Agroforestry systems with trees for biomass production in western Kenya

Abstract: Low agricultural production and a decline in fuelwood resources are serious constraints for subsistence smallholder farmers in western Kenya in the sub-Saharan African region. Furthermore, low soil fertility and general environmental degradation has contributed to the build-up of the parasitic weed Striga hermonthica. Improved cropping systems have to be introduced to address the interrelated problems of declining soil fertility and Striga infestation. Two studies were performed in the highlands of western Kenya, one with improved fallows with Sesbania sesban, and one with hedgerow intercropping. Farmers can use Sesbania not only for soil improvement, but also for fuelwood, poles and fodder. Maize (Zea mays L.) yields and levels of Striga infestation on farm land were assessed after improved fallows with leguminous tree/shrub Sesbania sesban. Six experimental treatments were arranged in a phased entry, and randomized complete block design. The treatments were 6 and 18 month improved fallow, 6 and 18 month natural fallow consisting of regrowth of natural vegetation without cultivation, continuous maize cropping with and without fertilizer application. Results showed that improved fallows increased maize yield relative to continuous unfertilized maize. The results also indicated that a new rotation of Sesbania could be recommended after 2-3 seasons to improve maize production. Short-duration natural fallows were ineffective. The 6 and 18 month improved fallow produced 21 t ha⁻¹ and 61 t ha⁻¹ Sesbania biomass, respectively. The high production of Sesbania biomass was an added benefit to this type of improved fallow systems. Striga plant populations were not significantly affected. Effects of hedgerow intercropping on maize yields was assessed in a farmer-participatory trial. Results showed that farmers established dense hedgerows, but annual yields of hedgerow pruning of Leucaena leucocephala and Calliandra calothyrsus were low compared to potentials in the region. There were no significant differences in maize yields, but reduced slopes significantly from 7.2% to 4.5% between alleys. The results showed that improved fallow systems can produce both increased maize yields and wood biomass.