Use of Calliandra Calothyrsus and Leucaena Tricandra Tree Species for Soil Nutrient Enhancement in Chuka Division, Central Highlands of Kenya
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The central highlands of Kenya are characterized by high soil and nutrient losses through soil erosion and leaching. Research has reported positive results from the use of appropriate vegetative contour hedges since they are able to hold topsoil while simultaneously capturing and pumping up leached nutrients. It has also been shown that farmers' adoption of new technologies is dependent on their perception of those technologies. Against this background, an on farm trial involving use of Calliandra, Leucaena and napier contour hedges was started in farmers fields of Chuka Division to evaluate the feasibility of these technologies in the control of soil and nutrient losses. The trial farmers were recruited on the basis of gender and slope after a Participatory Rural Appraisal (PRA). The slopes were categorized as 5-10, 10-20, 20-30 and> 30% slope. Treatments were laid down on these slope categories along the contours in a zig-zag manner with an inter-row spacing of 0.25 m, intra-row spacing of 0.5 m and a variable inter-hedge spacing depending on the slope. Soils were sampled at the start and 20 months after establishment of the trials at 0-30, 30-90 and 90-150 em depths. Soils from 0-30 ern depth were analysed for pH, Ca, Mg, K, C, N, P, and inorganic N, while soils from 30-90 and 90-150 em depth were analysed for inorganic N only. Farmers' perceptions of these technologies were determined by use of questionnaires. Treatments that had trees either as sole or combination hedges registered a significant (P<0.05) increment in pH, Ca, Mg, P and K as compared to those that were either under sole napier hedge or control after 20 months of experimentation. During the first sampling, all the plots had more mineral-N beyond 0-30 em depth. During the second sampling inorganic N in the 0-30 em depth was significantly higher for Leucaena than the control and napier. Leucaena plots also had higher concentration (P<0.05) of inorganic-N than sole napier plots. The other treatments did not show any significant difference at this depth. Inorganic N at 30-90 em depth was lower (P<0.05) in Calliandra, Leucaena and Leucaena + napier than the control plot. On the other hand at 90-150 em depth, Leucaena, Leucaena + napier and Calliandra significantly reduced (P<0.05) inorganic-N accumulation in comparison with the control and napier. The first season registered higher soil losses than second season for treatments with hedges and vice versa for the control. Soil losses during the first season and second season were lower (P<0.05) in hedge plots for 10-20, 20-30 and >30% slope categories in comparison to the control. However, soil loss on 10-20% slope category during the second season was significantly lower (P<0.05) for napier hedges than for all the other treatments. Calliandra + napier and Leucaena + napier plots lost significantly lower (P<0.05) amount of soil than Calliandra, Leucaena and control at this slope category. Farmers perceptions of appropriate hedgerow species showed that farmers would favor species that would provide quality and quantity fodder, improve crop production, enhance soil fertility, control soil erosion and provide cash income on sale of their products.