Rice Season Research Articles

Optimizing water footprints and yield sustainability in Boro rice through alternate wetting and intense drying: a climate-resilient strategy for Bangladesh

ABSTRACT Climate change and water scarcity pose significant challenges to rice production in Bangladesh, necessitating water-efficient practices. This study, conducted during the 2024 Boro rice season in Mymensingh, Bangladesh, compared the impacts of alternate wetting and intense drying (AWID), with irrigation at a 20-cm water level drop, against continuous flooding (CF) and alternate wetting and moderate drying (AWMD), with a 15 cm drop. The AWID resulted in 46.12% water savings and a 43.1% increase in crop–water productivity, yielding 5.10 t/ha, while AWMD saved 38.64% water with a yield of 6.13 t/ha. Despite a 22.7% yield reduction compared to CF (6.60 t/ha), AWID's superior water efficiency underscores its potential as a sustainable option in water-scarce regions. Excluding the first 15-day crop establishment phase, the water footprint was lowest for AWMD (1003.83 l/kg) and AWID (1079.68 l/kg) compared to CF (1439.00 l/kg). Climate projections for the 2040 and 2070s indicate increased temperatures, decreased rainfall, and higher evapotranspiration, potentially raising irrigation demands by up to 30% under RCP 8.5 scenarios. These water-saving techniques offer promising strategies for sustaining rice production while conserving water resources. Further research is recommended to optimize these practices across diverse agro-ecological zones, enhancing climate resilience in rice cultivation.

Straw return combined with potassium fertilization improves potassium stocks in large-macroaggregates by increasing complex iron oxide under rice–oilseed rape rotation system

Straw return combined with potassium fertilization improves potassium stocks in large-macroaggregates by increasing complex iron oxide under rice–oilseed rape rotation system

Effects of different biochars on Cd immobilization in rice paddy soil: A two-year field study

This study addressed the efficiency of different biochars in Cd immobilization in soil. An acidic sandy loam paddy contaminated with Cd was selected for the field trial, which was continued for three rice-growing seasons. Rice straw biochar (BR), wheat straw biochar (BW), and maize straw biochar (BM) were pyrolysed as pellets at 450 °C and applied at 0 t/ha (BC0), 10 t/ha (BR1/BW1/BM1), and 20 t/ha (BR2/BW2/BM2). Compared to BC0, BR and BW were more effective in decreasing Cd accumulation in rice grains, and BR2 achieved the highest reduction, averaging 43.4% over three rice seasons. The Cd contents in rice roots with BR2 treatment decreased by 15.2 to 55.3% compared with BC0. The bioconcentration factors for grains (BCFGrain), shoots (BCFShoot), and (BCFRoot) of BR2 treatment were averagely decreased by 53.3%, 27.4%, and 19.0% over BC0, respectively. There was a negative correlation between soil CaCl2-Cd and soil pH. FTIR analysis demonstrated that Cd complexed with SiO2 on aged BR2 particles. During the natural aging process, BR2 significantly and sustainably inhibited rice uptake Cd through co-deposition. Therefore, the BR was judged to be an effective soil amendment with high Si content and alkalinity for Cd immobilization in paddy soil.

Impacts of Plant Spacing and Nitrogen on Wet Season Rice Yield in the Non-Saline Coast of Bangladesh

Impacts of Plant Spacing and Nitrogen on Wet Season Rice Yield in the Non-Saline Coast of Bangladesh

Double transplanting of dry season rice: A unique technology to optimize yield of late transplanted rice in Northern Bangladesh

