Velvet bean (Mucuna pruriens (L.) DC cv. group utilis) is widely promoted as a GMCC for tropical regions. Reports of insufficient biomass production in certain environments and concerns over seed production, however, suggested a need for a more complete description of growth and development of velvet bean under different production scenarios and environments. The CROPGRO module was identified as offering the potential for facilitating an assessment of management strategies for different environments, soils and production systems. Research was undertaken by A.D. Hartkamp to review the physiology of velvet bean and using the generic legume model CROPGRO, to provide a structured and quantitative framework for describing crop response to management and environment (Hartkamp et al., 2002a). Model coefficients used to describe growth and development of soybean served as initial reference values. Information on velvet bean from published sources was then used to revise the functions and parameters of the model. Phenology, canopy development, growth and partitioning were calibrated for two velvet bean varieties using experimental data from three sites in Mexico. Compared to soybean, velvet bean has a much longer growth cycle, allowing a very large numbers of nodes to form. Velvet bean has larger, thinner leaves than soybean, resulting in more rapid leaf area development, and larger seeds, which affects germination, early season growth and pod development. A modification to CROPGRO to track senesced tissues was incorporated. Overall,the physiological processes underlying growth and development of velvet bean appear to be similar to other tropically adapted legumes. The model was incorporated as part of the DSSAT, version 3.5 suite of crop simulation models and has been carried forward without further modification of crop-specific features.
The velvet bean implementation has potential for evaluating management strategies in specific environments and to identify potential regions for introduction of velvet bean as a green manure cover crop.
A second paper (Hartkamp et al., 2002b) evaluated the performance of the model for phenology, growth, senescence and N accumulation for multiple locations that represent a range of environmental and agronomic management scenarios. Vegetative development, as described by main stem leaf appearance rate, varied linearly with thermal time. Time to flowering showed departures from the linear photoperiod response used in the model. Additional research is required to determine whether the crop is influenced by factors besides photoperiod and air temperature, especially water and nutrient deficits. The linear response to photoperiod did, however, provide reasonable values for partitioning to vegetative, reproductive and senesced materials. Simulation of nitrogen concentration for various plant components matched observed data. Sensitivity analyses evaluating the ability of the crop to provide ground cover, intercept light and develop adequate growth for soil protection and weed suppression indicated that a mean temperature of over 22 8C and a soil moisture holding capacity of at least 100 mm are required.
Hartkamp, A.D., Hoogenboom, G., White, J.W., 2002a. Adaptation of the CROPGRO growth model to velvet bean (Mucuna pruriens): I. Model development. Field Crops Research 78, 9-25.
Hartkamp, A.D., Hoogenboom, G., White, J.W., Gilbert, R., Benson, T., Barreto, H.J., Gijsman, A., Tarawali, S., Bowen, W., 2002b. Adaptation of the CROPGRO growth model to velvet bean as a green manure cover crop: II. Model testing and evaluation. Field Crops Research 78, 27-40.