Effects of organic transition strategies for peri-urban vegetable production on soil properties, nematode community, and tomato yield

Four organic transition strategies including tilled fallow (FA), mixed-species hay (HA), low intensity open-field vegetable production (FV) and intensive vegetable production under high tunnels (HT), each with and without annual compost amendment, were analyzed for nematode communities and soil properties from 2003 to 2006. Tomato was grown in all plots at the end of the transition period (2006). Overall the enrichment opportunist bacterivore nematodes belonging to c–p 1 (colonizer–persister) and general opportunist c–p 2 classes were favored by compost amendment. Hay (HA) had the highest abundance of c–p 1 bacterivores followed by HT with compost compared to other compost treatments. HA and HT without compost showed similar levels of c–p 2 but lower c–p 1 bacterivores compared to their compost-amended counterparts. Nematode food webs in all strategies with and without compost had low structure (SI) and enrichment index (EI) values. The lack of increase in EI in compost-amended plots was mainly due to the higher abundance of c–p 2 bacterivores compared to c–p 1 bacterivores. A decline of SI in HA plots after the incorporation of hay and consistently low SI in HT where soil disturbance was more frequent and temperature profiles were significantly different from those in open-field settings demonstrate that compost amendment alone is insufficient to increase trophic linkages in the soil food web. Although compost application increased the organic matter, microbial biomass (MB) and N levels compared with non-amended controls in general, N and MB were the highest in HT and HA. In temperate climates, soil temperatures in high tunnels covered year-round tend to exceed those in open fields in spring and fall months. The soil food web, in turn, may remain more active in these settings contributing to enhanced N mineralization. In this study, tomato yield in HT plots exceeded yield in other treatments potentially due to the season extension and higher N availability.