An investigation was carried out to determine an optimum micro-climate regimes for different promising varieties of rice for realizing higher yields under aerobic conditions. A field experiment was conducted in the Instructional Cum Research (ICR) Farm of Assam Agricultural University, Jorhat, Assam during autumn season of 2017. The experiment was laid out in a split-plot design with three replications. The treatments consisted of four micro-climatic regimes (M) in main plot viz., sowing of seed on 15th February (M1), 1st March (M2), 16th March (M3) and 1st April (M4) along with four different rice varieties (V) viz., CR-Dhan 205 (V1), CR-Dhan 203 (V2), CR-Dhan 204 (V3) and Inglongkiri (V4) in sub plot. The results of the experiment revealed that among the different micro-climatic regimes, the micro-climate associated with 1st April recorded positive effect on micro-climate related and yield parameters in terms of canopy temperature, light intensity, soil moister content, soil temperature, dry matter accumulation, leaf area index, number of effective tillers and grain yield (3004 kg/ha), followed by the micro-climate associated with 16th March sown crop. Among the varieties evaluated, CR-Dhan 203 recorded the highest value in terms of number of effective tillers (187/m2) followed by Inglongkiri, CR-Dhan 204 and CR-Dhan 205. The highest grain yield of 2860 kg/ha recorded in rice variety CR-Dhan 203 was significantly superior to that of other varieties except Inglongkiri. In terms of economics, the crop sown on 1st April recorded the highest net return (INR 51755 /ha) and B:C ratio (2.30) which was found to be the greatest.

Background: Rice (Oryza sativa L.) is the major cereal crop grown in India. Rice plays a pivotal role in the socio-cultural life of the people of Assam. The main objective of this study to investigate the influence micro climatic indices in relation to crop growth and yield of upland rice varieties with different dates of sowing in Assam. Methods: A field experiment was carried out at Instructional cum Research Farm, Assam Agricultural University, Jorhat during autumn season of 2017. The experiment consisted of four micro-climatic regimes (M) along with four different rice varieties (V). Result: The results of the experiment revealed that micro climatic indices viz., canopy temperature, growing degree days, soil moisture content, soil temperature, light intensity, depth of ground water table associated with 1st April sown crop recorded positive effect on growth and yield parameters in terms of plant height, leaf area index, number of filled grains per panicle, test weight, harvest index and grain yield (3004 kg/ha), followed by the micro-climate associated with 16th March sown crop. Among the varieties evaluated, CR-Dhan 203 recorded the highest grain yield of 2860 kg/ha and was significantly superior to that of other varieties except Inglongkiri.