Yield-scaled Global Warming Potential Research Articles

Effects of Ratoon Rice Cropping Patterns on Greenhouse Gas Emissions and Yield in Double-Season Rice Regions.

The ratoon rice cropping pattern is an alternative to the double-season rice cropping pattern in central China due to its comparable annual yield and relatively lower cost and labor requirements. However, the impact of the ratoon rice cropping pattern on greenhouse gas (GHG) emissions and yields in the double-season rice region requires further investigation. Here, we compared two cropping patterns, fallow-double season rice (DR) and fallow-ratoon rice (RR), by using two early-season rice varieties (ZJZ17, LY287) and two late-season rice varieties (WY103, TY390) for DR, and two ratoon rice varieties (YLY911, LY6326) for RR. The six varieties constituted four treatments, including DR1 (ZJZ17 + WY103), DR2 (LY287 + TY390), RR1 (YLY911), and RR2 (LY6326). The experimental results showed that conversion from DR to RR cropping pattern significantly altered the GHG emissions, global warming potential (GWP), and GWP per unit yield (yield-scaled GWP). Compared with DR, the RR cropping pattern significantly increased cumulative methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) emissions by 65.73%, 30.56%, and 47.13%, respectively, in the first cropping season. Conversely, in the second cropping season, the RR cropping pattern effectively reduced cumulative CH4, N2O, and CO2 emissions by 79.86%, 27.18%, and 30.31%, respectively. RR led to significantly lower annual cumulative CH4 emissions, but no significant difference in cumulative annual N2O and CO2 emissions compared with DR. In total, the RR cropping pattern reduced the annual GWP by 7.38% and the annual yield-scaled GWP by 2.48% when compared to the DR cropping pattern. Rice variety also showed certain effects on the yields and GHG emissions in different RR cropping patterns. Compared with RR1, RR2 significantly increased annual yield while decreasing annual GWP and annual yield-scaled GWP. In conclusion, the LY6326 RR cropping pattern may be a highly promising strategy to simultaneously reduce GWP and maintain high grain yield in double-season rice regions in central China.

Effects of Biodegradable Plastic Film Mulching on the Global Warming Potential, Carbon Footprint, and Economic Benefits of Garlic Production

This paper clarifies the farm applicability and feasibility of spreading biodegradable plastic film mulching for garlic production to ensure the green and sustainable development of the garlic industry. We set up a field trial of garlic planting with biodegradable plastic film mulching (BM) and plastic film mulching (PM), using no film mulching (CK) as the control, and measured CH4 and N2O emissions in the garlic fields. The yield-scaled global warming potential, carbon footprint, and net ecosystem economic benefit (NEEB) were used to assess the comprehensive impact of the different treatments. Compared to the CK, film mulching significantly increased CH4 absorption, with significantly higher seasonal cumulative CH4 emissions (20.5%) in BM than PM, but significantly increased N2O emissions, with significantly lower seasonal cumulative N2O emissions (23.53%) in BM than PM. Both BM and PM improved garlic yield, with PM significantly increasing garlic yield by 18.86% compared to the CK. Moreover, film mulching significantly decreased the yield-scaled global warming potential (by 52.06% and 40.82% in PM and BM, respectively). PM had a significantly higher carbon footprint than BM. Film mulching improved NEEB by 9.29–11.78%. Considering crop yields and environmental benefits, we propose BM as an effective method for a green and efficient garlic production.

Higher rice yield and lower greenhouse gas emissions with cattle manure amendment is achieved by alternate wetting and drying

