Midseason Drainage Research Articles

Meta-analysis of GHG emissions stimulated by crop residue return in paddy fields: Strategies for mitigation

The stimulating impact of crop residue return on greenhouse gas (GHG) emissions from paddy fields have been widely accepted, while the influence of site environmental and human factors on the simulating degree remains unclear. Here, we performed a meta-analysis to assess the GHG emissions affected by residue return, and its mitigation potential combined with key factors in paddy fields. Drawing upon 1047 observation sets of CH4 and N2O emissions from 155 peer-reviewed publications we found that residue return to paddy fields caused an average increase of 73% CH4 emissions and 14% in N2O emissions. Utilizing meta-analytical models, we identified pH as the most significant driver modulating GHG emissions, followed by soil organic matter (SOC) and total nitrogen. In alkaline soils, combining straw return with intermittent irrigation (285.2%) or mid-season drainage (118.9%) significantly reduced CH4 emissions compared to continuous flooding (1201.9%). Additionally, pairing straw return with higher nitrogen inputs (above 150 kg N ha−1) improved soil N2O uptake by −11.5%. In acid and neutral soils, straw carbonization achieved soil CH4 negative emissions (from −2.9% to −39.3%), but the long-term effects remained unclear. Reduced drainage frequency mitigates N2O emissions but may increase CH4 emissions. To efficiently mitigate GHG emissions, we proposed low-carbon schemes for acid or neutral soils based on specific SOC content: For soils with SOC content <10 g kg−1, prioritize nitrogen input control with rates not exceeding 174 kg N ha−1. For soils with SOC content >10 g kg−1, prioritize adjusting the type of straw. Our study underscores the significance of site-specific factors in modulating GHG emissions. Efficient GHG mitigation can be achieved by combining residue return with other agronomic measures tailored to different soil conditions.

Alternating wet and dry irrigation cycles enhance the nitrogen “cache” function of duckweed in a rice-duckweed system

In continuously-flooded paddies, the small, fast-growing aquatic plant duckweed (Lemna minor L.) considered to compete with rice for nitrogen, thereby having a negative impact on early rice growth. While duckweed overpopulation was known can be effectively overcome through field water management, the influence of such management on the N fate and its use efficiency in rice-duckweed systems is poorly documented. Accordingly, a three-year (2020–2022) field experiment was conducted to examine the combined impact on rice yield, as well as N loss and utilization, of two water management approaches (flood irrigation, FI vs. alternate wetting and drying irrigation, AWD), factorially combined with two rice production systems (rice-duckweed, +D, vs. duckweed-free rice, -D). In AWD+D fields, the density of duckweed generally remained below 250 g m−2 (about 85 % coverage), whereas in FI+D fields it reached 100 % coverage (300 g m−2) within 5 days after transplanting, with individual duckweeds overlapping one another. Following AWD irrigation, duckweed performed as a nitrogen “cache,” akin to a split fertilizer application, with the first of several splits occurring at the rice crop's early tillering stage. Within the first 2 days of a specific wet-dry cycle, duckweed can store 0.5–1.5 g N m−2, and then, within a further 3 days, release 0.3–1.0 g N m−2. In contrast, in FI+D paddies, this caching function occurred once under mid-season drainage, with further N being stored in the duckweeds during the remaining rice production season. As a result, at harvest the 0–0.10 m soil layer's N level increased significantly (p<0.05) in both FI+D (8.5–16.8 %) and AWD+D (14.9–20.8 %) compared to FI-D and AWD-D, respectively. Due to the coverage and storage-release function of duckweed, apparent N loss decreased in rice-duckweed system by 1.4–12.5 % in the FI field and 22.1–31.3 % in the AWD field compared to their respective duckweed-free systems. In FI fields, except for a 10 % relative reduction in nitrogen recovery efficiency (NRE) in 2020, duckweed didn't significantly affect rice yield or NRE. The yield reduction (3.5–6.7 %) and the NRE increase (0.8–7.4 %) under AWD-D (vs. FI-D) was, in the presence of duckweed, compensated for and overrun, resulting in a greater yield (5.3–6.7 %) and NRE (5.4–28.9 %) in the AWD+D vs. AWD-D field. When duckweed was present, AWD irrigation improved the by-path nitrogen cycling through duckweed, making the AWD+D system more beneficial for rice cultivation and the agroecosystem's environment health. The AWD+D system offers a promising measure for building an efficient and sustainable rice-duckweed agroecosystem.

