| dc.description.abstract | Farmers in the Central Kenyan Highlands are aware of the consequences of nutrient
depletion and practice complex integrated nutrient management strategies such as
addition of organic and inorganic fertilizers, soil erosion conservation and agroforestry
albeit at a minimal level. These past management practices have resulted in the
development of unproductive nutrient deficient patches that are located at a distance from
the homestead referred to as 'outfields'. Farmers are able to distinguish the unproductive
patches on yield basis and this was confirmed in the laboratory based soil nutrient
analysis.
The study site was Karura catchment scheme in Kiambu District of Kenya. The site is
characterized by humic Nitisols. The aim of this study was to identify the most limiting
nutrient(s) and the most effective soil fertility management practise hereto referred to as
the 'Best-Bet' for ameliorating the soil deficient patches so as to increase crop production
at on farm level. Two test crops commonly grown in the area were used for this study:
kale (Brassica oleracea var, acephala) and maize (Zea mays L.). To achieve this aim, a
study was carried out in three stages; greenhouse experiments, on-farm trials, and
laboratory nutrient analysis of both plants and soils.
The results obtained from both crops indicated that there was a positive response to P and
N application especially in the unproductive soil patches. Application of Cu and/or other
micronutrients (Fe, Mn, Zn, B, Mo and Co) reduced maize productivity especially in the
unproductive patches. Addition of copper improved crop yield only when major nutrients
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were added. Addition of 100 kg K /ha also reduced dry matter and grain yields of maize
in both soil categories meaning that K is not a limiting nutrient in the Nitisols currently.
Application of mieronutrients in combination with nitrogen and phosphorus in both soil
categories resulted in increased dry matter and grain yields. In the unproductive soil
patches where N and P were limiting crop productivity, addition of 100 kg N/ha and 44
kg P/ha, and/or the addition of 215 kg DAP/ha combined with 7 tons/ha cow manure
would be required to improve nutrient availability, restore soil fertility and result in
increased crop productivity. The most limiting nutrients to crop production were found to
be N, P and Cu. Plant nutrient deficiency symptoms could be used as rapid indicators of
plant nutrient deficiencies.
The 'Best-Bet' soil fertility practice of applying 215 kg DAP/ha combined with 7-tons/ha
of cow manure (fanners' practice) was the best soil ameliorative strategy in terms of dry
matter and grain yields in both productive and unproductive soil categories in Kiambu
District. This confirmed the notion that farmers have the best soil ameliorative strategy
but are hampered by internal and external factors e.g. capital and use of organic resources
in their endeavour to increase crop production in their fields.
Crop harvest removal is a major avenue for nutrient loss in these highlands. There is need
to increase the rate of fertilizer and manure application in order to meet the resultant
nutrient deficits following harvesting of kale and maize grains. Intensive nutrient balance
studies need to be incorporated in future research meant for these highlands, | en |
