignificant increasing trend, while both runoff and sediment load had significant reduction trends, with average annual change rates of —0.65 mm and —38.95 t/km², respectively. Both of the runoff and sediment changed abruptly in 1983 and 1999 synchronously. Compared to the period 1 of base (1955-1982), the average annual runoff and sediment load in the period 2 of soil and water conservation (1983-1998) decreased by 29.07 mm and 5 917.88 t/km² respectively, and in the period 3 of Grain for Green project (1999-2018), the amount of runoff and sediment load decreased by 33.18 mm and 6 967.34 t/km² respectively. The runoff and sediment load were analyzed by the duration curves, it was found that both of the runoff and sediment load showed a decreasing trend no matter in flood period, mean-flow period or in drought period, and the decreasing degree of sediment load was much greater than the changing degree of runoff. The contribution rates of land-use change to runoff and sediment reduction in the period 2 of soil and water conservation were 83.21% and 83.52% respectively in the basin, and they were 117.88% and 103.48% respectively in the period 3 of Grain for Green project. It can be seen that the change of land-use was the dominant factor of the variation of runoff and sediment in different periods, while climate change had little effect in the basin. Under the background of global climate change, soil and water conservation measures based on vegetation restoration should be carried out by adjusting the land-use structure and optimizing the land use mode in the basin, which is the fundamental approach to soil erosion control and ecological protection on the Loess Plateau.

Abstract:In order to explore the water movement law of karst shallow fractured soil, the infiltration characteristics of fractured soil and the adaptability of infiltration model were explored through field investigation and single ring infiltration test. The results showed that:(1) The initial infiltration rate of fissured soil was 21.06~57.90 mm/min, and the stable infiltration rate reached 4.21~13.69 mm/min after 20~60 min infiltration time, and there was a significant decrease from the initial to the final stable infiltration stages (40.89%~89.08%). Compared with non karst areas, the infiltration rate of karst fissured soil was faster, and the infiltration characteristics of fissured soil were in medium degree variation (coefficient of variation was 0.52~0.67). (2) Little significant correlations were observed between the infiltration characteristics and soil properties (P<0.05). The infiltration capacity of fissured soil had no significant correlation with soil bulk density, capillary porosity and root system. Affected by factors such as fissure rock soil interface, it was significantly different from that in non karst areas. The infiltration capacity of different land use types in karst fissure was grassland>farmland> arbor>shrub. (3) The results showed that Horton model was better than Philip model and Kastiakov model, and could better simulate and predict the infiltration capacity and infiltration process of karst shallow fissured soil. These results could provide new research ideas and scientific theoretical basis for the study of slope water movement and underground leakage in karst area.

Abstract:In order to reveal effects of freeze-thaw cycles on shear strength of brown soil, the undisturbed brown soil from 5 cm and 25 cm depths (H₅ and H₂₅, respectively) in Shenyang area were collected. The effects of freeze-thaw cycles and soil water contents on soil shear strength were analyzed through indoor freeze-thaw simulation and direct shear tests in laboratory. The results showed that:(1) The higher soil water content, the stronger damage effect of the first freeze-thaw cycle. After the first freeze-thaw cycle, soil cohesion of H₅ and H₂₅ samples with 25% soil water content decreased by 50.00% and 25.87%, respectively; and the soil cohesion with 35% soil water content decreased by 75.61% and 50.77%, respectively. After 15 freeze-thaw cycles, the cohesion of H₅ and H₂₅ samples with 10% soil water content increased by 74.36% and 60.08%, respectively; the cohesion of H₅ and H₂₅ samples with 35% soil water content increased by 14.63% and 26.15%, respectively. However, the mechanisms of cohesion increasing under two different soil water contents were different. (2) The internal friction angle of H₅ and H₂₅ samples with 15%, 20%, and 25% soil water contents fluctuated during the multiple freeze-thaw cycles, indicating that the effects of freeze-thaw cycles on the internal friction angle were complicated and uncertain in the soil water contents. The internal friction of H₅ and H₂₅ samples with the soil water content of 35% were hardly affected by freeze-thaw cycles and varied between (18.57°±0.88°) and (12.86°±1.14°), respectively. (3) The average shear strength mainly decreased exponentially with the increasing of soil water contents. Clay content might play important role in average shear strength at different water contents. When the soil water contents were below 25%, the average shear strength of H₂₅ soil samples were higher than that of H₅; while soil water contents were above 25%, the average shear strength of H₂₅ were lower.

Abstract:In order to study the difference in hydraulic characteristics of different soil layers in benggang, soil-water characteristic curves of different layer soils were measured by using the high-speed centrifuge method, and a suitable soil-water characteristic curve (SWCC) fitting model was screened. Soil equivalent pore size distribution, soil specific water capacity C(θ), unsaturated conductivity K(θ), and soil water diffusivity D(θ) were calculated and then analyzed based on the selected SWCC model and soil hydraulic statistical models. Results showed that soils shifted from clay to sand gradually with soil depth increased. Among the frequently-used SWCC models, the Fredlund & Xing model was the optimal one for benggang. The model fitting parameters θ_s, α, and n decreased when soil texture changed from sand to clay. As the depth of the soil layer increased, the water holding capacity of the soil decreased. The values of C(θ), K(θ), and D(θ) were influenced by both soil texture and water content (or suction). In the low suction stage, these three indices changed gently with soil suction, and the values of C(θ) and K(θ) of sandy layer soils were larger than those in other layers; while the performance of D(θ) was the opposite, which were mainly controlled by macropores. In the high suction stage, all those indices of sandy layer soils decreased rapidly and were lower than other layers; the difference of K(θ) and D(θ) values between different layer soils become bigger and bigger with the suction increased, which was due to the clay adsorption and soil capillarity of micropores.

Abstract:In order to explore the effects of different green manure cover on the runoff and nutrient loss of the citrus orchard on the purple soil slope farmland, four treatments (Lolium perenne L., Vicia villosa Roth var, Orychophragmus violaceus, and clean tillage control) were set up to quantitatively monitor the runoff and nitrogen and phosphorus loss of different treatments under natural rainfall conditions. The results showed that compared with the clean tillage control, green manure cover significantly reduced the surface runoff by 8.7%~27.0%, total nitrogen loss by 30.1%~50.6%, and total phosphorus loss by 32.4%~62.9%.However, the effects of green manure cover on runoff and nutrient control were different among different varieties, and the trend of overall performance was Lolium perenne L.>Vicia villosa Roth var. >Orychophragmus violaceus. Compared with clean tillage control, Lolium perenne L. treatment reduced the total loss of total nitrogen, soluble nitrogen, nitrate nitrogen, and ammonium nitrogen in runoff by 50.6%, 47.0%, 49.5%, and 48.1% respectively; total phosphorus, soluble phosphorus, and total loss of phosphate was reduced by 62.9%, 62.6%, and 62.6% respectively. In addition, the effect of green manure cover on different nutrient forms were also different, and the loss of soluble nitrogen and particulate phosphorus in the runoff were the largest, accounting for 59.6%~67.0% and 68.6%~71.8% of total nitrogen and total phosphorus, respectively. In summary, green manure cover cultivation can effectively reduce the runoff and nitrogen and phosphorus loss of citrus orchards on purple soil sloping farmland. Among them, Lolium perenne L. and Vicia villosa Roth var. cover were the best. Taken together, our results provide reference for water and soil conservation and non-point source pollution prevention and control in citrus orchards on purple soil slope farmland.

Abstract:Soil moisture is an essential variable in hydrology and ecology in karst region. In order to reveal the change rules of soil moisture during rainfall event, we monitored and analyzed the relationship between rainfall and soil moisture contents at 20 cm, 40 cm, 80 cm and 100 cm depth below surface in the grassland, cropland and bare land in Guizhou Province. Soil moisture was monitored by the ECH2O monitoring system and the EM50 data collector. The rainfall amount was collected by HOBO automatic weather station, and its measurement accuracy was 0.2 mm. The results showed that:(1) Vegetation cover, initial soil moisture content and rainfall density showed great influence on rainfall replenishment and redistribution of soil moisture in the soil profile. (2) To a certain extent, soil moisture affected by rainfall replenishment was not uniform in soil profile, which showed an up-down-up trend with the increase of soil depth, and 100 cm layer had the biggest rainfall replenishment compared with other layers. (3) The period in which soil moisture affected by rainfall could be divided into 3 stages:lag stage, rise stage and decline stage; as vegetation cover increased and rainfall density enhanced, the lag stage ended early, and the rise stage and decline stage started early. (4) The hysteresis effect in the lag stage enhanced with the increasing soil depth but receded with the increasing vegetation coverage. These results could provide a reference and theoretical basis for rational utilization and allocation of water resources and soil and water conservation.

Abstract:According to the water breakthrough curve and Poisssulle equation, the radius range, quantity and distribution of soil macropores covered by different land use types (secondary forest, citrus orchard, corn land, cedar forest, uncultivated land and eucalyptus forest) were quantitatively studied in granite area in southeast Guangxi. The results showed that:(1) There were differences in soil moisture breakthrough rates among different land use types. Soil water out flow rate reached a stable state in a short time, and only the stable outflow rate of citrus orchard changed greatly. (2) The soil macropore radius of different land use types was 0.4~2.4 mm, mainly distributed between 0.4~1.2 mm, the mean value was 0.85 mm, and there were a lot of small radius voidage <1.2 mm. (3) With the increase of soil depth and the decrease of pore radius, the number of soil macropores generally decreased, with fewer pores with large radius and more pores with small radius. (4) Under different land use types, soil macropores only accounted for 0.36%~6.38% of the soil volume, but their average volume of soil macropores was significantly correlated with stable outflow rate, average radius of soil macropores and saturated water conductivity, which determined the variations of stable outflow rate and saturated water conductivity by 79.92% and 36.45% respectively.