Biochar amendments to tropical paddy soil increase rice yields and decrease N2O emissions by modifying the genes involved in nitrogen cycling

Water management strategies are critical in regulating nitrous oxide (N2O) emissions from paddy soils under rice cultivation. Biochar is widely used as an amendment to decrease soil N2O emissions. However, the impacts of biochar amendment on N2O emissions under different water management strategies in paddy soils have not been investigated thoroughly, and the underlying mechanisms remain poorly understood. In particular, the effects of mid-season water drainage, a strategy used for water conservation, need to be better understood. In this study, a pot experiment was conducted including six treatments: alternating dry-wet conditions during the mid-season period without and with 2% (w/w) biochar (AWD1 and AWD2, respectively), continuous flooding during the mid-season period without (CF1) and with 2% (CF2) biochar, and regular mid-season drainage during the mid-season period without (CON1) and with 2% (CON2) biochar. All treatments received inorganic nitrogen, phosphorus and potassium fertilizers (NPK) administered in a split application. We found that fluxes of N2O emission peaked after the two fertilizers’ additions. No significant difference in the first N2O flux peak was found among different treatments. There also was no difference in the second N2O flux peak in both CF treatments, whereas biochar addition significantly decreased the second N2O flux peak in AWD2 and CON2 treatments. This was mainly due to increased nosZ gene copies and decreased ratios of denitrification and amoA genes to nosZ gene copies. Biochar amendments resulted in significant stimulation of nifH gene copies in the AWD2 treatment. Lastly, biochar increased rice yields in all treatments. Our study suggested that AWD2 was the optimal management strategy for mitigating N2O emissions and improving rice production in this tropical paddy soil.

Methane and nitrous oxide emissions from rice grown on organic soils in the temperate zone

Organic soils are important carbon stocks. The conventional (dry) cultivation of these soils turns them into strong sources of greenhouse gas (GHG) emissions. For situations where restoration of natural land cover is not possible, solutions to this problem include the wet cultivation of these soils, reducing CO2 and N2O emissions. One option, paddy rice cultivation, has begun in the Swiss Central Plateau, which hitherto did not provide a suitable climate for wet rice. Wet rice is however associated with high CH4 emissions. These need to be quantified for this region, as the increased CH4 fluxes might negate the expected reductions in CO2 and N2O. Here, we quantify CH4 and N2O emissions from wet rice on organic soil with chamber measurements, in an outdoor mesocosm experiment in the Swiss Central Plateau, located in the cool temperate moist zone. We apply two water treatments (a high water table (WT) treatment, − 6 cm with mid-season drainage, and two medium WT treatments, − 11 and − 17 cm without mid-season drainage) and additionally test the use of a mineral cover layer to reduce N2O emissions. Additionally, a deeply-drained grassland treatment is used as a reference treatment. Annual CH4 emissions from rice cultivation are 6.2 g CH4.m-2.a-1 for the higher WT treatment, 6.4 g CH4.m-2.a-1 for the medium WT treatment and 2.4 g CH4.m-2.a-1 for the medium WT treatment with mineral cover. The corresponding N2O emissions are 203, 190 and 56 mg N2O-N.m-2.a-1, respectively. These results show that adding a mineral cover layer reduces annual emissions from both GHGs substantially. In total, the maximum increase in CH4 and N2O emissions resulting from rice cultivation, compared to the drained grassland treatment, is 2.3 t CO2-eq.ha-1.a-1. Expected CO2 emissions savings (derived from a literature-based model) due to a higher WT are a factor of 5–9 greater than this. We thus conclude that the cultivation of these organic soils in this region with wet rice could reduce their induced warming compared to their cultivation with (deeply drained) grassland.

