The potential of agro-organic wastes to reduce nitrogen losses from cattle manure used by smallholder farmers in the central Kenyan highlands.

Abstract

Livestockmanure is a valuable source of plant nutrients for crop production in the Central Kenyan highlands but its quality in terms of available nitrogen is low due to considerable nitrogen losses through ammonia olatilization. This study aimed at assessing the potential of agro-organic wastes to reduce nitrogen losses from manure heaps during the storage period. Three organic amendments selected from a laboratory simulation experiment were evaluated under farmers' conditions based in Karura, Kiambu District for their ability to reduce nitrogen losses from cattle manure heaps. The effect of a polyethylene sheet covering of manure heaps on nitrogen retention was also determined. There were eight treatments that comprised three agro­organic amendments (maize stover, coffee pulp and sawdust) and the control. Agronomic effectiveness of the treated manure samples and N uptake by maize seedlings were evaluated in a glasshouse experiment. 19% and 46% of the initial nitrogen respectively. Maize growth improved significantly (p:s;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 nitrogen at 100 kg N ha-' had significantly higher (p:S;0.05) biomass of 21.55 g/p1ant while the control produced 2.78 g/p1ant only. Nitrogen uptake increased with increasing rates of manure and was higher (p-;O.O5) with manure amended with coffee pulp. Covering manure heaps to reduce moisture loss would also be beneficial in reducing nitrogen losses.