Screening of five broad leaf plants for use as tropical (warm season) cover crops

Cover crops (CC) can provide numerous ecosystem services to agricultural crop production systems that include soil conservation, soil quality/fertility improvement, increased biodiversity, and pest management benefits. Hot-humid environments of the tropics and the Southern U.S.A. pose difficult challenges for the sustainable management of soil and weeds. Cover crops that are mechanically terminated with a roller-crimper produce surface sheet mulch that can protect and improve soil health, suppress invasive weed development, reduce soil temperature, reduce soil moisture loss and increase water availability to the farming system. The proper selection and management of CCs is critical to the success of the farm system and little is known about CCs terminated with a roller-crimper under hot-humid conditions. This experiment evaluated 5 warm season CCs, determined their potential nutrient contribution, and measured the effect of roller-crimper termination on CC regrowth and weed development. Cover crop response to roller-crimper termination was determined by measuring CC regrowth at 3, 6. 9, and 12 weeks after termination. The five CCs evaluated are; velvet bean (Mucuna pruriens (L.) DC. cv. Vine 90; VB), sunn hemp (Crotalaria juncea L. cv. IAC-1; SH), pigeon pea (Cajanus cajan (L.) Millsp. cv. BRS Mandarim; PP), sesame (Sesamum indica L. cv. ns; SE), and sun flower (Helianthus annus L. cv. Black Oil; SF). Cover crops were planted on August 9, 2013 at the Agricultural Experiment Station located on St. Croix in the U.S. Virgin Islands. The CCs VB, SH, SE, and SE were terminated 70 days after planting (DAP) and PP was terminated 150 DAP with a roller-crimper. Of the CCs terminated 70 DAP, SH produced the greatest biomass with 7,967 kg/ha, had the second highest plant tissue nitrogen (N) percent of all CCs at 2.91%, and contributed an estimated 231 kg/ha of N which was greater than VB, SE, and SF, but lower than PP. Both SH and SE had the lowest weed biomass at termination with 419 and 235 kg/ha, respectively. PP had the highest total weed biomass at termination with 3,421 kg/ha. The roller-crimper termination of SF and SE resulted in 100% kill of the cover crop with zero regrowth measured at any point after termination. Velvet bean had more regrowth than all other CCs at 3 and 6 weeks after termination and had the highest weed biomass at 3 weeks after termination. At 6 weeks after termination SF weed biomass increased and was higher than the other treatments. Sesame, SF, and SH were effectively terminated with a roller-crimper and their residues exhibited weed suppressive potential up to 6 weeks after termination. Results of this study indicate that CCs with erect lignified stems can be effectively terminated with a roller-crimper in hot-humid climates resulting in little to no CC regrowth, however, complete termination is variable depending upon CC species, environmental conditions, and CC management practices.