|Ferris, Howard -|
|Sanchez-Moreno, Sara -|
Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 22, 2012
Publication Date: October 1, 2012
Citation: Ferris, H., Sanchez-Moreno, S., Brennan, E.B. 2012. Structure, functions and interguild relationships of the soil nematode assemblage in organic vegetable production. Applied Soil Ecology. 61:16-25. Interpretive Summary: Soil nematodes are an important part of the soil food web and include species that feed on bacteria, fungi, and plants, and other species that are omnivores or carnivores. Nematodes are good bioindicators of soil health and provide useful information on soil nutrient dynamics and decomposition of organic matter. Nematodes were sampled during 4 of the first 8 years of a long-term research study on the effects of cover crops and compost on high-value organic vegetable production. The study is formally known as the Salinas Organic Cropping Systems (SOCS) trial and is located in the central coast region of California. The SOCS trial includes 8 certified organic rotations that differ in cover crop frequency (annually versus every 4 years), cover crop variety (rye, legume-rye mixture, mustard mixture), cover crop seeding rate (standard 1x rates versus 3x) and compost application rate (0 versus 5-6 tons per acre prior to each vegetable crop). Romaine lettuce and broccoli were grown annually in all rotations for the majority of the first 8 years of the trial. Nematodes were unaffected by cover crop seeding rate. The abundance of bacteria and fungal feeding nematodes was greater in vegetable rotations with winter cover crops annually than in vegetable rotations with cover crop only every 4 years. Cover crops had a greater effect on soil food web than annual compost additions. Soil health based on the nematode community analysis were correlated with the yields of lettuce and broccoli.
Technical Abstract: The abundance and metabolic footprints of soil nematodes were quantified during four of eight years of an intensive organic vegetable production system. Treatment variables included cover crop mixtures and frequency, and compost application rates. The abundances of bacterivore and fungivore nematodes were enhanced by the annual use of winter cover crops but showed no relationship to the level of residual soil organic matter. Metabolic footprints, based on biomass and respiratory activity, were calculated for functional guilds and ecosystem services of the nematode assemblage. The enrichment footprint, representing the ecosystem service of nutrient mineralization, was related to the level of soil organic carbon. It was strongly related to the metabolic footprint of bacterivore nematodes and both were enhanced in treatments that were cover cropped annually. Cover-cropped treatments also had a slightly higher herbivore footprint, suggesting support of some taxa of plant-feeding nematodes. The structure footprint, reflecting the metabolic activity of higher trophic level nematodes, including the predators of opportunistic species, did not differ among cover crop and compost amendment treatments. However, enrichment footprints were correlated with bacterivore footprints, which represented the predominantly bacterivore resources available to predators. Abundance of predators increased as a function of the abundance of those nematode prey that can be amplified by organic inputs. The functional connectance, represented by spatial colocation, between predators and amplifiable prey was greater in treatments with a greater abundance of predators. The functional connectance between predators and herbivore prey, representing a management target, was strongly related to the functional connectance between predators and amplifiable prey. We conclude that cover crops not only affect organisms at the entry level of the web but that resources are also transferred to higher trophic links which increases top-down pressure on plant-parasitic nematodes.