Effect of γ-PGA and γ-PGA SAP on soil microenvironment and the yield of winter wheat

Agricultural poly-γ-glutamic acid (γ-PGA) and γ-PGA super absorbent polymer (SAP) are two forms of γ-PGA applied in agriculture. Different quantities of γ-PGA and γ-PGA SAP (40 kg/hm2, 80 kg/hm2, 120 kg/hm2 and 160 kg/hm2) were applied to the soil in order to investigate their effects on the microenvironment of soil root zone and the yield of winter wheat. The soil water content increased with increasing amounts of γ-PGA SAP. The content of nitrate nitrogen and ammonium nitrogen increased with the increasing amounts of γ-PGA, while γ-PGA SAP significantly increased the content of ammonium nitrogen. The number of soil microorganisms and soil enzyme activities in the root zone increased with the addition of γ-PGA and γ-PGA SAP. The yield of winter wheat increased with the addition of γ-PGA or γ-PGA SAP, but the increasing rate decreased when the amount of γ-PGA and γ-PGA SAP exceeded 80 kg/hm2, with increases of 5.95% and 6.77% compared to the control group, respectively. The addition of γ-PGA significantly increased the protein content of wheat grains, and the WUE increased with increasing amounts of γ-PGA and γ-PGA SAP.