Abstract:Compound soil erosion caused by various external forces is the main erosion characteristic of sloping farmland in Chinese Mollisol region. However, there are few reports on the quantitative study of interaction between freeze-thaw, wind and water-hydraulic on compound soil erosion. Thus, indoor freeze-thaw simulation, wind tunnel test and indoor simulated rainfall experiments were conducted to analyze previous freeze-thaw, wind and water agents impacts on hillslope soil erosion in Chinese Mollisol region. A series of experiments were designed, including test without previous freeze-thaw action and only wind erosion(Ⅰ), previous freeze-thaw action first and late on wind erosion test(Ⅱ), only water erosion (without previous freeze-thaw action and without wind erosion test)(Ⅲ), previous freeze-thaw test first, then followed by wind erosion test, and late on water erosion test(Ⅳ), so as to distinguish the contribution of previous freeze-thaw action to wind erosion, and the contribution of previous freeze-thaw and wind superposition action to slope water erosion. The results showed that the previous freeze-thaw action significantly increased the wind erosion amount on the slope (P<0.01). At the wind speed of 9 m/s and 15 m/s, the previous freeze-thaw action increased the amount of wind erosion by 1.02 and 1.44 times, respectively. It also significantly increased the total amount of wind erosion sediment transport at different heights from the soil surface (P<0.01). Under the two wind speeds, the previous freeze-thaw action increased the wind erosion sediment transport rate by 1.71 and 1.04 times, respectively. And the contribution rate of previous freeze-thaw action to wind erosion was 100.0% and 140.0% respectively at the two test wind speeds. The previous freeze-thaw and wind superposition action obviously increased the amount of water erosion on the slope. Compared with the treatment without previous freeze-thaw and wind superposition action, the amount of water erosion on the slope of previous freeze-thaw and wind superposition action increased by 11.9% and 20.6% respectively under 3° and 7° degree. Under the two gradients, the contribution rate of previous freeze-thaw and wind superposition action to slope water erosion was 11.9% and 20.6% respectively. Previous freeze-thaw action weakened the soil erosion resistance, after previous freeze-thaw action, the soil bulk density decreased 3.42%, less than 0.25 mm of dry aggregate increased by 14.1%, greater than 1.0 mm of dry aggregate decreased by 15.1%; Meanwhile, the early stage of the wind erosion produced a dent in the earth's surface and stripe micro topography, further increase the slope rainfall erosion and runoff erosion ability, as a result,the previous freeze-thaw action and wind erosion increased the severity of sloping soil erosion.

Abstract:In order to find the mechanism of soil erosion control and crop yield increase in ridge-furrow rainwater harvesting production in semi-arid regions of China, a modified SCS-CN model was used to estimate the runoff for ridges with 3 widths (30, 45, and 60 cm) and 3 different materials (soil crust, biodegradable film, and plastic film) based on the rainfall and runoff from 2012 to 2016. The parameters of CN, λ, and α in the modified SCS-CN model were calibrated according to the rainfall and runoff from 2012 to 2013, and the applicability of the modified SCS-CN model to rainwater harvesting ridges was evaluated using rainfall and runoff from 2014 to 2016. The results indicated that for ridges mulched with soil crust, biodegradable film, and plastic film, CN in the modified SCS-CN model ranged from 82.0 to 82.9, from 97.9 to 98.8, and from 98.3 to 99.9, respectively; The parameter of λ ranged from 0.045 to 0.071, from 0.251 to 0.327, and from 0.189 to 0.213, respectively; The parameter of α ranged from 2.35 to 2.89, from 4.21 to 4.82, and from 3.32 to 3.99, respectively; Mean relative error ranged from 1.36% to 3.41%, from 1.21% to 3.42%, and from 2.48% to 5.42%, respectively; the Nash-Sutcliffe efficiency ranged from 0.97 to 0.98, from 0.97 to 0.98, and from 0.96 to 0.98, respectively. Effects of classification of daily rainfall were not obvious on the parameters of CN, λ, and α in the modified SCS-CN model. The difference of CN, λ, and α between 3 different materials was greatly larger than that between 3 ridge widths. The Nash-Sutcliffe efficiency was higher than 0.95 and the relative error was lower than 10%. The results indicated that the modified SCS-CN model was applicable to runoff estimation for rainwater harvesting ridges and the model performance was acceptable. These findings may be helpful in controlling soil erosion and increasing rainwater use efficiency.

Abstract:In the face of potential environmental problems caused by large-scale fertilization of apple orchards, a typical watershed in the gully region area of the Loess Plateau was used as the research area, apple orchards of different tree ages and geomorphic types were selected, and soil moisture changes and the distribution characteristics of nitrogen in the soil profile of orchards of different tree ages were analyzed, which provide a theoretical basis for scientific fertilization and the promotion of sustainable agricultural development. In the Wangdonggou watershed of Changwu County, Shaanxi, apple orchards with different planting years (14, 18, 23, 28, and 32) and geomorphic types (table, ridge, and slope) were selected, 4 cm diameter sampler were used to collect 0—400 cm soil samples from 15 orchard plots at a distance of 1m from each fruit tree, and 12 orchard plots with typical deep section soil samples of 0—600 cm soil were used determine soil moisture, nitrate and ammonium nitrogen content. The results showed that with the increase of orchard planting years, the soil water content and water storage capacity of 0—600 cm decreased significantly, especially at 300—600 cm.The water storage capacity of 14, 23, and 32-year-old orchards was significantly different (P<0.05), and the water storage performance was 14-year-old orchard>23-year-old orchard>32-year-old orchard. The content of ammonium nitrogen in soil mineral nitrogen was low, and basically had no effect on the distribution characteristics of mineral nitrogen. Nitrate nitrogen accounted for a high proportion of mineral nitrogen, and directly affected the distribution of mineral nitrogen in the soil. The nitrate nitrogen content of 0—600 cm among different ages of orchard varied greatly, and the accumulation of nitrate nitrogen in deep soil was common. The nitrate nitrogen accumulation in 18, 23, and 32-year-old sloping orchards 0—200 cm soil accounted for 50%, 41%, and 38% of the 0—400 cm total accumulation amount, showing that the accumulation of soil nitrate nitrogen gradually deepened with the growth of the orchard tree age. The accumulation of nitrate nitrogen in soil increased with the age of the orchard trees. The accumulation of nitrate nitrogen in soil was 32 years old>23 years old>18 years old in the slope land orchards, 28 years old>23 years old in ridge land orchards, and 23 years old>18 years old>14 years old in table orchards. The deep desiccation of orchard soil and accumulation of nitrate nitrogen in the gully area of the Loess Plateau were obvious, and became more serious with the increase of the orchard age.

Abstract:The distribution of soil particle size is one of the most important physical indicators for studying its desertification. By studying the soil particle size characteristics of sand in different azimuths in the sand barrier grid, the micro-topography erosion status was analyzed to determine the indication effect of the particle size characteristics on the landform shape, and to provide technical support for selecting suitable sand barrier types. Samples were taken from different areas within the sand barrier of plant fiber mesh and geotextile bag distributed in the flowing dunes on the western edge of Tengger Desert to measure the sand particle size with the mastersizer range of laser diffraction particle size analyzers. The parameters, such as the composition and curve of soil particle distribution in different areas between and within the barrier, were compared and analyzed. The results showed that the sand interception in geotextile bag sand barrier is more vital than that in fiber mesh sand barrier, and the former is better than the latter in sand-blocking. The content of checkerboard sand in the western position was 18%~23% higher than that in the other places, indicating weak wind erosion or substantial accumulation in the west region. The sand content in the middle and south directions of the square in geotextile bag sand barrier was 8%~26% less than that in the other orientations, and the east and south directions were wind erosion areas. The sand content in the middle of the geotextile bag sand barrier gradually increased along the main wind direction, indicating that the sand barrier's sand deposition increases, while the change in the fiber mesh sand barrier square was not apparent. In the fiber mesh sand barrier area, the sand particle composition decreased gradually along the main wind direction(P<0.05), indicating that the sand barrier has a weak sand-blocking effect. The sand components of geotextile bag sand barrier were concentrated in the central and southern part of the sand barrier, and the sorting of the center was worse than that of the north and south part of the sand barrier, which indicates that the sand components deposit more in the downwind area of the leading wind direction. The content of fine sand and medium sand on the west side of the fiber mesh sand barrier on both sides of the middle was more than 24% higher than that on the east side of the geotextile bag sand barrier, while the content of coarse sand and very coarse sand were nearly 43% lower.

Abstract:The hydrogen and oxygen isotopic compositions (δD and δ¹⁸O) of stem water and its potential sources (rain water, soil water, and groundwater) were measured monthly from June to November, 2018 in a Salix psammophila forest (18~20 years) in Gechougou watershed of Mu Us Sandy Land. The dynamic changes and controls of root water source were studied by the multiple linear mixed model (IsoSource). Results showed that the variation range of δD were -82.41‰~-52.91‰, -144.81‰~-6.60‰, -96.94‰~-42.65‰, and -86.42 ‰~-71.82‰ for stem water, rain water, soil water, and groundwater, respectively. The variation range of δ¹⁸O were -10.77‰~-7.29‰, -18.86‰~-2.07‰, -12.85‰~-0.79‰, and -10.86‰~-9.74‰, respectively, during the monitored period (June-November). Rainfall amount and soil water content in the rainy season (July-September) were 24.80~90.10 mm and 0.95%~1.84% higher than that in the dry season (June, October, and November). However, the groundwater level during June to September were 2~7 cm lower than that in October and November. In June, S. psammophila mainly used deep soil water (>200 cm) (33.70%) and groundwater (26.20%). From July to September, the root water source mainly came from shallow soil water (<200 cm) (50.70%~54.00%). Compared with the rainy season (July-September), the contribution of shallow soil water (<200 cm) to root water source remarkably increased by 35.20%~40.00% in October and November due to the low air temperature, rainfall amount, and weak life activity of S. psammophila. There was a significant reduction in the use of groundwater in October and November (<5.00%). Therefore, S. psammophilais adaptable to the seasonal drought and is suitable for desertification control in the Mu Us Sandy Land. The root water source of S. psammophila changed with seasonal variations of rainfall amount, soil profile water content, and groundwater level.