Quantitative assessment and mitigation strategies of greenhouse gas emissions from rice fields in China: A data-driven approach based on machine learning and statistical modeling

The accurate prediction of greenhouse gas (GHG) emissions from paddy fields is critical for developing mitigation strategies to reduce emissions, while realizing the large-scale prediction of GHG emissions from paddy fields remains to be a challenge. Here, we established machine learning models to predict the GHG emissions from Chinese paddy systems using a dataset including 782 CH4 and 679 N2O emission observations based on 118 published studies across China. Our results identified XGBoost was the most suitable model with the outstanding efficiency and accuracy for predicting both CH4 (R2 = 0.754, RMSE = 0.485 kg ha−1) and N2O emissions (R2 = 0.762, RMSE = 0.423 kg ha−1) from rice fields in China. We found mineral and organic fertilizer rate, irrigation mode, straw returned proportion and tillage depth were key factors in regulating GHG emissions. Specifically, CH4 emissions trended to increase first and then decrease with increasing mineral nitrogen fertilizer rate, with the inflection point delayed under the application of organic fertilizer. On the other hand, N2O emissions continued to increase until the N fertilizer rate reached approximately 150 kg ha−1. The use of organic fertilizer, tillage, straw return in half and full quantity increased global warming potential (GWP) by 80.3 %, 33.8 %, 25.2 % and 111.6 %, respectively. Frequent drainage (FD) was identified as the most promising water management mode, with a higher potential for GHG emission mitigation of 39.5 % compared to continuous flooding, followed by mid-season drainage at 18.4 %. We found the combination of a mineral nitrogen fertilizer rate of 128 kg ha−1, FD water management, without straw, tillage, and organic fertilizer could achieve the most effective GHG emission mitigation, with a GWP of 3.13 Mg CO2 equivalent ha−1. Our findings provided a new insight for predicting GHG emissions from rice fields on a large scale, and offered guidance for mitigating GHG emissions from rice production in China.

Effects of drought stress on the oxidation of the reaction center chlorophyll of photosystem I and grain yield in paddy-field grown rice plants

ABSTRACT Drought is a serious abiotic stress that leads to decreased yield. In pot experiments, the reaction center chlorophyll of photosystem I (PSI) (P700) has been reported to be oxidized in response to drought stress. In the present study, we examined whether drought stress that decreases grain yield was detected by P700 oxidation in paddy-field-grown rice (Oryza sativa L.) plants. The P700 reduction and SPAD values were also evaluated. Drought stress was imposed by the prolonged mid-season drainage in 2019 and 2020. P700 oxidation was measured at saturated CO2 levels before heading. P700 oxidation was not stimulated in the 2019-drought plots. In contrast, P700 oxidation was stimulated in the 2020-drought plot. However, this phenomenon in 2020 was primarily accounted for by decreases in total leaf-N levels, as previously observed in the rice plants grown under low N availability. Rough rice yields and ratios of filled spikelets tended to decrease in the drought plots. Therefore, drought stress responsible for a decrease in grain yields could not be directly detected by P700 oxidation in paddy-field-grown rice plants, whereas the P700 oxidation responded to changes in total leaf-N levels due to the drought stress treatment. The same conclusion was drawn for the P700 reduction and SPAD value.

Effects of mid-season drainage on iron toxicity, rice yield, and water productivity in irrigated systems in the derived savannah agroecological zone of West Africa

Effects of mid-season drainage on iron toxicity, rice yield, and water productivity in irrigated systems in the derived savannah agroecological zone of West Africa

Is It Possible to Predict the Timing of Mid−Season Drainage by Assessing Rice Canopy Light Interception?