ABSTRACT Climate change and water scarcity threaten the sustainability of rice production systems. Alternate wetting and drying (AWD) is a promising option to reduce methane (CH4) emission from irrigated paddy fields. However, its effect on rice yield remains to be clarified. Organic amendment can increase rice yield but may also increase CH4 emission. We therefore hypothesized that the combination of AWD with organic amendment could both increase rice yield and decrease CH4 emission. We carried out field experiments in six consecutive rice seasons during 2019 − 2022 in Central Java, Indonesia. We examined the effect of water management (continuous flooding [CF] and AWD) with (+M) and without (−M) the amendment of cattle manure as a locally available organic matter on rice growth and yield and the emissions of CH4 and nitrous oxide (N2O). AWD significantly (p < 0.05) decreased CH4 emission by 29% but marginally (p < 0.1) increased N2O emission by 10% relative to CF. There was no significant effect of AWD alone on rice yield. AWD significantly increased water productivity (the ratio of rice yield to irrigated water volume) by 50%. Cattle manure amendment significantly increased CH4 emission by 12% and rice yield by 5% but did not affect N2O emission. The combination effect of AWD+M relative to CF−M (control) was additive and resulted in a 7% increase in rice yield, a 19% decrease in the global warming potential (GWP) of CH4 + N2O emissions during both growing and fallow periods, and a 24% decrease in yield-scaled GWP. Our results indicated that the combination of AWD with cattle manure amendment would be a promising means to increase rice yield while reducing total soil greenhouse gas emission from irrigated rice paddies.

Alternative fertilization practices lead to improvements in yield-scaled global warming potential in almond orchards

This study investigates the impact of alternative fertilization practices on the yield-scaled global warming potential (YS-GWP) in almond orchards. Almond production is a contributor to greenhouse gas emissions, primarily due to nitrogen-based mineral fertilizers. This research aims to identify strategies that reduce the environmental footprint of almond cultivation while maintaining yield. Field experiments were conducted in an almond orchard using three alternative fertigation practices: Advance Grower Practice (AGP), Pump and Fertilize (P&F), and High Frequency Low Concentration (HFLC). AGP is the current practice used by producers to meet annual N demand for almond tree growth; P&F is a reduction in applied N rate in response to measured N concentrations in the groundwater so that the added N and groundwater N reach the same total N applied; HFLC is a practice of applying smaller N rates per individual event. HFLC uses a greater number of fertigation events to reach similar total annual N load as other treatments. Cumulative N2O and CH4 emissions were used to determine GWP by converting the emissions to carbon dioxide equivalents (CO2eq) within a 100-year horizon. Nitrous oxide emissions were multiplied by a radiative forcing potential CO2eq of 298 and CH4 by 25 (UNFCCC, 2007). The results revealed that both P&F and HFLC reduced the YS-GWP compared to AGP. HFLC demonstrated 52% to 78% decrease in GWP per unit of almond yield compared to AGP, while P&F showed 48% to 58% decrease over AGP. These reductions were attributed to the reduced nitrous oxide emissions associated with P&F and HFLC. Further, P&F and HFLC tended to have higher N use efficiency than AGP. We demonstrate that adopting alternative fertilization practices can effectively mitigate the environmental footprint of almond orchards while maintaining crop yields. These practices offer viable options for almond growers to reduce greenhouse gas emissions, enhance sustainability, and contribute to climate change mitigation.

Biochar combined with different nitrogen fertilization rates increased crop yield and greenhouse gas emissions in a rapeseed-soybean rotation system

Biochar as agricultural soil amendment has been extensively investigated for its potential to sequester carbon, to mitigate greenhouse gases (GHGs) emissions, to enhance soil fertility and enhance crop yields. In this study, we investigated the impact of varying N fertilization rates in conjunction with biochar on soil properties, crop yield, and GHGs emissions in a rapeseed (Brassica napus L.)-soybean (Glycine max (L.) Merrill) rotation system for one year. Biochar and N fertilizer were applied following a factorial combination design of three biochar (B0: 0 t hm−2, B1: 15 t hm−2, and B2: 60 t hm−2) and three N fertilizer application rates (H: 100%, M: 75%, and L: 50% of the conventional application rates). In general, there was no significant effect of N fertilizer and its interaction with biochar application on soil water content, pH, and total carbon content, but the addition of biochar significantly increased these parameters (P < 0.05). The yield of both crops were significantly augmented by biochar up to 75% compared to using N fertilization alone, potentially due to enhanced N use efficiency. However, biochar significantly increased the cumulative N2O and CH4 emissions by as much as 2.2 times and 19 times, respectively, during the rapeseed season, thereby elevating the global warming potential (GWP) and the yield-scaled GWP. Nevertheless, the significantly increased soil carbon content following biochar addition might boost soil carbon sequestration, which could counterbalance the escalating GWP induced by GHGs. Therefore, we recommend a comprehensive and long-term evaluation of biochar's impact by considering crop yield, GHGs emissions, and carbon sequestration in agricultural systems to ensure sustainable agricultural management.

