CRITICAL POTASSIUM-DEFICIENCY LEVELS FOR A GRASS LEGUME PASTURE GROWNON SOILS OF THE SUBHUMID ZONE OF NIGERIA

A greenhouse experiment was conducted to determine the critical defici ency levels of potassium (K) in the subhumid zone soils for predicting response of a mixture of Andropogon gayanus and Stylosanthes hamata c v. Verano to K application. Twenty coarse textured soils, having loamy sand to sandy loam textures and with exchangeable K contents ranging from 0.08 to 0.97 cmol/kg, were used. Two rates of K applied were 0 an d 80 mg K/kg. Application of K on soils testing less than 0.18 cmol/kg significantly increased the dry matter yields of both Andropogon and style tops. Soil K was significantly related to relative yields of Sol e Andropogon (r = 0.60*), sole style (r = 0.78***), and Andropogon/st ylo mixture (r = 0.77**). There was a high correlation between the K concentration in plant tissue and the relative yields of sole Andropog on (r = 0.68*), sole style (r = 0.67**), Andropogon in mixture (r = 0 .65*), and style in mixture (r = 0.64**). The graphical model of Gate and Nelson indicated the critical levels of the available form of K i n soil to be 0.18, 0.20, and 0.21 cmol/kg for sole Andropogon, sole st yle and Andropogon/stylo mixture, respectively. The critical levels fo r K in plant tissues were also determined to be 1.30, 2.03, 1.38 and 1 .86% for sole Andropogon, sole style Andropogon in mixture, and style in mixture, respectively.