Maintenance of soil fertility under intensive maize cropping in Machakos District, Kenya
2000
Okalebo, J.R.(KARI-Headquarters, Nairobi, Kenya) | Simpson, J.R.(Holmes Cresent, Campbell, Act, Australia) | Probert, M.E.(CSIRO Divison of Tropical Crops and Pastures, Lucia, Australia) | Okwach, E.G.(KARI-Headquarters, Nairobi, Kenya) | McCowan, R.L.(QDPI/CSIRO Agriuculture Production Syatems Research Unit, Toowooba, Australia)
There is an urgent need to develop farmer¬acceptable methods of maintaining soil fer¬tility in medium-potential areas such as those in Machakos District where low¬input dryland cropping continues every season on acrisols, alisols and luvisols of low organic matter content. On soine of the farms, maize yields are already very low. In this paper we report the effects of treat¬ments involving differential applications of stover mulch, nitrogen (N) and phosphorus (P) fertilizers, and increased plant popula¬tion, in an experiment at the National Dryland Farming Research Centre, Katumani. This experiment began in 1989 cmd has been continually cropped for over five years (11 crops). The effects of treat¬ments on maize yields have been marked (means yields varied from 1.3 to 2.9 tonnes/ha) but the effects so far on total soil carbon (C) and N are less obvious, with a decline of about 20% at 'low inputs' and maintenance of the initial levels at 'high inputs' (40 - 70 kgN, 10 kg P /ha and stover return). The return of stover mulch increased available soil moisture, by reduc¬ing run-off, but an analysis showed no residual accumulation of fine particulate organic matter in the soil (by the TSBF method). Therefore the C and N added as stover appeared to be continually dissipat¬ed under cultivation. The inorganic fertil izers caused some acidification (0.36 pH units in H2O) at 0.15 cm depth on this low CEC soil.
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