Composting coffee pulp with Minjingu phosphate rock improves phosphorus availability for tomato uptake

A glasshouse experiment was conducted to evaluate the effect of composting coffee pulp with phosphate rock on phosphorus (P) availability for plant uptake. Coffee pulps composted with or without phosphate rock and Minjingu phosphate rock applied alone were evaluated as source of P for tomato growing on a Chromic Acrisol. All P sources were applied at varying rates of 0, 20, 40, 60, 80 and 100 mg P kg-1 and all other limiting nutrients were adjusted to recommend levels using industrial fertilizers and/or reagent grade laboratory salts. Phosphorus uptake of tomato plants receiving coffee pulp composted alone, Minjingu phosphate rock alone and coffee pulp composted with Minjingu phosphate rock increased 11, 13 and 18 times above the control. Observed P concentrations in tomato plants receiving external P sources were 23, 36%and 110% of the concentrations in control plants. Composting coffee pulp with Minjingu phosphate rock was concluded as a potential technique for improving phosphorus availability and uptake by tomato.  Key words: phosphate rock, coffee pulp, phosphate rock enriched compost, tomato, phosphorus uptake.