Vertical distribution of plant-parasitic nematodes in peanut-cotton cropping systems

Reniform nematode (Rotylenchulus reniformis) is a parasite of cotton (Gossypium hirsutum) and crop rotation is commonly used for its management. One specific rotation system is a sod-based rotation, which uses two years of bahiagrass (Paspalum notatum) followed by one year each of peanut (Arachis hypogaea) and cotton, versus a conventional peanut-cotton-cotton rotation. High population densities of reniform nematode are found below plow depth in the soil profile, yet conventional chemical management is often not able to manage these deeper populations, nor is much known about other plant parasites such as ring nematode (Mesocriconema ornatum) and spiral nematode (Helicotylenchus dihystera) at these deeper depths. Our study aimed to investigate how long-term cropping history (since 2000) affects the vertical spatial distribution of plant-parasitic (reniform, ring, and spiral) nematodes under different irrigation regimes. Between March 2017 and January 2019, soil samples were collected to a depth of 120 cm before planting, after harvest, and in the winter using a hydraulic probe. Nematode abundances (including enumeration of all reniform nematode life stages) were analyzed in 30 cm-sections. There were no significant effects of irrigation on nematode abundances (P > 0.05). In each sampling date, all reniform nematode abundances decreased stepwise as soil depth increased, but spiral and ring nematodes were nearly absent below 30 cm. Sod-based rotation generally reduced reniform nematode abundances at all depths compared with conventional rotation, although differences were more pronounced in the shallower depths (0–30 and 30–60 cm). Conversely, at 0–30 cm soil depth, ring nematode abundances were generally greatest in the peanut phase of sod-based rotation. Similarly, spiral nematode abundances, at 0–30 cm soil depth, were generally significantly greater in bahiagrass phases than other phases and variously greater in first-year cotton (sod-based or conventional). Overall, sod-based rotation helped manage reniform nematodes up to 120 cm deep in the soil profile. Sod-based rotation was detrimental for managing minor plant-parasitic nematodes spiral and ring nematodes, and those nematodes were scarce below 30 cm deep in the soil profile.