Reclamation of Coastal Soil Salinity towards Sustainable Rice Production and Mitigating Global Warming Potentials in the Changing Climate

Soil salinity has become a major constraint to rice productivity in the coastal region of Bangladesh, which threatened food security. Therefore, field experiment was conducted at salt stressed Shyamnagor Upazilla of Satkhira district to improve the soil salinity status, sustainable rice production and suppression of global warming potentials. Selected soil amendments viz. trichocompost, tea waste compost, azolla compost and phospho-gypsum (PG) were applied in the field plots one week prior to rice transplanting. In addition, proline solution (25 mM) was applied on the transplanted rice plants at active vegetative stage. Gas samples from the paddy field were collected by Closed Chamber technique and analyzed in by Gas Chromatograph. The 25% replacement of chemical fertilizer (i.e., 75% NPKS) with trichocompost, tea waste compost, Azolla compost and Phospho-gypsum amendments increased grain yield by 4.7% - 7.0%, 2.3% - 7.1% 11.9% - 16.6% and 9.5% - 14.2% during dry boro rice cultivation, while grain yield increments of 5.0% - 7.6%, 2.3% - 10.2%, 12.8% - 15.3% and 10.2% - 15.3% were recorded in wet Aman season respectively, compared to chemically fertilized (100% NPKS) field plot. The least GWPs 3575 and 3650 kg CO2 eq./ha were found in PG Cyanobacterial mixture with proline (T10) and tea waste compost with proline (T8) amended rice field, while the maximum GWPs 4725 and 4500 kg CO2 eq./ha were recorded in NPKS fertilized (100%, T2) and NPKS (75%) with Azolla compost (T5) amended plots during dry boro rice cultivation. The overall soil properties improved significantly with the selected soil amendments, while soil electrical conductivity (EC), soil pH and Na+ cation in the amended soil decreased, eventually improved the soil salinity status. Conclusively, phospho-gypsum amendments with cyanobacteria inoculation and proline solution (25 mM) application could be an effective option to reclaim coastal saline soils, sustaining rice productivity and reducing global warming potentials.

Mitigation Rice Yield Scaled Methane Emission and Soil Salinity Stress with Feasible Soil Amendments

Sea level rise and saline water intrusion have been affecting land use and crop production especially rice in the coastal areas of major rice growing countries including Bangladesh. The upward trend in salinity intrusion has been hampering crop production, particularly rice cultivation in the coastal areas of Bangladesh. Therefore, an experiment was conducted on rice planted saline soils under the Nethouse at Bangladesh Agricultural University, Mymensingh to improve the properties of salt affected soils for rice cultivation as well as controlling methane (CH4) emissions with feasible soil organic amendments and recommended inorganic fertilizers. The experimental treatments were arranged under 25 mM NaCl, 50 mM NaCl and 75 mM NaCl salinity levels with different combinations of NPKSZn, biochar, phosphogypsum and Trichocompost. It was found that CH4 emission rates were suppressed with phospho-gypsum and biochar amendments within the salinity level 25 mM to 50 mM, beyond this salinity level (at 75 mM), soil amendments were not effective to control CH4 emissions. From panicle initiation to grain ripening stages treatment T4 (100% NPKSZn + 75 mM NaCl stress) showed the highest CH4 emission rate, while lower CH4 emission rate was recorded in T5 (100% NPKSZn + 25 mM NaCl stress + Phospho-gypsum) and T8 treatment (100% NPKSZn + 50 mM NaCl + Phospho-gypsum). In case of seasonal total CH4 emission, Phospho-gypsum was found most effective to mitigate total CH4 emissions followed by biochar and trichocompost amendments in all salinity levels, probably due to the improved soil redox potential status (Eh), decreased electrical conductivity (EC), increased SO42-, NO3- , Mn4+ etc. in the rice rhizosphere. Rice growth and yield components were badly affected by increasing salinity levels. Phospho-gypsum, biochar and trichocompost amendments increased plant height, panicles number/hill, shoot biomass and grain yield/hill at 25 mM NaCl stress condition. However, salinity stress 50 mM to 75 mM severely affected rice growth and yield components, eventhough phospho-gypsum, biochar and trichocompost were applied. Among the amendments, phosphogypsum and biochar significantly decreased yield scaled CH4 emission (GHGI) in salinity levels 25 mM to 75 mM. After harvesting rice, the overall soil properties such as organic matter content, available P, available S, exchangeable K+ and Ca2+, K+/Na+, Ca2+/Na+ ratios etc. were increased with the biochar, phospho-gypsum and trichocompost amendments. The highest ratios of K+/Na+ and Ca+/Na+ were found in the extract of saline soil at 25 mM with phospho-gypsum amendments followed by biochar and trichocompost amendments. Furthermore, soil SO42-, NO3- , Mn4+ and Fe3+ contents in rice root rhizosphere were increased in the amended saline soils, which caused significant reduction in seasonal methane emissions. Therefore, it could be concluded that the combined application of phospho-gypsum and biochar with the recommended NPKSZn fertilizers in saline soils may be a good practice for increasing tolerance to salinity in rice by increasing K+/Na+, Ca2+/Na+ ratios, while decreasing yield scaled CH4 emission (GHGI) in salinity levels 25 mM to 75 mM.

