Numerous researchers have stressed the widespread soil fertility depletion faced by mixed croplivestock smallholder farms in western Kenya. Within smallholder mixed farms, cattle manure can be important nitrogen addition pathways but poor management limits their impact. The goal of this research was to characterize cattle management and the magnitude of related nutrient losses, particularly for nitrogen (N) which is known to be a limiting nutrient and highly susceptible to losses. While N is the main focus, phosphorus (P) and potassium (K) were also considered.
Cattle and manure management of 10 mixed crop-livestock smallholder farms from Vihiga District (western Kenya) were analysed in-depth to determine nutrient cycling efficiencies (NCE), causes and key entry points to improve management. A typology for cattle subsystem management was used to group farmers according to production goals and constraints. This approach clarified why improved nutrition (as a means to improve cattle productivity and, as a positive side-effect, manure quality) is not an open option given the production constraints for part of these farmers. Type 1 producers, given their labour and income constraints have as main production goal herd maintenance and adjust their production level to what is available. In type 3, due to greater labour and income availability farmers are closer to a situation in which they adjust their feed input level to the requirements by their production goals - milk in this case. 2nd type farmers represent an intermediate situation.
Nutrient efficiency losses across these case studies occurred mainly through: (1) low proportion of excreted manure being collected due to considerable off-farm cow dung excretion (i.e. type 1 and 2), losses before collection when cattle are tethered on-farm (i.e. type 1) and partial collection of on-farm excreted manure when ZG units are present but feed availability is reduced (i.e. type 2); and, (2) important material losses (i.e. type 1 and 3) as well as reduction of nitrogen concentration (i.e. all cases) through volatilization of NH3, leaching of soluble N (i.e. NH4+ and NO3-) and denitrification from unprotected heaps and pits. As a result differences between type 1 and 3 (i.e. 29 and 30%, respectively) are insignificant while type 2 (i.e. 45%) have slightly greater efficiencies.
Nitrogen additions to the fields were done mainly via stored manure (i.e. 40%) followed by collected manure (i.e. 31%) and inorganic fertilizers (i.e. 29%). However, current overall low quality of excreted manure (i.e. 14 kg N, 3 kg P and 13 kg K per ton DM of excreted manure), even under best found feeding strategies (i.e. type 3), implies greater NCE would not counteract soil fertility depletion without significant supply of external inputs. Given the low nutrient concentration of stored and collected manure, soil organic matter improvement (and its impact in soil workability and reduced soil erosion) could constitute the farmers’ main driving factor when using this resource.