Warm-season legume cover crops in subtropical environments provide many agroecosystem services but have not been widely adopted because their use usually entails replacing cash crops. Planting short-term legume cover crops following maize ( Zea mays L.) to replenish soil nitrogen (N) pools for cool-season cash crops, such as wheat ( Triticum aestivum L.), is an innovative approach for integrating legumes into subtropical cereal cropping systems that has not been widely investigated. A maize – legume cover crop – wheat cropping sequence under conservation tillage management was investigated with the following objectives: 1. Evaluate the performance of short-term cowpea Vigna unguiculata (L.) Walp) and sunn hemp ( Crotalaria juncea L.) cover crops in terms of N accumulation, 2. Track soil N availability and wheat N recovery following cover crops, and 3. Assess wheat productivity in response to cover crops terminated and left on the soil surface. A five site-year study was conducted in Citra and Jay, Florida, USA beginning in 2016. The experiment was arranged as a split-plot in which cover crop (cowpea, sunn hemp, and weed-free fallow) was the main plot factor, while N rate (0, 34, 67, and 101 kg N ha −1 ) to wheat was the split plot factor. Corn was planted under strip-tillage, while cover crops and wheat were planted into residues using a no-till grain drill. Cover crops accumulated 58–126 kg N ha −1 in eight to 11 weeks, with cowpea and sunn hemp deriving up to 67 and 90% of N from biological N fixation, respectively. Plant Root Simulator probes and Normalized Difference Vegetation Index data provided evidence for higher N uptake by wheat following cover crops compared to weed-free fallow during early stages of wheat growth. However, N availability following cover crops was either short-lived or insufficient as wheat stover production, grain yields, and grain N recovery were not affected by cover crops in most cases. On the few occasions when positive cover crop effects were detected, results were both marginal and inconsistent. Maintaining cowpea and sunn hemp residues on the soil surface may be beneficial from a soil conservation perspective, but this strategy does not result in consistent improvements in the productivity of cool-season cereals. Additional research that elucidates the environmental pathways by which legume cover crop-derived N is lost from soil is warranted to facilitate the development of management practices that increase the likelihood and size of N benefits from short-term legumes. • Short-term legumes planted after maize via no-till accumulated up to 126 kg N ha −1 . • NDVI data suggested legume surface residues improved initial wheat N uptake. • Legume surface residues had a marginal and inconsistent impact on wheat yields. • Legume surface residues provide soil conservation, but minimal yield, benefits.
Jani et al. (Mon,) studied this question.