In irrigated condition, double transplanting (DT) of dry season rice in Potato-Rice-Rice cropping pattern emerges as a promising technology to reduce yield losses associated with late-planted dry season rice. A consecutive three-year experiment encompassing three planting dates (20, 28 February and 08 March) and four seedling ages (45, 60, 75 days, and with 75-day for double transplanting- 35 days in the seedbed and 40 days in the first transplanted plot) was conducted to assess the performance of double-transplanted dry-season rice in comparison to conventional transplanting methods. Across the years, the grain yield of dry season rice exhibited a gradual decline with the advancement of planting time. However, the higher grain yield was consistently found from double transplanted dry season rice in all planting times. The yield advantage from double transplanting was 17%, 13%, and 16% for planting times on February 20, February 28, and 08 March, respectively compared to conventional transplanting. The system productivity of Potato-Double transplanted dry season rice-wet season rice cropping pattern was higher (1-6%) in all planting times compared to the cropping pattern with traditional transplanting method. Double transplanting technology found more stable compared to traditional method in late planting situation. The average added net returns with double transplanted dry season rice over traditional transplanted rice was US$139 to US$187 ha−1 in 20 February, US$67 to US$117 ha−1 in 28 February and US$68 to US$171 ha−1 in 08 March planting. These findings highlight the profitability of adopting double transplanting in the Potato-Rice-Rice cropping system. Bangladesh Rice J.27(1): 13-29, 2023

The effect of planting time on nutrients, phenolics, and antioxidant activities of rice grown in different soil salinities

Rice (Oryza sativa) is a staple food crop with a significant role in nutrition and health. Its production yield mainly depends on climatic conditions. Soil salinity, an abiotic factor as a resulting from drought, also impacts rice growth, production, and quality. Researchers have widely investigated newly developed salt–tolerant rice varieties and suitable fertilizers to enhance rice yield and quality. However, the effects of planting times of in– season and off–season rice varieties grown in soils with varying salinity levels on rice qualities, such as nutrients, bioactive compounds, and health–related properties remain unexamined. This study evaluated the qualities (nutrients, phenolics, and antioxidant activities) of thirty-eight in season– and off–season rice samples grown in soils with different physicochemical properties: electrical conductivity extract (ECe), pH (pHH2O), organic matter (OM), available minerals (potassium and phosphorus), and soluble salts (calcium, magnesium, sodium, and potassium). Results indicated that rice nutrients, total phenolic contents (TPCs), and antioxidant activities were influenced by planting seasons rather than rice varieties or the soil salinity marker ECe. The in–season rice samples exhibited higher levels of protein, iron (Fe), TPCs, and antioxidant activities compared to the off–season rice samples, which had higher vitamin B3 content. Principal Component Analysis (PCA) and Pearson’s correlation were used to determine the relationships among rice qualities and soil physicochemical properties. The rice samples were divided into four groups: Group 1 consisted of rice samples grown in soil with high ECe and soluble salts, showing unrelated rice nutrients, TPCs, and antioxidant activities; Group 2 included off–season rice samples grown in soil with high OM that contained high vitamin B3 content; Group 3 contained in–season rice samples grown in soil with high pHH2O that had high energy and fat content, and Group 4 comprised in–season rice samples with high protein, Fe, TPCs, and antioxidant activities, demonstrating moderate to very weak correlations with soil properties. This information can be used to determine the appropriate utilization of fertilizer in soil with different salinity levels and assist in the selection of applicable planting seasons for specific rice qualities.

Optimizing STCR-IPNS fertilizer prescription for targeted rice yield in North Eastern agro climatic zone of Tamil Nadu

