An evaluation of the effectiveness of nonconventional p fertilizers derived from Zimbabwe phosphate rock using ryegrass as a test crop

Abstract

Zimbabwe and many other African countries lack high-quality phosphate ores for the production of conventional phosphate fertilizers. The objective of this study was to investigate the agronomic potential of an igneous phosphate rock derived from Dorowa (Zimbabwe) in a greenhouse experiment using rye grass (Lolium perenne) as test crop on a Hartsells silt loam. Three phosphate fertilizer materials: finely ground (0.150-mm screen) Dorowa phosphate rock (DPR); DPR partially acidulated with 50 % of the sulfuric acid required for complete acidulation (PADPR); and a compacted mixture of DPR + triple superphosphate + urea + potassium chloride (DTUK) with half of phosphorus from DPR and half from TSP were made from Dorowa rock and their agronomic effectiveness compared with that of single superphosphate. The relative agronomic effectiveness of the fertilizers based on dry matter yield of ryegrass followed the orders: DTUK=SSP>PADPR>DPR=Check and SSP>DTUK=PADPR>DPR=Check during the first 12 weeks and the second 12 weeks, respectively. For phosphorus uptake by ryegrass, the orders were: DTUK>SSP>PADPR>DPR=Check, DTUK=SSP>PADPR>DPR=Check, and SSP>DTUK>PADPR>DPR=Check during the first six, second six, and last 12 weeks, respectively. The results confirmed that the effectiveness of DPR could be greatly enhanced by partially acidulating DPR or compacting DPR with TSP, urea, and KCl.