Legume Cover Crops Response to Shade, Herbicide Application, and Phosphate Fertilization.

Legume cover crops are planted in multiple agroecosystems to prevent soil erosion, manage weeds and pests, increase soil organic matter, and release nutrients to the soil. Cover crops, however, require certain agronomic conditions to achieve a good establishment in order to provide those benefits. We carried out four separate experiments in a greenhouse at the University of Costa Rica between 2012 and 2014. We evaluated the effect of five shade conditions, simulating different growth stages of a perennial crop plantation, on five legume cover crops. We also assessed the tolerance of five legume cover crops to pre- and post-emergence herbicides and the response of those legumes to four rates of P₂O₅. Shade tolerance varied among legume species. Overall, plant dry biomass decreased as shade increased from 0% to 90%. Two species, Desmodium heterocarpon and Mucuna pruriens, had similar growth at 0%, 30% and 50% of shade. No differences were detected between dry biomass of Crotalaria spectabilis, M. pruriens, Vigna radiata, Pueraria phaseoloides and the control when applied with the post-emergence herbicides bentazon, clethodim and fluazifop-P-butyl. The pre-emergence herbicides linuron, alachlor and pendimethalin did not reduce dry biomass of C. spectabilis, M. pruriens, V. radiata, and P. phaseoloides. Vigna radiata and M. pruriens were also tolerant to oxyfluorfen. Finally, C. spectabilis, V. radiata and P. phaseoloides achieved their highest dry biomass when fertilized with 60 kg P₂O₅ ha^-1, whereas phosphate fertilization had no effect on growth of two cultivars of M. pruriens. These results provide useful information for those interested in establishing cover crops in different farm and crop conditions. Furthermore, it reveals the ability of certain legume species to grow in shaded and low fertility environments, a desired quality for cover crops grown in low external inputs cropping systems.