MODELING GROWTH, DEVELOPMENT AND SEED-COTTON YIELD FOR VARYING NITROGEN INCREMENTS AND PLANTING DATES USING DSSAT

Csm-cropgro-cotton model under dssat v 4.0.2.0 has been extensively tested and validated in many studies, mainly in united states. the objective of this study was to test and validate this model in three cotton growing regions of pakistan (faisalabad, multan and sahiwal) for dynamic simulation of development, growth and seed cotton yield of four cotton cultivars (cim-496, cim-506, niab-111 and slh-284) at varying nitrogen increments (50, 100, 150 and 200 kg ha^-1) sown at different timings (20 may and 10 june). the model was first calibrated with data (phenology, biomass, lai, and yield components) collected during 2009 at all locations against the best performing treatment may 15 sowing, cv. cim-496 and 200 kg n ha^-1 (d1v1n4) in field trials. the model was then tested with data recorded against remaining thirty-one treatments for all locations. similarly, the data of year 2010 was used for validation. the simulated values of crop phenology (days to anthesis and maturity) by the model were reliable with the recorded data, with root mean square error (rmse) less than 2 days during both years. although rmse values for lai approached higher than 1 in many of the treatments, these values for total dry matter and seed-cotton yield were reasonably good (367 to 497 kg ha^-1 and 122 to 227 kg ha^-1, respectively). there is a dire need to assess impact of climate variation on seed cotton yield under various climatic regions of pakistan to ensure fiber quality and yield in future.