Effects of Plasticulture and Conservation Tillage on Nematode Assemblage and Their Relationships with Nitrous Oxide Emission following a Winter Cover Cropping and Vegetable Production System

Agriculture production emits significant amounts of nitrous oxide (N₂O), a greenhouse gas with high global warming potential. The objectives of this study were to examine whether different husbandry practices (tillage and plasticulture) following winter cover cropping would influence soil food web structure and whether a change in the soil community could help mitigate N₂O emission in vegetable plantings. Three consecutive field trials were conducted. A winter cover crop mix of forage radish (Raphanus sativus), crimson clover (Trifolium incarnatum) and cereal rye (Secale cereale) were planted in all plots. Winter cover crop was terminated by flail mowing followed by (1) conventional till without surface residues [Bare Ground (BG)], (2) conventional till with black plastic mulch (BP) without surface residues, (3) strip-till (ST) with partial surface residues, or (4) no-till (NT) with surface residues. The cash crop planted subsequently were eggplant (Solanum melongena) in 2012 and 2014 and sweet corn (Zea mays) in 2013. The soil food web structure was consistently disturbed in the BP compared to other treatments as indicated by a reduction in the abundance of predatory nematodes in 2012 and 2014, and nematode maturity index in 2013 in BP. Changes in soil food web structure in the conservation tillage (NT or ST) treatments based on the weight abundance of nematode community analysis were not consistent and did not improve over the 3-year study; but were consistently improved based on functional metabolic footprint calculation at termination of cover crops of 2013 and 2014. None-the-less, the N₂O emissions increased as the abundance of fungivorous nematodes increased during all three trials. It was also found that improved soil food web structure [higher abundance of omnivorous in 2012 or predatory nematodes in 2013 and 2014, and structure index (SI) in all 3 years] reduced N₂O emissions. These findings suggested that proper soil husbandry practices following winter cover cropping could mitigate N₂O emissions over time.