Abstract:In order to construct a long-term series of soil moisture in the Yangtze River Delta, which is frequently used for the validation of various satellite products and agricultural production, the linear regression and BP neural network models were constructed respectively to describe the quantitative relationship between soil moisture and meteorological factors. Based on the paired data of in-situ soil moisture and meteorological observation in the Yangtze River Delta including the city of Shanghai and the provinces of Jiangsu, Anhui and Zhejiang, four effective principal components were obtained by principal component analysis as the input of the established models, and the accuracies of these models were evaluated systematically. The results showed that, although both based on all paired data from soil moisture and meteorological observation, the prediction accuracy of the single BP neural network model (the R² were all above 0.64, and RMSE and MAE were less than 0.043 m³/m³ and 3.4% separately in the sets of the training, validation and testing data) was better than the single linear regression model (R², RMSE and MAE were 0.34, 0.046 m³/m³ and 3.67% respectively). However, accuracies of both these models were worse than the BP neural network models based on each paired soil moisture and meteorological observation data, with the average of R²above 0.75, and RMSE and MAE less than 0.039 m³/m³ and 3% respectively. By constructing the BP neural network models based on each paired soil moisture and meteorological observation data, a more accurate and stable soil moisture fitting result was obtained.

Abstract:In order to provide a biomechanical reference for the selection of excellent tree species for soil fixation and erosion resistance,and to reveal the mechanical characteristics of plant roots for continuous soil fixation and erosion resistance,three typical native plant roots of 3-year-old Caragana korshinskii, Hippophae rhamnoides and Medicago sativa in the complex erosion area of wind and water in the central and Western Inner Mongolia were taken as the research objects. Under the same site conditions,using the self-made portable root radial and axial mechanical properties test bench and HG100 digital display push-pull meter, 70% ultimate bending force of single root was damaged in the test diameter range of 0.5~4 mm. After 3 months of self-healing, the changes of anti-fracture forces and anti-fracture strength of three kinds of plant roots after damaged callus were studied, and the differences among different plant species were compared. The results showed that the average comparison of anti-fracture strength of three kinds of plants after restoration were Caragana korshinskii (15.504 Mpa)>Hippophae rhamnodes (12.342 Mpa)>Medicago sativa (6.584 Mpa), indicating that the bending resistance of Caragana korshinskii was better than that of Hippophae rhamnodes and Medicago sativa, and Hippophae rhamnodes was better than Medicago sativa. However, in numerical value, there was no significant difference in single root anti-fracture strength between Medicago sativa parallel control group and after callus. For the average anti-fracture forces, Caragana korshinskii, Hippophae rhamnodes and Medicago sativa decreased by 64%, 28% and 27% respectively. For the average anti-fracture strength, Caragana korshinskii, Hippophae rhamnodes and Medicago sativa decreased by 40%, 22% and 12% respectively. These results showed that the biological characteristics of different plant species were different, and the recovery ability of erosion resistance was different after damaged callus.

Abstract:In order to study the effects of bamboo charcoal and carbon-based slow release fertilizer on soil nitrogen loss and bacterial community structure in Moso bamboo forest soil, the concentrations of NH₄⁺—N and NO₃^-—N in leaching water were measured by soil column experiment in laboratory, and the diversity and composition of bacterial community were analyzed. The results showed that compared with the control, the cumulative losses of NH₄⁺—N and NO₃^-—N in the leachate of soil columns with the addition of carbon-based slow-release fertilizer could be reduced by 12.5% and 13.6% (P<0.05), respectively. In addition, the addition of bamboo charcoal could significantly reduce the cumulative losses of NH₄⁺—N, but the effect on NO₃^-—N was not significant. The addition of carbon based slow-release fertilizer could increase the relative abundance of Nitrospira, Nitrospora and Nitrobacter, and increase the relative abundance of Burkholderia, Cupriavidus and Bradyrhizobium which is the dominant denitrification bacteria (abundance > 0.1%) in the lower leaching soil. The leaching effect of carbon-based slow release fertilizer on soil NH₄⁺—N and NO₃^-—N may be closely related to soil nitrogen cycling microorganisms.

Abstract:Based on the land use information of four stages (1995, 2000, 2010, and 2018) in Haixi Mongolian and Tibetan Autonomous Prefecture, the intensity and stability of land use change from 1995—2018 were investigated using the analysis method of land use change intensity from three aspects of interval level, category level, and transfer level, and the change process and pattern of land use intensity at different levels were thoroughly analyzed. The results showed that:(1) At the interval level, the land use intensity of Haixi Mongolian and Tibetan Autonomous Prefecture changed slowly from 1995 to 2010, while the intensity changed rapidly during the period of 2010—2018. (2) At the category level, the cultivated land as well as the urban and rural, residential and construction land were the most active categories between 1995 and 2010. During the period 1995—2000, the change of the water area was relatively stable. The change of the water area, woodland, and grassland were relatively active from 2000 to 2010. In contrast, in 2010—2018, the change of the water area and the woodland were relatively active, while the change of the unused land was relatively stable. (3) At the transfer level, the increased grassland area mainly came from unused land, water area, and woodland during the period of 1995—2018. The transformation process of cultivated land as well as urban and rural, residential and construction land to grassland presented a stable avoidable system conversion pattern. In addition, the reduced cultivated land was mainly converted to urban and rural, residential and construction land. And the transformation of cultivated land to urban and rural, residential and construction land showed a stable tendentious system pattern.

Abstract:In order to research soil water characteristics of water terrace in southwestern China, the Hani terraces were taken for example, 4 kinds of land use types(woodland, grassland, dry land, and paddy field) in the Hani terraced fields core (Quanfuzhuang watershed) were selected, the main soil physical and chemical index, soil water characteristic curve, water holding capacity, and moisture availability were measured in 0—10 cm, 10—20 cm, 20—40 cm, 40—60 cm, 60—80 cm, and 80—100 cm soil layers. The results showed that:(1) The soil bulk density varied from 0.61~1.41 g/cm³, and showed significant difference between 0—40 cm and 40—100 cm, and the content of soil organic matter was 1.17%~9.65%. The changes of soil total porosity and non capillary porosity were consistent with bulk density, and the soil capillary porosity was woodland>dryland and paddy field>grassland. (2) The soil texture was mainly silt loam, with the highest silt content (52.74%~82.55%), followed by sand content (14.44%~45.31%), and clay content (0~3.68%). (3) Under the same soil water suction, the soil water characteristic curve of each soil layer in woodland was relatively higher, and the soil water holding capacity was the strongest, followed by dry land and paddy field, and the lowest in grassland. Soil available water content was paddy field>woodland>dry land>grassland. (4) Soil particle composition and capillary porosity were the key factors affecting soil water characteristics in the Hani terrace. Soil water holding capacity was significantly positively correlated with particle composition, and soil available water content was significantly positively correlated with soil capillary porosity. Generally speaking, woodland in Hani terrace ecosystem has a good capacity of storing and discharging water, while terrace can retain water and redistribute water. Both of them play a very significant role in maintaining the sustainable development of the ecosystem. The results provide a reference for further research on soil moisture and irrigation management of terrace in southwest China.

Abstract:In order to establish an efficient total nitrogen fertilizer application technology, and provide technical basis for simplified cultivation maize in arid area, a four-year field experiment was conducted to investigate the effects of controlled-release nitrogen fertilizer (CRNF) application on yield, water and fertilizer use efficiency, dry matter accumulation and transfer of maize in Rain fed highland of China Loess Plateau from 2016—2019. Results showed that the CRNF could increase SPAD value of leaves and dry matter accumulation, as well the output and contribution rates of stem sheath and leaf dry matter at the grain filling stage. Regardless of what kind of rainfall years, the application of CRNF could optimize the maize yield composition. The grain number and grain weight increased by 4.0% and 4.9%, respectively, and maize yield significantly increased by 9.7% on average in four years. Under the significant increase in yield and no significant increase in water consumption, CRNF improved the water use efficiency of maize in arid area, with an increase of 4.0% on average in four years. Besides, CRNF significantly increased the partial factor productivity of nitrogen fertilizer and agronomic nitrogen use efficiency, with the increases of 9.5% and 24.7% on average in four years respectively, both decreased significantly with the increases of nitrogen application. Compared to the conventional nitrogen fertilization, the application of release-controlled urea (CU) could have a positive effect on maize aboveground growth, and increase yield, water and fertilizer use efficiencies of maize.

Abstract:In order to determine the effects of land-use types and dam-triggered flooding intensity on soil active organic carbon fractions and identify the main influencing factor in the riparian zone of the Three Gorges Reservoir, soils from different flood intensities and land-use types were collected as study objects and were used to quantitatively analyze soil active organic carbon fractions, while the relationships between soil active organic carbon fractions and soil physical and chemical properties were analyzed. The results showed that the content of soil active organic carbon decreased with the increase of flooding intensity. The land-use types, flooding intensity, and their interaction explained by 22.1%, 13.7%, and 9.3% respectively, on soil organic carbon variation. Soil microbial biomass carbon was mainly affected by land-use types and the interaction between land-use types and flooding intensity, and their variation partitioning for the effects on soil microbial biomass carbon were 3.9% and 0.6%, respectively. Soil dissolved organic carbon and soil particulate organic carbon were mainly affected by the dam-triggered flooding intensity, and the explanations for their variation partitioning were 65.1% and 5.5%, respectively. Multiple factor analysis showed that significant correlations between the MBC content of soil active organic carbon and soil electrical. However, Water flooding intensity might affect TN and C:N in soil properties, and further affect the distribution of DOC. Soil POC content was significantly positively correlated with SOC content, and POC can be used as an indicator to measure the flooding intensity changes of organic carbon pool in the riparian zone of the Three Gorges Reservoir.

