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Achieving high-yielding crops while also improving nitrogen use efficiency is a significant challenge for agricultural production in Bangladesh. We investigated the impacts of applying nitrogen (N) using different management options in wetland rice on a calcareous dark gray soil over three seasons. These included (1) the recommended dose of available N as prilled urea, (2) the recommended N dose plus 25% extra of available N as prilled urea, (3) 25% less than the recommended dose of available N as prilled urea, (4) the recommended dose of prilled urea in 2 t ha−1 cow dung, (5) the recommended dose as urea super granules (USGs) by deep placement, (6) 4 t ha−1 biochar with the recommended dose of prilled urea, and (7) Zero N. It was found that the growth, yield, and N use efficiency (NUE) were significantly different from the results obtained for prilled urea in all the alternative fertilizer options. The deep placement of USG consistently increased plant height, total number of tillers per plant, effective tillers per plant, chlorophyll content, panicle length, grains per panicle, and 1000-grain weight. The yield increases over recommended prilled urea were 5.22% for USG followed by biochar with the recommended dose. Similarly, using the deep placement of USG gave the highest yield and harvest index. In addition, compared to the recommended dose of prilled urea, the deep placement of USG increased NUE by 13%, agronomic N efficiency by 20%, and recovery N use efficiency by 19%. This suggests the rate of N application could be reduced by up to 8% without impacting yield by using deep placement of USG instead of prilled urea. The cost–benefit ratio was higher for the deep placement of USG than all other treatments. Biochar with the recommended dose of prilled urea also showed good results in terms of growth, yield, and NUE (41.8, 43.0, and 41.7, respectively, during three sequential years), but the extra cost of the biochar reduced the cost–benefit ratio. These findings suggest that the deep placement of USG is the best option for improving the yield of rice while also improving N use efficiency.

The impact of climate change on methane (CH4) emissions from rice production systems in the Coimbatore region (Tamil Nadu, India) was studied by leveraging field experiments across two main treatments and four sub-treatments in a split-plot design. Utilizing the closed-chamber method for gas collection and gas chromatography analysis, this study identified significant differences in CH4 emissions between conventional cultivation methods and the system of rice intensification (henceforth SRI). Over two growing seasons, conventional cultivation methods reported higher CH4 emissions (range: from 36.9 to 59.3 kg CH4 ha−1 season−1) compared with SRI (range: from 2.2 to 12.8 kg CH4 ha−1 season−1). Experimental data were subsequently used to guide parametrization and validation of the DeNitrification–DeComposition (DNDC) model. The validation of the model showed good agreement between the measured and modeled data, as denoted by the statistical tests performed, which included CRM (0.09), D-index (0.99), RMSE (7.16), EF (0.96), and R2 (0.92). The validated model was then used to develop future CH4 emissions projections under various shared socio-economic pathways (henceforth SSPs) for the mid- (2021–2050) and late (2051–2080) century. The analysis revealed a potential increase in CH4 emissions for the simulated scenarios, which was dependent on specific soil and irrigation management practices. Conventional cultivation produced the highest CH4 emissions, but it was shown that they could be reduced if the current practice was replaced by minimal flooding or through irrigation with alternating wetting and drying cycles. Emissions were predicted to rise until SSP 370, with a marginal increase in SSP 585 thereafter. The findings of this work underscored an urgency to develop climate-smart location-specific mitigation strategies focused on simultaneously improving current water and nutrient management practices. The use of methanotrophs to reduce CH4 production from rice systems should be considered in future work. This research also highlighted the critical interaction that exists between agricultural practices and climate change, and emphasized the need to implement adaptive crop management strategies that can sustain productivity and mitigate the environmental impacts of rice-based systems in southern India.

Rice growing under anaerobic conditions followed by spring wheat under an aerobic environment differentially impact the net ecosystem exchange (NEE) of carbon dioxide (CO2) in rice-wheat systems of the north-western Indo-Gangetic Plains (IGP). This is the first estimation of the NEE in a rice-spring wheat sequence via the eddy covariance technique in the north-western Indo-Gangetic Plains, which was partitioned into gross primary productivity (GPP) and ecosystem respiration (RE) and correlated with the environmental variables. Higher CO2 uptake of −10.43 g C m−2 d−1 was observed in wheat during heading as compared to −7.12 g C m−2 d−1 in rice. The net uptake of CO2 was 25% lower in rice. The average daily NEE over the crop season was −3.74 and −5.01 g C m−2 d−1 in rice and wheat, respectively. The RE varied from 0.07–9.00 g C m−2 d−1 in rice and from 0.05–7.09 g C m−2 d−1 in wheat. The RE was positively correlated with soil temperature at 5 cm depth (0.543, p < 0.01) in rice and with air temperature (0.294, p < 0.01) in wheat. The GPP was positively correlated with air temperature (0.129, p < 0.05) and negatively correlated with vapor pressure deficit (VPD) (−0.315, p < 0.01) in rice. In wheat, GPP was positively correlated with air temperature (0.444, p < 0.01) and soil moisture (0.471, p < 0.01). The rate of GPP over the crop duration was nearly the same in both rice and wheat, however, the RE was higher in rice as compared to wheat, thus, the ratio of cumulative RE/GPP was 0.51 in rice and much lower at 0.34 in spring wheat. Rice contributed 46% and 43% to the annual totals of RE and GPP, respectively, while spring wheat contributed 36% and 51%. The NEE of CO2 was higher in spring wheat at −576 g C m−2 d−1 as compared to −368 g C m−2 in rice. Thus, while estimating the carbon sink potential in the intensively cultivated northern IGP, we need to consider that spring wheat may be a moderately stronger sink of CO2 as compared to rice in the rice-wheat system.