Rice is the major crop in the North Eastern zone of Tamil Nadu. In Tiruvallur district, rice is the major crop cultivated in 96967 ha with a share of 6.7% of the state. At present, the productivity of rice in Tiruvallur district is 4200 kg ha-1 . Due to intensive cropping and application of chemical fertiliz- ers without organic manures, the organic matter content of the soils in Tiru- vallur district is very low in most of the areas with the occurrence of multi- nutrient deficiencies, especially zinc and iron deficiency in rice. In Soil Test Crop Response-Integrated Plant Nutrition System (STCR-IPNS) technology, the fertilizer doses are tailored to specific yield target levels, considering the nutrient requirement of the crop, and the contribution of nutrients from soil, fertilizers, and organic manures. The field experiments were conducted during samba season in irrigated rice to refine the existing Fertilizer Pre- scription Equations (FPEs) for specific yield target levels on the Kadambady soil series in the Tiruvallur district for sustainable rice production and soil quality. Observation on growth and yield attributes was recorded. Grain yield, straw yield, and dry matter production were recorded. Post-harvest soil and plant samples were collected from all the plots. Based on the initial soil analysis of available NPK (Kg ha-1 ) and NPK content in FYM, the STCR- based IPNS fertilizer recommendations were worked out with FPEs of Irugur soil series (Rabi) under yield target levels of 50, 60, and 70 q ha-1 . Using the data on the grain yield, total uptake of NPK, initial soil test values for availa- ble NPK, and doses of fertilizer N, P2O5, K2O, and FYM applied, the basic pa- rameters, viz., the nutrient requirement (NR), contribution of nutrients from soil (Cs), fertilizer (Cf), response ratio (RR), and farmyard manure (Cfym) were computed. Using the basic parameters, viz., NR, Cs, Cf, and Cfym, the FPEs were developed under NPK alone and IPNS. From the test verification trials, the STCR-based fertilizer prescriptions under IPNS for 7 t ha-1 , i.e., applica- tion of fertilizer N, P2O5 and K2O based on initial soil test values with FYM at 12.5 t ha-1 (with a manurial composition of N: 0.48 %, P: 0.23%, K: 0.42 %, and moisture: 24%) contributed fertilizer N, P2O5 and K2O at 40:20:32 kg ha-1 from the recommended dose of fertilizers based on soil test values. This can be recommended for achieving higher yield, RR and benefit-cost ratio (BCR) for rice. The increase in yield with STCR-IPNS-7 t ha-1 was 41.5% over blanket (100% RDF alone), 24.8% over blanket + FYM at 12.5 t ha-1 ,and 56.7% over farmer’s practice. The increase in RR was 4.54, 1.98 and 5.25 kg kg-1 due to STCR-IPNS-7 t ha-1over blanket (100% RDF alone), blanket + FYM at 12.5 t ha- 1 and farmer’s practice respectively, on Kadambady soil series and allied soil series, especially in Tiruvallur district of North Eastern agro climatic zone of Tamil Nadu.

Management of BPH Using Cultural Techniques Experienced from Bangladesh

A series of experiments was conducted in three Agro-Ecological Zones, namely AEZ 11, AEZ 12, and AEZ 13, at Khulna Metropolitan Thana, Dumuria, and Batiaghata Upazila under Khulna District of Bangladesh, to comprehend the incidence pattern of Brown Plant Hopper (BPH) in relation to cultural factors during the wet season rice (T. Aman) and dry season rice (Boro). The incidence of BPH at different growth stages of the rice crop and the number of affected/non-affected hills, together with rice yields, were evaluated. Two peaks of BPH were reported during the year, the first one during March-April and the other during September-October. Older rice plants received a higher number of BPH than young rice plants. Among the five arrangements of missing hills, 7 lines + missing line offered the best performance. In the case of five spacing arrangements, 20 cm × 30 cm spacing was the most suitable against BPH. The increase in the dose of urea fertilizer from recommended doses could cause higher BPH infestation. Among the five wet rice varieties, BRRI dhan49, BRRI dhan62, and BRRI dhan72 performed better, while among the five varieties in Boro, BRRI dhan58 performed the best, followed by BRRI dhan28, BRRI dhan47, BRRI dhan50, and BINA dhan8 against BPH. Among the five manipulation tactics against BPH, recommended dose of chemical fertilizer, spacing, chemical control, bili, and draining out water from the rice field treatment showed the lowest number of affected hills at all phases of rice with maximum yield compared to other treatments. In conclusion, this study offers a comprehensive incidence pattern of BPH in the rice grown areas that might help to manage in a comprehensive manner without affecting the environment. South Asian J. Agric., Vol. 10, No.1-2, 2024: 72-81

Weed Growth Observation in Transplant Aman Rice Field as Influenced by the Organic Manures and Fertilizers with Rice Straw Allelopathy