Is scale production more advantageous than smallholders for Chinese rice production?

In this study, field data from 148 farmers were combined with energy equivalents, greenhouse gas emission factors, and product prices obtained from the literature and official statistics to evaluate and compare the energy use, environmental impact, and economic benefits between smallholders' rice production mode (SHM) and scale rice production modes (Big grain growers' rice production mode; Micro cooperatives’ rice production mode). Compared with SHM, the scale rice production modes increased the net energy by 425.02 MJ ha−1–13148.29 MJ ha−1, increased the energy use efficiency by 16.85%–22.89%, increased the net economic return by 15.67 USD ha−1–531.31 USD ha−1, increased the net profit-to-labor use ratio by 26.02%–393.87%, decreased the global warming potential (GWP) by 19.48%–27.23%, and decreased the yield-scaled GWP by 19.93%–29.50%. These results demonstrate that the scale rice production modes can satisfy the needs of reduced labor inputs, energy conservation, emission reduction, and increased profitability of rice production, thereby promoting sustainable and low-carbon development of the agricultural industry in China. Based on these findings, it is recommended that the government increase its support for developing scale rice production modes and encourage farmers to take equity in their lands or lease them to micro cooperatives for more efficient production.

Higher Food Yields and Lower Greenhouse Gas Emissions from Aquaculture Ponds with High-Stalk Rice Planted.

Aquaculture ponds are an important artificial aquatic system for global food fish production but also are a hot spot of greenhouse gas (GHG) emissions. The GHG mitigation strategy and the underlying mechanism for aquaculture ponds are still poorly understood. In this study, we conducted a 2 year field experiment to determine the effects of planting high-stalk rice (an artificially bred emergent plant for ponds) on GHG emissions from aquaculture ponds. Our results showed that planting high-stalk rice reduced CH4 emission by 64.4% and N2O emission by 76.2% over 2 years. Planting high-stalk rice significantly increased the content of O2 and the abundance of pmoA in the sediment, thus prompting CH4 oxidation in the ponds. The reduction of N2O emission from ponds was attributed to the decreased inorganic nitrogen, amoA-B and nirS in the sediment induced by rice. Furthermore, high-stalk rice culture in the pond increased shrimp yields and gained rice yields, resulting in a significant reduction of yield-scaled global warming potential. Our findings suggest that breeding appropriate emergent aquatic plants is a potential pathway to mitigate GHG emission from aquaculture ponds with more food yields and economic benefits.

A combination of organic fertilizers partially substitution with alternate wet and dry irrigation could further reduce greenhouse gases emission in rice field

Alternate wet and dry (AWD) irrigation and organic fertilizers substitution (OFS) have contrasting effects on CH4 and N2O emissions in rice cultivation. Combining these two practices may be feasible for simultaneous reduction of CH4 and N2O emission from paddy. Hence, we conducted a two-year field experiment to explore the reduction of greenhouse gases under the combination of AWD and OFS. The field experiment which was designed with two irrigation methods (continuous flooding (CF) irrigation and AWD irrigation), and five nitrogen regimes (N0, N135, and N180 represent 0, 135, and 180 kg N ha-1, respectively, ON25 and ON50 represent 25% and 50% OFS for inorganic fertilizer, respectively). The results showed a single-peak emission for CH4 fluxes during the whole rice growing season in all water and nitrogen treatments while the N2O fluxes peak only observed during tillering period with AWD irrigation. AWD irrigation and OFS showed a limited reduction in global warming potential (GWP). These were owing to that AWD irrigation reduced 38.3% CH4 emissions while increase 145.9% N2O emissions when compared to CF irrigation, and the low rate (25%) OFS only reduced CH4 emission by 29.4% while high rate (50%) only reduce N2O emission by 38.8% when compared to conventional inorganic nitrogen fertilizer (N180). Combined AWD and ON25 could maximize the reduction in GWP and yield-scaled GWP, which were reduce 58.0% and 52.5%, respectively, compare to the conventional water and nitrogen management (CF and N180). Furthermore, the structural equation modelling (SEM) indicated that the soil dissolved organic carbon (DOC) and rice aboveground biomass showed a significant positive effect on CH4 fluxes while soil NH4+ with a negative effect, and the soil NH4+, nitrification potential, denitrification potential significant affected N2O fluxes with a positive effect while DOC with a negative effect. These results investigated that 25% OFS rate for inorganic fertilizer could further reduce warming potential in AWD irrigation rice field.

