Soil food webs in sugarcane fields: Sweet dreams for soil organisms in subtropical Africa

Sugarcane cultivation covers large areas in southern Africa, where it provides local employment and a substantial part of farming incomes. Maintaining soil quality in these areas is essential to prevent environmental damage following long-term cultivation. Soil biodiversity constitutes a good proxy to monitor soil quality. However, soil organisms and their interactions remain poorly studied in southern Africa. Soil food web studies contribute to the understanding of these complex belowground interactions. This study is the first to investigate soil food webs in sugarcane cultivation areas in Africa. We sampled 10 sugarcane fields subjected to different cropping (conventional versus regenerative) and harvesting (burning versus green cane) practices, and an unmanaged site included as a reference. Stable isotope analyses were conducted on sugarcane leaves, roots and crop residues, soil, and on the most abundant arthropod taxa including Araneae (spiders), Blattodea (cockroaches), Collembola (springtails), Dermaptera (earwigs), Diplopoda (millipedes), Formicidae (ants; Pheidole and Tetramorium genera), Hemiptera (leafhoppers) and Oribatida (oribatid mites). Food webs and trophic niches of arthropod taxa were characterized by assessing C and N stable isotope ratios (δ 13 C and δ 15 N) and by computing isotopic metrics. Higher δ 15 N values were observed for Araneae, Formicidae and Dermaptera, intermediate values for Oribatida and Collembola followed by Diplopoda and Blattodea, and lower values for Hemiptera. Food chain length was significantly shorter in fields with regenerative than conventional practices, and longer with green harvest than with pre-harvest burning or in the unmanaged site. Isotopic uniqueness and evenness were lower in green-harvested than in burnt fields. Our results highlight the trophic functional diversity of decomposers (Blattodea, Diplopoda, Collembola) and soil predators (Araneae, Dermaptera, Formicidae) in sugarcane fields, and the effects of agricultural practices on these food webs. Overall, this study contributes to further our knowledge on the composition and factors influencing soil biodiversity that remains understudied in Africa. • First study on sugarcane soil food webs, using stable isotopes, in southern Africa. • Soil food web was influenced by sugarcane cropping and harvesting practices. • Food chain length was the shortest in fields with regenerative cropping practices. • Food chain length was the longest in green-harvested fields and unmanaged site. • Isotopic uniqueness and evenness were lower in green-harvested than burnt fields.