The present experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh from June 2022 to November 2022 to estimate the combined effect of manures and fertilizers with the rice straw allelopathy on the weed growth of transplant aman rice season. It had two cultivars viz., BRRI dhan71 (V1), and BRRI dhan49 (V2) and eight treatments comprising with rice straw, manures and fertilizers (t ha-1): Control (T1), Recommended doses of NPKS (T2), Rice straw 1.5 t ha-1 + Cow dung 5 t ha-1 (T3), Rice straw 1.5 t ha-1 + Cow dung 2.5 t ha-1 + 50% less of recommended doses of NPKS (T4 ), Rice straw 1.5 t ha-1 + Vermicompost 5 t ha-1 (T5) , Rice straw 1.5 t ha-1 + Vermicompost 2.5 t ha-1 + 50% less of recommended doses of NPKS (T6), Rice straw 1.5 t ha-1 + Trichocompost 10 t ha-1 (T7), Rice straw 1.5 t ha-1 + Trichocompost 5 t ha-1 + 50% less of recommended doses of NPKS (T8) and was laid out in a randomized complete block design (RCBD) with three replications. Nine weed species belonging to four different families infested the experimental plots. Weed population and weed dry weight were significantly affected by treatments. The maximum weed growth was obtained from Control (T1) while the minimum was found in (T6). Results of this current study indicate that combination of rice straw with manures and fertilizer showed potentiality to inhibit weed growth and enhances the yield of transplant aman rice. Therefore, combination of rice straws with manures and fertilizers could be a potential package of sustainable and eco-friendly weed management and yield enhancement element for the nearest year’s crop production.

Photosynthesis and senescence gene expression drive yield improvements in early season rice under long-term method of fertilization

This study investigated the effects of long-term method of fertilization on growth and yield formation in early-season rice. Based on a 42-year field experiment initiated in 1981, three treatments: chemical N, P, and K (NPK), a double dose of chemical NPK (HNPK), and a combination of chemical and organic fertilizers (NPKM) were selected for comparison. Measurements included rice yield, yield components, tiller dynamic, dry matter accumulation, chlorophyll content (SPAD values), and transcriptome analysis of leaves at full heading stage in 2022. Results showed that rice yield followed the order NPKM > HNPK > NPK. The HNPK and NPKM treatments increased by 56.64% and 90.33%, respectively (p < 0.05). Spikelet density and 1000-grain weight increased by 9.16–22.89% and 3.74–4.28%, respectively. Both HNPK and NPKM enhanced the tillering rate by 43.84–72.73%, leading to an 18.95–57.54% increase in effective panicles. Dry matter accumulation from heading to filling stages was highest in NPKM-treated rice, with an increase of 3.31–4.25 g/plant in dry matter transport from leaves and stems to spikes during the filling to maturity stages. The SPAD values of NPKM-treated plants were consistently higher than those of HNPK and NPK treatments, with a smaller decline (6.94%) from heading to filling stages compared to 18.23% and 26.29% for HNPK and NPK, respectively. Correlation analysis indicated a positive relationship between yield and SPAD values or dry matter accumulation and a negative correlation with the decline in SPAD values from full heading to filling stage. Transcriptome analysis revealed significant enrichment of photosynthesis and plant senescence pathways among treatments. Overall, long-term combined application of chemical and organic fertilizers (NPKM) improved yield components, delayed chlorophyll degradation, promoted dry matter accumulation and transport, and regulated the expression of photosynthesis-related and senescence-related genes, ultimately optimizing growth and yield in early-season rice.

Effect of establishment methods and irrigation scheduling on growth indices of wet season rice

Effect of establishment methods and irrigation scheduling on growth indices of wet season rice

Village level fertilizer management for increasing nitrogen use efficiency, rice yield and household income

ABSTRACT Limited soil nitrogen (N) availability constrains crop growth and yield. Low N use efficiency (NUE) coupled with overuse of fertilizer-N result in environmental pollution and huge economic loss. Hence, effects of N management practices on rice grain yield and NUE were studied in two separate experiments in experimental farm and farmer’s field. Each of the study was conducted in two consecutive rice seasons of Boro (dry season rice) and Transplanted Aman (T. Aman) (wet season rice) using several N treatments. Results revealed that compared with the recommended dose of N (RDN), urea super granule (USG) and biochar with RDN (BRDN) increased grain yield by 6–18% irrespective of experimental sites and cropping seasons. USG contributed to the highest NUE, while. USG and BRDN increased agronomic efficiency (1.3–2.3 folds), apparent N-recovery (1.3–1.9 folds) efficiency and physiological efficiency (0.9–1.3 folds), compared to RDN. USG appeared to be economically the most viable option, with a benefit-cost ratio (BCR) of 1.5–1.6 over locations and seasons. BRDN showed a lower BCR (1.1–1.2) due to additional expense on biochar. Biochar might contribute towards a carbon-negative economy, and its economic benefits require to be addressed. Supportive government policies are needed for adoption of USG and biochar in agriculture.

