STUDIES ON THE ENERGY BALANCE AND IMPACT OF ELEVATED TEMPERATURE AND CO2 UNDER RICE-COWPEA CROPPING SYSTEM
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Date
2022
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INDIRA GANDHI KRISHI VISHWAVIDYALAYA RAIPUR (Chhattisgarh)
Abstract
Present investigation on “Studies on the surface energy balance and impact of elevated temperature and CO2 under rice-cowpea cropping system” was conducted at Research Farm, ICAR-IIWM, Deras, Mendhasal, Khurdha District of Odisha during kharif & rabi seasons of 2018-19 and 2019-20. For the study of weather characterization, weather data were collected from Agromet observatory situated at farm research field. Intercepted Photosynthetically Active Radiation (IPAR) and soil moisture were measured through standard micrometeorological instruments at regular intervals. Net Ecosystem Exchange (NEE) and energy balance components were studied through Eddy Covariance tower over rice and cowpea crop. Elevated temperature and CO2 concentrations was evaluated with the help of DSSAT model. Marksim software was used for future temperature scenario data projection. Results revealed that highest rainfall of 1540.9 mm in kharif and 42.5 mm in rabi season was recorded in 2nd season as compared to 1st season. During the rice and cowpea growing periods, the 1st season had the highest weekly mean maximum and minimum temperatures, relative humidity, and bright sunlight hours as compared to the 2nd season. When irrigation and rainfall occurred during both crop growth seasons, the soil moisture content behaved in a zig-zag function during both seasons. Due to more rainfall in 2019-20 than in 2018-19, the soil moisture content was higher in 2019-20 than in 2018-19. In both years of the study, the highest soil moisture content was reported in the first week of February (5 SMW) and the lowest in the fourth weeks of January (4 SMW) for the cowpea crop. The transplanted rice and cowpea crop showed highest accumulated AGDD (2334 0C & 1097 0C) and APTU (26138 0C & 13167 0C) respectively during 2nd season as compared to 1st season. While the highest AHTU i.e. 18152 0C day & 8089 0C day was observed in 1st growing season under rice and cowpea crops. Higher radiation and heat use efficiency were observed 1.46 g/MJ & 0.58 g/m2/0C day for rice crop plant and for cowpea crop 0.28 g/MJ & 0.14 g/m2/0C day in 2nd season as compared to 1st season, respectively.
Diurnal variation of IPAR,increased from morning till noon time (12:00 to 13:00 hrs) and then decreased consistently till evening. Crop reproductive stages recorded highest IPAR value over both the cropping seasons. Among seasons, maximum IPAR value of 720 MJm-2 was observed at 90 DAT while 663 MJm-2 was recorded in 2018 at 75 DAT, respectively. In cowpea crop, maximum IPAR value of 423 MJm-2 was recorded at 60 DAS in 2019-20 while, 2018-19 showed 401 MJm-2 at 60 DAS. Diurnal pattern of f IPAR exhibited a very interesting pattern on rice and cowpea crop. It increased a little soon after sunrise and it continued till 7:00-8:00 hrs. Then it gradually decreased from a low point at 12:00 hrs after that it increased till 16:00-17:00 hrs and then its decrease continued up to sunset. In seasonal profile maximum value 0.62 of f IPAR was found in 75 DAT in season 2018 while in 2019, higher value of 0.70 was observed in 90 DAT under rice crop. In cowpea crop, maximum f IPAR value of 0.46 was found at 60 DAS in 2nd season. Diurnal pattern of extinction coefficient (K) increased,from morning till noon hrs (12:00 to 1:00 hrs) and then decreased consistently. Crop reproductive stages recorded lowest K value over both the cropping seasons. Highest K value (0.58 & 0.64) was found in 30 DAT in both seasons while lowest (0.40) was observed in 75 DAT during 1st season and 0.46 in 90 DAT during 2nd season under rice crop. Whereas, cowpea crop highest K value (1.14 & 1.31) was found in maturity and lowest (0.86 & 0.89) was observed in 60 DAS in both the seasons. Season 2019-20 showed higher value as compared to season 2018-19 under rice and cowpea growing seasons.
