62 June 2013] Calibration and validation of DSSAT model for kharif groundnut PAPER 11 Journal of Agrometeorology 15 (1) : 62- 65 (June 2013) Groundnut is the major oilseeds crop of Gujarat with 1.92 million ha area and 3.36 million tonnes of production with 1836 kg ha -1 productivity (Anon., 2011). Groundnut crop is grown in areas receiving the rainfall between 500 and 1250 mm and performs better in the sandy loam and loamy soils. In Saurashtra, groundnut is grown in black calcareous soils. The major groundnut growing districts in Gujarat are Junagadh, Jamnagar, Amreli, Bhavnagar, Rajkot, Mehsana and Bhuj. In Gujarat, groundnut is mainly grown in kharif season and Junagadh is the most productive among all the districts (Sahu et al ., 2004). Majority of the groundnut cultivars are insensitive to photoperiod and therefore grown in all the three seasons, viz. summer, kharif and rabi . In Saurashtra region, about 80 % of the crop is grown under rain-fed condition and due to vagaries of monsoon the year-to-year yield fluctuations are more. The productivity of groundnut is curtailed due to biotic and abiotic stresses. Weather is one of the important factor, which affects all stages of groundnut growth and finally the yield. The crop growth simulation models show considerable potential to evaluate crops, crop varieties, cropping pattern and genetic potential pattern for yield (Boote et al., 1987). In this paper attempt has been made to calibrate and validate the DSSAT model for groundnut in Saurashtra, Gujarat. Calibration and validation of DSSAT model for kharif groundnut in north-Saurashtra agro-climatic zone of Gujarat P. K. PARMAR, H.R. PATEL, S. B. YADAV and V. PANDEY Department of Agricultural Meteorology, Anand Agricultural University, Anand, Gujarat – 388 110 *Corresponding author: pravinsinh351@yahoo.com ABSTRACT The DSSAT model was calibrated and validated for kharif groundnut (cv. GG-2 and GG-20) using past experimental data (2007 to 2009) of Dry Farming Research station, J.A.U., Targhadia, Rajkot (20 0 18È N 70 0 56È E), Gujarat with two dates of sowing (D 1 : Onset of monsoon 1 st July; D 2 : After 15 days of D 1 15 th July). The yield and yield attributes, phenological stages, harvest index, shelling percentage as simulated by model were compared with the observed data. The results revealed that the model underestimated the LAI and haulm yield for both the cultivars and overestimated rest of the parameters. The average error percent of pod yield for cv. GG-2 as simulated by DSSAT model was 2.2 % and for cv. GG-20 it was 1.6 %. Key words : Crop growth model, DSSAT, groundnut, simulation, calibration, validation. MATERIALS AND METHODS The experimental data (2007-09) of kharif groundnut Dry Farming Research Station, J.A.U., Targhadia, Rajkot, Gujarat. Comprising date of sowing (kharif : D 1 -1 st July., D 2 -15 th July.) and varieties (GG-2 and GG-20) were used in this study. The package and practices for cultivation was followed as per the recommendation of Crop parameters such as pod yield, haulm yield, phenology, LAI, harvest index and shelling percentage were used for calibration of the DSSAT 4.5 model. The genetic coefficients of groundnut were estimated by repeated interactions until a close match between simulated and observed phenology and yield was obtained in respective treatments. The values of genetic coefficients as derived from calibration of the model are presented in Table 1. Generally, correlation coefficient (r) and regression coefficient (R) are determined to evaluate the association between the observed and predicted values despite the fact that their magnitudes are consistently not related to accuracy of prediction. Hence, to achieve accuracy, the test criteria suggested by Wiltlmott (1982) were followed while evaluating the performance of the models. The observed (O) and simulated (P) values were used to