Agronomic benefits and risks associated with the irrigated peanut–maize production system under a changing climate in northern Australia

Rationale: Greenhouse gas (GHG) emissions from crop agriculture are of great concern in the context of changing climatic conditions; however, in most cases, data based on lifecycle assessments are not available for grain yield variations or the carbon footprint of maize. The current study aimed to determine net carbon emissions and sequestration for maize grown in Bangladesh. Methods: The static closed-chamber technique was used to determine total GHG emissions using data on GHG emissions from maize fields and secondary sources for inputs. A secondary source for regional yield data was used in the current study. GHG emission intensity is defined as the ratio of total emissions to grain yield. The net GHG emission/carbon sequestration was determined by subtracting total GHG emissions (CO2 eq.) from net primary production (NPP). Results: Grain yields varied from 1590 to 9300 kg ha−1 in the wet season and from 680 to 11,820 kg ha−1 in the dry season. GHG emission intensities were 0.53–2.21 and 0.37–1.70 kg CO2 eq. kg−1 grain in the wet and dry seasons, respectively. In Bangladesh, the total estimated GHG emissions were 1.66–4.09 million tonnes (MT) CO2 eq. from 2015 to 2020, whereas the net total CO2 sequestration was 1.51–3.91 MT. The net CO2 sequestration rates were 984.3–5757.4 kg ha−1 in the wet season and 1188.62–5757.39 kg ha−1 in the dry season. This study observed spatial variations in carbon emissions and sequestration depending on growing seasons. In the rice–maize pattern, maize sequestered about 1.23 MT CO2 eq. per year−1, but rice emitted about 0.16 MT CO2 eq. per year−1. This study showed potential spatiotemporal variations in carbon footprints. Recommendation: Special care is needed to improve maize grain yields in the wet season. Fertiliser and water use efficiencies need to be improved to minimise GHG emissions under changing climatic conditions. Efforts to increase the area under cultivation with rice–maize or other non-rice crop-based cropping systems are needed to augment CO2 sequestration. The generation of a regional data bank on carbon footprints would be beneficial for combating the impact of climate change.

Organic Carbon Sequestration and Ecosystem Service of Indian Tropical Soils

Short rotation willow (SRW) is a land management strategy involving the cultivation of rapidly growing, biomass-rich herbaceous-woody plants. This practice holds promise for renewable energy production, water quality preservation, carbon sequestration, greenhouse gas (GHG) mitigation, enhancement of soil extracellular enzyme activities (EEAs), and promotion of overall soil health. The rapid growth of SRW demands substantial water and nutrient resources, posing concerns when cultivated in marginal riparian lands within the Prairie Pothole Region (PPR), potentially leading to alterations in groundwater table (GWT) depth fluctuations, elevated soil salinity levels, and disruptions to biogeochemical cycles. Hence, this study comprehensively evaluated the effects of establishing SRW as a degraded marginal riparian land use practice in the PPR and attempted to answer several vital questions in the field and microcosm scale on soil hydrology, salinity, nutrients, soil organic carbon (SOC), GHG emissions, and EEAs involved in biogeochemical cycling. In a field experiment, the effects of SRW were evaluated by measuring the depth to GWT, groundwater and soil electrical conductivity (EC), macronutrients (N, P, K, and S), and SOC content in different fractions and chemical compositions during the first rotation (3-year cycle) compared with adjacent annual crop and pasture in two semi-arid PPR sites. In a microcosm experiment, GHG (CO2, CH4, and N2O) emissions and EEAs [β-glucosidase (BG), N-acetyl glucosaminidase (NAG), and alkaline phosphatase (AP)] were measured in intact soil cores treated with declining water tables and different groundwater salinity levels. No consistent land use impacts on GWT or soil EC were observed between sites. Land use in site B significantly impacted GWT depth, implying site-specific factors, such as topography and soil characteristics, may be dominant over land use effects. Under SRW, the levels of macronutrients in the soil varied but did not significantly reduce the overall nutrient content of the soil. Total SOC was highest in pasture; light fraction organic carbon and particulate organic carbon followed a similar land use pattern, i.e., pasture > SRW = annual crop. Land uses affected GHG emissions significantly in the order of pasture > annual crop = SRW. GHG emission varied with salinity and GWT but there was no interaction with land use practices. Soil EEAs were significantly impacted by different land uses, i.e., pasture > annual crop = SRW, suggesting that the effects resulted from associated SOC. Our microcosm experiment suggests that the SRW land use practice holds promise as a sustainable Nature-Based Solution for enhancing climate resiliency in PPR. It exhibits a lower global warming potential compared to annual crop and pasture. Therefore, widespread implementation of the SRW land use practice in degraded marginal land could help mitigate the effects of climate change in the region.

