Manure Management Methods to Enhance Nutrient Quantity and Quality on Smallholdings in the Central Kenya Highlands

Abstract

Smallholder mixed farming systems of the Central Kenya Highlands rely upon organic inputs, particularly manure, to maintain soil nutrient levels and stabilize crop yields. However, nutrient losses during collection, composting and application of manure can be substantial. The effects of simple methods for combining cattle faeces, urine and rejected maize stover forage on the conservation of nutrients during storage and composting and on maize productivity over two seasons after field application of manure were investigated. The methods were; (1) faeces (F) + urine (U) + feed refusals (FR) mixed in a deep-litter system by a steer (method S), (2) F + U + FR, (3) F + FR, (4) F + U, all collected and mixed manually, and (5) F (faeces only). F + FR effectively conserved the N in the faeces and feed refusals. With S and F + U + FR, after 60 days collection and 84 days composting, the additional N from urine was completely lost and only 5.5–5.6 g N kg−1 steer initial liveweight (LWi) was obtained compared with 6.5 g N kg−1 LWi for F + FR. With F + FR, 4.7 g N kg−1 LW, from urine was also potentially available for direct return to the soil, resulting in a 11.2 g N kg−1 LWi return to the soil. Composted F and F + U manures had lower N concentrations than F + FR. They also had higher C:N ratios than F + FR and F + U + FR, though they did not differ significantly from S. All of the experimental manures, applied at a rate to give 75 kg N ha−1, significantly improved maize grain and stover yield in the first season compared with an unfertilized control. With the experimental manures, the greatest yield (F + FR, 4336 kg ha−1) was significantly higher than the lowest yield (F + U, 2916 kg ha−1). With the best manure collection strategy, F + FR, the manure from one steer (mean liveweight 212 kg) was worth an extra 356 kg of maize grain and 295 kg of stover above the control level from 0.1 ha of land over the two seasons. The best collection method gave up to twice as much additional grain as the worst strategy. Livestock make an important contribution to intensive smallholder farming through their contribution to soil fertility. This research has shown that crop yield increases gained by adopting simple techniques for better care of manure during collection and storage can be substantial and extend over at least two seasons.