Mid−season drainage (MSD) is a widely used water management practice in rice (Oryza sativa L.) cultivation. However, the timing of the initiation and termination of MSD is highly arbitrary and subjective, and a quantitative indicator is lacking in precision agronomic practice. In this study, datasets (91 cases) from previous field experiments were obtained and used to fit adjusted exponential growth models, incorporating rice canopy light interception (CLI) and tillering development dynamics. Different criteria for initiating and terminating MSD were developed based on CLI indicators. The results showed that the CLI indicator at 80% of the projected panicle could be used to predict the initiation of MSD; however, it was highly variable, depending on the growing season and rice cultivated variety. The values for Indica rice were 0.26 to 0.31 and 0.31 to 0.42 in the late and single seasons, respectively, while the values for Japonica rice were 0.15 to 0.29 and 0.23 to 0.33, respectively. In addition, the CLI values at 7 to 10 days prior to panicle initiation (PI) ranged from 0.77 to 0.87 and from 0.56 to 0.83 for the Indica and Japonica varieties, respectively, and were calculated to determine MSD termination. The CLI indicators for MSD were greatly dependent on the cultivated variety, growing season, and planting method. The results of the correlation study and principal component analysis (PCA) indicated that the differences in CLI values attributed to rice type and growing season were driven by the tillering and canopy characteristic traits, respectively. Therefore, the current parameters could provide a reference for subsequent field applications in specific areas, but further optimization is needed to increase their robustness. To evaluate the usefulness of the CLI indicator for determining MSD initiation and termination, a set of devices for monitoring canopy light interception and water level was developed, and an on-farm trial was carried out in the middle and lower reaches of the Yangtze River in China in 2022. The field application demonstrated that MSD could be scheduled automatically based on the current system, and that the effect was consistent in practice.

Characteristics of soil N2O emission and N2O-producing microbial communities in paddy fields under elevated CO2 concentrations

The effects of elevated carbon dioxide (CO2) concentration (e[CO2]) on nitrous oxide (N2O) emissions from paddy fields and the microbial processes involved in N2O emissions have recently received much attention. Ammonia-oxidizing microorganisms and denitrifying bacteria dominate the production of N2O in paddy soils. To better understand the dynamics of N2O production under e[CO2], a field experiment was conducted after five years of CO2 fumigation based on three treatments: CK (ambient atmospheric CO2), T1 (CK + increase of 40 ppm per year until 200 ppm), and T2 (CK + 200 ppm). N2O fluxes, soil physicochemical properties, and N2O production potential were quantified during the rice-growth period. The functional gene abundance and community composition of ammonia-oxidizing archaea (AOA) and bacteria (AOB) were analyzed using quantitative polymerase chain reaction (qPCR) and those of ammonia-denitrifying bacteria (nirS- and nirK-type) were analyzed using Illumina MiSeq sequencing. N2O emissions decreased by 173% and 41% under the two e[CO2] treatments during grain filling and milk ripening, respectively (P < 0.05). N2O emissions increased by 279% and 172% in the T2 treatment compared with T1 during the tillering and milk-ripening stages, respectively (P < 0.05). Furthermore, the N2O production potential was significantly higher in the CK treatment than in T1 and T2 during the elongation stage. The N2O production potential and abundance of AOA amoA genes in T1 treatment were significantly lower than those in CK treatment during the high N2O emission phase caused by mid-season drainage (P < 0.05). Although nirK- and nirS-type denitrifying bacteria community structure and diversity did not respond significantly (P > 0.05) to e[CO2], the abundance of nirK-type denitrifying bacteria significantly affected the N2O flux (P < 0.05). Linear regression analysis showed that the N2O production potential, AOA amoA gene abundance, and nirK gene abundance explained 47.2% of the variation in N2O emissions. In addition, soil nitrogen (N) significantly affected the nirK- and nirS-type denitrifier communities. Overall, our results revealed that e[CO2] suppressed N2O emissions, which was closely associated with the abundance of AOA amoA and nirK genes (P < 0.05).