Bioavailability of water extractable organic carbon fractions in forest and agricultural soil profiles

Effect of alternate wetting and drying water management on rice cultivation with low emissions and low water used during wet and dry season

ABSTRACTWater and rice straw (RS) management practices can potentially affect the accumulation of soil organic carbon (SOC) in agricultural soils. Field experiments were conducted in two consecutive rice-growing seasons (wet and dry) to evaluate SOC stocks under different water (continuous flooding [CF], alternate wetting and drying [AWD]) and RS management practices (RS incorporation [RS-I], RS burning [RS-B], without RS incorporation and burning [WRS]) in a double-cropped paddy field. RS-I under AWD had higher volumetric water content than the same RS management under CF at tillering in both growing seasons. Total SOC was significantly higher under AWD at tillering in both wet and dry seasons and after harvesting in the dry season compared with CF. The same trend was also observed for C:N ratio at tillering and after harvesting in the dry season. RS-B plots had lower SOC stocks than RS-I and WRS plots across most of the measuring periods regardless of the growing seasons. SOC stocks were 33.09 and 39.31 Mg/ha at RS-B and RS-I plots, respectively, in the wet season, whereas the respective values were 21.45 and 24.55 Mg/ha in the dry season. Incorporation of RS enhanced SOC stocks under AWD irrigation, especially in the dry season before planting. Soil incorporation of RS in combination with AWD could be a viable option to increase SOC stocks in the double-cropped rice production region as it is strongly linked with soil fertility and productivity. However, the environmental consequences of RS incorporation in irrigated lowland rice production system should be taken into consideration before its recommendation for paddy field on a large scale.

Alternate wetting and drying (AWD) water management is being promoted to replace continuous flooding (CF) water regime in rice cultivation for agricultural countries, including Thailand, to achieve the net zero greenhouse gas (GHG) emissions and cope with drought. However, its adoption in different areas yielding variable results that requires the careful approaches to prevent negative impacts on rice yield, particularly the aroma of fragrant rice, along with mitigating GHG emissions, mainly methane (CH4) and nitrous oxide (N2O). This study aims to assess the impacts of AWD on CH4 and N2O emissions, productivity, water use, and soil characteristics of fragrant rice cultivation in Thailand. Khao Dawk Mali (KDML) 105 cultivar was cultivated in the wet season and Pathum Thani (PTT) 1 cultivar was planted in the dry season under CF and AWD at different dry levels of 10 cm (AWD10), 15 cm (AWD15), and 20 cm (AWD20) below the soil surface. The emissions of GHG and water use were measured throughout the study period using closed-chamber technique and water meter equipment, respectively. Rice yields and soil properties were analyzed after crop harvesting. The results showed that rice cultivation under AWD in both wet and dry seasons reduced CH4 emissions (18.4%–27.6%) but stimulated N2O emissions (11.8%–15.0%). However, its global warming potential (GWP) was lower than CF, lowered by an average of 17.7%, 26.8%, and 25.5% under the AWD10, AWD15, and AWD20, respectively. Relative to CF, unsuccessful AWD in the wet season did not change rice yield quantity and aroma (2-acetyl-1-pyrroline: 2AP) of KDML 105. Conversely, successful AWD10 and AWD15 in the dry season promoted rice grain yield and 2AP (0.27–0.33 ppm) of PTT1, while AWD20 did not alter rice yield amount but increased rice aroma (0.47 ppm). AWD can save irrigation water in the range of 12.8%–23.0% and 15.5%–18.7% in the wet and dry seasons, respectively. AWD water regime did not importantly change the soil characteristics after crop harvest. This study concludes that AWD, especially AWD15 and AWD20, has the potential to reduce GHG emissions without affecting the quantity and quality of rice yield, along with saving water.

