Effect of lime on plant-extractable phosphorus in acidic soil
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Zambia like many other tropical countries is dominated by soils that are very deficient in phosphorus. Currently all phosphate fertilizers that are imported from outside Zambia are relatively expensive for small scale farmers. An incubation study was conducted in laboratory to determine the effect of CaCO3, Ca(0H)2and CaO on soil pH and Bray-1 extractable phosphorus in an acid soil. Five rates of lime equivalent to 1. 2. 3. 4 and 5 ton CaCO3/ha, were applied as treatments in 500g of a strongly acid soil. Each lime treatment was replicated thrice. The soil was incubated at field capacity for 8 weeks during which it was analysed for available phosphorus using Bray I solution. Soil pH was monitored using 0.01 M CaCl2. The application of lime significantly increased soil pH and available P. T he highest mean amount of P was 8.3 mg P/kg and was generated by CaO and the lowest was 7.1 mg P kg generated by CaCO;,. The period of incubation also had a significant effect on available P, but not pH, At week 8. the mean available P was 9.529 mg/kg as the highest at the lowest pH of 5.4. At 3weeks. the mean available phosphorus was 6.235mg/kg as the lowest and its lowest pH of 5.5. Although there were differences in the amounts of extractable P, there was a weak positive correlation of 0.24 between P and pH at 99% confidence level.
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