Interactive effects of water management and liming on CH4 emissions and rice cadmium uptake in an acid paddy soil.

Rice agriculture is both an important source of the potent greenhouse gas methane (CH4) and a bioaccumulator of cadmium (Cd), which is hazardous to human health. Avoiding flooding during rice production is effective for reducing CH4 emissions, but it increases rice Cd uptake. Although lime application decreases Cd concentration in rice grains, it is not clear whether combining appropriate water management with liming can simultaneously reduce CH4 emissions and Cd uptake in rice paddies. Thus, a pot experiment was performed to investigate the interactive effects of water management (F: continuous flooding, FDF: flooding - midseason drainage - flooding, FDI: flooding - midseason drainage - intermittent irrigation) and lime application on CH4 emissions and rice Cd uptake in an acid paddy soil spiked with Cd. Results showed that neither water management nor liming significantly affected grain yield. Overall, liming reduced CH4 emissions by 42.2%. Compared to F, the FDF and FDI treatments reduced CH4 emissions by 43.5% and 54.2%, respectively. Liming reduced CH4 emissions by 32.6% under F, but with a greater decrease of 48.6% and 52.7% under FDF and FDI, respectively. Overall, liming reduced rice Cd uptake by an average of 47.3%. Compared to FDI, F and FDF significantly reduced Cd uptake by 84.0% and 75.1%, respectively, but there was no significant difference between F and FDF. Liming did not significantly affect Cd uptake under F and FDF, whereas liming reduced Cd uptake by 55.9% under FDI. These results suggest that maintaining flooding following midseason drainage can help in reducing rice Cd uptake, though slightly promoting CH4 emissions. Therefore, we recommend FDF combined with liming to mitigate CH4 emissions without increasing rice Cd uptake in acid paddy soils.

Drainage in paddy systems maintains rice yield and reduces total greenhouse gas emissions on the global scale

Rice sustains the survival of nearly half of humanity, meanwhile, paddy systems are also a significant source of greenhouse gas (GHG) emissions in agriculture. Drainage is widely accepted as a key agricultural management practice (AMP) to reduce CH4 emissions in paddy systems, however, its impact on rice yield and global warming potential (GWP) under different soil and APM conditions remains uncertain. Here, we performed a global meta-analysis of 519 samples from 74 fields in 64 peer-reviewed publications, including measurements of rice yield and at least one of GHG emissions (N2O, CH4, and CO2). Overall, the effects of implementing drainage in paddy systems on yield, N2O emissions, CH4 emissions, CO2 emissions, GWP, and GWP intensity (GWPI) were +0.3% (p = 0.85), +149.9% (p< 0.0001), −57.8% (p< 0.0001), +27.7% (p = 0.12), −44.9% (p< 0.0001), and 57.7% (p< 0.0001), respectively. Drainage in lower total N soils was more capable of maintaining yield (+0.9% vs. −1.4%), and drainage in higher pH and organic carbon soils resulted in greater reductions in CH4 emissions (−46.73% vs. −37.3%, −46.36% vs. −38.12%). Mid-season drainage was superior to early-season and fallow season drainage in CH4 emissions reduction. Extending the duration and increasing the events of drainage would increase N2O emissions but contribute to a better CH4 emissions reduction effect. Implementing drainage in paddy systems with organic amendment can achieve greater GHG emissions reduction (both N2O and CH4) than in that without organic amendment. The GWPI decreased by the installation of drainage system might disappear when the nitrogen fertilizer application rate (N rate) reached over 530 kg ha−1. As for different N rates, single drainage is more suitable for the N rate below 115 kg ha−1, while multi-drainage has more advantages on reducing GWPI in the high N rate (≥ 115 kg ha−1).

Extended methane mitigation capacity of a mid-season drainage beyond the rice growing season: a case in Spain.