Effects of Hydrochar Incorporation on the Nitrogen Leaching Flux Pattern and Load in Rice Paddy Soil and Crop Production.

Hydrochar (HC) incorporation affects soil nitrogen (N) transformation, which could further affect the N leaching loss. We conducted a soil lysimeter experiment to evaluate the responses in terms of N leaching and rice yield to HC applied at a low (0.5%) or high (1.5%) rate, while considering three N inputs, i.e., 240, 192, and 144 kg/ha (named N240, N192, and N144, respectively). The results showed that the rice grain yield was highest (124.3 g/pot) for N192, while being significantly reduced to the minimum yield achieved in the study (110.3 g/pot) for N144. Interestingly, for the N input 144 kg/ha, HC application increased the rice grain yield by 6.9-8.0%, which was equivalent to that of N240. NH4+-N leaching occurred mainly during the first 4 weeks of the rice season, and HC did not influence NH4+-N leaching for both the N inputs, 192 and 240 kg/ha. However, compared to N144, N144 + HC1.5% recorded a significantly higher NH4+-N leaching loss of 34.6%. This suggests that the application of a high amount of HC increases the NH4+-N leaching risk when the N input is low. HC application resulted in 10.2-45.3% more NO3--N leaching loss when the three N inputs were applied, the effect of which was significant in regard to the applications involving a 20 and 40% N reduction, but this occurred only with the applied treatments involving 1.5% HC. Moreover, we found that organic N was the main form of leachate N (>80%). More specifically, N144 + HC recorded 7.8-8.3% lower organic N leaching than N192. Based on the effects of HC on the rice grain yield and N leaching, we recommend applications involving a 40% N reduction (N144) with a lower amount of HC (HC 0.5%) to ensure high crop production and to protect the water environment.

The near-optimal adjustment of carbon and nitrogen allocations into different organs in early-season rice cultivars with drastically different yield components under nitrogen application.

Optimized photosynthesis and transport of photosynthate from the upper three leaves in a rice plant is critical for yield formation in rice. In this study, we selected two high-yielding early-season rice cultivars, i.e. a large-panicle inbred rice Zhongzao39 (ZZ39) and a plural-panicle hybrid rice Lingliangyou268 (LLY268) with high effective panicle number, to study the translocation of photosynthate from the flag and the basipetal 2nd leaves to the other organs under different nitrogen application scenarios. 13CO2 labeling was study the proportion of newly assimilated carbon partitioned into different organs. Results demonstrate that the ratio that 13C assimilated in the flag leaves and the basipetal 2nd leaves, and the distribution ratio 13C in the organs of ZZ39 and LLY268 cultivars were not affected by nitrogen application. However, at the booting stage, the translocation rate of photosynthate was slower under N150 compared with CK in both flag and the basipetal 2nd leaves labeled with 13C. At the grain filling stage, an average of 51% of photosynthetic products labeled with 13C was translocated to the panicle in both cultivars under CK treatment; in contrast, only 43% of leaf photosynthate was translocated to panicles in the N150 treatment. At maturity, the photosynthate labeled with 13C distribution ratio in the panicle was greater in the basipetal 2nd leaves than in the flag leaves for ZZ39, whereas the opposite was observed in LLY268. These different photosynthate allocation patterns and their responses to nitrogen application were linked with their corresponding tiller number and number of grains per panicle. This study shows that early-season rice has the ability to flexibly adapt their carbon and nitrogen allocation patterns to gain optimized yield components for higher yield under different nitrogen status. Early season rice can be used as a model system to study the growth strategy selection of plants to changing environment conditions.

How does forest fine root litter affect the agricultural soil NH3 and N2O losses?

