Effects of poly-γ-glutamic acid (γ-PGA) on soil nitrogen and carbon leaching and CO2 fluxes in a sandy clay loam soil

Poly-γ-glutamic acid (γ-PGA) has shown a significant promotional effect on plant production. However, little is known of the environmental footprint generated from the application of γ-PGA. A laboratory trial was conducted to study the effects of γ-PGA on soil nitrogen and carbon leaching loss and carbon dioxide (CO2) emission by applying 0, 0.0125, 0.025, 0.05, 0.1, 0.2, 0.4, and 0.8 g γ-PGA kg-1 soil to soil receiving 150 kg N ha-1 in the form of urea. Results showed that the cumulative loss of ammonium and nitrate decreased by 17.81%–29.31% and 8.27%–52.42% when the application rate of γ-PGA reached 0.1 g kg-1 soil. Cumulative total dissolved nitrogen loss was diminished by 7.16%–40.10% when the γ-PGA application rate was 0.2–0.8 g kg-1 soil. Cumulative loss of dissolved organic carbon was rarely affected by the γ-PGA, whereas cumulative CO2 flux was notably enhanced by 26.87%–180.70%. Soil total nitrogen (TN) and soil organic carbon (SOC) contents varied with the different application rates of γ-PGA; soil TN increased by 6.34%–8.04%, and SOC remained unchanged only when the γ-PGA application rate was 0.4–0.8 g kg-1 soil. In conclusion, before considering using γ-PGA in an agroecosystem, its effects on both the environment and plant production should be examined.