Cross‐linked polymers increase nutrient sorption in degraded soils

Abstract

AbstractCross‐linked polymer hydrogels, polyacrylamide co‐polymer (XPAM) or polyacrylate (XPAA) offer potential solutions for soil degradation, declines in soil resilience, and poor productivity in marginal soils. However, little is known about their long‐term effect on soil nutrient availability. This 9‐yr, irrigated, outdoor, cropped pot study evaluated a single, one‐time addition of XPAM or XPAA at 0.25 or 0.5% dry wt. (5.6 or 11.2 Mg ha–1) in a degraded (artificially eroded) soil. Controls included an unamended degraded soil and an unamended, non‐degraded soil (i.e., topsoil). We measured nutrients in soil and leachate water each year, and in the first 5 yr, crop yields and nutrient uptake. Both hydrogels increased average soil pH and electrical conductivity (EC), soil extractable K, Na, and total organic carbon (TOC), and decreased soil extractable Mg relative to the control. Unlike XPAM, XPAA produced a greater increase in soil extractable K, increased extractable Fe, Zn, Mn, and Cu, increased Olsen P, and decreased total inorganic carbon (TIC). Neither hydrogel affected crop yields but XPAA increased K and Zn and decreased Mg and Na uptake in crops compared to controls. Relative to the control, both hydrogels decreased cumulative Ca, Mg, and S leaching mass losses and increased mean EC of leachate. Unlike XPAM, XPAA increased cumulative leaching mass losses of K, P, NO3–N, and NH4–N relative to the control. The hydrogels’ soil effects persisted for ≥7 yr, differing as a function of the quantity of included counterions and the stability of the gel structure after soil placement.