Surface energy balance components varied with crop growth stages. A considerable amount of net radiation is consumed in the form of latent heat flux, which is then followed by sensible heat flux and soil heat flux were observed at 8:00 hrs to 17:00 hrs in both the cropping field under two growing seasons. The highest average Rn value was recorded 344.58 Wm-2, LE was found 151.64 Wm-2, H 38.95 Wm-2 and G was found -0.84 Wm-2, respectively in 2nd rice growing season. Highest LE/Rn ratio was recorded at Panicle initiation stage (0.51) and lowest was observed at maturity stage (0.33) on both growing season of rice crop. Highest H/Rn ratio (0.47) was observed at physiological maturity. In cowpea crop, the average Rn was recorded (351.63 Wm-2), LE (130.87 Wm-2), H (71.53 Wm-2) and G (0.06 Wm-2) during 2019-20 as compared to 2018-19 growing season. The LE/Rn ratio was recorded highest (0.74) in full flowering stage of cowpea during 1st growing season but full maturity stage was found highest ratio (0.52) in 2nd growing season. H/Rn ratio was recorded highest (0.53) at crop emergence stage of cowpea in 1st growing season but highest ratio (0.28) was found at full flowering stage in 2nd growing season. G/Rn ratio was found mostly positive values and diurnally morning hours was found negative values of different growth stages.
The CO2 fluxes quantified by the EC technique were used to study the NEE of CO2 and partitioning NEE (Net Ecosystem Exchange) into two components viz., gross primary productivity (GPP) and ecosystem respiration (RE). Plant photosynthesis during the day time led to the uptake of CO2 from the atmosphere whereas respiration at night contributed to an efflux of CO2 to the atmosphere in the absence of photosynthesis. Diurnal maximum NEE and GPP by rice and cowpea crop was found between 11.00 and 01.00 h. Whereas, maximum RE was found between 12.00 and 15.00 h over the cropping season. The highest NEE was recorded at the panicle to flowering stage (-13.72 μmol CO2 m–2 s–1) and GPP value was observed highest at flowering to dough stage (-17.33 μmol CO2 m–2 s–1) in 2nd season as compared to 1st season. Cumulative value of GPP (-695 μmol m–2 s–1), NEE (-311 μmol m–2 s–1) was recorded highest in 2019-20 but highest RE (347 μmol m–2 s–1) was observed in 1st season (2018-19). Similarly, for cowpea crop highest NEE (-12.83 μmol CO2 m–2 s–1), GPP (-16.17 μmol CO2 m–2 s–1) was found during branching to flowering stage whereas highest RE (2.07 μmol CO2 m–2 s–1) was observed during flowering to pod development stage in 2nd season.
The sensitivity analysis was studied through DSSAT model for elevated CO2 concentration (450, 500 and 550 ppm) under prevailing weather condition. Results revealed that the grain yield of rice crop was increased by 11.19%, 12.02% and 12.95 % at elevated CO2 concentration of 450 ppm, 500ppm and 550ppm, respectively and for cowpea crop, grain yield increased by 34.07%, 40.17% and 41.83% under elevated CO2 concentration levels of 450 ppm, 500ppm and 550ppm, respectively. Greater tillering and more grain bearing panicles were attributed to the higher growth response with increased CO2 concentration. With increasing CO2 concentrations, net absorption rate and net photosynthesis both increased. Under elevated CO2 and future temperature scenario (2030, 2050 & 2070) grain yield and biomass of rice crop showed highest reduction -10.56% and -9.54%, respectively in 2070 at 550 ppm level. For the cowpea crop, highest reduction in yield and biomass was observed -13.20% and -9.9% in 2070 at 550 ppm level as compared to prevailing weather condition.
2nd season of rice and cowpea crop was found good due to better crop environment and favourable meteorological conditions during crop growth and development. Better radiation interception and energy balance components was found in 2nd season due to higher leaf area and growth of plants. In rice crop the Net Exchange Ecosystem (NEE) is a net CO2 sink practically the whole crop season, with the exception of a few days around maturity when it becomes a net CO2 emitter. Both crops revealed that higher CO2 concentrations had more favourable than negative effects of temperature on yield and yield components.
Description
STUDIES ON THE ENERGY BALANCE AND IMPACT
OF ELEVATED TEMPERATURE AND CO2 UNDER
RICE-COWPEA CROPPING SYSTEM