Abstract:In order toclarify the water-saving and fertilizer-conserving effects of a new environmental sustained-release water-retaining agent,γ-polyglutamic acid (γ-PGA),four kinds of γ-PGA gradients (0, 0.1%, 0.2% and 0.4%) were applied at the same nitrogen application rate (2 g/kg), and no γ-PGA was taken as control.The effects of γ-PGA application rate on soil nitrogen transport characteristics were studied by one-dimensional soil column infiltration experiment in laboratory. The results showed that: (1) Under the condition of constant head infiltration, the cumulative infiltration amount, infiltration rate and the distance of wetting front migration all decreased with the increasing of γ-PGA application amount.Compared with the control group,the cumulative infiltration amount, infiltration rate, and distance of wet front migration in the experimental group with 0.4% γ - PGA application decreased by 27.64%, 73.45% and 31.58%, respectively. (2) According to Philip formula simulation results, the permeability S decreased with the increasing of γ-PGA application, showing a negative correlation; in the results of Kostiakov formula simulation, empirical coefficient K decreased with the increasing of γ-PGA application, showing a negative correlation,and empirical index a increased with the increasing of γ-PGA application, showing a positive correlation.(3) With the increasing of γ-PGA application, the water content of surface soil (0-15 cm) increased gradually,while that of the deep soil (below 15cm) was the opposite.At the same time, the greater the γ-PGA application amount, the greater the content of nitrate nitrogen and ammonium nitrogen in each soil layer in the same period. On the fourth day after stopping the water supply, the average nitrate nitrogen content of the experimental group added with 0.1%, 0.2% and 0.4% γ-PGA, respectively, increased by 29.55%, 42.49% and 59.50% compared with thecontrol group,and the average ammonium nitrogen content increased by 43.97%, 123.40% and 156.74%.In conclusion, applying γ-PGA to soil could effectively slow down water infiltration, gather more water in shallow soil layer, reduce fertilizer leaching rate,increase water and fertilizer utilization,reduce frequency and cost of irrigation, and achieve the purpose of improving soil structure and increasing crop yield.