Long‐term water retention increases in degraded soils amended with cross‐linked polyacrylamide

Abstract

AbstractCross‐linked polymer hydrogels, polyacrylamide co‐polymer (XPAM), and K‐polyacrylate (XPAA) increase soil water availability under drought, but their long‐term effects are unknown despite the importance of such knowledge in assessing economic feasibility. This 9‐yr outdoor pot study evaluated a one‐time addition of XPAM or XPAA at 0.25 or 0.5% dry weight (5.6 or 11.2 Mg ha−1) in a degraded calcareous silt loam. Controls included an unamended degraded soil and an unamended nondegraded soil (topsoil). Soil water retention and plant available water (PAW, g water g−1 dry soil−1) were measured in soil samples collected in spring for seven of the nine years. Across all years, the 0.5% XPAM produced the greatest PAW (0.318) and the PAW of other treatments followed in the order: 0.5% XPAM > 0.25% XPAM > Topsoil > 0.5% XPAA > 0.25% XPAA = control (0.224). In all years, the 0.25% XPAM and 0.5% XPAM treatments increased soil PAW relative to the control, that is, their PAW ratios exceeded unity. Topsoil PAW exceeded that of the control in six of the seven years measured. The PAW of 0.25% XPAM and 0.5% XPAM peaked in Year 1 after application and declined linearly with time (P < .03), at −0.0036 yr−1 and −0.0044 yr−1, respectively. Hence, the mean residence time the XPAM‐related water‐retention benefit is 24–29 yr. In this study, soil water‐retention benefits from XPAM amendments exceeded projections proposed by the industry (5 yr) and suggests that the cost‐benefits of field‐level XPAM applications might be more favorable than previously anticipated.