Limestone, Minjingu Phosphate Rock and Green Manure Application on Improvement of Acid Soils in Rwanda

A study was conducted to assess the effects of limestone, Minjingu Phosphate Rock (MPR) and green manures (GMs) on maize yield, soil properties and nutrient uptake. 13 treatments were tested namely an absolute control, recommended rate of NPK and burned lime, NP and limestone, combinations of any two of the following materials: limestone, MPR, tithonia GM, tephrosia GM, and combinations of three of these amendments. Soil analysis at the beginning of the experiment revealed that the soil was deficient in N, P, and K, had low levels of Ca and Mg and toxic levels of exchangeable Al. Application of GMs improved the supply of N and K appreciably while limestone played a great role in reducing exchangeable Al. A significant contribution of P was from MPR. A combination of MPR, GMs and limestone supplied ample amounts of N, P, K, Ca, Mg and reduced exchangeable Al and hence resulted into high yield. In general tithonia application gave higher yields than tephrosia. These results were consistent with the higher quality of tithonia biomass relative to tephrosia biomass. The green manures in combination with MPR increased P uptake significantly. Nutrient concentration data indicated serious deficiencies of P, K and N consistent with soil analysis data but Ca and Mg were in the sufficiency range. Furthermore, the results indicated that using a combination of limestone, MPR and GMs is the best strategy in improving acid soils in Tonga, Rwanda.