Agronomic evaluation of unacidulated and partially acidulated Minjingu and Chilembwe phosphate rocks for clover production in Ethiopia

Most soils in sub-Saharan Africa are P deficient, but the high cost of water-soluble P fertilizers limits the use of P fertilizers by resource-poor farmers. A low-cost alternative is to apply phosphate rocks. We evaluated the effectiveness of unacidulated (PR), 25 percent partially acidulated (PAPR25), and 50 percent partially acidulated (PAPR50) Minjingu and Chilembwe phosphate rocks relative to triple superphosphate (TSP) on Trifolium quartinianum grown on a Vertisol in the Ethiopian highlands. The fertilizers were applied once at 0-80 kg P ha-1 and their effects were followed in four consecutive clover crops. In the Minjingu phosphate rock experiment, clover DM yields without applied P were below 1 t DM ha-1 in all except the first of four consecutive crops. With P application, herbage yields reached as high as 14 t ha-1. Significat (P