Effects of poly‐γ‐glutamic acid on soil structure and water retention characteristics under dry‐wet cycles

Poly‐γ‐glutamic acid (γ‐PGA) has been demonstrated to exhibit a soil water retention effect; however, the agricultural irrigation practices induce a cyclic pattern of wetting and drying in the soil, and its synergistic interaction with γ‐PGA remains unclear. To explore the amendment effects of γ‐PGA on pores structure, aggregates distribution, and soil water retention characteristics under dry‐wet cycles, an experiment was established with the number of dry‐wet cycles (0, 2, 4, and 8 times; a single dry‐wet cycle involved reducing soil water content from 80% to 40% of field water capacity) and γ‐PGA addition rates (0%, 4%, and 8%, represented by P0, P4, and P8, respectively). The results indicated that γ‐PGA enhanced the structure of soil pores and distribution of aggregates; especially, P8 exhibited a remarkable increase in pore number by 91.68% and mean weight diameter of aggregates by 17.17%, compared to P0. Additionally, the soil enhanced by γ‐PGA exhibited higher water retention capacity, with P4 and P8 showing average increases of 4.26% and 12.58% in saturated water content compared to P0. Notably, the effect of γ‐PGA on pores structure, aggregates distribution, and water retention characteristics was regulated by dry‐wet cycles. The γ‐PGA had the most significant improvement effect on soil structure under 8 times dry‐wet cycles, the optimal development on water retention characteristics under four times dry‐wet cycles. Therefore, these findings suggest that the optimal approach to enhance soil structure and water retention capacity is by incorporating γ‐PGA at a concentration of 0.8% in conjunction with 4–8 dry‐wet cycles.