Optimized tillage methods increase mechanically transplanted rice yield and reduce the greenhouse gas emissions

Biaxial rotary tillage in dryland (DBRT) can complete biaxial rotary tillage with straw incorporation, secondary suppression, and ditching, and it has been previously studied in direct-seeded rice and wheat. However, the effects of DBRT on the mechanically transplanted rice yield and greenhouse gas emissions remain unclear. To evaluate the effects of DBRT on improving the food security of mechanically transplanted rice and reducing the greenhouse gas emissions, we conducted an experiment for two years with wheat straw incorporation. Three tillage methods were set up: DBRT, uniaxial rotary tillage in dryland and paddy (DPURT), and uniaxial rotary tillage in paddy (PURT). The results showed that compared with DPURT and PURT, DBRT increased the yield of machine-transplanted rice by 7.5–11.0% and 13.3–26.7%, respectively, while the seasonal cumulative CH4 emissions were reduced by 13.9–21.2% and 30.2–37.0%, respectively, and the seasonal cumulative N2O emissions were increased by 13.5–28.6% and 50.0–73.1%, respectively. Consequently, DBRT reduced the global warming potential by 10.7–15.5% and 23.7–28.6%, respectively, and the yield-scaled global warming potential by 18.2–21.8% and 36.4–39.3%, respectively, compared to DPURT and PURT. These results were mainly related to the fact that DBRT significantly reduced soil bulk density and increased soil redox potential (Eh). Therefore, implementing DBRT in machine-transplanted rice fields is feasible, which cannot only increase the rice yield, but also reduce the greenhouse gas emissions.

Straw management effects on global warming potential and yield-scaled greenhouse gas emissions in a subtropical rice ecosystem

Global warming potential (GWP) of rice paddies depends on straw management. This study evaluated methane (CH4) and nitrous oxide (N2O) emissions and soil C stocks to determine GWP and yield-scaled GWP under different strategies and intensities of rice straw management in a subtropical climate. We hypothesized that decreasing soil management intensity and straw incorporation in the soil would reduce GWP. Methane fluxes were substantially higher during the rice growing season than in the off-season, while the opposite was observed [...]

Combined Effects of Biochar and Inhibitors on Greenhouse Gas Emissions, Global Warming Potential, and Nitrogen Use Efficiency in the Tobacco Field

Biochar (BC), nitrification inhibitors (methyl 3-(4-hydroxyphenyl) propionate, MHPP), and urease inhibitors (n-butyl phosphorothioate triamine, NBPT) have emerged as effective soil greenhouse gas (GHG) mitigation strategies in agroecosystems. However, the combined use of BC and inhibitors in karst areas has no available data. Therefore, the combined effects of BC, MHPP, and NBPT on GHG emissions, global warming potential (GWP) and nitrogen use efficiency (NUE) in roasted tobacco cropping systems were studied to improve the understanding in climate mitigation. CO2, CH4, and N2O emissions from soils were measured using static chamber-gas chromatography. Results showed that the combined use of BC and inhibitors significantly increased soil total nitrogen, available potassium, electric conductivity, pH, and soil organic matter compared to the control. The combined use of BC and MHPP or NBPT significantly increased cumulative soil CO2 emissions by 33.95% and 34.25%, respectively. The exponential–exponential function of soil CO2 fluxes with soil moisture and temperature demonstrated good fit (R2: 0.506–0.836). The combination of BC and NBPT increased the cumulative soil CH4 emissions by 14.28% but not significantly compared to the fertiliser treatment. However, the combination of BC and MHPP resulted in a significant reduction in cumulative soil CH4 emissions by 80.26%. In addition, the combined use of BC and MHPP or NBPT significantly reduced the cumulative soil N2O emissions by 26.55% and 40.67%, respectively. The inhibition effect of NBPT was better than MHPP. Overall, the combined use of BC and inhibitors significantly reduced the yield-scaled GWP, markedly increased crop yield and NUE, and mitigated climate change in the southwest karst region.