Abstract:A long-term localization experiment of peanut-sweet potato rotation system was studied to investigate the effect of different types of organic fertilizer on sweet potato yield, soil microbial abundance, and enzyme activities. This study aimed to provide the basis for selecting appropriate organic fertilizers to increase crop yield and improve soil biological characteristics. Five fertilization treatments were selected:(1) CK, no fertilization control; (2) NPK, chemical fertilizers treatment; (3) NPK + SR, chemical fertilizers + straw return treatment; (4) NPK + M, chemical fertilizers + manure treatment; (5) NPK + P, chemical fertilizers + pig manure treatment. The results showed that the yield and aboveground biomass of sweet potato increased significantly under NPK, NPK+SR, NPK+M, and NPK+P treatments compared with CK treatment, while NPK+P treatment had an optimal effect among NPK, NPK+SR, NPK+M, and NPK+P treatments. In comparison with CK treatment, the abundances of bacteria, fungi, diazotrophic, and microorganism associated with soil organic phosphorus transformation decreased significantly under NPK treatment, while NPK+SR, NPK+M, and NPK+P treatment had mitigatory suppression effect on abundance of these microorganisms mentioned above in different degree. The geometric mean of the assayed enzyme activities (GMea) could be used to evaluate the overall activity of soil enzymes to some extent. The GMea decreased significantly under NPK, NPK+SR, and NPK+M treatments compared with CK treatment, whereas NPK+P treatment improved the geometric mean of the assayed enzyme activities. For single enzyme activity, NPK+P treatment significantly reduced soil urease activity compared with CK treatment (P<0.05), however, NPK+P treatment significantly increased acid phosphatase, alkaline phosphatase, and catalase activities, respectively. In addition, the results of principal component and pearson correlation analysis suggested that soil nutrients and soil organic carbon content were significantly positively correlated with yield and aboveground biomass of sweet potato. Soil pH was the main factor that drives the change of soil microbial abundance and soil enzyme activities. Therefore, long-term combined with organic and inorganic fertilization has achieved a good efficiency on increasing sweet potato yield and improving soil biological properties through increasing soil nutrients, organic carbon content as well as influencing soil pH. Among all the fertilization treatments as we selected, chemical fertilizers plus pig manure had the best effect on enriching the soil fertility and improving crop production.

Abstract:To comparatively explore the effects of the application of biochar and plant growth-promoting rhizobacteria (Bacillus subtilis and Bacillus mucilaginosus, PGPR) on the soil aggregate content, soil aggregate stability, and soil moisture of the silty loam soil of the mountain apple orchard on the loess hilly region, we adopted field research and set four treatments:65 t/hm² biochar (BC), 20 t/hm² B. subtilis (PGBS), 20 t/hm² B. mucilaginosus (PGBM), and control (CK). The aggregate content of different soil particle size were examined by wet sieving method, and the mean weight diameter (MWD), geometric mean diameter (GMD), and fractal dimension (D) of water-stable aggregates were calculated. The results showed that compared with CK, the soil organic carbon (SOC) increased by 18.04%~206.91%, and the total nitrogen (TN) content increased by 6.11%~66.56% in BC, PGBS, and PGBM treatment. The content of > 0.25 mm aggregates in the 0—60 cm soil layer increased significantly in treatment BC, PGBS, and PGBM. Compared with CK, the fractal dimension D was decreased and the MWD and GMD were increased in different treatments, of which the order of magnitude was PGBS>PGBM>BC and this indicated that the application of amendments can increase the stability of soil aggregates. The saturated hydraulic conductivity and soil water content of the 0—60 cm soil in each treatment were increased. The application of PGPR and biochar could significantly increase the content of soil organic carbon and total nitrogen, enhance the stability of soil structure, and increase soil saturated hydraulic conductivity and water content. The improvements of soil organic carbon and total nitrogen content by biochar treatment was better than that by plant growth-promoting rhizobacteria, while the plant growth-promoting rhizobacteria treatment improved the stability of soil structure better.

Abstract:Soils derived from granite (G), quaternary red earth (Q), and sand shale (S) with forestland (FL), paddy field (PF), and upland (UL) were collected in Guangdong lateritic red soil region. The content of ferric oxide, organic carbon and its fractions in soil aggregate were analyzed, and the differences of soil aggregate stability and the factors affecting the aggregate stability were explored. The results showed that:(1) Aggregates larger than 0.25 mm in soil dominated under three land use types with three parent materials; 2~5 mm aggregates was the highest (58.51%) in forestland soil derived from granite; 0.25~2 mm aggregates was the highest in paddy field and upland soils derived from granite (62.93%) and quaternary laterite (59.21%). Geometric mean diameter (GMD) and mean weight diameter (MWD) of soil aggregates were highest in forestland with sand shale parent materials. (2) The soil organic carbon (SOC) and component content in forest land soil were mainly distributed in 2~5 mm aggregates derived from three parent materials, and that in paddy and upland soils were mainly distributed in <0.053 mm aggregates. The ferric oxide form content in forestland soil were mainly distributed in <0.053 and 0.25~2 mm aggregates derived from three parent materials, and that in paddy and upland soils were mainly distributed in <0.053 mm aggregate. (3) Correlation analysis and principal component analysis showed that the MWD and GMD had significant correlations with HAC, HAC/FAC, Fe_fr, and Fe_co. Forestland soil aggregates derived from sand shale parent materials had the best cementing ability among different land use types and parent materials. The results showed that the influence of parent materials and utilization modes on the stability of aggregates was significant, mainly due to the differences of HAC, HAC/FAC, Fe_fr, and Fe_co. At the same time, forestland soil aggregates with sand shale parent materials had higher structural stability.

Abstract:The soil of 0—20 and 20—40 cm layers under different vegetations along an elevation gradient of Helan Mountains were investigated. We analyzed the variation characteristics of aggregate content of different particle sizes and aggregate stability with the increasing elevation, and explored the correlation between soil physicochemical properties and aggregate stability.The results showed that 0.25~0.053 mm aggregates were the main aggregates in 0—20 cm soil layer. With the increases in elevation, the contents of water-stable macroaggregates (>0.25 mm) increased, and the contents of <0.053 mm aggregates decreased, indicating that the soil aggregates changed from small particle size to large aggregates with the increasing elevation.In the 20—40 cm soil layer, the contents of water-stable macroaggregates reached the highest at mid-elevation (2 139 m), which was 65.73%. The mean weight diameter (MWD) and geometric mean diameter (GMD) at both 0—20 and 20—40 cm soil layers increased first and then decreased with the increasing elevation, with the peak value at 2 139 m.The MWD and GMD of soil aggregates in different elevation gradients were positively correlated with soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), silt and sand content, and negatively correlated with clay content and pH. These results suggestted that the overall stability of soil aggregates along the elevations of Helan Mountains were ranked as medium elevations>high altitude>low altitude. Higher content of macroaggregates and soil nutrients contributed to the stability of aggregates.

Abstract:The aim of this study was to quantitative analyze the effect of influence factors on particulate organic carbon in soil water-stable aggregates (POC_agg) with different vegetation recovery patterns in degraded red soil area. It could provide theoretical basis for ecosystem reconstruction and soil quality improvement in degraded red soil area. The vegetation restoration and reconstruction base in Taihe County, Jiangxi Province was selected to explore the POC_agg variation, establish the correlation of POC_agg and other physicochemical properties. The research object included six vegetation restoration patterns which were Pinus massoniana Lamb. pure forest (PM), Pinus elliottii pure forest (PE), Schima superba Gardn. et Champ. pure forest (SS), Pinus massoniana replanting Schima superba (RMS), Pinuse lliottii replanting Schima superba (RES) and virgin mixed forest of Pinus elliottii replanting Schima superba (MES). The results showed that:(1) The degraded soil was mainly of water-stable macro-aggregate (>0.25 mm, accounting for 87%). The contents of macro-aggregates in SS and RMS were the lowest. POC_agg in the surface soil (0—10 cm) was most significantly affected by the recovery patterns (P<0.01), which was the highest (14.44 g/kg) in topsoil of PE. (2) The soil physical and chemical properties showed significant differences due to the recovery patterns, among which the contents of organic matter (SOM), total nitrogen (TN) and total phosphorus (TP) were the highest in the topsoil of RES, SS and PE, respectively. (3) The aggregate composition in artificial coniferous pure forest had the greatest influence on POC_agg. The grey correlation analysis showed that aggregate composition, SOM and TN were the important factors influencing POC_agg (P<0.01), and the correlation increased significantly in deeper soil layer (P<0.01). Path analysis showed that the direct and indirect effects of each factor on POC in micro-aggregates (<0.25 mm) were significant. TN in <0.053 mm aggregates had the greatest effects on POC_agg. SS could significantly improve soil structure and fertility, and PE had higher retention capacity for soil nutrients, especially POC_agg. Combined with the practice of ecological restoration in degraded red soil area, it should improve soil properties better by planting PE as a pioneer and then replanting SS in the tending process.

