Simultaneous diversification of cover and cash crops: Short-term agronomic and soil health outcomes

Abstract

Positive relationships between plant diversity and ecosystem functioning are frequent in natural systems, however research on year-round plant diversification to improve agroecosystem outcomes is limited. Challenges such as lag times for soil health benefits during the early transition years of cover cropping may be compensated by increases in crop yield from cash crop rotations. To better understand management strategies that could promote agroecosystem productivity and sustainability, we explored responses of agronomic and soil multifunctionality to simultaneous winter cover crop mixes and cash crop rotation using a three-year field experiment in western Tennessee, USA. Cover crop treatments included a no cover crop control (winter fallow), single-species winter wheat (Triticum aestivum L.), single-species crimson clover (Trifolium incarnatum L.), two-species wheat-clover mix, and five-species mix of cereal rye (Secale cereale L.), oat (Avena sativa L.), clover, hairy vetch (Vicia villosa Roth), and radish (Raphanus sativus L.). Cropping systems included continuous corn (Zea mays L.), continuous soybean (Glycine max L.), corn-soybean rotation, and corn-cotton (Gossypium hirsutum L.)-soybean rotation. Total agronomic and soil health multifunctionality were weakly correlated across treatment combinations. The single-species clover and both mixes led to the highest agronomic multifunctionality in all cropping systems. Single-species wheat and wheat-clover mix provided the greatest cover crop biomass inputs, but both cover crops decreased overall cash crop yields (corn, cotton, and soybean scaled within crop and year) relative to the five-species mix. This result for yield was driven by year-one reductions in corn yield by averages of 2.15 and 1.74 Mg ha⁻¹ in single-species wheat and wheat-clover mix cover cropped plots (respectively) compared to all other cover crop treatments. Cash crop rotation did not influence agronomic multifunctionality, although in year three, rotation with soybean increased corn yield by 1.49 Mg ha⁻¹ yr⁻¹ relative to monocropped corn, and rotation with corn and cotton increased soybean yield by 0.34 Mg ha⁻¹ yr⁻¹ relative to monocropped soybean. Wheat-clover mix as a cover crop increased mineral-associated organic C relative to winter fallow in the continuous soybean system, however there were no strong overall influences of cover crop or crop rotation on soil multifunctionality. Overall, our results suggest that winter cover crops can increase agronomic benefits of cash cropping systems in the southeastern United States within three years of adoption, but soil health benefits may be more difficult to detect in this short timeframe.