The study is focused on impact of manure application, rice varieties and water management on greenhouse gas (GHG) emissions from paddy rice soil in pot experiment. The objectives of this study were a) to assess the effect of different types of manure amendments and rice varieties on greenhouse gas emissions and b) to determine the optimum manure application rate to increase rice yield while mitigating GHG emissions under alternate wetting and drying irrigation in paddy rice production. The first pot experiment was conducted at the Department of Agronomy, Yezin Agricultural University, Myanmar, in the wet season from June to October 2016. Two different organic manures (compost and cow dung) and control (no manure), and two rice varieties; Manawthukha (135 days) and IR-50 (115 days), were tested. The results showed that cumulative CH4 emission from Manawthukha (1.084 g CH4 kg-1 soil) was significantly higher than that from IR-50 (0.683 g CH4 kg-1 soil) (P<0.0046) with yield increase (P<0.0164) because of the longer growth duration of the former. In contrast, higher cumulative nitrous oxide emissions were found for IR-50 (2.644 mg N2O kg-1 soil) than for Manawthukha (2.585 mg N2O kg-1 soil). However, IR-50 showed less global warming potential (GWP) than Manawthukha (P<0.0050). Although not significant, the numerically lowest CH4 and N2O emissions were observed in the cow dung manure treatment (0.808 g CH4 kg-1 soil, 2.135 mg N2O kg-1 soil) compared to those of the control and compost. To determine the effect of water management and organic manures on greenhouse gas emissions, second pot experiments were conducted in Madaya township during the dry and wet seasons from February to October 2017. Two water management practices {continuous flooding (CF) and alternate wetting and drying (AWD)} and four cow dung manure rates {(1) 0 (2) 2.5 t ha-1 (3) 5 t ha-1 (4) 7.5 t ha-1} were tested. The different cow dung manure rates did not significantly affect grain yield or greenhouse gas emissions in this experiment. Across the manure treatments, AWD irrigation significantly reduced CH4 emissions by 70% during the dry season and 66% during the wet season. Although a relative increase in N2O emissions under AWD was observed in both rice seasons, the global warming potential was significantly reduced in AWD compared to CF in both seasons (P<0.0002, P<0.0000) according to reduced emission in CH4. Therefore, AWD is the effective mitigation practice for reducing GWP without compromising rice yield while manure amendment had no significant effect on GHG emission from paddy rice field. Besides, AWD saved water about 10% in dry season and 19% in wet season.

The study is focused on impact of manure application, rice varieties and water management on greenhouse gas (GHG) emissions from paddy rice soil in pot experiment. The objectives of this study were a) to assess the effect of different types of manure amendments and rice varieties on greenhouse gas emissions and b) to determine the optimum manure application rate to increase rice yield while mitigating GHG emissions under alternate wetting and drying irrigation in paddy rice production. The first pot experiment was conducted at the Department of Agronomy, Yezin Agricultural University, Myanmar, in the wet season from June to October 2016. Two different organic manures (compost and cow dung) and control (no manure), and two rice varieties; Manawthukha (135 days) and IR-50 (115 days), were tested. The results showed that cumulative CH4 emission from Manawthukha (1.084 g CH4 kg-1 soil) was significantly higher than that from IR-50 (0.683 g CH4 kg-1 soil) (P<0.0046) with yield increase (P<0.0164) because of the longer growth duration of the former. In contrast, higher cumulative nitrous oxide emissions were found for IR-50 (2.644 mg N2O kg-1 soil) than for Manawthukha (2.585 mg N2O kg-1 soil). However, IR-50 showed less global warming potential (GWP) than Manawthukha (P<0.0050). Although not significant, the numerically lowest CH4 and N2O emissions were observed in the cow dung manure treatment (0.808 g CH4 kg-1 soil, 2.135 mg N2O kg-1 soil) compared to those of the control and compost. To determine the effect of water management and organic manures on greenhouse gas emissions, second pot experiments were conducted in Madaya township during the dry and wet seasons from February to October 2017. Two water management practices {continuous flooding (CF) and alternate wetting and drying (AWD)} and four cow dung manure rates {(1) 0 (2) 2.5 t ha-1 (3) 5 t ha-1 (4) 7.5 t ha-1} were tested. The different cow dung manure rates did not significantly affect grain yield or greenhouse gas emissions in this experiment. Across the manure treatments, AWD irrigation significantly reduced CH4 emissions by 70% during the dry season and 66% during the wet season. Although a relative increase in N2O emissions under AWD was observed in both rice seasons, the global warming potential was significantly reduced in AWD compared to CF in both seasons (P<0.0002, P<0.0000) according to reduced emission in CH4. Therefore, AWD is the effective mitigation practice for reducing GWP without compromising rice yield while manure amendment had no significant effect on GHG emission from paddy rice field. Besides, AWD saved water about 10% in dry season and 19% in wet season.

