POTASSIUM REQUIREMENTS OF A GRASS LEGUME PASTURE ESTABLISHED ON SELECTED SOILS OF THE SUBHUMID ZONE OF NIGERIA/

The fast depletion of available potassium (K) in soils of the subhumid zone (SHZ) of Nigeria has become a problem for the formulation of fer tilizer recommendations, especially in the grass/legume mixtures of th e fodder bank system. Five different K fertilizer recommendation model s viz. Control, Conventional Rate, Fractional Recovery, Mitscherlich B aule Units, and Nutrient Supplementation Index were employed to determ ine the amount of K required to satisfy the needs of an Andropogon/sty lo mixture. Andropogon gayanus (grass) and Stylosanthes hamata cv. Ver ano (legume) seeds were sown in June 1991. Cutting started two months after planting and continued at monthly intervals during the rainy sea son and bimonthly in the dry season till mid dry season when there is usually feed crisis. The Andropogon/stylo mixture grown on soils of th e SHZ will require no K fertilization when the soil test value is more than 0.20 cmol/kg. The soils require an application of 52 kg K2O/ha w hen the soil test value is less than 0.20 cmol/kg. Dry matter yield an d K uptake of the Andropogon/stylo mixture increased up to October 199 1 and started decreasing with subsequent cuttings. Among the recommend ation models tested for K fertilization of the Andropogon/stylo mixtur e, the Fractional Recovery model was the most appropriate and is there fore recommended for determining K levels to apply to Andropogon and s tyle in the SHZ.