Effects of a super-absorbent polymer derived from poly-γ-glutamic acid on water infiltration, field water capacity, soil evaporation, and soil water-stable aggregates

The poly-gamma-glutamic acid super-absorbent polymer (gamma-PGA SAP) is an environmentally friendly material. Five different gamma-PGA SAPs contents based on weight, including 0% (CK), 0.05% (T1), 0.10% (T2), 0.15% (T3), and 0.20% (T4), were added to the soil in this study. The results showed that cumulative infiltration decreased by 32.4% (T1), 39.2% (T2), 51.0% (T3), and 52.0% (T4) at 90 min and the field capacity was increased by 18.7% (T1), 26.0% (T2), 37.8% (T3), and 58.3% (T4) compared with the CK. The cumulative evaporation of the different treatments with gamma-PGA SAPs was 17.1% (T1), 23.5% (T2), 24.4% (T3), and 25.3% (T4) higher than that of the CK at the end of the evaporation experiment. The evaporation experiment lasted 96 h (CK), 132 h (T1), 144 h (T2), 180 h (T3), and 312 h (T4) to progress from field capacity to a soil water content of 10%. Adding gamma-PGA SAPs to the soil significantly increase the water-stable aggregate content below 0.25 mm when the gamma-PGA SAP addition exceeded 0.10%. So reasonable utilization of gamma-PGA SAP can improve water use efficiency and improve soil structure in semi-arid areas.