Emission factors and global warming potential as influenced by fertilizer management for the cultivation of rice under varied growing seasons

Accurate estimation of wetland carbon densities is a prerequisite for wetland conservation and implementation of carbon sink enhancement plans. This study was designed to investigate spatial distribution in Soil Organic Carbon (SOC) and Total Nitrogen (TN), and Soil Organic Carbon density (SOCD) and Total Nitrogen density (TND) stocks in Lagos lagoon wetlands and the influence of other soil physicochemical. The SOC content generally exhibited high seasonal variations for all the sampling points in the wetlands. During wet season it ranges from 12.71±0.15 - 164.995±1.65 g/kg with a coefficient of variation of 40.99%, and dry season ranged from 132.02±3.520 - 383.570±8.43 g/kg with a coefficient of variation of 34.45%. The soil carbon content in the wet season was much lower than the dry season. The total nitrogen content in the wet season ranged from 4.53 – 16.58 g/kg with a COV of 27.96%, while the dry season ranged between 10.16 and 40.31 g/kg with a coefficient of variation of 29.39%.The SOC density of Lagos lagoon wetlands for tops soils ranged from 10.53 to 37.89 kgm−2 with an arithmetic mean of 26.70±1.41 kgm−2 and TND ranged from 0.61 to 2.37 kgm−2 with an arithmetic mean of 1.96±0.09 kgm−2. Pearson correlation reveal a positive correlation between SOC and TN (r=0.643), bulk density and SOC (r=0.344), TN and bulk density (r=0.478) and soil moisture and pH (r=0.085). In the present study, a negative correlation was observed in SOC and pH, and TN and pH. The results suggest that nitrogen content, moisture content and bulk density, which are significantly influenced by vegetation, seasons and topography, are some of the factors affecting their accumulation and seasonal variation. Thus, density of nitrogen and carbon in wetlands are important for soil quality. They also influence the carbon and nitrogen sequestration potential as well as reducing atmospheric CO₂ and mitigating the threat of global warming.Background: Soil organic carbon and total nitrogen are important components of wetland soils; they can greatly influence the wetland ecosystem fertility, quality and productivity. Accurate estimation of wetland carbon densities and pools is aprerequisite for wetland resource conservation and implementation of carbon sink enhancement plans. This study was designed to investigate the dynamics and spatial distribution in Soil Organic Carbon (SOC) and total nitrogen (TN), and SOC and TN density stocks in Lagos lagoon wetlands and the influence of other soil physicochemical parameters on them.Results: The SOC content generally exhibited high seasonal variations for all the sampling points in the wetlands. For wet season it ranges from 12.71±0.15 - 164.995±1.65 g/kg with a coefficient of variation of 40.99%, and dry season ranged from 132.02±3.520 - 383.570±8.43 g/kg with a coefficient of variation of 34.45%. The soil carbon content in the wet season was much lower than the dry season. The total nitrogen content in the wet season ranged from 4.53 – 16.58 g/kg with a coefficient of variation of 27.96%, while the dry season ranged between 10.16 and 40.31 g/kg with a coefficient of variation of 29.39%.The SOC density of Lagos lagoon wetlands for tops soils ranged from 10.53 to 37.89 kgm−2 with an arithmetic mean of 26.70±1.41 kgm−2 and TND ranged from 0.61 to 2.37 kgm−2 with an arithmetic mean of 1.96±0.09 kgm−2. Pearson correlation reveal a positive correlation between SOC and TN concentrations (r=0.643), bulk density was positively correlated also with SOC (r=0.344), TN and bulk density (r=0.478) and soil moisture content and pH (r=0.085) were also positively correlated. In the present study, a negative correlation was observed in SOC and pH, and TN and pH. The results suggest that nitrogen content, moisture content and bulk density, which are significantly influenced by vegetation cover and types, seasons and topography, are some of the factors affecting soil organic carbon and nitrogen accumulation and seasonal variation.Conclusion: This study provided an insight in the understanding of the seasonal and spatial distribution of SOC and TN density in the Lagos lagoon wetland. In conclusion, the estimation of the density and storage of nitrogen and organic carbon in the wetlands are important for knowing and maintaining the quality of the soils, and they also influence the carbon and nitrogen sequestration potential of the wetlands as well as reducing atmospheric CO₂ and mitigating the threat of global warming.