Rice cultivation is a major source of methane (CH4) emissions. Intermittent irrigation systems in rice cultivation, such as the mid-season drainage (MSD), are effective strategies to mitigate CH4 emissions during the growing season, though the reduction rates are variable and dependent on the crop context. Aeration periods induce alteration of soil CH4 dynamics that can be prolonged after flooding recovery. However, whether these changes persist beyond the growing season remains underexplored. A field experiment was conducted in Spain to study the effect of MSD implemented during the rice growing season on greenhouse gas (GHG) emissions in relation to the standard permanently flooded water management (PFL). Specifically, the study aimed at (1) assessing the CH4 mitigation capacity of MSD in the studied area and (2) testing the hypothesis that the mitigating effect of MSD can be extended into the following winter flooded fallow season. Year-round GHG sampling was conducted, seasonal and annual cumulative emissions of CH4 and N2O as well as the global warming potential were calculated, and grain yield was measured. MSD reduced growing season CH4 emissions by ca. 80% without yield penalties. During the flooded fallow season, MSD reduced CH4 emissions by ca. 60%, despite both fields being permanently flooded. The novelty of our observations lies in the amplified mitigation capacity of MSD by extending the CH4 mitigation effect to the following flooded winter fallow season. This finding becomes especially relevant in rice systems with flooded winter fallow season given the large contribution of this season to the annual CH4 emissions.

Blue revolution for food security under carbon neutrality: A case from the water-saving and drought-resistance rice

Blue revolution for food security under carbon neutrality: A case from the water-saving and drought-resistance rice

The life cycle assessment of subsurface drainage performance under rice-canola cropping system

The life cycle assessment (LCA) concept is a widely used tool to assess the environmental aspects of any activity throughout its life cycle. This study is the first application of LCA for assessing the agro-environmental sustainability of subsurface drainage systems under rice-canola cropping rotation. The systems included D0.65L15, D0.65L30, and D0.9L30, consisting of two depths (D=0.65 and 0.9 m) and two spacing (L= 15 and 30 m) and a bi-level drainage system with alternate depths of 0.9 and 0.65 m with 15 m spacing (Bilevel). A paddy plot with conventional surface drainage and similar cropping system was considered as control (Control). Two water management strategies, including mid-season drainage (MSD) and alternate wetting and drying (AWD), were practiced during rice-growing period. Free drainage (FD) was adopted during canola-growing period. Required field data were collected during 2011–2016, including four rice-canola-growing cycles (two MSD-FD cycles and two AWD-FD cycles). Using the LCA concept, the effectiveness of different drainage systems were assessed under the cycles of MSD-FD and AWD-FD. The AWD-FD system showed 7% less environmental impacts than MSD-FD. Also, AWD-FD reduced human health, climate change, and resource depletion indicators by 7.7%, 9.9%, and 8.4%, respectively, compared with MSD-FD, which improved the ecosystem quality index by 7.2%. The Bilevel, D0.9L30, D0.65L30, and D0.65L15 drainage systems, respectively, reduced the environmental impacts by 11.8%, 11.1%, 2.6%, and 5.9% under AWD-FD and 25.4%, 17.6%, 25.1%, and 14.1% under MSD-FD compared with Control. On average, Bilevel reduced the environmental impacts by 18.6% compared with the conventional surface drainage system. Based on the results, the LCA concept can be used as a suitable tool to evaluate the performance of subsurface drainage systems before implementation on a large scale.

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.

