Influence of long-term organic and mineral fertilization on soil nematofauna when growing Sorghum bicolor in Burkina Faso

Soil degradation has led crop yield to decline in many Sahelian countries and is a fundamental agricultural and economical threat for local populations. In Saria, Burkina Faso, long-term experiments are being performed to find efficient soil management practices that could improve soil fertility. A randomized block experiment comprising organic amendment (unamended control, straw at 8.3 t ha−1, manure at 10 t ha−1) coupled with mineral fertilization (no urea, urea at 60 kg ha−1) was started in 1980 with a continuous sorghum (Sorghum bicolor) cropping system. Twenty-six years after the settlement of the treatments, we compared their effects on nematode populations, community structure, and ecological indices, as well as soil physical and chemical properties at three stages of sorghum’s cropping cycle. The addition of manure led to significantly higher soil C, N, and P content and produced a higher sorghum grain yield in comparison to unamended or straw-amended soils. The number of plant-parasitic nematodes (mainly Pratylenchus and Tylenchorhynchus) was significantly higher in plots fertilized with manure in comparison to unamended or straw-amended plots. They were also significantly more abundant when urea was added. Mineral nitrogen fertilization had little impact on free-living nematodes, regardless of S. bicolor development stage, whereas organic amendment significantly raised the abundance of bacterivorous and fungivorous nematodes. Moreover, microphagous nematodes were significantly more numerous in plots amended with straw than with manure. Our results show that, on the long-term, only manure amendment seemed able both to store C and nutrients whereas both manure and straw led to greater microphagous nematode communities.