Integrated Rice-Based Shrimp and Crabs Farming: Adaptation to Climate Change and Potential Mitigation of Global Warming in the Coastal Wetlands of Bangladesh

Coastal agriculture is vulnerable to climate change, thereby may affect food production systems and food security in Bangladesh. Methane (CH4) emission from coastal wetlands rice farming is a major environmental concern due to its global warming potential. Therefore, field experiments were conducted at the southern coastal region of Shyamnagar, Satkhira, to investigate the feasibility of Rice-Shrimp and Rice-Crabs mixed farming for adaptation to the changing climate and sustaining food production system. The experimental treatments were designed on rice-based diversified farming systems such as rice sole cropping with no NPKS + no soil amendments (T1), rice sole cropping following farmers’ practice (FP) without soil amendment (T2), rice sole cropping following FP with phosphogypsum (PG) amendment (T3), Rice-Shrimp mixed culture with PG amendment (T4), Rice-Crabs mixed culture with PG amendment (T5), Rice-Shrimp mixed culture + PG amendment with Spirulina (Cyanobacteria) inoculation (T6), and Rice-Crabs mixed culture + PG amendment with Spirulina inoculation (T7). A closed chamber technique was followed to collect gas samples from the rice paddy field and samples were analyzed by Gas Chromatograph. It was found that Rice-Shrimp (T6) and Rice-Crabs mixed farming (T7) practices significantly decreased GWPs compared to the rice sole cropping system. In the dry boro season, the maximum GWPs 4175 kg CO2 eq. ha-1 was recorded from rice sole cropping (T2), which was decreased by 30% and 36.7% under Rice-Shrimp (T6) and Rice-Crabs (T7) mixed farming practices, respectively. Furthermore, in the wet aman season, maximum GWP 4525 kg CO2 eq. ha-1 was recorded from rice sole cropping (T2), which was decreased by 33.0% and 38.8% under Rice-Shrimp and Rice-Crabs mixed farming, respectively. Rice grain yield was low under rice sole cropping (3500 kg/ha), which was increased by 11.0% and 14.7% under Rice-Shrimp mixed farming amended with PG and Spirulina (T6) during wet aman and dry boro seasons, respectively. The postharvest soil properties, such as soil organic matter content, redox potential value (Eh), and exchangeable K+ and Ca2+, contents in soil increased significantly with Phosphogypsum and Spirulina applications, however, decreased Na+ content and electrical conductivity (EC) eventually improved rice plants’ tolerance to salinity and enhanced overall productivity of Rice-Shrimp and Rice-Crabs mixed farming. Conclusively, the conversion of wetland mono rice cropping into mixed Rice-Shrimp and Rice-Crabs farming would be a feasible strategy to sustain rice aquaculture-based farming, ensure food security and mitigate GWPs in coastal wetlands ecosystem.

Effect of Water Saving Irrigation Management Practices on Rice Productivity and Methane Emission from Paddy Field