Crop rotations are considered a promising strategy for mitigating greenhouse gas (GHG) emissions and enhancing soil organic matter in agricultural land. However, studies often focused solely on either GHG emissions or soil organic carbon (SOC) changes, rather than integrating both indicators. We conducted a 4‐year (2018–2021) crop rotation study to examine effects of six rotation systems in three ecoregions (sub‐humid, sub‐semiarid, and semiarid) on GHG emissions, SOC changes, and C footprints in Saskatchewan, Canada. The six rotation systems include (i) control, (ii) intensified, (iii) diversified, (iv) market‐driven, (v) high‐risk, and (vi) soil‐health cropping system. GHG emissions were estimated using the Holos model, and SOC changes were estimated using the Campbell model, and C footprints were calculated as the difference between GHG emissions and SOC changes. The 4‐year cumulative GHG emissions, expressed as CO2 equivalent (CO2e), were highest in the sub‐humid ecoregion due to higher background SOC levels, nitrogen (N) fertilizer inputs, and precipitation. The diversified and soil‐health systems reduced GHG emissions by reduced N fertilizer inputs. Carbon footprints revealed net CO2e emissions for the market‐driven system but net CO2e withdrawals for the soil‐health and diversified systems. The results indicated that the diversified systems significantly mitigated GHG emissions, increased soil C stocks, and withdrew CO2e.

Agriculture is a major source of greenhouse gas (GHG) emissions. Biochar has been recommended as a potential strategy to mitigate GHG emissions and improve soil fertility and crop productivity. However, few studies have investigated the potential of biochar co-compost (BCC) in relation to soil properties, rice productivity, and GHG emissions. Therefore, we examined the potential of BC, compost (CP), and BCC in terms of environmental and agronomic benefits. The study comprised four different treatments: control, biochar, compost, and biochar co-compost. The application of all of the treatments increased the soil pH; however, BC and BCC remained the top performers. The addition of BC and BBC also limited the ammonium nitrogen (NH4+-N) availability and increased soil organic carbon (SOC), which limited the GHG emissions. Biochar co-compost resulted in fewer carbon dioxide (CO2) emissions, while BC resulted in fewer methane (CH4) emissions, which was comparable with BCC. Moreover, BC caused a marked reduction in nitrous oxide (N2O) emissions that was comparable to BCC. This reduction was attributed to increased soil pH, nosZ, and nirK abundance and a reduction in ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) abundance. The application of different amendments, particularly BCC, favored rice growth and productivity by increasing nutrient availability, soil carbon, and enzymatic activities. Lastly, BCC and BC also increased the abundance and diversity of soil bacteria, which favored plant growth and caused a reduction in GHG emissions. Our results suggest that BCC could be an important practice to recycle organic sources while optimizing climate change and crop productivity.

Previous studies indicate that biochar additions sometimes increase soil respiration and CO2 emissions which could partially offset C credits associated with soil biochar applications. Little is known, however, about the impact of biochar on the mineralization of manure in soil systems and how interactions between biochar and manure impact C sequestration and greenhouse gas (GHG) emissions from soils. We studied the effect of biochar and dried swine manure additions on changes in soil bulk density (Db), total soil organic carbon (SOC), and emissions of N2O and CO2 during a 500-d soil column incubation study. The addition of biochar to the soil increased SOC content measured after the 500-d incubation by 17.6 to 68.8%, depending on the treatment. Biochar additions reduced N2O emissions measured once near the end of the incubation. The N2O emissions were weakly correlated with Db, suggesting that enhanced soil aeration contributed to the reductions in N2O emissions. Biochar additions consistently increased CO2 emissions (measured 13 times during the incubation) relative to no-biochar controls with cumulative CO2–C emissions equivalent to 17 to 23% of biochar C applied. However, a distinct biochar-by-manure interaction for CO2 flux indicated that biochar either helped stabilize manure C or the presence of manure reduced the effect of biochar on the mineralization of SOC. For the studied system, we conclude that biochar additions sequestered large amounts of highly stable C, reduced N2O emissions, increased CO2 emissions from the soils, and reduced rates of CO2 emissions following a manure addition.

Benefits of biochar, compost and biochar–compost for soil quality, maize yield and greenhouse gas emissions in a tropical agricultural soil