Effectiveness of partially acidulated and beneficiated Minjingu rock phosphate as sources of phosphorus for maize and sorghum in three acid soils of Tanzania.

摘要

Pot and field experiments were conducted to compare the agronomic effectiveness (yield and P uptake) of partially acidulated rock phosphate (25% PARP and 50% PARP) and beneficiated Minjingu rock phosphate (BMRP, obtained by sieving, drying and concentration of P in the rock phosphate) with that of triple superphosphate (TSP) as sources of P for maize and sorghum. Two pot studies and 2 field experiments were conducted. Maize was the test crop in the initial pot study and in the field experiments while sorghum was used to evaluate residual P in pots. Three soils, Magadu (Oxic Haplustult), Gate (Tropeptic Eustrustox) and Mlama (Volcanic derived soil), varying widely in properties were used. Results from the initial pot experiment with maize indicatedthat all the P carriers had similar effectiveness to YSP in the strongly acidic Mlama soil (pH 4.7) but were inferior to TSP in the less acidic Magadu and Gate soils (pH 4.9 and 5.8, respectively). In the residual P pot study with sorghum, all the P amendments were equally effective to TSP in the Mlama and Gate soils and generally superior to TSP in the Magadu soil indicating that over time the rock P sources underwent considerable dissolution. Field experiments revealed trends similar to the initial pot experiment in the Magadu and Gate soils. The PARPs and BMRP were generally inferior to the reference TSP fertilizer. It is suggested that the Minjingu rock phosphate products may be effective sources of P for the Mlama soil and other soils with similar characteristics. The PARPs could also be economically attractive P alternatives on soils which are not very acidic.