Managing Striga infestation on maize using organic and inorganic nutrient sources in western Kenya

Although the use of foliar biomass (organic residues) of trees and shrubs as a source of nutrients to food crops has been recommended in many countries in sub-Saharan Africa, the effects of biomass quality on Striga (Striga hermonthica) infestation and yields of maize are not known. Organic residues of six species Tithonia diversifolia, Sesbania sesban, Senna spectabilis, Calliandra calothyrsus, Lantana camara and Croton megalocarpus were compared with inorganic nutrients applied through fertilizers at five rates of phosphorus (0, 10, 25, 50 and 150 kg P ha(-1)) in combination with 120 kg N ha(-1), and 150 kg P ha(-1) applied alone. The study was conducted in western Kenya over 2 years (four cropping seasons) on a farm severely infested with Striga hermonthica and deficient in P. The fresh foliage of species at 5 t (dry weight) ha(-1) and fertilizers were applied every season to the respective plots. Striga infestation was lowest where 120 kg N was applied with or without P. Phosphorus application alone did not influence Striga infestation. Reduction of Striga by organic residues depended on their rate of decomposition and N mineralization, which in turn was determined by quality in terms of C:N and lignin+polyphenol to N ratios. With a high tissue concentration of N and low lignin and polyphenols, Tithonia biomass rapidly mineralized N and reduced Striga, similar to inorganic N. Although Sesbania biomass also decomposed rapidly, it reduced Striga only in the fourth season. Other organic residues did not affect Striga infestation probably because of slow decomposition and slow release of N. Crop yields were primarily affected by P deficiency, so the reduction of Striga alone did not result in increased yields unless P deficiency was corrected, Although biomass of Croton and Lantana had limited effect on Striga, they increased yield on this P-deficient soil by supplying 10-13 kg P ha(-1) per season. Only the high quality organic residues such as Tithonia can suppress Striga infestation, besides supplying nutrients for increasing crop productivity on smallholder farms.