Irrigation water supply is one of the vital components for sustainable rice farming, which is becoming a limiting resource in the changing climatic condition. An experiment was conducted at the research field of Bangladesh Agricultural University, Mymensingh during dry season from January-June of 2017 to investigate the suitability of Alternate Wet and Dry Irrigation (AWDI) for sustainable rice production and reducing methane emission. The modern rice variety BINA Dhan 10 was used as test crop. There were five irrigation treatments viz. T1 (saturated condition), T2 (continuous flooded, 5 cm standing water), T3 (AWDI-10 cm;irrigated when water level fell 10 cm from surface), T4 (AWDI-15 cm;irrigated when water level fell 15 cm from surface) and T5 (AWDI-20 cm;irrigated when water level fell 20 cm from surface). Results of the field trial showed satisfactory grain yield and low seasonal methane emission along with significantly high irrigation water savings (%) in AWDI treated field plots. Among the treatments, T3 (AWDI-10 cm) and T4 (AWDI-15 cm) showed higher yield performance (6250kg.ha-1 and 5810 kg.ha-1, respectively) with lower CH4 emission (reduced up to 36% and 40%, respectively) compared to continuous flooded treatment (T2, CF 5 cm water). In AWDI field plots less irrigation frequency (6 - 9) was required which significantly saved the amount of irrigation water (12% - 24%). Although T5 (AWDI-20 cm) showed the highest water savings (24%) and lowest CH4 emission (reduced up to 50%);however the lowest grain yield (4283 kg.ha-1) was found under this treatment. On the other hand, continuously irrigated (T2, 5 cm standing water) field plot showed lower yield (4783 kg.ha-1) but significantly higher methane emissions compared to other treatments during rice cultivation. Water productivity index was also found higher in AWDI treated field plots compared to continuously irrigated field plot. At the reproductive stage of rice plant well-developed aerenchyma tissue was observed in root cortex under the continuous irrigated field plot, which indicates higher diffusion pathway of methane gas from root rhizosphere to the atmosphere compared to other treatments. Therefore, alternate wet and dry irrigation water management practice may be recommended at farmers’ level for sustainable rice production and reducing methane emission during dry winter Boro season which will reduce the cost of production by water saving as well as energy saving.

Development of Environment Friendly Paddy Ecosystem for Sustainable Rice Farming through Soil Amendments with Biochar and Alternate Wetting-Drying Irrigations

Climate change may badly affect the availability of water and soil nutrients to rice plant. Research experiments were conducted at the Environmental Science Departmental field, Bangladesh Agricultural University, Mymensingh during July 2017 to June 2019, to find out the suitable combination of biochar with inorganic fertilizers for minimizing seasonal yield scaled CH4 emissions, reducing global warming potentials (GWPs) and sustainable rice farming under feasible irrigation practices. There were ten experimental treatments with different combinations of inorganic NPKS fertilizers and biochar (15 - 30 t/ha) under conventional flooding (CF) and alternate wetting-drying irrigations (AWDI). This study revealed that NPKS fertilization (50% of the recommended doze) with 15 t/ha biochar amendments under AWD irrigation maximized rice yield 6750 kg/ha and 4380 kg/ha in dry boro and wet aman seasons respectively, while the lowest rice yield 1850 kg/ha and 1550 kg/ha were recorded in continuously irrigated control treatment (T1) during the dry and wet seasons respectively. Seasonal cumulative CH4 emission, yield scaled CH4 emission and GWPs were suppressed significantly with biochar amendments 15 - 30 t/ha under both conventional and AWDI irrigation systems during the wet and dry seasons of rice cultivation. Significant interactions were observed among biochar amendments and irrigation practices during the dry boro rice cultivation. Dry seasonal cumulative CH4 emissions were decreased by 14.7%, 18.9% and 24.8% with biochar amendments at 15 t/ha, 20 t/ha and 30 t/ha respectively under conventional irrigation;while cumulative CH4 emissions were reduced by 10.6%, 26% and 41.6% respectively, under AWDI system. Finally, total global warming potentials (GWPs) were decreased by 6% - 15%, 13% - 30% with biochar amendments under conventional and AWDI irrigations respectively, in wet season;while global warming potentials (GWPs) also decreased by 14% - 25%, 11% - 42% with biochar amendments under conventional and AWDI irrigations, respectively, in the dry boro season. Biochar amendments increased water productivity index to some extent, but AWD irrigations significantly increased water productivity over the conventional irrigation in both wet and dry seasons. After experimental period, it was found that soil porosity, redox status, soil organic carbon (SOC) as well as overall soil properties were improved significantly with biochar amendments and AWD irrigations. Conclusively, biochar amendments @15 - 20 t/ha with half of the recommended inorganic (NPKS) fertilizers under alternate wetting-drying irrigations revealed an environment friendly integrated package approach to reduce seasonal cumulative CH4 emissions as well as GWPs, while improving rice rhizosphere environment and rice productivity to meet the national food security.