Impact of soil nutrient management practices on plant parasitic nematodes of maize in central Kenya
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Maize (Zea mays L.) is the staple food in Kenya. The current average production of 1.5-2 t per ha is far below the germ plasm potential of 3-7 t per ha. Low soil fertility, nematode and insect pests, diseases and poor quality of seed and advisory services are some of the maize production constraints in Kenya. However, there have been major efforts to overcome these production constraints in order to increase maize production. For example, useof animal manure and green manure alone or in combination with sub-optimal levels of inorganic fertilisers and interplanting maize with leguminous trees and shrubs are being recommended to farmers for replenishing soil nutrients. Some of these soil nutrient management strategies have negative or positive effect on plant parasitic nematode populations. The objective of the study was to assessthe impact of some of the soil nutrient management strategies on plant parasitic nematodes of maize, especially lesion nematodes (Pratylenchus spp.), which cause yield losses of up to 50% in maize. The soil nutrient management strategies whose impact on nematodes was assessed were mucuna and crotalaria alone, as intercrops or in combination with half the recommended rate of N fertiliser, and incorporation of cattle manure and green manure (Tithonia diversifolia, Calliandra calothrysus and Leucaena trichandra) singly or in combination with half the recommended rate of N fertiliser. Mucuna and crotalaria intercrops reduced nematode diseaseseverity and population by 20%. Addition of inorganic N fertiliser reduced efficacy of mucuna by 99% but not that of crotalaria against the nematodes. Incorporation of green manure had no effect or increased lesion nematode population and, consequently, diseaseseverity. In most cases addition of N fertiliser did not affect the effects of the green manure on nematodes. Cattle manure in combination with inorganic N reduced lesion nematodes and the associated disease severity by up to 75%.