Abstract:The objective of this study was to explore the effect of amendments on soil organic carbon in reclaimed soil. A series of micro field experiments were set to study the effect of peat and humic acid on particulate organic carbon (POC) and mineral-bound organic carbon (MOC) of soil and water-stable aggregates in the soil, which has been reclaimed for seven years in Xiangyuan, Shanxi province. The results showed that peat and humic acid increased the content of water-stable macroaggregates (>0.25 mm) in reclaimed soil. After 6 months, the content of water-stable macroaggregates was decreased and the content of water-stable microaggregates (<0.25 mm) was increased, the change of aggregates with >2 mm and <0.25 mm aggregates were obvious. Compared with the two amendments, the changes of soil macroaggregate and microaggregate in humic acid treatment were greater than those in peat. Peat and humic acid increased the contents of POC and MOC of soil and all level water-stable aggregates in reclaimed soil. When the application ratio was the same, the increases of POC and MOC in soil with humic acid were greater. After applying peat for 6 months and 1 year, the POC contents were 2.14~8.89 g/kg and 1.53~5.00 g/kg, and after applying humic acid for 6 months and 1 year, the POC contents were 8.07~20.12 g/kg and 5.63~19.36 g/kg. After applying peat for 6 months and 1 year, the MOC contents were 4.84~10.51 g/kg and 5.41~8.08 g/kg, and after applying humic acid for 6 months and 1 year, the MOC contents were 9.10~35.34 g/kg and 5.91~30.00 g/kg. However, after 6 months, the contents of POC and MOC were decreased. Peat and humic acid reduced the stability of soil organic carbon, it's not beneficial for the storage of organic carbon.

Abstract:The distribution and mechanism of soil aggregates in the source area of the Hanjiang river and Jialing River were studied by experimental and data analysis of soil aggregates and physic-chemical properties. The results showed that:(1) The content of aggregates of >0.25 mm (R_0.25), mean weight diameter (MWD) and geometric mean diameter (GMD) of aggregates in the source area of Hanjiang River decreased from 83.73%, 2.17 and 1.11 of surface layer to 59.18%, 0.40 and 0.26 of parent material layer, respectively, while those of Jialing River decreased from 69.72%, 1.03 and 0.46 of surface layer to 56.55%, 0.52 and 0.27 of parent material layer. While the fractal dimension (D) increased with the depth deepening, and the D of the former increased from 2.46 of surface layer to 2.53 of parent material layer, and those of the latter increased from 2.50 of surface layer to 2.57 of parent material layer, indicating that the stability of soil aggregates decreased with the increases of depth. The >2 mm and 1~2 mm aggregates had important contribution to the stability of soil. (2) Organic matter, iron and aluminum oxides and silt in particle composition were important factors to promote the formation of soil aggregates and maintain their stability, while SiO₂, K₂O, clay, sand and calcium carbonate had the opposite effects on aggregate stability in different soil environments. In other words, the first three factors were unfavorable to the stability of aggregates in LJH profile, but are beneficial to maintain their stability in YJS profile. The last two factors promoted the formation of aggregates in LJH profile, but destroyed the stability of YJS profile. It had a dispersion effect on aggregates after Na₂O dissolved by water. (3) In the source area of Hanjiang River, the stability of aggregates in surface layer was stronger than that in Jialing River source area, and the main factors were silt, organic matter and iron aluminum oxide. The soil mass of leaching layer was dense and weak in permeability, which was unfavorable for the formation of aggregates, and the stability was weaker than the latter. The stability of aggregates of the parent material layer in both places was poor. Besides, the stability difference of soil in the source area of Hanjiang River in different genetic layers was greater than that in the Jialing River.

Abstract:A three-year (2016—2018) field trial was conducted at the Changchun Comprehensive Experiment Station of the Northeast Institute of Geography and Agroecology, Chinese Academy of Science, which is located in Changchun city, Jilin province, China. The purpose of this study was to investigate the effects of biochar (BR), straw (SR) and combination of biochar and straw (BS) on physicochemical properties and dissolved organic matter (DOM) characteristics of black soil. The results showed that the BR, SR and BS treatments significantly increased the maize yield and biomass, mean weight diameter of soil aggregates, and leucine amino peptidase activity compared with the control (CK). In addition, compared with the CK treatment, the BR treatment significantly reduced the humification index (HIX) by 10.0% and significantly increased the contents of KMnO₄-oxidizable carbon and available phosphorus by 35.6% and 51.3%, respectively. Meanwhile, compared with the CK treatment, the SR treatment significantly increased the maximum fluorescence intensity of emission wavelengths of 440~470 nm, when excitation wavelength was 355 nm (Fn (355)), HIX, the ratio of the absorbance at 254 nm to the dissolved organic carbon concentration (SUVA₂₅₄) and total nitrogen/total phosphorus by 43.6%, 4.1%, 45.5% and 18.8%, respectively. Moreover, the BS treatment significantly increased soil pH, organic carbon/total phosphorus, available potassium contents and the ratio of absorbance at 250 nm to absorbance at 365 nm (E2/E3) compared with the CK treatment. In general, biochar application could reduce the humification degree and complexity of DOM and improve the content of soil labile organic carbon, whereas straw return could enhance the humification degree and complexity of DOM.

Abstract:To better understand the mechanism of soil organic carbon (SOC) sequestration in the reclaimed coal-mining subsiding region, we investigated the response of the structure of reclaimed soil and maize quality. Top soil samples (0—20 cm) and maize grain were collected from different treatments of a 1-year reclaimed field, and the wet sieving method was used to analyze the changes of soil organic carbon and total nitrogen (TN) contents within water-stable aggregates and silt and clay fractions, and grain analyzer was used to analyze protein, starch and fat contents in maize grain. The experiment was set up with four treatments:no fertilizer (CK), chemical fertilizer (NPK), organic fertilizer (M) and combined application of organic and inorganic fertilizer (MNPK).The results showed that compared with CK, NPK treatment significantly increased TN content, maize grain yield, starch and fat content by 11.23%, 98.53%, 1.16% and 12.71% respectively. The M treatment significantly increased SOC, TN, the organic carbon contents, grain yield, protein, starch and fat contents in >2 mm and 0.25~2 mm aggregates by 44.77%, 13.23%, 52.73%, 60.22%, 255.15%, 23.28%, 1.67% and 12.71%, respectively. The MNPK treatment significantly increased SOC, TN, SOC and TN contents in aggregates of various particle sizes and powder clay components (except for total nitrogen content in 0.25~2 mm aggregates), maize grain yield, protein, starch and fat contents. The increase was 46.21%, 29.08%, 39.23% (>2 mm-C), 49.07% (0.25~2 mm-C), 110.41% (0.053~0.25 mm-C), 40.35% (<0.053 mm-C)), 22.48% (>2 mm—N), 43.29% (0.053~0.25 mm—N), 33.33% (<0.053 mm—N), 211.37%, 35.34%, 0.48% and 25.18%, respectively. This study shows that when the nutrient input is the same, the combined application of organic and inorganic fertilizers (MNPK) is beneficial to the physical protection of organic carbon by reclaimed soil aggregates in the coal mining subsidence area, increasing SOC accumulation, improving soil fertility, and increasing crop yields and quality.

Abstract:We selected four adjacent plant communities with almost the same habitat conditions in Changsha County, Hunan Province, China. The four vegetation communities were composed of Loropetalum chinense-Vaccinium bracteatum-Rhododendron simsii scrub-grass-land (LVR), L. chinense-Cunninghamia lanceolata-Quercus fabri shrubbery (LCQ), Pinus massoniana-Lithocarpus glaber-L. chinense coniferous-broad leaved mixed forest (PLL), L. glaber-Cleyera japonica-Cyclobalanopsis glauca evergreen broad-leaved forest (LAG) to represent the secondary forest successional sequence in this region. Fixed sample plots were set up, and soil samples (0-40 cm) were collected and divided into four layers (0-10, 10-20, 20-30 and 30-40 cm). The contents and density of soil soluble organic nitrogen (SON), ammonium nitrogen (NH₄⁺—N) and nitrate nitrogen (NO₃^-—N) were determined, and the correlations between the contents of SON, NH₄⁺—N and NO₃^-—N and soil clay percentage, total nitrogen (TN), organic carbon (SOC) and microbial biomass were analyzed. The results showed that the contents of SON and NH₄⁺—N in each soil layer increased with the vegetation restoration. Compared with LVR, contents of SON in 0-40 cm soil layers in LAG, PLL and LCQ increased respectively by 225.78%, 121.22% and 54.73%, while contents of NH₄⁺—N increased respectively by 22.10%, 14.74%, and 7.80%. The contents of NO₃^-—N in each soil layer decreased first and then increased with the vegetation restoration. The NO₃^-—N contents in each soil layer of LAG were the highest, while LCQ was the lowest. The densities of SON and NH₄⁺—N in the 0-40 cm soil layer were 143.82~528.12 kg/hm² and 55.73~65.57 kg/hm² respectively. Compared with LVR, the densities of SON in LAG, PLL and LCQ increased by 267.20%, 98.40%, and 86.30%, while NH₄⁺—N increased by 17.70%, 7.90%, and 11.60%, respectively. The densities of NO₃^-—N in 0-40 cm soil layer was 22.91~25.87 kg/hm². Compared with LVR, LAG increased by 13.16%. The growth rates of SON and NH₄⁺—N densities between different stages showed the characteristics of fast-slowly-fast, while that of NO₃^-—N showed the characteristics of slow-slowly-fast. The effects of soil physicochemical properties and microbial biomass on SON and NH₄⁺—N were greater than that of NO₃^-—N. In conclusion, the vegetation restoration was conducive to the accumulation of soil N, improved the contents and densities of soil soluble nitrogen components and increased soil available N.

