Abstract:
Soil nutrient depletion as a result of
continuous cultivation of soils without adequate
addition of external inputs is a major challenge in
the highlands of Kenya. An experiment was set
up in Meru South District, Kenya in 2000 to
investigate the effects of different soil-incorporated
organic (manure, Tithonia diversifolia, Calliandra
calothyrsus, Leucaena leucocephala) and
mineral fertilizer inputs on maize yield, and soil
chemical properties over seven seasons. On average,
tithonia treatments (with or without half
recommended rate of mineral fertilizer) gave the
highest grain yield (5.5 and 5.4 Mg ha–1 respectively)
while the control treatment gave the
lowest yield (1.5 Mg ha–1). After 2 years of trial
implementation, total soil carbon and nitrogen
contents were improved with the application of
organic residues, and manure in particular
improved soil calcium content. Results of the
economic analysis indicated that on average
across the seven seasons, tithonia with half
recommended rate of mineral fertilizer treatment
recorded the highest net benefit (USD 787 ha–1)
while the control recorded the lowest (USD
272 ha–1). However, returns to labor or benefitcost
ratios were in most cases not significantly
improved when organic materials were used.