Multiyear methane and nitrous oxide emissions in different irrigation management under long-term continuous rice rotation in Arkansas.

Rice paddies are one of the major sources of anthropogenic methane (CH4 ) emissions. The alternate wetting and drying (AWD) irrigation management has been shown to reduce CH4 emissions and total global warming potential (GWP) (CH4 and nitrous oxide [N2 O]). However, there is limited information about utilizing AWD management to reduce greenhouse gas (GHG) emissions from commercial-scale continuous rice fields. This study was conducted for five consecutive growing seasons (2015-2019) on a pair of adjacent fields in a commercial farm in Arkansas under long-term continuous rice rotation irrigated with either continuously flooded (CF) or AWD conditions. The cumulative CH4 emissions in the growing season across the two fields and 5 years ranged from 41 to 123kg CH4 -C ha-1 for CF and 1 to 73kg CH4 -C ha-1 for AWD. On average, AWD reduced CH4 emissions by 73% relative to CH4 emissions in CF fields. Compared to N2 O emissions, CH4 emissions dominated the GWP with an average contribution of 91% in both irrigation treatments. There was no significant variation in grain yield (7.3-11.9 Mg ha-1 ) or growing season N2 O emissions (-0.02 to 0.51kg N2 O-N ha-1 ) between the irrigation treatments. The yield-scaled GWP was 368 and 173kg CO2 eq. Mg-1 season-1 for CF and AWD, respectively, showing the feasibility of AWD on a commercial farm to reduce the total GHG emissions while sustaining grain yield. Seasonal variations of GHG emissions observed within fields showed total GHG emissions were predominantly influenced by weather (precipitation) and crop and irrigation management. The influence of air temperature and floodwater heights on GHG emissions had high degree of variability among years and fields. These findings demonstrate that the use of multiyear GHG emission datasets could better capture variability of GHG emissions associated with rice production and could improve field verification of GHG emission models and scaling factors for commercial rice farms.

Nitrous oxide and methane emissions from coffee agroforestry systems with different intensities of canopy closure

Agroforestry-based coffee production systems (AFs) contribute to climate change mitigation through carbon sequestration. However, it is unclear whether AFs produce lower nitrous oxide (N2O) and methane (CH4) emissions than the open-shade coffee production system. In addition, little to no evidence is available to explain the relationship between canopy cover levels and greenhouse gas (GHG) emissions in AFs. The aim of this study was to investigate N2O, CH4 and yield-scaled emissions in AFs with differing shade-tree canopy levels. Three canopy cover levels were identified: (i) dense shade (80 % canopy closure), (ii) medium shade (49 % canopy closure), and (iii) open-shade (full sun) production. To determine the effect of canopy cover on GHG emissions under varying soil fertility management practices, three soil fertilization strategies were included: (i) mineral fertilizer, (ii) compost, and (iii) control (i.e., without soil amendment). The results showed that N2O emissions were two-to-three times greater when there was dense canopy cover than from open-shade production. The effect of canopy cover on N2O emission was more pronounced under the mineral fertilizer treatment. CH4 emissions were 44–64 % greater under the open-shade production system than under AFs. The yield-scaled global warming potential of 1 kg of fresh coffee cherries was 0.72 kg CO2eq for open-shade production, 0.58 kg CO2eq for medium canopy cover and 0.52 kg CO2eq for dense canopy cover. This study provides the first evidence of the importance of considering canopy cover intensity when determining the spatial-temporal variations in GHG emissions from agroforestry systems.