Abstract:Drying and rewetting cycles caused by rainfall and irrigation influence the availability of soil nutrient. In order to estimate the effects of drying-rewetting intensity on nutrient availability, three moisture treatments (rewetting to 60%,45% and 30% WHC) were designed in this study compared with a constantly moist control (CM, 60% WHC during the whole incubation period). The pH of DW1 (rewetting to 60% WHC) was 0.25~0.45 lower than other treatments while the differences among other treatments were not significant. After incubation, the DOC in CM decreased by 20.01%, while decreased by 37.04%~41.36% in drying-rewetting treatments, and there were no significant differences among different intensities. The ammonium nitrogen decreased by 18.19%~42.02% in the drying-rewetting treatments, but the reduction came down with the increasing intensity. The nitrate nitrogen increased sharply in each treatment but the increase came down with the increasing intensity. The ammonium nitrogen and nitrate nitrogen in DW2 (rewetting to 45% WHC) were consistent with CM. Available P and available K had little change after the incubation, but available P in DW2 was lower than other treatments as well as available K in DW3 (rewetting to 30% WHC). Drying-rewetting cycles led to a reduction of DOC and ammonium nitrogen and an increase of nitrate nitrogen but had little effect on pH, available P and available K. Following the growth of drying-rewetting intensity, soil pH and ammonium nitrogen gradually increased, while nitrate nitrogen and available K decreased.

Abstract:This study aimed to study how phosphorus availability changes during soil reclamation with organic fertilizer and at what level of phosphorus application can different organic fertilizer make crops achieve maximum productivity and enriching the soil resonable. For these reasons, a two-year experiment was conducted at the coal mining collapse test base (Piancheng Village, Xiaoyi city, Shanxi Province), with setting four fertilization types (chicken manure, pig manure, cow manure and fertilizer) and four phosphorus levels of 0, 25, 50 and 100 kg/hm² (pure phosphorus). The results showed that:(1) Different fertilization treatments could significantly increase the yield of corn grain yield. With the increase of phosphorus application, the corn grain yield increased first and then remained unchanged. Through constructing the two-year phosphorus fertilizer effect equation, it was found that the optimal phosphorus application ranges of chemical fertilizer, chicken manure, pig manure and cow manure treatment were 67.54~83.02, 24.91~38.65, 26.10~29.26 and 50.33~58.38 kg/hm², it can be seen that the optimal phosphous application of three organic fertilizer is less than chemical fertilizer treatment. (2) The phosphorus uptake and apparent use efficiency of phosphate fertilizer of maize showed that chicken manure ≥ pig manure>cow manure. The phosphorus uptake of maize increased first and then decreased with the increase of the phosphorus application levels, and the recovery rate of phosphate fertilizer decreased. (3) After continuous fertilization for two years, the depth of soil available P influenced by different fertilization treatments on the reclaimed soil was different. The content of Olsen—P in the 0—60 cm soil layer was significantly increased by the chemical treatment at the dosages of 50 and 100 kg/hm² phosphorus. However, the content of Olsen—P in 0—40 cm soil layer was significantly increased by chicken manure treatment at the dosages of 50 kg/hm² phosphorus, the content of Olsen—P in 0—60 cm soil layer was significantly increased by chicken manure treatment the dosages of 100 kg/hm² phosphorus. The pig manure treatment at the dosages of 50 and 100 kg/hm² phosphorus only significantly increased the content of Olsen—P in the 0—40 cm soil layer, and cow manure treatment only increased the content of Olsen—P in the surface layer. In a word, both the effects of different organic fertilizers on crop growth and soil Olsen—P content showed chicken manure ≥ pig manure>cow manure. In addition, the different amounts of phosphorus was recommended to the newly reclaimed soil for different organic fertilizers, among which chicken manure and pig manure were least, followed by cow manure.

Abstract:The poor soil fertility, lower nitrogen fertilizer retention and total fertilizer application before sowing, are the key factors which result in the nitrogen imbalance between soil supplying and crop requirement, causing the wheat presenility and the limited soil water productivity potential on the semiarid rain-fed loess plateau. A field experiment was conducted in 2016 and 2017 on the rain-fed central Gansu province, to understand the effects of different treatments on the wheat dry matter accumulation, soil available nitrogen changing dynamics and yield formation. The three treatments were:(1) Whole field mulched by soil-plastic (PMS), (2) PMS with organic fertilizer application, and (3) without soil-plastic mulching and organic fertilizer application (CK), the chemical nitrogen (N), potassium (P) and phosphate (K) were applied before sowing totally in all treatments and with same amount. The results showed that the dry matter of PMO averagely increased by 11.93% in the whole growth period, further increased the dry matter accumulation rate in jointing-heading and filling-harvesting stages, as compared with PMS. Correspondingly, the max growth rate and average growth rate of dry matter increased by 11.53% and 11.42%, but the rapid growth stage did not significantly differ between PMO and PMS. The soil organic matter (SOM) content in 0—30 cm profile of PMO increased by 42.79% and 43.73% compared with PMS and CK, respectively. The soil available nitrogen (SAN) content in 0—50 cm profile correspondingly increased by 110.67% and 42.80%. The decrease extent of soil nitrogen accumulation in 0—50 cm profile from sowing to harvesting stage of PMO decreased by 111.15% but increased the SAN down-transporting, as compared with PMS. Compared with PMS, PMO optimized the grain yield component factors, significantly increased grain yield and biomass. However, it decreased the nitrogen fertilizer partial productivity and increased the SAN accumulation at harvesting stage. Consequently, the chemical fertilizer with organic fertilizer increased wheat biomass, dry matter accumulation rate and relieved nitrogen limitation in post-flowering stage, resulting in the higher grain yield. However, the SAN accumulation risk also occurred, which should be regulated by decreasing fertilizer application amount.

Abstract:In this study, a long-term saline water irrigation experiment was carried out on wheat-maize farmland since 2006, and studied the change characteristics of soil salinity (EC_e), water-stable aggregates particle size distribution and their stability index under the condition of continuous saline water irrigation with different salinity in the 13th and14th year (in 2018 and 2019). Five salinity levels of irrigation water were tested:2 (T1), 4 (T2), 6 (T3), and 8 (T4), and fresh groundwater (1 g/L) was used as control treatment (CK). The salinity level from T1 to T4 was formed by mixing sea salt into the freshwater. The results showed that saline water irrigation increased soil EC_e. Compared with CK, the EC_e in the treatment of 2 g/L showed no significant difference, but a significant increase when the salinity of irrigation water beyond 4 g/L. Saline water irrigation affected the particle size distribution of soil water-stable aggregates. When the salinity of irrigation water was less than 4 g/L, the macroaggregate (>0.25 mm) was the dominant particle size of soil water stable aggregates in 0—40 cm soil layer. With the increase of irrigation water salinity, the mass fraction of macroaggregate decreased, while the mass fraction of microaggregate (0.053~0.25 mm) and silt + clay aggregate (<0.053 mm) increased. When the salinity of irrigation water reached 6 g/L, silt + clay aggregate was dominant in 0—40 cm soil layer. With the increase of irrigation water salinity, the average weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregates decreased, while the fractal dimension (D) increased, which meant that the stability of soil water stable aggregates decreased. Under this irrigation system, saline water with salinity greater than or equal to 4 g/L significantly increased soil salinity and destroyed soil aggregate structure, which should be used cautiously in the irrigation of wheat-maize crop system.

Abstract:In order to clarify the effects of freeze-thaw cycling (FTC) on the nitrogen (N) bioavailability in the cultivated layer in the mollisol, incubation method was explored to detect the vertical distribution of soil available nitrogen (AN) in the profile of different freezing temperatures, soil bulk density (BD), soil moisture, and FTC frequency. The results showed that after FTCs, soil AN contents decreased with the increasing soil depths. The lower the freezing temperature was, the greater the fluctuation of AN with increasing depth was. The lower the freezing temperature was, the lower the peak value and mean value of AN in soil column were. The mean value of AN in the entire soil column (0—30 cm) at -15℃ was 9.3%~44.6% lower than that at -10℃; the increase of BD resulted in the AN value decreased and the AN/TN value increased. Compared with BD of 1.0 g/cm³, AN of BD 1.1 g/cm³ was reduced by 13.0%~18.6% in 0—30 cm soil depth, while AN/TN of BD 1.1 g/cm³ significantly increased by 0.6~4.7 times. When the soil water contents increased, the AN increased in surface layer (0—8 cm) and decreased in low soil layer (20—30 cm)under low BD treatment (1.0 g/cm³); while the AN increased in the layer of (4-8 cm) and decreased both of 0—4 cm and 20—30 cm soil depth under high BD treatment (1.1 g/cm³). AN was negatively correlated with pH, while positively correlated to the soil moisture, TDS, conductivity, and freezing temperature. Both the FTC happened or not influenced vertical distribution of AN, followed by temperature and FTC frequency (p<0.05). This study aimed to provide the theoretical basis and technical support for soil N management during FTCs in mollisol areas, e.g. improving soil fertility and reducing N loss.

Abstract:This study aims to investigate the effects of acidified zeolite (SF) on nitrogen leaching and nitrogen use efficiency of grain under the condition of urea reduction. The adsorption properties of acidified zeolite for NH₄⁺—N and NO₃^-—N, and the effects of acidified zeolite on nitrogen leaching and nitrogen utilization under different nitrogen application gradients were studied by isothermal adsorption test, soil column leaching, and maize pot experiment. Three nitrogen reduction gradients were set up, i.e., farmers' conventional fertilization (CN), nitrogen reduction by 15% (CN1), nitrogen reduction by 30% (CN2), and 0.2% acidified zeolite was added to the three nitrogen reduction gradients (CN+SF, CN1+SF, and CN2+SF), respectively. The results showed that the maximum adsorption capacities of NH₄⁺—N and NO₃^-—N by acidified zeolite were 25.44 mg/g and 31.59 mg/g, respectively. The adsorption process could be well fitted by Langmuir model. When nitrogen was reduced by 15% and 30%, the cumulative leaching loss of NH₄⁺—N with acidified zeolite was 7.10% and 8.76% lower than that of CN1 and CN2, respectively. Acidified zeolite could effectively adsorb NO₃^-—N only when nitrogen was reduced by 30%. The cumulative leaching loss of NO₃^-—N was 15.90% lower than that of CN2. The acidified zeolite could effectively improve soil nitrogen content and nitrogen use efficiency of maize grain. Compared with urea application (CN, CN1, and CN2), adding acidified zeolite (CN+SF, CN1+SF, CN2+SF) increased nitrogen use efficiency of grain by 10.37%, 20.79%, and 47.14%, respectively. Under the condition of reducing the use of urea, acidified zeolite can effectively reduce soil nitrogen leaching, improve nitrogen use efficiency of maize, and has potential agronomic value.

