Effects of Duration of Contact and Rates of Minjingu Phosphate Rock (MPR) on its Release of P in a Kanhaplic Haplustult

Abstract

An incubation pot experiment was conducted at the Sokoine University of Agriculture, Morogoro, Tanzania to study the effects of times of contact and rates of Minjingu phosphate rock (MPR) applied to a Kanhaplic Haplustult on the release of P from the MPR. The soil was mixed with MPR at rates equivalent to 0.0, 25.0, 37.5, 50.0 and 75.0 mg PI kg soil. The incubation periods were 30, 60, 90, and 120 days. The moisture content of the soil in the pots was maintained at about field capacity during the incubation periods using distilled water. Release of P from the MPR increased with increase in MPR rates and incubation periods. The interaction between incubation periods and MPR rates explained about 86.8% of the variation in P release from the MPR. MPR rates accountedfor 76.6% of the release of P, while incubation periods accounted for 10.3% of the dissolution. The soil pH and extractable Ca were found to increase slightly with increase in MPR rates but decreased with increase in incubation periods. The exchangeable acidity and exchangeable Al decreased with increase in MPR rates, and slightly increased with incubation periods.

Keywords: Minjingu phosphate rock, Kanhaplic Hapluslult, Bray-I-P, exchangeable acidity, exchangeable AI, exchangeable Ca, soil pH, P-release

Tanzania J.Agric.Sc. (2006) Vol.7 No.1, 8-15