Using DMPP with cattle manure can mitigate yield-scaled global warming potential under low rainfall conditions

Organic fertilisers can reduce the carbon (C) footprint from croplands, but adequate management strategies such as the use of nitrification inhibitors are required to minimise side-effects on nitrogen (N) losses to the atmosphere or waterbodies. This could be particularly important in a context on changing rainfall patterns due to climate change. A lysimeter experiment with maize (Zea mays L.) was set up on a coarse sandy soil to evaluate the efficacy of 3,4-dimethylpyrazole phosphate (DMPP) to mitigate nitrous oxide (N2O) emissions, nitrate (NO3−) leaching losses and net global warming potential from manure, with (R+) and without (R-) simulated rainfall events. Soil water availability was a limiting factor for plant growth and microbial processes due to low rainfall during the growing season. Nitrification was effectively inhibited by DMPP, decreasing topsoil NO3− concentrations by 28% on average and cumulative N2O losses by 82%. Most of the N2O was emitted during the growing season, with annual emission factors of 0.07% and 0.95% for manure with and without DMPP, respectively. Cumulative N2O emissions were 40% higher in R-compared to R+, possibly because of the higher topsoil NO3− concentrations. There was no effect of DMPP or rainfall amount on annual NO3− leaching losses, which corresponded to 12% of manure-N and were mainly driven by the post-harvest period. DMPP did not affect yield or N use efficiency (NUE) while R-caused severe reductions on biomass and NUE. We conclude that dry growing seasons can jeopardize crop production while concurrently increasing greenhouse gas emissions from a sandy soil. The use of nitrification inhibitors is strongly recommended under these conditions to address the climate change impacts.

Influence of Rice Establishment Methods on Water Productivity, Methane Emissions and Rice Grain Heavy Metals Content from Irrigated Rice Paddies in Bangladesh

Reducing methane (CH4) emissions and water use in irrigated rice systems while maintaining production to feed the ever-increasing population is vital in Bangladesh. Different rice establishment methods viz. alternate wetting &amp; drying (AWD), system rice intensification (SRI) and direct wet seeded rice (DWSR), have a promising mitigation potential to reduce CH4emission compared to continuous flooded (CF) rice fields. A field experiment was conducted at Bangladesh Agricultural University, Mymensingh, during the Boro season in 2018 to examine whether rice establishment methods could maintain grain yield with reduced water use and CH4emissions. A split-plot design was employed with water management in the main plots and fertilizer management in the subplots. The yield difference was not significant (p&gt;0.05) in CF, AWD, and SRI systems other than DWSR. Planting methods in combination with organic fertilizer amendment had little effect on the grain Fe, Zn, and Cd concentration but significantly affected the as concentration. AWD, SRI, and DWSR significantly reduced the total water use by 17-33% and increased water productivity by 22-35% compared to CF. SRI system performed superior (p&gt;0.05) by increasing the water productivity coupled with reducing water consumption compared to CF. The impact of water management on changing climate in rice fields was compared using seasonal CH4emission and yield-scaled global warming potential (GWP). Total seasonal CH4emissions were significantly distinct (p&lt;0.05) from different rice establishment methods. Seasonal CH4 emissions from CF, AWD, SRI, and DWSR systems were 147.85, 128.11, 110.35, and 91.52kg CH4 ha-1, respectively. Emissions were reduced by about 13-38% in contrast with continuous flooded soil. The emissions of greenhouse gases per unit grain yield (yield-scaled GWP) followed the order; CF&gt;AWD&gt;DWSR&gt;SRI, while reducing yield-scaled emissions from AWD, SRI and DWSR decreased around 15-25% over that of the CF system. In conclusion, it is recommended that both SRI and AWD can mitigate CH4 emission, powered reduce water consumption as well as grain content from irrigated rice fields without yield penalty.

