Evaluation of the CSM-CROPGRO-Soybean model for dual-purpose soyabean in Kenya

Limited information is available on the potential performance of introduced dual purpose varieties across different Kenyan soils and agro-ecological environments and consistency across sites and seasons. Crop simulation modeling offers an opportunity to explore the potential of and select introduced cultivars for new areas before establishing costly and time-consuming field trials. Dual purpose soybeans were introduced due to their ability to improve soils and at the same time provide substantial grain yields. The objective of this study was to derive genetic coefficients of recently introduced dual purpose soybean varieties and to explore the reliability of the Cropping System Model (CSM)-CROPGRO-Soybean model in simulating phenology and yield of the dual purpose varieties under different environments. Field trials for seven varieties were conducted across three sites in two seasons and data on phenology and management, soil characteristics and weather was collected and used in the CROPGRO model. A stepwise procedure was used in the calibration of the model to derive the genetic coefficients. Two sets of data from Kakamega and Kitale were used in calibration process while 2006 data for Kakamega and Msabaha, were used for evaluation of the model. The derived genetic coefficients provided simulated values of various development and growth parameters that were in good agreement with their corresponding observed values for most parameters. Model evaluation with independent data sets gave similar results. The differences among the cultivars were also expressed through the differences in the derived genetic coefficients. CROPGRO was able to accurately predict growth, phenology and yield. The model predicted the first flowering dates to within 2¿3 days of the observed values, the first pod dates within 3 days of the observed values and yields within 5¿300 kg ha-1 of the observed yields. The genetic coefficients derived in CROPGRO model can, therefore, be used to predict soybean yield and phenology of the dual purpose soybean varieties across different agro-ecological zones. (Résumé d'auteur

Evaluation of the FAO Aqua Crop model for winter wheat on the North China Plain under deficit irrigation from field experiment to regional yield simulation

Winter wheat is the main crop on the North China Plain (NCP), and in this region the most limiting factor for the crop is water. The objective of this study was to adapt and test the ability of the FAO-developed AquaCrop model (v3.1) to simulate winter wheat grain yield, biomass, actual evapotranspiration (ETa) and total soil water content (0-120 cm). Field experiments were conducted under deficit irrigation at the Luancheng Agro-ecosystem station (NCP) in 1998-2001, and the AquaCrop model was calibrated with treatment D(1999-2000); the rest of the data was used for validation of the model. The AquaCrop model was revalidated with data on measured grain yield from the experimental station for 1990-2010, considering actual field conditions. The second revalidation was done with the statistical grain yield for 1995-2010 in the study region. For the model validation, the significant differences between simulated and observed grain yield, biomass and ET, were in the order of: rainfed treatment> well-watered treatment> moderate water stress. Total soil water simulated by AquaCrop tends to follow closely the trend in the measured data, but with slight underestimations for irrigated treatments and significant overestimations for rainfed treatments. In general, errors in the model's evaluation such as RMSE and Willmot's d statistics were for grain yield (0.58 Mg ha(-1), 0.92), biomass (0.87 Mg ha(-1), 0.95), ETa (33.2 mm, 0.93) and soil water content (24.5-37.6 mm, 0.85-0.90). The overall results based on extensive validation and revalidation showed that AquaCrop is a valid model and can be used with a reliable degree of accuracy for optimizing winter wheat grain yield production and water requirement on the NCP