Utilizing the cover crop Sunn Hemp (Crotalaria juncea L.) to improve vegetable cropping systems

Sunn hemp (Crotalaria juncea L.; [SH]) is an important warm season cover crop that has the potential to provide ecosystem services and cover crop legacy effects to subsequent vegetable crop rotations. Smallholder farmers rely heavily upon mechanized soil disturbance and hand labour for weed control. These farmers have little incentive to reduce tillage events and minimize soil disturbance when faced with extreme weed pressure; particularly when few practical alternative weed management options exist. One alternative management strategy is to terminate SH with a roller-crimper and utilize the SH residue to form a dense weed suppressive mulch layer in which vegetables may be planted via no-till transplanting. Adoption of this practice by small farmers could reduce soil disturbance, provide extended weed suppression, and increase the soil’s water holding potential. A series of experiments have been conducted to further develop the use of SH as a cover crop to produce surface mulch (grown in-situ) in vegetable cropping systems to reduce herbicide reliance in conventional cropping systems and to provide alternative weed suppression strategies in organic cropping systems. Studies were conducted in the US Virgin Islands (USVI) and Florida to compare cropping systems where the SH cover crop was soil incorporated followed by three common weed management practices (plastic film mulch, cut and carry hay mulch, and bare ground with no mulch) to SH surface mulch produced from SH terminated with a roller-crimper. Jalapeno (Florida) and Cubanelle (USVI) peppers (Capsicum annum L.) were evaluated to determine cropping system productivity. Cut and carry hay mulch systems provided a high level of weed suppression and resulted in the greatest pepper yields compared to either the no mulch or plastic mulch systems in both Florida and the USVI. In Florida, SH surface mulch served as an effective means to suppress weeds and produced comparable yields to conventional systems when adequate SH biomass was present. However, the weed suppressive potential of the SH surface mulch and corresponding pepper yields were reduced in the USVI due to low SH biomass production. In previous experiments in the USVI, when SH biomass exceeded 5,000 kg ha-1 and was terminated with a roller-crimper to produce surface sheet mulch, subsequent pepper yields were similar to or in excess of yields produced in conventional production systems. Sunn hemp terminated with a roller-crimper, followed by no-till vegetable transplanting can reduce soil disturbance as part of a greater conservation tillage approach and can provide adequate weed suppression in vegetable cropping systems. However, the success of the system is dependent upon adequate SH cover crop biomass, careful planning, and intensive farm management.