Effects of potassium and sodium application to soil on growth and cation accumulation of herbage

Abstract

The effects of potassium (K) and sodium (Na) applications to soil on growth and cation accumulation of herbage were investigated in pot and field experiments. The application of K to K-deficient soil was more efficient at increasing growth than was the application of Na; however, at suboptimal K availability, yield was increased by Na application. Growth responses to Na were restricted when the soil contained insufficient K to satisfy the minimum K requirement of pasture plants. The Na concentration of herbage was markedly reduced by K applications, whereas Na had little effect on K uptake. It was found that an application of Na to soil containing a low level of Na raised the Na concentration of herbage sufficiently to satisfy animal needs. Both K and Na reduced the calcium (Ca) and magnesium (Mg) concentration of herbage, although Na was less inhibitive than an equivalent amount of K. The decline in Ca and Mg in plant tissue with increasing concentrations of soil K and Na was exponential and, as the decline approached the asymptotic concentration, further increases in soil K and Na had only a small effect on Ca and Mg uptake. The implications of these findings are discussed.