Carbon and nitrogen mineralization from selected organic resources available to smallholder farmers for soil fertility improvement in Zimbabwe

Abstract

A study was conducted to assess the N release dynamics of three organic resources widely used by smallholder farmers in sub-Saharan Africa to improve soil fertility. Addition of cattle manure, miombo and mango (Mangifera indica) litter to soil increased (p < 0.05) CO2-C evolution compared to unamended soil. Cumulative CO2-C evolution in all the three organic amendments followed first order kinetics (R2 = 0.89 - 0.99). Slight N mineralization occurred when cattle manure was added to soil and addition of manure in combination with mineral N had no effect on the extent of N mineralization. Compared to unamended soil, miombo litter induced net immobilization of N for 60 days and thereafter net N mineralization occurred. Both untreated and composted mango litter immobilized N (up to 15 mg N kg-1) during the 77 day incubation. It was concluded that all the three organic resources were poor and inadequate sources of N for plant growth in the short term and should therefore be supplemented with mineral N to reduce N immobilization and consequent N deficiency in plants. However the organic resources may improve the soil physical environment and also contribute to soil organic matter build up in the long term. Key words: Cattle manure, Mangifera indica, miombo litter, N mineralization and immobilization