Nematode community profiling as a soil biology monitoring tool in support of sustainable tomato production: A case study from South Africa

Management of the biological component of agricultural soils is a vital aspect of sustainable food production systems. There is a need for soil biology metrics that producers can use as a decision support tool when it comes to managing the soil biological component of agricultural soils. We evaluated the usefulness of nematode community profiling as a soil biology monitoring tool in support of a sustainable commercial-scale tomato production system in South Africa. The objectives were to: (1) study the effects of land use change on nematode communities in the tomato production region, and (2) explore the correlation between tomato crop productivity and the nematode community metrics. The enrichment index was a sensitive indicator of land use change, but the structure index was not. Although the number and proportion of free-living and plant-parasitic nematodes increased and decreased respectively, the selective amplification of specific herbivorous genera was observed. Helicotylenchus spp. was sensitive to land use change and might serve as soil health indicator in this tomato production region. Regression analysis indicated a combination of variables associated with soil pH, free-living nematodes (notably the bacterivores) and specific plant-parasitic nematode genera (Paratrichodorus spp. and Rotylenchus spp.) predicted tomato yield (R2 = 0.846). Despite the useful information gleaned from the nematode community metrics regarding soil food web functioning, the importance of ecologically and economically important nematode genera was re-emphasized. The results of this study highlight an important principle regarding development of soil health metrics for tomato agroecosystems: tomato crop health was not necessarily predicted solely by indicators of soil food web health and functioning.