Phasic development model using thermal indices for rice (Oryza sativa L.) in the central zone of Kerala

Abstract

The present study, “Phasic development model using thermal indices for rice (Oryza sativa L.) in the central zone of Kerala” was carried out at the Department of Agricultural Meteorology, College of Horticulture, Vellanikkara, Thrissur during 2015-2016. The experiment was laid out in split plot design with five dates of planting viz., 5th June, 20th June, 5th July, 20th July and 5th August as the main plot treatments and two varieties viz., Jyothi and Kanchana as subplot treatments and there were four replications. Location of the experiment was Agricultural Research Station, Mannuthy. Growth and yield characters like plant height, leaf area index, dry matter accumulation, 1000 grain weight, grain yield, straw yield, number of panicles per unit area, spikelets per panicle, filled grains per panicle and duration of different growth phases were recorded along with monitoring of the incidence of various pests and diseases. The daily weather parameters like maximum and minimum temperatures, forenoon and afternoon relative humidity, forenoon and afternoon vapour pressure deficits, bright sunshine hours, evaporation, wind speed, rainfall and rainy days were recorded during the experimental period. Heat units viz., Growing Degree Days (GDD), Heliothermal Units (HTU), and Photothermal Units (PTU) were found to affect the yield of both Jyothi and Kanchana varieties of rice. In both varieties, early dates of planting accumulated more heat units to attain physiological maturity compared to later plantings. Reduction in yield in the later plantings was noticed due to the increase in GDD, HTU and PTU.The weather parameters such as minimum temperature (23.8°C), forenoon (23.0mmHg) and afternoon vapour pressure deficit (23.6mmHg), forenoon relative humidity (94.7%) and afternoon relative humidity (77.1%), rainfall (1581.5 mm) and rainy days (71days) were found to be higher in early dates of planting, while maximum temperature (31.8°C), bright sunshine hours (5.2h) , evaporation (2.9mm). Number of days taken to complete different phenological stages of both varieties was low for late planted crops. Plant height, dry matter accumulation, yield and yield parameters such as number of panicles per unit area , spikelets per panicle, filled grains per panicle and 1000 grain weight were highly variable among the different planting dates. The total chlorophyll content (soluble protein and growth indices such as LAI, CGR, LAD and NAR were found to be highest on June 5th planting. Grain yield was highest for June 5th planting for both varieties. The recorded grain yield for Jyothi and Kanchana was The crop genetic coefficients that influence the occurrence of developmental stages in the CERES-rice models were derived, to achieve the best possible agreement between the simulated and observed values. The performance of the CERES-rice simulation model was tested and evaluated using the calibrated genetic coefficients for both the varieties with their respective planting dates. The results of simulation studies in respect of phenophases and yield of rice were compared with the observed values from the field experiment. Root Mean Square Error (RMSE) and D- stat (index of agreement) were used to evaluate the model performance and found that predicted yield of both rice varieties Jyothi and Kanchana under different planting dates were reasonably close to the observed values.