Adaptation of the CROPGRO growth model to velvet bean (Mucuna pruriens) : I. Model development

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, suggest a need for a more complete description of growth and development of velvet bean under different production scenarios and environments. Process-based simulation models offer the potential for facilitating an assessment of management strategies for different environments, soils and production systems. The objective of this study was 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. Model coefficients used to describe growth and development of soybean (Glycine max (L.) Merr.) 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 new model, incorporated as part of the DSSAT, version 3.5 suite of crop simulation models, 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.