Cross-linked polymer hydrogels, such as polyacrylamide co-polymer (XPAM) or K-acrylate have been shown to increase soil H2O retention in agricultural soils, potentially mitigating effects of drought. The persistence of polymer-derived H2O-retention benefits in soils has been little studied, yet this information is critical for assessing economic feasibility of the practice, particularly at the farm-scale. This 9-yr, outdoor, large-pot study amended an irrigated, artificially-eroded, calcareous silt loam with a single, one-time, 0.25% or 0.5% dry wt. (5.6 or 11.2 Mg ha-1) application of either XPAM or K-acrylate; an untreated control, and untreated, uneroded topsoil. The soils were hand-tilled and planted to crops each year. Soil water retention and plant available water (PAW, g H2O per g dry soil) was measured on soil samples collected in spring for 7 of the 9 yrs. Across all years, the 2% XPAM produced the greatest PAW (0.313) and the PAW of other treatments followed in the order: 2% XPAM &gt; 1% XPAM &gt; Topsoil &gt; 1% K-acrylate = 2% K-acrylate = control (0.222). In all years, the 1% XPAM and 2% XPAM treatments increased soil PAW relative to the control, i.e. their PAW ratios exceeded unity. Topsoil PAW exceeded that of the control in 6 of the 7 yrs measured. The PAW of 1% XPAM and 2% XPAM peaked in year one after application and declined linearly with time (P&lt;0.004), at -0.0061 yr-1 and -0.0066 yr-1, respectively. The half-life of the XPAM-related H2O-retention benefit was 14 to 20 years. In this study, soil H2O-retention benefits from XPAM amendments exceeded projections proposed by the industry (5 to 6 yrs in the soil) and suggest that the cost-benefits of farm-scale XPAM applications are more favorable than previously anticipated.

Long-term persistence of polymer hydrogels in silt loam soil: Soil water retention

2019 Fall National Meeting

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