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ARS Home » Pacific West Area » Kimberly, Idaho » Northwest Irrigation and Soils Research » Research » Publications at this Location » Publication #368066
Research Project: Improving Water Use Efficiency and Water Quality in Irrigated Agricultural Systems

Location: Northwest Irrigation and Soils Research

Title: Long-term water retention increases in degraded soils amended with cross-linked polyacrylamide

Author
item Lentz, Rodrick

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2020
Publication Date: 3/19/2020
Citation: Lentz, R.D. 2020. Long-term water retention increases in degraded soils amended with cross-linked polyacrylamide. Agronomy Journal. 112(4):2569-2580. https://doi.org/10.1002/agj2.20214.
DOI: https://doi.org/10.1002/agj2.20214

Interpretive Summary: It is important to develop cost-effective means of increasing plant available water (PAW) in soils because soil erosion has removed organic carbon and reduced PAW in millions of acres agricultural soil worldwide; climate change has decreased precipitation and reduced irrigation water supplies on lands currently used for growing crops; and a burgeoning world population with attendant nutritional demands will require that lands with marginal soil water potential be brought into production. Polymer hydrogels such as cross-linked polyacrylamide co-polymer (XPAM) and K-polyacrylate (XPAA), increase soil water availability under drought, but their long-term effects are unknown, even though such knowledge is important for assessing economic feasibility at the farm-scale. This 9-year study shows that the polymer type and rate of application radically influence long-term hydrogel effects on PAW. In some cases, the persistence of the water retention benefits greatly exceeded expectations, which substantially increases the cost effectiveness of the practice. This information provides important guidance for hydrogel use, particularly at the farm scale.

Technical Abstract: Polymer hydrogels, cross-linked polyacrylamide co-polymer (XPAM) and K-polyacrylate (XPAA), increase soil water availability under drought, but their long-term effects are unknown even though such knowledge is important for assessing economic feasibility at the farm-scale. This 9-yr, outdoor study amended an irrigated, calcareous silt loam with a one-time, 0.25% or 0.5% dry wt. (5.6 or 11.2 Mg/ha) application of either XPAM or XPAA; and included an untreated control and untreated, uneroded topsoil. Soil water retention and plant available water (PAW, g H2O per g dry soil) were measured in soil samples collected in spring for 7 of the 9 years. Across all years, the 2% XPAM produced the greatest PAW (0.318) and the PAW of other treatments followed in the order: 0.5% XPAM > 0.25% XPAM > Topsoil > 0.25% XPAA = 0.5% XPAA = control (0.224). In all years, the 0.25% XPAM and 0.5% 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 years measured. The PAW of 0.25% XPAM and 0.5% XPAM peaked in year one after application and declined linearly with time (P<0.03), at -0.0036 /yr and -0.0044/yr, respectively. Hence, the half-life of the XPAM-related water-retention benefit is 10 to 16 years. In this study, soil water-retention benefits from XPAM amendments exceeded projections proposed by the industry (5 years in soil) and suggests that the cost-benefit of farm-scale XPAM applications might be more favorable than previously anticipated.