Abstract
Case studies on the assessment of local organic fertilisers (OFs) in their quality (decomposition characteristics and nutrient availability for crops) are few in sub-Saharan Africa (SSA). This study assessed the quality of local OFs from the Ethiopian Rift Valley. The decomposition characteristics were assessed by acid detergent fibre analysis methods, while the short-term nitrogen availability was assessed by a combination of laboratory incubations and inorganic nitrogen and acid detergent soluble nitrogen determinations. A commercial hand-held reflectometer (RQFlex) was used for determining nitrogen components. The mean acid detergent soluble organic matter contents exceeded 250 mg g−1, indicating the OF feedstock contained much of the readily decomposable organic matter. Some of the indigenous compost (kosi) samples showed net nitrogen immobilisation during the initial period of incubation, followed by net nitrogen mineralisation in one month of incubation with 4% of the nitrogen mineralisation rate. Kosi should be applied to a field one month before seeding. Short-term nitrogen availability from kosi was too low to substitute for inorganic fertilisers. The combination of the simple analysis methods shown in this study is a quick, cost-saving, and accurate quality assessment approach for OFs, which can be useful in the field and at experimental stations in SSA.
Highlights
In broader parts of Eastern and Southern Africa, cattle are the most important livestock and are kept for ploughing, milk, and manure uses[1]
Both the organic matter (OM) decomposable within 14 days and the OM decomposable within 3 months of the barley and tef straws was the highest among the organic materials, no significant difference was observed between the organic materials
This suggests that mineralised N that was derived from decomposable OM in approximately 1 month of incubation was nearly 0, which was supported by the OM fraction that is decomposable within 14 days contained in the kosi and fast compost (Table 3)
Summary
In broader parts of Eastern and Southern Africa, cattle are the most important livestock and are kept for ploughing, milk, and manure uses[1]. Available organic resources among smallholder farmers in SSA have divergent qualities[7], which decompose and release various qualities of nutrients in soils at different times[8], reflecting differences in nutrient availability and overall crop yields from each resource[9] Besides these two parameters, i.e., decomposition characteristics and nutrient availability, maturity and stability are other important parameters for quality assessment of OFs10. How farmers’ management practices affect chemical composition of manure[13,14,15]; (iii) analysis of the relationship between farmers’ simple methods for manure/compost quality assessment and those chemical compositions[16]; and (iv) analyses of how different production and storage methods of cattle manure affected the manure organic N composition and release in soil[17] Of these previous studies, (i) discussed decomposition characteristics of OFs and (iv) discussed N availability from OFs for crops.
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