Effect of grazing intensity on plant-parasitic nematodes in an integrated crop–livestock system with low plant diversity

Integrated crop–livestock (ICL) systems increase food production and improve environmental quality, but these benefits may be outweighed by overgrazing, monocropping, and the use of plants susceptible to plant-parasitic nematodes (PPN). The objective of this work was to study the occurrence of PPN in an ICL system cultivated for 16 years with low plant diversity and managed with four grazing intensities. The experiment was conducted on a 22-hectare experimental area cultivated with Glycine max for grain production (summer) and Avena strigosa + Lolium multiflorum for cattle grazing (winter), in a subtropical region of Brazil. The treatments consisted of different grazing intensities, represented by sward heights of 10, 20, 30, and 40 cm; ungrazed plots; and a natural pasture as the reference system. The soil samples were collected during flowering of soybeans and of pasture to identify and quantify PPN (genera and species) and determine the physical, chemical, and soil cover properties. Eleven genera of PPN were identified. Helicotylenchus was the dominant taxon in all treatments, but only the species H. dihystera was present. A greater grazing height resulted in greater PPN abundance in the winter but did not affect the nematode abundance where soybean was subsequently grown. Despite low plant diversity and overgrazing in some treatments, the conditions of this ICL system limit the growth of PPN populations.