Neog, PrasantaSaikia, Raktim Jyoti2020-10-052020-10-052019-07https://krishikosh.egranth.ac.in/handle/1/5810152404A field experiment was conducted during rabi, 2018-19 in the Instructional-Cum-Research (ICR) Farm of Assam Agricultural University, Jorhat to study the impact of thermal and radiation regimes on growth and yield of Potato under varying microenvironments. The cultivar Kufri Jyoti was grown in split plot design with four dates of planting (P1 - 10th Nov, P2 - 20th Nov, P3 - 30th Nov and P4 - 10th Dec) in main plots and mulches (M0 - non mulch, M1 - water hyacinth and M2 - black polythene) in sub-plots, following recommended agronomic practices. Microclimatic parameters like soil temperature (daily), soil moisture and photosynthetically active radiation (PAR) were recorded periodically. Occurrences of different phenological events along with periodic LAI, plant biomass, yield attributing characters and tuber yield were recorded. Phenophase-wise agroclimatic indices viz., growing degree days (GDD), heliothermal unit (HTU), day temperature, phenothermal index (PTI) and heat use efficiency (HUE) were computed following established procedure. The weekly maximum and minimum temperature throughout the crop growth period ranged from 21.3 to 27.2℃ and 8.1 to 16.1℃, respectively. A total of 110.7 mm rainfall from 16 rainy days was received during the growing period and weekly average BSSH ranged from 1.5 to 7.7 hr. The maximum soil moisture depth (mm) was recorded under water hyacinth (85.7 mm) followed by non-mulched (81.2 mm) and lowest under black polythene mulch (79.7 mm). Among different dates of plantings P1 recorded highest (83.3mm) soil moisture depth, followed by P4 (82.0 mm), P2 (81.8 mm) and P3 (81.5 mm). The weekly mean morning and evening soil temperature ranged from 13.6 to 19.3°C and 19.6 to 28.6°C, respectively under different planting dates and mulching treatments. Irrespective of planting dates, soil temperatures under black polythene was higher in morning and evening by 0.8 to 1.9°C and 1.5 to 2.8°C, respectively, while soil temperatures under water hyacinth were 0.3°C to 0.9°C higher in the morning and 0.5 to 2.2°C lower in the evening as compared to non mulched treatment. No considerable difference in incident PAR was observed among mulching treatments. However, it varied considerably when measured at different days in all planting dates. Irrespective of planting dates the reflected PAR increased in later growth period of the crop with the onset of senescence. The lowest (65 μ mol s-1 m-2) RPAR values under black polythene treatment were attributed to greater absorption by black surface. The transmitted PAR was lowest, when measured on 55 DAP with full coverage of canopy, after that it increased again with maturity of the crop. PAR interception was highest on 55 DAP (74.8 %) in all the planting dates and mulching treatments. Among the mulching treatments, crops under water hyacinth recorded highest (80.6%) interception of PAR. The duration of the crop was highest under first date of planting (100.33 days) followed by second (96.7 days), third (90 days) and fourth (87.6 days) date of planting. The maximum leaf area index (LAI) was observed under water hyacinth (2.77) followed by black polythene (2.44) and non-mulched (2.14) treatment. Maximum partitioning of photosynthates towards tuber was found in case of water hyacinth (386.77 g m-2) and lowest in non-mulched (241.63 g m-2). Highest average total dry matter accumulation was obtained in P1 (465.2 g m-2) followed by P2 (431.6 g m-2), P3 (309.6 g m-2) and P4 (284.8 g m-2). The tuber yield was found to be highest on P1 (135.6 q ha-1) followed by P2 (118.3 q ha-1), P3 (86.3 q ha-1) and P4 (60.0 q ha-1). The RUE for tuber yield was highest under water hyacinth (2.35 g MJ-1) followed by black polythene (2.03 g MJ-1) and non-mulched (1.67 g MJ-1) condition. From correlation study it was observed that tuber yield, biomass accumulation and LAI were found significant and positively correlated with PAR interception and RUE as well as with AGDD, AHTU, HUE and PTI. The predictive model have been developed by using stepwise regression to predict tuber yield from radiation and thermal indices with higher R2 value of 0.96 and 0.99, respectively.EnglishThesis