Effects of no-tillage on greenhouse gas emissions in maize fields in a semi-humid temperate climate region

Agricultural tillage practices have a significant impact on the generation and consumption of greenhouse gases (GHGs), the primary causes of global warming. Two tillage systems, conventional tillage (CT) and no-tillage (NT), were compared to evaluate their effects on GHG emissions in this study. Averaged from 2018 to 2020, significant decreases of CO2 and N2O emissions by 7.4% and 51.1% were observed in NT as compared to those of CT. NT was also found to inhibit the soil CH4 uptake. In this study, soil was a source of CO2 and N2O but a sink for CH4. The effect of soil temperature on the fluxes of CO2 was more pronounced than that of soil moisture. However, soil temperature and soil moisture had a weak correlation with CH4 and N2O flux variations. As compared to CT, NT did not affect maize yields but significantly reduced global warming potential (GWP) by 8.07%. For yield-scaled GWP, no significant difference was observed in NT (9.63) and CT (10.71). Taken together, NT was an environment-friendly tillage practice to mitigate GHG emissions in the soil under the tested conditions.

Direct and Residual Impacts of Olive-Mill Waste Application to Rice Soil on Greenhouse Gas Emission and Global Warming Potential under Mediterranean Conditions

The olive oil industry produces high amounts of waste, which need to be valorized in a more sustainable way as an alternative to its traditional use as an energy source, with high associated CO2 emissions. Rice (Oryza sativa L.) is one of the most important crops for global food security; however, the traditional cropping systems under flooding lead to an important decrease of soil quality, as well as relevant emissions of greenhouse gases (GHG). The aim of this study was to assess the GHG emission from rice fields amended with composted two-phase olive mill waste (C-TPOW), in Mediterranean conditions. A field experiment was carried in rice cultivated by the traditional system, either unamended (Control) or amended with C-TPOW (Compost). GHG emissions were measured over three years following a single C-TPOW application (80 Mg ha−1 only in the first year of study), so that the results found in the first and third years correspond to its direct and residual effects, respectively. Compost decreased CO2 emissions relative to Control by 13% and 20% in the first and third year after C-TPOW application, respectively. However, in the case of CH4 and N2O, increases in the total cumulative emission were recorded in Compost relative to Control throughout the study, in agreement with the highest β-glucosidase and urease activity observed in the amended soil. The values of global warming potential (GWP) and yield-scaled GWP increased by 14% and 11%, respectively, in Compost relative to Control in the first year, but no significant differences between treatments were observed three years after application for GWP and yield-scaled GWP. Therefore, the use of C-TPOW as soil amendment in rice fields could be a good option since its impact on GHG emissions seems to decrease over time, while the benefit for soil remained clear even after 3 years.

Zeolite application increases grain yield and mitigates greenhouse gas emissions under alternate wetting and drying rice system

Clinoptilolite zeolite (Z) has been widely used for reducing nutrient loss and improving crop productivity. However, the impacts of zeolite addition on CH4 and N2O emissions in rice fields under various irrigation regimes are still unclear. Therefore, a three-year field experiment using a split-plot design evaluated the effects of zeolite addition and irrigation regimes on greenhouse gas (GHG) emissions, grain yield, water productivity and net ecosystem economic profit (NEEP) in a paddy field. The field experiment included two irrigation regimes (CF: continuous flooding irrigation; AWD: alternate wetting and drying irrigation) as the main plots, and three zeolite additions (0, 5 and 10 t ha−1) as the subplots. The results indicated that AWD regime decreased seasonal cumulative CH4 emissions by 54%–71% while increasing seasonal cumulative N2O emissions by 14%–353% across the three years, compared with CF regime. Consequently, the yield-scaled global warming potential under AWD regime decreased by 10%–60% while grain yield, water productivity and NEEP improving by 4.9%–7.9%, 19%–27% and 12%–14%, respectively, related to CF regime. Furthermore, 5 t ha−1 zeolite addition mitigated seasonal cumulative CH4 emissions by an average of 36%, but did not significantly affect N2O emissions compared with non-zeolite treatment. In addition, zeolite addition at 5 and 10 t ha−1 significantly increased grain yield, water productivity and NEEP by 11%–21%, 13%–20% and 13%–24%, respectively, related to non-zeolite treatment across the three years. Therefore, zeolite addition at 5 t ha−1 coupled with AWD regime could be an eco-economic strategy to mitigate GHG emissions and water use while producing optimal grain yield with high NEEP in rice fields.

