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Abstract
Enhanced plant growth following the application of hydrophilic polymers has been assumed to result from increased water supply. However, little attention has been paid to the contribution of counter ions to plant nutrition or to their effects on soil characteristics, such as pH, that might influence plant growth and nutrient availability. We investigated the effects of polyacrylate polymers with different counter cations, sodium (Na+) and potassium (K+) or NH4 +, on some characteristics of an acid soil, and on dry matter accumulation, water use efficiency, and the mineral composition of perennial ryegrass. Addition of polymers to the soil enhanced plant growth to a greater extent than did liming. The presence of the Na‐polymer or the Na—NH4 +‐polymer resulted in the greatest biomass accumulations by perennial ryegrass. Evapotranspiration was greatest in the soil amended with the Na‐polymer and similar in soils amended with the Na K‐polymer or the Na NH4 +‐polymer. Total plant dry matter was correlated with evapotranspiration and soil levels of mineral nitrogen (N), phosphorus (P) and Na at the end of the experiment, suggesting that these factors were limiting plant growth. The concentration ofNa was enhanced in plants from amended soils. The concentration of P was increased in plants from unlimed amended soil. The concentration of N was greatest in plants from unamended soil or from soil amended with the Na NH4 +‐polymer, but total N uptake was greatest in the amended soil.