Intercropping Millet with Cowpea Reduces Pratylenchus Abundance and Improves Land Use Efficiency in a Low Input Sub-Saharan Cropping System

Millet/cowpea intercropping is a promoted practice in Sub-Saharan agriculture. However, because cowpea is known as a host for plant-parasitic nematodes that may also infect millet, we examined whether intercropping may increase the risk of nematode-mediated millet damage, and if this risk may be controlled by organic amendments. In twelve Senegalese farmers’ fields which had been either non-manured or regularly manured over the past 10 years at least, we assessed the effects of intercropping millet and cowpea on the abundance of free-living and plant-parasitic nematodes, ecological indices, and land equivalent ratios (LER). Six fields were manured, and six non-manured. Each field included four plots: millet and cowpea as pure stands, and two plots with millet intercropped with cowpea sown at two densities. Soil nematofauna was evaluated before sowing and at cowpea flowering. Soil nematofauna was dominated by plant-parasitic nematodes. Before manure application and crop sowing, regularly manured fields had higher structure indices of nematofauna than non-manured ones, and Pratylenchus was almost absent. At crop flowering, abundance of Pratylenchus increased and was drastically higher in pure cowpea (149 individuals 100 g −1 dry soil) than in intercropping and pure millet (18 and 17 individuals 100 g −1 dry soil, respectively), regardless of the manuring regime. Manuring had significant positive effects on various bacterivorous families, on fungivorous and plant-parasitic trophic groups, but not on Pratylenchus . Millet and cowpea yields of manured fields were the highest, regardless of cropping pattern. LER averaged 1.7 and 1.5 in manured and non-manured intercropping, respectively. Regardless of the treatments, ecological indices indicated that the soil food web was undisturbed, with moderate enrichment, and suppressive against crop pests. Intercropping millet with cowpea, even in poorly manured fields and with high cowpea density, constitutes an appropriate way to improve productivity without increasing Pratylenchus pressure in nutrient-poor soils of central Senegal.