How does forest fine root litter affect the agricultural soil NH3 and N2O losses?

Re-examine the Relationship between the Climatic Factors and Rice Yield in Bangladesh

The agriculture of Bangladesh, especially rice production is indissolubly linked climate and also be affected with the change in different climatic variables. The main focus of the study is to examine the relationship between the yield of three seasonal rice (e.g., Aus, Aman and Boro) and climatic factors/variables mainly maximum temperature, minimum temperature and rainfall for Bangladesh. Time series data have been used for the period 1990 to 2020 at an aggregate level to assess the relationship between climatic variables and rice yield using the Ordinary Least Squares (OLS) method. The findings of this study confirm that climate variables have had significant effects on rice yields but these effects are seen to vary among three rice crops. Maximum temperature is statistically significant with positive effects for the yields of Aus and Boro rice. On the contrary, statistically insignificant with adverse effects on Aman rice. On the other hand, Minimum temperature has a statistically significant with negative effect on Aman rice and a significantly positive effect on Aus and Boro rice. However, rainfall has a statistically significant effect on Aus, Aman and Boro the rice yields and has adverse effect on Boro rice. Also, the influences of maximum temperature and minimum temperature are more pronounced compared with that of rainfall.

Paddy–Upland Rotation Improves Rice Growth and Reduces Greenhouse Gas Emissions in Winter Paddy Fields

From May 2019 to May 2022, a field experiment was conducted to clarify the effects of paddy–upland rotations on rice yield and greenhouse gas emissions in winter paddy fields. Four types of rotation pattern, rice–oilseed rape, rice–radish, rice–faba bean, and rice–fallow (flooded), were investigated and the N2O, CH4, and CO2 emissions in situ and rice yield were determined. The results showed that the paddy–upland rotation mode required fertilization during the winter cropping season. Compared with the rice–fallow (flooded) mode, the flux rate and annual cumulative emissions of N2O were significantly higher in the paddy–upland rotation modes. The rice–radish mode had the highest flux rate and annual cumulative emissions of N2O. When the soil in each paddy–upland rotation mode was exposed to air in winter, the soil redox potential increased and reducing substances were oxidized. Compared with the rice–fallow (flooded) mode, the flux rate and annual cumulative emissions of CH4 significantly decreased in the paddy–upland rotation modes, with the rice–radish mode producing the lowest flux rate and annual cumulative emissions of CH4. Fertilization and crop planting were conducted in winter, and the soil moisture was low. Compared with the rice–fallow (flooded) mode, the flux rate of CO2 of the paddy–upland rotation modes increased significantly. The flux rate of CO2 in the rice–oilseed rape mode was the highest. Furthermore, the N2O and CH4 emissions produced during the rice season and annually were significantly positively correlated with those in the winter season, indicating that the winter season had a significant effect on greenhouse gas emissions from winter paddy fields. Because of the significantly higher annual cumulative emissions of CH4 and the significantly lower rice yield in the rice–fallow (flooded) mode than in the paddy–upland rotation modes, this mode’s global warming potential (GWP) and greenhouse gas intensity (GHGI) during the rice season are significantly higher than those of the paddy–upland rotation modes.

Resource Utilization and Profitability of Rice Production in The Terai Region of Nepal

Rice is the most important staple food crops in Nepal; however, the national yield of rice is low which has led in insufficient supply and heavy annual import. So, this study assessed the profitability and resource utilization of main and spring season rice production. A Semi-structured interview schedule was administered in 2022 among 360 randomly selected main-season rice-producing farmers across three major rice-producing districts of the Terai region of Nepal. Similarly, it conducted four Focus Group Discussions (FGDs) to collect necessary data for spring season rice from two Terai districts within similar agro-ecological regions. Cobb-Douglas production function was used to assess the resource utilization in main season rice production. The result revealed that the total cost and revenue of spring season rice production per hectare was higher, with a benefit-cost ratio of 1.63 compared to the main season. It was found that major resources such as the cost of seed, farm yard manure (FYM), chemical fertilizer, micronutrients, and pesticides were underused. On the other hand, the cost of labor, tillage, and harvesting were found to be overused in the main season of rice production. The proportion of the increase in rice income to the increase in costs of inputs for main season rice production was less, as indicated by the return to scale being less than unity. Hence, the study recommends to focus on addressing on prioritization to increase the cropping area under spring season rice and optimization in the use of resources supported by improved technologies to improve profitability and increase farmers’ income from rice this can eases the constraints in the domestic supply of rice and thereby contribute to lowering the annual volume of rice import. SAARC J. Agric., 22(2): 153-167 (2024)

