Effects of poly-γ-glutamic acid and poly-γ-glutamic acid super absorbent polymer on the sandy loam soil hydro-physical properties

The main forms of poly-gamma-glutamic acid (gamma-PGA) applied in agriculture include agricultural gamma-PGA and gamma-PGA super absorbent polymer (SAP). Laboratory experiments were conducted with a check treatment CK (no gamma-PGA added) and two different forms of gamma-PGA added to sandy loam soil (T and TM stand for gamma-PGA and gamma-PGA SAP) at four different soil mass ratios (0.05% (1), 0.10% (2), 0.15% (3) and 0.20% (4)) to determine their effects on sandy loam soil hydro-physical properties. Both of them could reduce the cumulative infiltration of soil water. The total available water (TAW) which the soil water content (SWC) from field water capacity (FC) to permanent wilting point (PWP) after gamma-PGA added into sandy loam soil had no significant different compared with CK, and the TAW was highest at the treatment of gamma-PGA with 0.10% addition amount into sandy loam soil. However, the TAW of sandy loam soil increased dramatically with the gamma-PGA SAP addition amount increasing. TM3 had the highest soil water absorption among the treatments with gamma-PGA SAP. The T1 to T4 treatments with gamma-PGA addition slightly prolonged retention time (RT) when SWC varied from FC to PWP compared with CK. For gamma-PGA SAP addition treatments, the time for SWC varied from FC to PWP was 1.48 times (TM1), 1.88 times (TM2), 2.01 times (TM3) and 2.87 times (TM4) longer than that of CK, respectively. The results of this study will provide further information for the use of these materials in agricultural application.

Automated summary

The experiments showed that both agricultural gamma-PGA and gamma-PGA SAP could reduce soil water infiltration in sandy loam soil. The addition of gamma-PGA had no significant impact on total available water in the soil, while the addition of gamma-PGA SAP greatly increased the total available water content. The study provides valuable information for the use of these materials in agricultural applications.