Abstract:In order to explore the effects of groundwater depth and nitrogen reduction on summer maize nitrogen uptake, utilization and yield, based on large lysimeters, the effects of groundwater depth and nitrogen application rate on summer maize nitrogen utilization efficiency, plant nitrogen accumulation, yield and its component factors were studied. Among them, the groundwater depth was set at 3 levels of 2 m (G1), 3 m (G2) and 4 m (G3); the nitrogen application amount was set at 2 levels of conventional nitrogen application (300 kg/hm², N2), nitrogen reduction treatment by 20% (240 kg/hm², N1), and no groundwater depth with no nitrogen application (G0N0) as the control group, where a total of 7 treatments were used. The results showed that:(1) Under N1 treatment, the yield of summer maize decreased with the increases of groundwater, the nitrogen harvest index at G1 was significantly higher than that at G2 and G3, with an increase of 5.71% and 7.22% respectively. (2) The nitrogen uptakes of stem and leaf treated with N2 at G1 were significantly higher than those at G2~G3, with the increases of 19.52%~50.31%. But the nitrogen uptake, nitrogen harvest index and grain yield at G1 were significantly lower than those at G2~G3, with the decreases of 17.28%~29.28%. (3) At the depth of G1, the yield, agronomic efficiency, physiological utilization rate, grain N uptake utilization rate of N fertilizer and N harvest index under N1 were significantly higher than those under N2, with the increases between 22.18% and 115.35%. Under the condition of 2 m groundwater depth, the nitrogen application rate of 240 kg/hm² could be beneficial to improve the yield increasing effect of nitrogen fertilizer, increase the efficiency of nitrogen conversion into yield and dry matter after nitrogen application, enhance the transfer rate of nitrogen to grain and maintain yield not to decrease. So, it was feasible to reduce nitrogen by 20% under this groundwater depth. The results could provide theoretical reference for nitrogen fertilizer control in shallow groundwater area.

Abstract:The objective of this study was to explore the effects of salt and nitrogen on the dynamic accumulation, transport and use efficiency of nitrogen in cotton. Taking cotton Xinluzhong 68 as material, afield plot experiment was carried out under threesoil salt contents of S1 (2.5~3 g/kg), S2 (5~6 g/kg) and S3 (8~9 g/kg), respectively, also with three nitrogen levels of N1 (105 kg/hm²), N2 (210 kg/hm²) and N3 (315 kg/hm²), respectively. The results showed that the biomass of vegetative organs (root, stem and leaf) under S1N3 was the largest, while the biomass of cotton boll under S1N2 was the largest, and the biomass of cotton boll was N3>N2>N1 under S3 condition. In S1 and S2, nitrogen accumulation in stem was N2>N3>N1. In S2 and S3, N3>N2>N1. Nitrogen accumulation of cotton boll was S1>S2>S3, N3>N2>N1. Root nitrogen accumulation was N3>N2>N1. Logistic growth function model was used to fit the accumulation of biomass nitrogen in each organ, R²>0.9. The maximum cumulative rate V_m and duration Δt were two dynamic characteristics. In N1S3 treatment, Δt was the smallest and V_m was the largest. Salt significantly inhibited the biomass, nitrogen accumulation and V_m incotton organs. There was an obvious interaction between nitrogen application and soil salinity. The results showed that N2 in S1 and S2, and N3 in S3 were the best for biomass accumulation and V_m of reproductive organs. The higher the salinity, the lower the nitrogen transfer rate. The amount of nitrogen applied promoted the nitrogen transfer rate. The maximum yield of S1N2 was 6 683 kg/hm². The accumulation of nitrogen accumulation in various organs and the distribution of nitrogen in vegetative organs madethe distribution of crop nitrogen more balanced, resulting in the optimal yield. The nitrogen use efficiency of N1 was the best in S1 and S2, and N2 was the best in S3. Therefore, applying 105 or 210 kg/hm² nitrogen fertilizer in soil with salinity less than 6 g/kg is most beneficial to cotton production and benefit. 315 kg/hm² of nitrogen fertilizer should be applied when the soil salinity is 8~9 g/kg. These findings could provide scientific basis for rational utilization of saline alkali soil and fertilization management.

Abstract:In order to study the water conservation effect and regeneration of typical plantations in northern mountainous, Larix principis forests in the Lüliang Mountains were selected. The indoor soaking method was used to determine the water holding capacity of litter under different densities. The RDA analysis method was used to explore the relationships between stand structure and litter thickness and interception function. The results showed that:(1) The thickness of litter was 0.84~4.50 cm in different densities, and the accumulation was in the range of 9.64~24.14 t/hm². 350 trees/hm² had the largest amount and 200 trees/hm² had the smallest. (2) The maximum water holding capacity of the sample plots was 27.12~62.07 t/hm², the water holding capacity of 500 trees/hm² was the largest, the water holding capacity of 150 trees/hm² was the smallest, and the water holding rate ranged from 213% to 374%. The effective interception capacity of each plot was 10.75~30.40 t/hm², the interception capacity of 500 trees/hm² was the best, and 150 trees/hm² was the worst. The interception capacity was positively correlated with water holding capacity. (3) The water holding capacity of litter had a significant logarithmic function relationship with the soaking time, and the water-holding rate had a power exponential function relationship with the soaking time. (4) The intercepted amount of litter was closely related to the structures of the forest, showing as tree height>forest density>canopy density>slope>forest age>regeneration>tending thinning years. Tree height had the closest relationship to the intercepted amount of litter. The effects of forest age, seedling regeneration and tending years on litter interception were small. Altitude and average DBH of stand had no effect on litter interception. The results of the study could provide some references for tending and management of Larix principis plantation from the perspectives of water conservation and soil and water conservation.

Abstract:With the increasing chemical fertilizers application and serious soil degradation, the greenhouse gas emissions from agriculture field have been also concerned. The experiment combined organic nitrogen and inorganic nitrogen in order to study N₂O emissions in dry tobacco field. There were 6 treatments:CK0 (no fertilizer), CK1 (100% inorganic nitrogen), T1 (50% inorganic nitrogen/50% cake fertilizer nitrogen), T2 (50% inorganic nitrogen/50% sheep manure nitrogen), T3 (25% inorganic nitrogen/75% cake fertilizer nitrogen), T4 (25% inorganic nitrogen/75% sheep manure nitrogen). Totally 45 kg/hm² nitrogen was applied for each treatment. With in 142 days from applying basic fertilizer, the N₂O emission flux, NO₃^-, NH₄⁺, 0—5 cm soil temperature and moisture content were analyzed. The results showed that:(1) The N₂O emission flux of the soil reached a high flux after 3~7 days of basic fertilization. The inorganic fertilizer and the combined fertilizer of inorganic and organic for the first high flux were lasting about 20 days and 9 days respectively. The N₂O emission flux of the soil reached a high flux one more time after 3 days of the second fertilization, and lasted 9 days. During the tobacco growing, soil N₂O emissions tended to be stable. (2) The cumulative emissions of N₂O could reach 27.4%~32.6% of the total emissions after one month of basic fertilization. The relationship of the emissions flux and the N₂O emission factors among treatments was inorganic>organic + inorganic (1:1)>Organic + Inorganic (3:1). The organic fertilizer reduced the loss of nitrogen in the fertilizer in the form of N₂O. Compared with the inorganic fertilizers, the yield of T1 and T2 increased by 9.44% and 6.37% respectively; and the N₂O emission intensity of each treatment were reduced. (3) Principal component analysis results showed that soil temperature and moisture content of 0~5 cm were the dominant factors of N₂O flux in non-fertilized tobacco fields. Analyzing correlation, temperature and moisture in this treatment were significantly positively and extremely significantly positively correlated with N₂O flux, respectively. After fertilization, soil NH₄⁺and soil moisture content were the dominant factors of N₂O flux from, and the correlation showed a significant positive correlation (P<0.01). In summary, the N₂O flux of tobacco soil was extremely affected by the type of nitrogen fertilizer. After fertilizing, the responses of tobacco field N₂O fluxes to soil temperature declined, and the main influencing factors were NH₄⁺ and soil moisture. Under the same nitrogen content, the combined fertilizer of organic and inorganic rate of 1:1 reduced the N₂O cumulative emissions significantly, and enhanced the tobacco yield. The cake fertilizer and sheep manure with this organic and inorganic rate reduced the emission intensity by 20.4% and 23.7%, respectively.