Simulating the Long-Term Effects of Fertilizer and Water Management on Grain Yield and Methane Emissions of Paddy Rice in Thailand

Rice is an important economic crop in Thailand. However, paddy rice fields are one of the largest anthropogenic sources of methane (CH4) emissions. Therefore, suitable crop management practice is necessary to reduce CH4 emissions while rice grain yield is maintained. This study aimed to evaluate appropriate options of fertilizer and water management practices for Thai rice cultivation with regards to improving rice grain yield and reducing CH4 emissions. The Denitrification–Decomposition (DNDC) model was used to simulate grain yield and the emission of CH4 under the three fertilizer options (chemical fertilizer (F), manure (M) and chemical fertilizer + manure (F + M)) with three water management options (continuous flooding (CF), mid-season drainage (MD) and alternate wet and dry (AWD)) during the years 2011–2050. Rain-fed and irrigated rice cropping systems were used. A total of 24 sites distributed in 22 provinces were studied. The data sets of daily climate, soil properties, and rice management practices were required as inputs in the model. Model validation with observation data in a field experiment indicated that simulated grain yields (R2 = 0.83, slope = 0.98, NRMES = 0.30) and cumulative seasonal CH4 emissions (R2 = 0.83, slope = 0.74, NRMES = 0.43) were significantly and positively correlated with the observation. At the end of the simulation period (2046–2050), fertilizer management options of F and F + M gave more grain yield than the M management option by 1–44% in rain-fed rice cropping and 104–190% in irrigated rice cropping system, respectively. Among options, the lower CH4 emissions were found in AWD water management options. The appropriate options with regard to maintaining grain yield and reducing CH4 emissions in the long term were suggested to be F + M with AWD for the rain-fed rice, and F with AWD for the irrigated rice cropping systems.

Gross Ecosystem Productivity Dominates the Control of Ecosystem Methane Flux in Rice Paddies

Although rice paddy fields are one of the world’s largest anthropogenic sources of methane CH4, the budget of ecosystem CH4 and its’ controls in rice paddies remain unclear. Here, we analyze seasonal dynamics of direct ecosystem-scale measurements of CH4 flux in a rice-wheat rotation agroecosystem over 3 consecutive years. Results showed that the averaged CO2 uptakes and CH4 emissions in rice seasons were 2.2 and 20.9 folds of the wheat seasons, respectively. In sum, the wheat-rice rotation agroecosystem acted as a large net C sink (averaged 460.79 g C m−2) and a GHG (averaged 174.38 g CO2eq m−2) source except for a GHG sink in one year (2016) with a very high rice seeding density. While the linear correlation between daily CH4 fluxes and gross ecosystem productivity (GEP) was not significant for the whole rice season, daily CH4 fluxes were significantly correlated to daily GEP both before (R2: 0.52–0.83) and after the mid-season drainage (R2: 0.71–0.79). Furthermore, the F partial test showed that GEP was much greater than that of any other variable including soil temperature for the rice season in each year. Meanwhile, the parameters of the best-fit functions between daily CH4 fluxes and GEP shifted between rice growth stages. This study highlights that GEP is a good predictor of daily CH4 fluxes in rice paddies.

Optimizing spikelet fertilizer input in irrigated rice system can reduce nitrous oxide emission while increase grain yield

Nitrogen (N) fertilizer provides an essential nutrient for rice production, but it also leads to nitrous oxide (N2O) emissions. We investigated twenty years’ literature and conducted two years of field experiments to assess the effects of N fertilizer application on N2O emissions, N use efficiency (NUE), and rice yield in the middle and lower reaches of the Yangtze River, China. This work described the time series of N2O emissions during the total rice-growing period based on the literature’s dataset; the peak N2O fluxes (about 1800 µg m−2 h−1) were observed at 0.4–0.55 relative days after transplanting (during the mid-season drainage period). Moreover, we established a positive linear correlation between the seasonal N2O emission and N fertilizer input in this study region (R2 =0.36). The literature’s results suggested that 30%–60% total N fertilizer input as spikelet fertilizer helps obtain an approximate 38% NUE and 8.8% grain yield rise in lower N2O emissions. Regarding the field experiments’ results, they confirmed that the rate of basal fertilizer had a significant influence on N2O emissions. The results also found that the yield scaled N2O emissions would decrease with more spikelet fertilizer input. Furthermore, an improvement in N fertilizer utilizes efficiency (agronomic efficiency and partial factor productivity) with the more spikelet fertilizer application while the total N fertilizer would not change. The grain yield in the spikelet fertilizer plots was approximately 20% higher than in the no spikelet fertilizer plots. Altogether, this study indicates that reducing N applied in the earlier growth stages could be an effective and easy-to-follow approach to increase NUE and grain yield while reducing N2O emissions in paddy production.