Conservation Agriculture With Optimum Fertilizer Nitrogen Rate Reduces GWP for Rice Cultivation in Floodplain Soils

Wetland rice cultivation contributes significantly to global warming potential (GWP), an effect which is largely attributed to emissions of methane (CH4). Emerging technologies for wetland rice production such as conservation agriculture (CA) may mitigate greenhouse gas (GHG) emissions, but the effects are not well defined. Investigations were carried out in an irrigated rice (Boro rice) field in the fifth crop after conversion of conventional tillage (CT) to strip tillage (ST). Two crop residue levels (low versus high, LR versus HR) and three nitrogen (N) application rates (N1 = 108, N2 = 144, and N3 = 180 kg N ha−1) were laid out in a split-plot experiment with three replicates. Yield-scaled GHG emissions and GWP were estimated to evaluate the impacts of CA on mitigating CH4 and N2O emissions in the rice paddy field. There was a 55% higher N2O emission in ST with HR coupled with N3 than that in CT with LR coupled with N1. The N2O emission factors ranged from 0.43 to 0.75% in ST and 0.45 to 0.59% in CT, irrespective of the residue level and N rate. By contrast, CH4 emissions were significantly lower in CA than in the conventional practices (CT plus LR). The ST with LR in N2 reduced the GWP by 39% over the GWP in CT with HR in N1 and 16% over the conventional practices. Based on our investigation of the combination of tillage, residue, and N rate treatments, the adoption of CA with high and low residue levels reduced the GWP by 10 and 16%, respectively, because of lower CH4 and N2O emissions than the current management practices. The relatively high N2O emission factors suggest that mitigation of this GHG in wetland rice systems needs greater attention.

Single midseason drainage events decrease global warming potential without sacrificing grain yield in flooded rice systems

Rice (Oryza sativa L.) cultivation is an important part of global food security, yet it is also responsible for a significant portion of agricultural greenhouse gas (GHG) emissions, particularly methane (CH4). Midseason drainage of flooded rice fields can decrease CH4 emissions, but the magnitude of CH4 reduction and its effect on grain yield are variable due to variation in the timing and soil-drying severity of drainage across studies. Therefore, in this two-year study, we aimed to quantify the effect of timing and severity of a single midseason drainage event on seasonal GHG emissions and grain yields, compared to a continuously flooded (CF) control. Treatments varied in terms of soil-drying severity (low, medium, and high, corresponding to approximately 5, 8, and 12 days of drying, respectively) and the timing of when drainage events occurred (between 34–49 and 45–59 days after seeding, or roughly between tillering and panicle initiation). Soil moisture parameters (perched water table, volumetric water content, gravimetric water content (GWC), and soil water potential), soil mineral nitrogen, CH4 and nitrous oxide (N2O) emissions, grain yield, and yield components were all quantified. Midseason drainage reduced seasonal CH4 emissions by 38–66%, compared to the CF control. Seasonal CH4 emissions decreased with increasing drain severity, and for every 1% reduction in soil GWC during the drainage period, seasonal CH4 emissions were reduced by 2.5%. The timing of drainage had no significant impact on CH4 emissions. Emissions of N2O were low (average = 0.035 kg N2O-N ha−1) and accounted for only 0.5% of the seasonal global warming potential (GWP) across all drainage treatments. Within each year, drainage did not significantly affect grain yield compared to the CF control. Additionally, midseason drainage reduced both GWP and yield-scaled GWP by approximately the same amount as seasonal CH4 emissions, as N2O emissions were minimal and yields were similar across treatments. These results indicate that midseason drainage may be a viable GHG mitigation practice in flooded rice systems with limited risk for yield reduction, however, this practice should also be further tested under a broad range of soil types and different environments to determine its widespread adoptability.