Abstract:Forest transpiration plays an important role in maintaining the water balance of forest ecosystem. Studying transpiration regulations of Quercus acutissima and Quercus variabilis is helpful to understand the hydrology process and water balance of Quercus spp. forest. In this study, the transpirations of Q. acutissima and Q. variabilis were observed continually by the thermal diffusion probe method in Jurong City, Jiangsu Province. Meanwhile, the daily dynamic characters of transpiration and the impact mechanism of climatic factors on transpiration rate under different weather circumstances were studied. The results showed that the daily variation of transpiration rate showed single peak curve in sunny days and cloudy days, and fluctuate peak pattern in rainy days. The peak value was appeared in 11:30—12:30 in sunny days and 13:30—14:00 in cloudy days. The daily mean transpiration for Q. acutissima and Q. variabilis under different weathers were showed as follow:Q. acutissima>Q. variabilis, sunny day>cloudy day>rainy day. The transpiration rate of Q. acutissima and Q. variabilis were significantly positive correlated to the total solar radiation, the atmospheric temperature, and the vapor pressure deficiency. The total solar radiation had the greatest contribution to the transpiration rate of Q. acutissima and Q. variabilis. The contribution rate were 91.7% and 85.5% in sunny days, 71.0% and 80.1%in cloudy days, 50.4% and 57.9% in rainy days. The total solar radiation among climatic factors had the most important influence on the transpiration rate of Q. acutissima and Q. variabilis, followed by vapour pressure deficit, air temperature, and soil water content.

Abstract:Through fixed field experiment, the effects of organic fertilizer substitute part of chemical fertilizer on soil extracellular enzyme activity and multi-functionality was analyzed, and this study could provide theoretical basis for soil fertility improvement and rational fertilization in rice-rapeseed rotation. Based on the principle of total nutrient substitution amount of nutrients, 4 treatments, which including no fertilizer (CK), full amount of chemical fertilizer (CF), organic fertilizer substitute 20% chemical fertilizer (CFM1), and organic fertilizer substitute 40% chemical fertilizer (CFM2) were set up. Soil chemical properties, microbial properties, and extracellular enzyme activity were assessed, and the Multiple regression analysis was used to explore the effects of soil properties on soil extracellular enzyme activity and multi-functionality. The results showed that compared with CF, soil microbial biomass carbon, microbial biomass nitrogen, and soil respiration of CFM1 and CFM2 increased 275.27%, 41.90%, and 64.29% in rapeseed season, and increased 115.06%, 338.32%, and 60.87% in rice season. Organic fertilizer application increased the contents of soil organic matter, total nitrogen, total phosphorus, and available nutrients by 13.25%~95.48%. Compared with the single application of chemical fertilizer, the replacement of part of chemical fertilizer by organic fertilizer significantly increased the activity of β-glucosidase, cellulase, xylanase, leucine aminopeptidase, N-acetyl-aminoglucosidase, and acid phosphatase in the carbon, nitrogen, and phosphorus cycle, with an increase of 20.33%~140.31% in rapeseed season, while in rice season, only xylanase activity was significantly increased, with an increase of 133.63%~159.86%. The key factors for the changes of soil extracellular enzyme activities was soil microbial biomass carbon in rapeseed season, and was soil available phosphorus in rice season. Compared with no fertilizer treatment and full amount of chemical fertilizer, organic fertilizer replacement treatment significantly increased soil multi-functionality, the main predictive factors of soil multi-functionality were available potassium and available nitrogen in rapeseed season, and were available phosphorus and microbial biomass nitrogen content in rice season. In a word, the substitution of organic fertilizer for part of chemical fertilizer is beneficial to the improvement of soil nutrients, microbial biomass, and soil extracellular enzyme activity, which is an important measure to maintain stable crop yield and soil biological health.

Abstract:The greenhouse effect induced by elevated CO₂ can be alleviated by increasing capacity of carbon (C) sequestration in terrestrial ecosystems. Here, we carried out an indoor column simulation experiment with saline and sodic soils to assess the responses of ecosystem C stocks (including the C stock in soil and plant biomass) under the different amounts of flue gas desulfurization gypsum (FGDG) application (0, 10, 20, 21.78, 30, and 40 t/hm²). The results showed that:Compared with the control treatment, soil C stock decreased by 8.78%~15.72% in the saline soils as a result of the decrease in soil organic C stock. In contrast, soil C stock increased by 5.00%~23.94% in sodic soils with the application of FGDG largely derived from the increase of soil inorganic C stock. The C stock of wheat biomass decreased by 23.14% in saline soils and increased by 30.44% in sodic soils. The C stock of ecosystem increased by 0.09~0.42 kg/m² in sodic soils and decreased by 0.33~0.56 kg/m² in saline soils with the application of FGDG. These changes of C stock in the saline-sodic soils ecosystems were dominantly attributed to the amount of FGDG application, soil electrical conductivity, and the changes of water holding capacity caused by the application of FGDG. In a word, our study indicated that the C stock of ecosystems decreased in saline soils and increased in sodic soils, especially at the amount of 30 and 40 t/hm² FGDG. This study will provide a scientific reference for increasing soil C sequestration in arid areas.

Abstract:The natural spruce-fir coniferous and broad-leaved mixed forests in Wangqing Forestry Bureau of Jilin Province were taken as the research object, and four representative square fixed plots of 1 hm² were set up with a cutting intensity of 0, 6.29%, 11.22% and 21.21%. The standing crop of litter under various cutting intensities was measured, and the water holding capacity (maximum water holding capacity, maximum water holding rate, effective retention capacity, etc.) of litter at different decomposition stages was studied using an indoor immersion method. The results showed that:(1) The total standing crop of litter in the four cutting intensities was between 29.04 and 35.26 t/hm². (2) With the increase of cutting intensities, the maximum water holding capacity and effective interception capacity of litter in the fresh horizon and complete decomposed horizon decreased first, then increased and decreased again, whereas the opposite trend was found for the litter in the semi-decomposed horizon. (3) The cutting intensity had no significant effect on the water holding capacity of litter, but the decomposition stage had a significant impact on it. The two-way analysis of variance showed that the interaction between the cutting intensity and the decomposition stage had a significant influence on the water holding capacity of litter. (4) The regression fitting indicated that there was a logarithmic function relationship between the water holding capacity, water holding rate and immersion time of litter in each decomposition stage under different cutting intensities, and there was a power function relationship between water absorption rate and immersion time before the litter reached the saturation state. Therefore, moderate cutting would not have a significant negative impact on the water holding capacity of the litter, the decomposition stage was an important factor affecting the water holding capacity of the litter in the spruce-fir coniferous and broad-leaved mixed forest, and the interaction of decomposition stage and cutting intensity could significantly affect the water holding capacity of litter.

Abstract:To explore the remediation of Liquidambar formosana Hance to lead-contaminated soil and provide scientific reference for the promotion of planting maple in contaminated heavy metals, annual L. formosana Hance seedlings were used as test materials, the physiological characteristics and accumulation characteristics of L. formosana Hance seedlings under 6 Pb²⁺ concentrations (0, 100, 300, 500, 800, and 1 000 mg/kg) were studied. The principal component analysis method was used to screen the 12 physiological indexes of L. formosana Hance and evaluate the tolerance. The results showed that with the increase of Pb²⁺ concentration, the biomass, soluble sugar content, soluble protein content, free proline content, superoxide dismutase (SOD), and peroxidase (POD) of L. formosana seedling leaves showed a upward-downward trend, which indicate a "low promotes high suppression" effect. The content of malondialdehyde (MAD) showed an upward trend. Both chlorophyll a and chlorophyll b showed a downward trend, but the downward trend of chlorophyll a was not significant. Net photosynthetic rate (P_n), stomatal conductance (G_s), CO₂ concentration (C_i), and transpiration rate (T_r) all showed an upward-downward trend. The lead content in the underground part of L. formosana>the lead content in the above-ground part, the transfer coefficient was the largest at T2 and T3, and the enrichment coefficient was negatively correlated with the stress concentration. The results of principal component analysis showed that the cumulative contribution rate of the two principal components extracted was as high as 92.462%, indicating that these two principal components can reflect most of the information. Free proline, net photosynthetic rate, stoma conductance, intercellular CO₂ concentration, transpiration speed, and SOD activity were the simplified 6 indexes. The principal component scores showed that the lead tolerance of L. formosana seedlings is ranked as T3>T4>T2>T1>T5>T6. Comprehensively, the L. formosana Hance seedlings have certain tolerance, enrichment, and transfer ability to heavy metal lead, and this study provide theoretical basis for introducing L. formosana Hance to areas with heavy metal pollution and alleviating soil heavy metal pollution.

Abstract:To investigate the effect of development stage on soil C:N:P stoichiometry characteristics of Nitraria tangutorun nebkhas. Taking Nitraria tangutorun nebkhas at different development stages (for rudimental stage, developing stage, stabilizing stage and degrading stage) in desert area of Jilantai as research object, and measure vertical distribution of soil C:N:P stoichiometry from 0 cm to 100 cm in depth under Nitraria tangutorun nebkhas. The results showed that:(1) Soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) showed first increased and then decreased with the succession of N. tangutorum nebkhas (rudimental stage→developingstage→stabilizingstage→degrading stage). The effect of succession stage on SOC was significant (P<0.05), but not on TN and TP (P>0.05). The contents of SOC, TN and TP in the four stages of evolution were 0.42~0.58 g/kg, 0.04~0.07 g/kg and 0.22~0.25 g/kg in 0—100 cm soil depth, respectively, and the contents was far less than national average levels (11.12, 1.06, 0.65 g/kg). (2) There was no obvious change rule for the contents of SOC, TN, TP and soil C:N:P stoichiometry in the four succession stages of Nitraria tangutorun nebkhas decreased with the increase of soil depth. (3) The content and stoichiometry of SOC, TN and TP belonged medium variability, and which decreased with the increase of soil depth. (4) Soil bulk density, soil capillary porosity and non-capillary porosity had significant effect on TN, C:N, N:P, and soil water content and pH had no significant effect on the contents of SOC, TN, TP and soil C:N:P stoichiometry. Confirm the importance of SOC and TN in regulating the soil C:N:P stoichiometry of Nitraria tangutorun nebkhas. Therefore, the present results clarify the response of C:N:P stoichiometry of Nitraria tangutorum to different succession stages. It provides scientific basis for the protection, utilization and vegetation restoration and reconstruction of Nitraria tangutorum community in this area.