A vital option for food security and greenhouse gases mitigation: planting elite super rice in double- to single-rice cropping fields in China

Double-rice cropping (DRC) in southern China has made outstanding contributions to ensuring food security, along with a large amount of greenhouse gas (GHG) emissions. The observed significant shift from double- to single-rice (DtS) cropping since 1990 in southern China has led to great concerns on food security, despite its contribution to GHG emissions reduction. How to ensure food security without compromising the goal of mitigating GHG emission requires innovative thinking and a comprehensive tradeoff analysis of all plausible options. This study adopts a multi-model coupling method to simulate the yield and GHG emissions trade-offs across grid-cells by incorporating the option of planting elite super rice in the DtS areas. The simulation results indicate that planting elite super rice with longer growth period in the DtS areas has the potential to compensate the annual yield loss caused by the DtS shift while significantly mitigating GHG emissions in comparison with the conventional DRC. In more detail, while the yield and GHG emissions of prevailing single-rice cropping are 48% (±2%) and 54% (±4%) lower than the corresponding (two-season sums) figures of conventional DRC under the current irrigation practice of midseason drainage, the yield and GHG emissions of super rice are 15% (±4%) and 44% (±6%) lower than the above reference figures if the emerging irrigation regime of alternate wetting and drying is adopted. Furthermore, our modeling simulations demonstrate the feasibility of promoting elite super rice cultivars across southern China. The research suggests a viable option for China to balance the trade-off between food security and GHG mitigation.

Cattle biogas effluent application with multiple drainage mitigates methane and nitrous oxide emissions from a lowland rice paddy in the Mekong Delta, Vietnam

Household biogas production from livestock manure is popular in Vietnam. Effluent from the biogas production can be effectively used as organic fertilizer for rice cultivation. However, there is concern about enhanced methane (CH4) emission from the flooded soil under reductive conditions because the effluent contains labile organic carbon, the substrate for microbial CH4 production. We therefore combined multiple drainage with “cattle biogas effluent” (BE) application to mitigate CH4 emission by ameliorating the reductive soil conditions while obtaining grain yields comparable to the conventional practice, a combination of synthetic fertilizers (SY) application and continuous flooding (CF). We performed a 1-year experiment on a lowland (0 m a.s.l.) paddy field in the Mekong Delta, Vietnam, under a triple cropping system. We examined the effects of fertilizer type (SY and BE) and water management (CF, alternate wetting and drying [AWD], and midseason drainage followed by intermittent irrigation [MiDi]) on rice growth and yield and on CH4 and nitrous oxide (N2O) emissions. For AWD, a surface water level of −15 cm was used as the threshold for re-irrigation after natural drainage, whereas MiDi used a fixed irrigation schedule with one-time forced drainage during the midseason drainage period. Surface water level did not drop sufficiently in either AWD or MiDi due to the lowland conditions, and both practices caused similar seasonal changes in water level except for the forced drainage in MiDi. A significant (P = 0.05) interaction between fertilizer type and water management on grain yield was found only in dry season (winter–spring) with the highest yield level. Despite the poorly drained conditions, CH4 emission was significantly reduced by AWD and MiDi (by 27–30%), and both practices offset the significant CH4 emission enhancement by BE application. N2O emission was significantly reduced by BE application, whereas it was not affected by water management because flooded conditions were maintained during every nitrogen fertilizer application. Our results indicate that the combination of BE application and multiple drainage can mitigate CH4 and N2O emissions from a lowland rice paddy in the Mekong Delta without yield loss.