The potential of short duration improved fallows with selected trees and shrubs for crop productivity enhancement in the highlands of western Kenya

The potential of short-duration improved fallow (6–12 months) with MPTs for crop production in the highlands of Western Kenya was investigated through a series of experiments comprising species screening, establishment methods and determination of optimum planting densities. In the first experiment, 12 multipurpose trees and shrubs were compared. The highest biomass productivity and nutrient yields (nitrogen and phosphorus) after one season's (6 months) growth were obtained from Crotalaria grahamiana (300 kg N and 27 kg P/ha), Crotalaria mucronata (252 kg N and 16 kg P/ha) and Crotalaria striata (219 kg N and 16kgP/ha). In the second experiment, six herbaceous legumes were tested. The most productive species in terms of nutrient yields were Calopogonium mucunoides, Desmodium uncinatum, Macroptilium atropurpureum and Glycine wightii (more than 150 kg of N and 19 kg of P/ha after 6 months). In a third experiment, an improved fallow system was tested with four species and two methods of planting over two seasons (12 months). The fastest growth was obtained with T. vogelii and T. diversi folia which produced 100 kg of N each at 6 months. Sesbania sesban was more productive at 12 months (161 kg/ha) compared with 6 months (60–73 kg/ha). In terms of nutrient yields, direct seeded plants of T. vogelii were as productive as transplanted seedlings. For S. sesban, the fastest growth was obtained by seedlings, but at 12 months the productivity of S. sesban from seedlings and that from direct seeding was similar The highest maize grain yield following 12 months of fallow was obtained with S. sesban (3840–5089 kg/ha) and T. vogelii (4162–4849 kg/ha) compared to natural fallow (1968 kg/ha) which was not significantly different from continuous cropping (1854 kg/ha). In a fourth trial, seven densities (from 10,000 to 160,000 plants/ha) were tested. In terms of biomass and nutrient yields 2 months after planting the performance of the different densities were similar. Maize grain yields following 12 months of fallow were also similar and were not different from those obtained from continuous cropping and natural fallow treatments without inorganic P application. The difference in maize grain yield between improved fallow with sesbania (2875 to 3343 kg/ha) couch grass-infested natural fallow (1277 kg/ha) and continuous cropping (12017 kg/ha) were significant (P0.05) when inorganic P was applied.

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DOI:

https://doi.org/10.1080/00128325.1996.11663295

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