The Effect of Composting Cover Crop Biomass with Rock Phosphates on Nitrogen and Phosphorus Availability Under Smallholder Maize Production in the Northern Zone of Tanzania.

Nitrogen (N) and phosphorus (P) are the key nutrients limiting crop production in most tropical countries including Tanzania where more than 50% soils are highly weathered, leached and deficient in N and P. While such soils require substantial N and P fertilizer inputs for crop production; fertilizer use by smallholder maize producers is primarily limited by their high cost. This results into continuous cultivation with limited or without fertilizer application, soil mining, and consequently declining crop yields. P-enriched composts produced from leguminous cover crops and locally available phosphate rocks could serve as an affordable alternative to alleviate N and P deficiencies but phospho-composting is not exploited in Tanzania. A study was conducted to evaluate the potential of composting selected leguminous cover crop biomass with two Tanzanian phosphate rocks and the possibility of using the composts as alternative for industrial N and P fertilizers under smallholder maize production in Tanzania. Three cover crops (Dolichos lablab, Mucuna pruriens and Crotalaria juncea) were grown on strips, harvested at flowering stage and air dried before composting. Air dry biomass was analyzed for nutrient content; then, composted by pit method with Minjingu or Panda Hill rock phosphate. Mature composts were used to fertilize maize with control plots receiving no external inputs or combinations of phosphate rocks with Urea for comparison. Combinations of phosphate rocks and Urea resulted into higher maize yield than composts, while compost produced from Crotalaria biomass and phosphate rock performed better than other composts. 

Key words: Cover crops, phosphate rocks, Nitrogen, Phosphorus, Smallholder maize production