Greenhouse gas emissions from dry season rice irrigation in Bangladesh

Pumping groundwater for irrigation in Bangladesh is a major energy-consuming process and mostly depends on diesel fuel, which is related to greenhouse gas (GHG) emissions. But that issue has not yet been addressed in Bangladesh. `In this study, we have estimated GHG emissions for dry season (DS) irrigated rice considering all irrigation devices with their lifting heads, area coverage, and water sources (surface and groundwater) and power sources (diesel and electricity) during 2019–2020. GHG emissions varied with locations, sources of irrigation, fuel and water sources used. Irrigation water driven GHG emission in Bangladesh is about 2.27 million tons (Mt) CO2e DS−1, which is about only 4% of agricultural sector GHG emission. Groundwater pumps contributed the lion shares (2.04 Mt CO2e DS−1), and surface water pumps contributed only 0.23 Mt CO2e DS−1. Based on the GHG emissions, Rajshahi Division is the main hotspot followed by Rangpur and Mymensingh Divisions, because of intensive groundwater used in these areas. Current deep tubewells (DTWs), shallow tubewells (STWs) and low lift pumps (LLPs) area coverage is about 19.2%, 56.8% and 24.0% of the total cultivable areas of the country; but it contributes about 49.1%, 40.6% and 10.3% of emitted GHG, respectively. The results revealed that withdrawal of groundwater is an important source of GHG emission. Therefore, expansion of surface water irrigation facilities with the adoption of different improved distribution systems, water and energy saving technologies like alternate wetting and drying practices, conservation agriculture along with water use-efficient varieties for rice cultivation can be promoted for reducing GHG emission.

Converting Biochar Into Biochar‐Based Urea Promotes Environmental and Economic Sustainability in Rice‐Wheat Rotation System

ABSTRACTBiochar amendments in rice‐wheat systems are sustainable for reducing GHGs (greenhouse gases) and improving soil health but the widespread adoption of biochar faces economic challenges. To address limitation, a novel biochar‐based urea was formulated for environmental and cost advantages. A pot experiment within a rice‐wheat rotation was conducted to evaluate comparative effects of biochar‐based urea (CKBU), biochar + urea (BCU), and biochar‐based urea + biochar (BCBU) over conventional mineral fertilizer (CKU) on soil ammonia (NH3) volatilization, GHG emissions, soil structure, and crop productivity. Furthermore, fertilizer N fate was tracked using the 15N isotope during wheat season. The results indicated that compared to CKU, CKBU, BCU, and BCBU treatments significantly mitigated NH3 volatilization by 22%–31% during the rice season, and a 19% reduction was observed under the BCBU treatment during the wheat season due to the response of N‐cycling microorganisms. Regarding GHG emissions, the CKBU, BCU, and BCBU treatments significantly decreased the global warming potential (GWP) value by 49%–55% during the rice season and by 26%–45% during the wheat season, compared to CKU. Additionally, CKBU enhanced 15N use efficiency by 29% during wheat season, without affecting the rice season. The economic performance indicated that applying BU alone offered a net economic benefit, whereas biochar amendment led to a net economic loss. However, biochar amendment improved SOC and aggregation structure, with a significant increase in macroaggregate distribution over 50% compared to CKU and CKBU. Therefore, BU with small portions of biochar can be as effective in reducing NH3 emissions and mitigating GHG emissions as the use of a large quantity of biochar. Additionally, the BCBU did not show additional synergistic benefits regarding emission reduction or yield enhancement. Therefore, shifting biochar to BU could be a cost‐effective approach to achieving sustainable productivity in rice‐wheat crop rotation systems.