Poly‐γ‐glutamic acid application rate effects on hydraulic properties of sandy soil under wetting‐drying cycles conditions

Abstract

AbstractWhen amending soil to increase sandy soil water holding capacity, amendment application rate and environment need consideration. Recently, poly‐γ‐glutamic acid (γ‐PGA) as a soil amendment has been increasingly applied in agricultural development. The purpose of this study was to determine the effect of γ‐PGA on soil water retention and soil hydraulic conductivity under wetting‐drying (W‐D) conditions. Specifically, this study investigated the influence of different γ‐PGA application rates (wt%: 0, 0.4, 0.8, 1.2, and 1.6%) on the soil water characteristic curve, saturated hydraulic conductivity (Ks), and the other hydraulic characteristic parameters (saturated water content [θs], field capacity [FC], permanent wilting point [PWP], and available water content [AWC]). Results showed that γ‐PGA significantly increased sandy soil water retention by increasing θs, FC, PWP, and AWC. Poly‐γ‐glutamic acid could decrease the proportion of large pore size (2–15 μm) and Ks and enhance the proportion of particles with small pore size (0.2–2 μm). Nevertheless, the effect of γ‐PGA on hydraulic properties of sandy soil depended on γ‐PGA application rate and the number of W‐D cycles. Under 8‐W‐D and 12‐W‐D, there was no significant difference on soil water retention among all treatments. Increasing the application rate of γ‐PGA was not more effective; P3 (1.2%) and P4 (1.6%) treatments had little difference in soil water holding capacity. This study quantitatively investigated effects of γ‐PGA on soil water retention under different W‐D cycles. Our results suggest that 1.2% might be recommended as an appropriate γ‐PGA application amount.