Improving Phosphate Rock Use Efficiency In Organic Farming

Between 45 to 81% of the total phosphorus (P) fertilizer applied to soils in sub-Saharan Africa is absorbed in the soil, which among other factors reduce crop yield and contributes to high poverty in the region.  The objective of the study was to assess the effect of different phosphorus rock (PR) management on carrot yields, P recovery and use efficiency.  Different volumes (100, 200, 300, 400, and 500 mLs) of organic (lemon and pineapple) juices and water were used to dissolve 100 g of PR. The available P concentration in the solution was determined using a standard protocol. The solution with the high P concentration as well as powdered PR was each composted with manure and crop residues. Thereafter, a field experiment was set up on Humic andosols and Orthic acrisols to compare the effect of the dissolved PR applied directly with compost, to dissolved PR composted,  powder PR composted, powdered PR applied directly with compost, Triple supper phosphate applied directly with compost, compost and the soil alone (as a control). Our findings showed that lemon juice could release over 65% of the available P from PR and the combined application of the dissolved PR and compost at planting increased P recovery and use efficiency, and carrot yields on both soils as compared to the other treatments.