Evaluation of agronomic effectiveness of minjingu rock phosphate using 32 isotope dilution technique
2000
Peter, K(Kenya Agricultural Research Institute, Nairobi (Kenya). National Agricultural Research Laboratories) | Maingi, S.W(Kenya Agricultural Research Institute, Nairobi (Kenya). National Agricultural Research Laboratories)
Agronomic effectiveness of Minjingu Phosphate Rock (MPR) and Tororo Phosphate Rock (TPR) was compared to triple superphosphate (TSP) in a glass house pot experiment using wheat as a test crop. TPR and TSP were applied at 120 mg P 12 kg soil while MPR was applied at 240 mg P /2kg soil. 32p was added at 80 \}lei + 2.5 mg P as KH2P04 per pot (2 kg soil). Basal fertilizer Nand K were applied at 120 kg N Iha as CAN and 100 kg K/ha as KCl respectively. The treatments were replicated four times. The test soil was of good fertility status except it was acidic (pH 4.75), deficient in P (6.5 ppm), low in Ca (1.70 m.e./lOO g soil) and unfavourable Ca:Mg and Ca:K ratios. The test crop was harvested after 6 weeks and the results showed that TSP (120 mg/2 kg soil) gave similar dry matter yield to MPR (240 mg/2 kg soil) but TSP had a greater P (112.92 mg PI pot) uptake than MPR (92.64 mg P /pot) and TPR (38.16 mg P /pot). The phosphate fertilizer use efficiency for TSP, MPR and TPR were 94.1 %,38.6% and 31.8% respectively. The relative phosphate fertilizer use efficiency for MPR and TPR was 40% and 34% respectively. It was tentatively concluded that MPR and TPR have very low agronomic value for the study soils.
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