Soil food web structure and function in annual row-crop systems: How can nematode communities infer soil health?

Increased agricultural management intensity is known to degrade soil food web structure and function, however, the impact of 50+ years of contrasting agricultural management practices on soil food webs is largely unknown. The relationship between soil food web structure and sensitive soil health indicators has seldom been quantified in row crop agricultural systems in the Midwest, USA. This study aims to 1) quantify soil food web structure and function in long-term systems that range in tillage intensity and perenniality over the course of a single growing season; and 2) identify the relationship between soil health indicators and soil food web structure. Nematode feeding groups and nematode indices were used to indicate soil food web structure and soil food web function, respectively. Additionally, a suite of soil health indicators including permanganate oxidizable carbon (POXC), β-glucosidase (GLU), and N-Acetyl-β-glucosaminidase (NAG) were measured in two identical long-term experimental trials with contrasting soil types (clay versus silt loam) under two tillage intensities (chisel till (CT) vs. no-till (NT)) combined with two crop rotations (corn-soy (CS) vs. corn-forage-forage (CFF)). All samples were collected in the corn phase of the rotation. Non-metric multidimensional scaling of nematode community assemblage and vector analysis demonstrated that soil food web structure was significantly related to POXC, GLU, and NAG within CFF systems. Nematode families Thornenematidae and Rhabditidae served as indicators of improved and degraded soil food web function, respectively. Our findings indicate that including perennials within a crop rotation fosters a soil food web structure that can enhance carbon and nitrogen cycling in large scale row-crop agriculture. Moreover, this study emphasizes the potential for specific nematode families to serve as indicators of soil food web function, demonstrating that nematodes should be integrated into the soil health framework.