The Role Of Farmyard Manure In Improving Maize Production In The Sub-Humid Highlands Of

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Francis Muchoki Kihanda
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Francis M K
The fanning systems in the highlands of central Kenya are characterised by continuous cultivation and cropping due to pressure on agricultural land and low nutrient input resulting in low crop yields. N is one of the major soil nutrients limiting maize production in the region and farmers rely heavily on farmyard manure (FYM) produced at the farm level to improve soil and crop productivity. Soil acidity is also a major constraint in maize production in the Ando-Humic Nitisol soil. A study was therefore conducted to detennine the role of FYM as a source of plant N under field and controlled experiment in two of the major soil types in the area. Recovery of plant N derived from FYM and inorganic N fertilizers was determined using 15N isotopic techniques. FYM samples produced from the study area were collected, characterised and based on their C:N ratio and ash content, N mineralization studies were conducted in pot experiments using mineral N measurements and crop uptake. Maize yields were increased with increasing rates of FYM application but maize grain yields above 3.5 t ha-1 were only obtained when both FYM and NP fertilizer were applied. Removal of acidity constraint through liming was essential in order to obtain response to applied FYM or NP fertilizer to maize growth and yield in the acidic Ando-Humic Nitisol. Combined application of FYM and K resulted in maize grain depression in the Humic Nitisol of Embu. A decline in soil organic matter was observed in the two field trial sites which were under continuous cropping and cultivation but combined application of FYM and NP fertilizer reduced the organic carbon loss by 1-3 t ha-1 in the soil (0- 20 cm). Plant N derived from soil organic matter decreased by 30 % where both FYM and NP fertilizer were applied. Based on the N uptake by maize from plots that had received NP fertilizer, it was concluded that the uptake of N from FYM was not in synchrony with the period of rapid growth in maize. The recovery of fertilizer N by the maize plants was low and less than 20 % while the recovery of FYM N in the maize plants applied at similar rate to that of inorganic N fertilizer was 25% in both soil types.