Promoting the use of tropical legumes as cover crops in Puerto Rico.

摘要

Degradation and misuse of agricultural land has made it necessary to identify solutions to address this serious problem. Cover crops have long been used in the tropics to increase soil and water conservation, especially on steep land, and to improve soil structure. This investigation involved two types of experiments; experiment station studies and on-farm trials. Seed density trials were conducted at the Isabela Substation to identify appropriate production practices for seed production of jack bean (Canavalia ensiformis ) and velvet bean (Mucuna pruriens) variety V-90. On-farm trials were conducted on 20 citrus farms in the central mountain region of Puerto Rico to evaluate the performance of jack bean, velvet bean, cowpea (Vigna unguilata) and sunn hemp (Crotolaria juncea ) as cover crops. An additional objective of this research was to inform farmers of the advantages of using green manures to improve their cropping systems. At the Isabela Substation, a determinate velvet bean cultivar produced an average seed yield of 900 kg ha-1. An indeterminate velvet bean cultivar produced a seed yield of 2,400 kg ha-1 and the jack bean cultivar produced a mean seed yield of 3,810 kg ha-1. Canopy cover was estimated in the on-farms trials at 6, 9 and 12 weeks after planting. At flowering (102 days after planting), the jack bean had a mean canopy coverage of 60%. Velvet bean flowered at 67-days after planting and produced an average canopy cover of 82%, whereas the sunn hemp flowered at 96-days after planting and had a mean canopy cover of 73%. Biomass (kg dry weight /ha) and nitrogen accumulated in the biomass was determined at 120 DAP. Jack bean produced the greatest amount of biomass and nitrogen (2,477 kg/ha; 93 kg/ha), followed by velvet bean (1,817 kg/ha; 69 kg/ha) and sunn hemp (1,849 kg/ha; 60 kg/ha). The amount of biomass produced by each legume during a specific period of time did not necessarily correspond to the amount of area covered by the canopy of leaves. The use of legume cover crops in farming systems can be a viable management practice for Puerto Rico. Citrus producers expressed willingness to use legume cover crops to improve their production practices and reduce soil loss.