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Studies were conducted under pot and field conditions to evaluate the effects of Minjingu phosphate rock (MPR) placement methods and rates of organic residues on MPR dissolution, phosphorus (P) availability and maize yields from a Dystropept soil in Sasanda, Mbeya and from an Oxic Haplustult in Magadu, Morogoro, Tanzania. The treatments in the pot experiment were control, broadcasted MPR at the rate of 80 kg/ha, banded MPR on a 5 cm-wide strip, and 20-cm band MPR + OM applied together at 2, 4, or 8 t/ha and incorporated down to 20cm depth. In the field experiment an additional treatment, 20-cm wide MPR band incorporated to 20 cm, was included. The field experiment was laid out using the Randomized Complete Block Design with four replications while the pot experiment was laid out using the Completely Randomized Design with three replications. The results showed that MPR alone increased yields over those of the control treatments. Banding of MPR together with OM at the rates of 2, 4, or 8 t/ha significantly (P=0.05) contributed to increased P availability from MPR and to higher maize dry matter and grain yields. In the pot experiment, MPR + OM at 2, 4 and 8 t/ha increased DM yields from 4.10 to 70.87 g/pot in Sasanda soil and from 14.14 to 76.17 g/pot in Magadu soil. In the field experiment at Sasanda, MPR + OM at 2, 4 and 8 t/ha increased extractable P in the soil from 0.18 to 0.47 mg/kg, and maize grain yields from 0.36 to 3.38 t/ha. The yield increases were proportional to the increasing rates of the OM applied. |
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