A field experiment entitled “Resource use efficiency in winter rice (Oryza sativa L.) unde r SRI concept as influenced by microclimate ” was carried out during the year 2016 and 2017 at the farmer‟s field located at Nepalikhuti Village (Lat. 26066ʹ99ʹʹ N, Long. 93068ʹ26ʹʹE) in Bokakhat sub-division of Golaghat district, Assam to study the performance of winter rice with respect to production maximization, resource use efficiency and economic return under varied microclimatic regime imposed by methods of crop establishment, dates of transplanting and hill densities. The experiment was comprised of 24 treatment combinations with two crop establishments viz. C1: System of Rice Intensification (SRI), C2 : Conventional; three dates of transplanting viz. D1 : 26th June, D2 : 10th July, D3 : 25th July and four hill densities viz. H1 : 20 cm x 15 cm (i.e. 33 hills m-2); H2 : 20 cm x 20 cm (i.e. 25 hills m-2); H3: 20 cm x 25 cm (i.e. 20 hills m-2); H4 : 25 cm x 25 cm (i.e. 16 hills m-2), laid out in a factorial split-plot design with crop establishment methods and dates of transplanting in the main plots and hill densities in the sub plots and were replicated thrice. The soil of the experimental site was sandy loam; acidic in reaction; medium in organic carbon and available N; low in available P2O5 and K2O. The phenological study revealed that SRI crops required significantly lesser days to attain various phenophases viz. MTS, panicle emergence, flowering and physiological maturity as compared to the conventional crops in both the years of investigation. On the other hand, both early transplantation (26th June) and lower hill density (16 hills m-2) took more days for attainment of different phenophases. Among the different growth and physiological parameters viz. plant height, tillers m-2, leaf area, dry matter production, LAI, chlorophyll content, CGR, RGR and NAR; the highest had been recorded by SRI with an exception of lower magnitude of leaf area, LAI and chlorophyll content at the tillering stage. Similar results were also observed in case of lower hill density showing better growth and physiological parameters. The early transplanting showed significant improvement in growth parameters, however, failed to show any significance with respect to physiological parameters viz. CGR, RGR and NAR. SRI portrayed lower magnitude of microclimatic parameters such as light intensity, light transmission ratio (LTR), AGDD throughout the crop growth, and AIPAR, AHTU and APTU at maturity. However, comparatively higher RUE (1.37 g MJ-1) and HUE (2.48 kg ha-1 0d) was recorded under SRI method. Throughout the crop growth, early crops recorded highest value of AGDD, and lowest value of light intensity and LTR. In both the years, superior values of AIPAR and APTU were found in early 29 crops; however, improved HUE of 2.16 kg ha-1 0d and RUE of 1.22 g MJ-1 were noticed in 2016 and 2017, respectively. In case of hill density, increased value of light intensity and LTR were recorded with increase in hill density and highest were observed at higher hill density of 33 hills m-2, whereas higher AGDD, AIPAR, AHTU, APTU, RUE and HUE were found in lower density (16 hills m-2). Marked variation with respect to yield attributes was observed due to methods of crop establishment. Significantly higher numbers of panicles m-2, longer panicle length, more filled grains panicle-1 and heavier test weight were registered in SRI. Improvement in yield attributes was also observed in early transplantation as well as under reduced hill density. The results from the pooled data revealed that SRI recorded significantly the higher grain yield, straw yield and harvest index of 57.13 q ha-1, 61.43 q ha-1 and 48.15 per cent, respectively, compared to conventional method. In case of date of transplanting, higher grain yield of 56.51 q ha-1 along with 62.00 q ha-1 of straw yield and 47.60 per cent of harvest index was documented in early date of 26th June. Further, crops raised under lower hill density of 16 hills m-2 showed significant improvement in terms of grain yield (56.75 q ha-1), straw yield (61.83 q ha-1) and harvest index (48.01%). The water use studies revealed comparatively higher magnitude of consumptive use (CU) of water (535.43 to 543.76 mm) and WUE (10.20 to 10.95 kg ha-1mm-1) in SRI than that of conventional method during transplanting to maturity stage. It was observed that the quantum of CU coupled with WUE were maximum in early transplanting (26th June) which got reduced with delaying of dates. Further, the lowest hill density (16 hills m-2) recorded the maximum quantum of CU and an increased magnitude of WUE in 2016 and 2017 as well. Results showed more quantum of CO2 efflux of 5935.42 to 6082.47 mg CO2 m-2 d-1 in 2016 and 2017, respectively in SRI whereas conventional establishment recorded 5481.31 and 5626.03 mg CO2 m-2 d-1 during the respective years of investigation. In 2016, highest efflux (5816.50 mg CO2 m-2d-1) was recorded in 10th July planting, which was comparable to late planting (25th July) and significantly superior to the early one. However, in 2017, maximum emission of (5972.25 mg CO2 m-2d-1) was registered in late planting which was followed by 10th July and lastly by 26th June planting. Moreover, CO2 emission was found to be increasing significantly with the increase of hill density the maximum release of 6102.28 to 6247.78 mg CO2 m-2d-1 was recorded at highest density i.e. 33 hills m-2. The N, P, K and total uptake was found to be significantly more under SRI. The crop transplanted early showed comparatively better result in respect of NPK uptake barring the K- uptake by straw. In the case of hill density, the higher density 30 recorded significantly lower uptake of nutrient, and with the reduction of density, uptake increased and reached the maximum at the lowest density i.e. 16 hills m-2. There were no such significant variations in available N, P and K status at harvest barring N (289.59 kg ha-1) and P2O5 (28.37 kg ha-1) in 2017, where SRI as a crop establishment method observed to be better. Correlation study on pooled data showed that grain yield was strongly correlated with LAI, chlorophyll content in all the stages, and RUE and HUE at harvest. On the other hand, significant but negative relationship was noticed with LTR in MTS and AHTU at harvest. Similar correlation pattern was also recorded in cases of straw yield, panicles m-2, filled grains panicle-1, test weight and harvest index. The seven models of significant linear relationship for yield and yield attributes with microclimatic parameters showed that the value of high determining factors (R2) for combination of microclimatic parameters to explain the variability in grain yield, straw yield, panicles m-2, panicle length, filled grains panicle-1, test weight and harvest index were 0.987, 0.995, 0.947, 0.954, 0.991, 0874 and 0.926, respectively. A magnitude of 98.7 per cent variation in grain yield was found to be predicted collectively by chlorophyll content and LTR at MTS, and AGDD and RUE at maturity. At MTS, chlorophyll content, LTR and AGDD was found to be critical influencer whereas at maturity, AGDD and HUE were significant predictive factors of yield determining parameters and yield. Amongst all, RUE was found to be outstanding as the most determining factor for predicting yield attributes and yield followed by chlorophyll content and LTR at MTS and, AGDD and HUE at maturity. On the economic analysis of different treatments, maximum net return (` 90,703.73) along with the highest net return per rupee invested (2.06) was obtained by the crop transplanted on 26th June with a spacing of 25cm x 25cm (16 hills m-2) under SRI establishment method.