Multispecies swards support lower plant-parasitic nematode abundance in agricultural grasslands

AbstractReducing reliance on mineral nitrogen (N) fertilizer is central to improving the sustainability of agricultural grassland management. Increasing sward diversity and the application of organic N fertilizer are potential strategies to achieve this, but their combined effects on soil biodiversity remain less understood. This study examined how different sward types and N fertilization influence soil biodiversity and soil food-web functioning in the short term, using soil nematodes as bioindicator. A field-plot experiment was conducted with four sward types: permanent pasture, perennial ryegrass, six- and twelve-species swards; and three N fertilizer treatments: organic, mineral and a combination of both N fertilizers. Redundancy analysis revealed that nematode community structure differed among the swards but not between N fertilizer treatments. Specifically, the abundance of plant-parasitic nematodes was significantly lower in the sown six- and twelve-species swards compared to perennial ryegrass monoculture and permanent pasture. Plant-parasitic nematode abundance was positively related to the proportion of grasses and negatively to the proportion of legumes and proportion of forbs. The abundance of bacterial feeders in swards fertilized with organic N was comparable to those fertilized with mineral N. Soil food web trophic complexity, as indicated by Structure Index did not vary among the swards nor among N fertilizer treatments. Our findings indicate that increasing sward diversity reduces plant-parasitic nematodes, while organic N fertilizer had limited effect on soil nematode communities in the short term. This suggests that enhancing plant species diversity, specifically the inclusion of legumes and forbs, can contribute to reducing the prevalence of plant-parasitic nematodes, potentially improving sustainability in agricultural grasslands.