Reclamation of an acidic soil of Rwanda’s central upland by composts based on natural vegetation biomass

Abstract

A study on total acidity reduction and the exchangeable aluminium neutralization by composts made from natural vegetation biomass was carried out on an acidic soil of Rwanda. The initial soil analysis showed that the average pHW (pH measured in water) was 4.4; the average concentration of exchangeable Al and the total acidity were respectively 3.70 and 4.45 cmolc.kg^{- 1} of soil. Five types of composts and NPK_17-17-17 fertilizer were applied to the soil under a splitplot experimental design. Two doses of composts (30 and 60 t.ha-1) were applied while the NPK fertilizer was applied to a dose of 300 kg.ha^{- 1}. The experiment lasted two years and four samplings were carried out to evaluate the impact on pH, exchangeable aluminium and total acidity. The results at the end of two years show that the pHW increased by 0.2 units with only the application of the compost at the beginning of the experiment at a dose of 60 t.ha^{- 1}. In addition, the results show that the pH remained low in the control plots and those received NPK. After only five months, the Al3+ was reduced of 32 and 53 % respectively with 30 and 60 t.ha^{- 1} of compost. At the end of the two years of experimentation, the concentration of Al3+ increased again but without reaching the initial level except for the plots treated with the mineral manure NPK. The same trend was observed for the case of the exchange total acidity.

Keywords: acidic soil, compost, exchangeable aluminium, soil pH, Rwanda