Composting cattle manure from zero graziing systems with agro-organic waste to minimise nitrogen losses in smallholder farms in Kenya. Tropical and Subtropical Agro ecosystems 2006 (6)
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Livestock manure is a valuable source of plant nutrients for crop production in the Central Kenyan highlands but its quality in terms of available nitrogen (N) is low due to considerable N losses through ammonia volatilization. This study aimed at assessing the potential of agroorganic wastes to reduce N losses from manure heaps during the storage period. Three organic amendments selected from a laboratory simulation experiment were evaluated under farmers’ conditions in Karura, Kiambu District for their ability to reduce N losses from cattle manure heaps. The effect of a polyethylene sheet covering of manure heaps on N retention was also determined. There were eight treatments that comprised three agro-organic amendments (maize stover, coffee pulp and sawdust) and the control, with or without a polyethylene cover. Agronomic effectiveness of the “treated” manure samples and N uptake by maize seedlings was evaluated in a glasshouse experiment. Total N content of manure amended with organic materials ranged from 1.26 to 1.85%. The N in manures with organic amendments at the start and at the end of storage was significantly different (p ≤ 0.05). Cumulative N loss ranged from 1.60 to 6.80 g kg-1 depending on the type of amendment. Nitrogen lost from non-amended manure was 2.74 g kg-1 with polyethylene cover and 6.80 g kg-1 without the polyethylene cover, which represented 19 and 46% of the initial N respectively. Maize growth improved significantly (p≤0.05) with increasing rates of manure irrespective of the organic treatments except for manure amended with sawdust. Treatments that received the recommended rate of N at 100 kg N ha-1 had significantly higher (p≤0.05) biomass (21.55 g plant-1) than the control which produced only 2.78 g/plant. Nitrogen uptake increased with increasing rates of manure and was higher (p≤0.05) with manure amended with coffee pulp. Covering manure heaps to reduce moisture loss was also beneficial in reducing N losses.