Potential of Tephrosia vogelii hook F. and Tithonia diversifolia (Hemsley) A. Gray short duration fallows for improving the productivity of maize in western Kenya

Abstract

Earlier studies showed beneficial effect of 1 to 3 years-improved fallows on maize production compared to the natural fallow. This period however is still too long for small-scale farmers who must use the land to produce food at least once a year. In fallow systems the rotational effect and the effect of above ground biomass on maize yield have not yet been studied separately. The objective of this study was to evaluate the potential of Tephrosia vogelii and Tithonia diversifolia short duration fallows in improving soil fertility and maize yield when compared to the natural fallow and continuous maize crop with or without fertilisers. Two cycles of Tephrosia, Tithonia and natural vegetation six month fallows alternating with two consecutive maize crops were grown at Maseno, in Western Kenya on well-drained deep clay soils low in available nitrogen (N) and phosphorus (P). At the fallow cutting time, the biomass produced and nutrient accumulated were quantified and decomposition patterns determined. The fallow biomass were applied to the maize crop as fertiliser input and each plot was then split into two for o and 20 kg inorganic P addition. Soil samples were taken at the beginning and the end of each fallow and crop season. Both, Tephrosia and Tithonia produced more biomass than the natural fallow vegetation. Roots obtained from 0 to 45 em soil depth were a significant component and contributed 18, 36 and 65 % of total biomass and 15, 8 and 21% of total biomass N for Tephrosia, Tithonia and natural fallow, respectively. Tithonia produced more litterfall than the other two fallows. Tephrosia material and Tithonia litter and above ground biomass had higher N content, compared to the natural fallow biomass. The proton consumption capacity of Tithonia leaves was high, about 50 cmol(+)/kg of biomass while that of Tephrosia materials, natural fallow leaves and maize stover was medium, about 20 cmol(+)/kg. Natural fallow roots mainly comprising of Digitaria sclarum rhizomes had the least proton consumption capacity. Tithonia leaves decomposed very fast while Tephrosia stems, Tithonia and natural fallow roots were the slow to decay. More than 80 % of nutrients accumulated in the mixture of Tithonia leaves plus stems were released during the first month after biomass incorporation into the soil whereas Tephrosia and natural vegetation biomass required two to three months to get the same percent nutrient release. Grain yield of the maize following the shrub fallow was about 2.5 to 3 Mg ha-1 compared to continuous maize crop which produced 1.3 Mg ha-1 . Inorganic P added to these systems increased the yield by about 40%. Plots where the biomass was removed produced less maize, compared to the fallow or biomass incorporated systems. The yield of maize subsequent to the natural fallow was lower compared to that of the maize following the shrub fallow, but higher than that of the continuous cropping system. The effect of organic and inorganic P inputs on the second and third maize crop decreased progressively over time. No significant changes in soil bulk density and chemical properties were found at the fallow cutting or at the maize harvesting periods. However, mineral N was leached down the soil profile during the first maize-growing season. The various organic inputs obtained from the three fallow species were all low in P and showed different nutrient release patterns. When these inputs were applied to the crop at the same time, the pattern release of nutrients was not always properly matching with the maize nutrient requirement stages. Three observations, namely: an N deficiency in plots where large amount of Tithonia biomass was applied, a lack of effect of fallows or single biomass application on soil properties and a decrease over seasons of the effect of biomass on maize performance indicated that sustained crop production can not be obtained with one short duration fallow. In highly depleted soils, 'fallow-maize-fallow' rotation may be more sustainable than 'fallow-maize-maize-fallow' or 'fallow-maize maize- maize-fallow' rotations. In a no-fallow system, application of biomass once or twice a year will be more beneficial than a single application every 3 or 4 cropping seasons