Effect of Mixed Application of Polyacrylamide and Humic Acid on Water Infiltration Characteristics of Purple Soil

Abstract

[Objective] The objective of this study was to determine the impact of the combined application of PAM (polyacrylamide) and humic acid on the vertical infiltration characteristics of purple soil in order to provide theoretical references for water and soil conservation, soil improvement, water regulation, and efficient utilization of agricultural water resources in the purple soil region of western Sichuan. [Methods] An indoor soil column simulation experiment was conducted with one check treatment (CK, no mixing), three PAM application levels (PAM-1: 1%, PAM-3: 3%, PAM-5: 5%), and two humic acid application levels (HA-1: 0.1%, HA-5: 0.5%). Infiltration rate, cumulative infiltration volume, and wetting peak transport distance were measured and the variation characteristics were analyzed. The infiltration process was simulated and analyzed using infiltration models. [Results] Compared with CK, the other treatments effectively reduced water infiltration rate, and the infiltration rate gradually decreased with increasing application rate. Under the same cumulative infiltration amount, the infiltration time of each treatment (except H1P1) was greater than that of CK, among which H1P3 and H2P3 were 14.7 times and six times, respectively, the infiltration time of CK. H1P1 had an infiltration time that was 25% less than CK. Within 220 min, the wetting peak transport distances in all treatments were lower than that of CK, with the lowest wetting peak transport distance (4.98 cm) in H1P3, which was significantly shorter (57.67%) than that of CK. Model applicability followed the order of general empirical formula>Kostiakov formula>Horton formula>Philip formula. However, the steady permeability rate (fs) of the general empirical formula deviated from the measured values. [Conclusion] PAM mixed with humic acid can effectively decrease infiltration rate, reduce cumulative infiltration, and slow down the transport distance of the wetting peak. The infiltration reduction effect became more evident with increasing application amount. The optimal treatment was H1S3 (humic acid 0.1 g/g and PAM 3 g/g. Compared with other formulas, the Kostiakov formula was more suitable for describing the soil water infiltration process in the study area.

Keywords

• humic acid
• infiltration rate
• wetting peak
• infiltration model
• polyacrylamide
• cumulative infiltration amount