Double Rice Cropping System Research Articles

Basic soil productivity in the double rice cropping system under long-term fertilization regimes in the Poyang Lake region, China

We aimed to explore changes in basic soil productivity (BSP) under different fertilization regimes in the Poyang Lake region, Jiangxi Province, China. Soil samples were collected from a long-term fertilization experiment (since 1981) that included treatments of no fertilization (CK), chemical fertilization (NPK), and combined chemical and organic fertilization (NPKM). Then, a three-year pot experiment (from 2012 to 2014) with double rice cropping was conducted with two different fertilization regimes (no fertilization, F0; fertilization, F1) using CK, NPK and NPKM soils. Grain yield and BSP were analyzed among soils with different fertilization regimes to identify the key factors driving changes in BSP. Results showed that grain yields in NPKM soil were higher than in NPK and CK soils regardless of fertilization in the pot experiment. Under the F0 condition, annual grain yields of NPKM soil were 37.7%-143.9% and 20.8%-66.7% higher than CK and NPK soils, respectively. The BSP values of CK, NPK and NPKM soils in three years were 41.8%-53.1%, 45.2%-62.6% and 59.1%-88.1%, respectively. NPKM soil had significantly higher BSP than NPK and CK soils. Furthermore, there were significant positive correlations between soil organic matter and BSP as well as between organic carbon balance and BSP. These results suggested that long-term application of chemical and organic fertilizers could improve BSP in the double rice cropping system of the Poyang Lake region. In addition, soil organic matter and organic carbon balance are important factors for improving BSP in this region.

Actual evapotranspiration and crop coefficients of irrigated lowland rice (Oryza sativa L.) under semiarid climate

Lowland irrigated rice is the predominant crop produced in the Senegal River Valley characterised by very low annual rainfall, high temperatures, and low relative humidity. The Senegal River is shared by Senegal, Mali, Mauritania, and Guinea, and serves as the main source of irrigation water for the adopted double rice cropping system. Developing appropriate resource management strategies might be the key factor for the sustainability of rice production in the region. This study aims to estimate rice seasonal evapotranspiration (ETa), irrigation water requirement, and to develop rice growth stage specific crop coefficients (Kc) to improve rice water productivity. Field experiments were conducted during the hot and dry seasons in 2014 and 2015 at the AfricaRice research station at Fanaye in Senegal. Irrigation water inputs were monitored and actual crop evapotranspiration was derived using the water balance method. Daily reference evapotranspiration (ETo) was estimated using the Penman-Monteith equation and the weather variables were collected at the site by an automated weather station. The results showed that the ETo during the hot and dry season from February 15th to June 30th varied from 4.5 to 9.9 mm and from 3.7 to 10.8 mm in 2014 and 2015, respectively, and averaged 6.8 mm d–1 in 2014 and 6.6 mm d–1 in 2015. The seasonal irrigation water amount for the transplanted rice was 1110 mm in 2014 and 1095 mm in 2015. Rice daily ETa varied from 4.7 to 10.5 mm in 2014 and from 4.4 to 10.5 mm in 2015 and averaged 8.17 mm in 2014 and 8.14 mm in 2015. Rice seasonal ETa was 841.5 mm in 2014 and 855.4 mm in 2015. The derived rice Kc values varied from 0.77 to 1.51 in 2014 and 0.85 to 1.50 in 2015. Rice Kc values averaged 1.01, 1.31, and 1.12 for the crop development, mid-season and late season growth stages, respectively. The Kc values developed in this study could be used for water management under rice production during the hot and dry season in the Senegal River Valley.

Extreme stress threatened double rice production in Southern China during 1981–2010

Global warming has increased the frequency of extreme weather, resulting in severe losses in crop production. Double rice (Oryza sativa L.) cropping system, a system where two seasons of rice are grown per year, is thus facing challenges in maintaining its yield stability throughout Southern China. Therefore, the current study was focused on the multiple stresses induced by climate change, yield anomaly, and losses for the double rice were then examined across different growth stages. Results showed the increase in both high-temperature and water-related stresses during the past three decades, while the low temperature stress for the late rice was not severe. However, the middle and lower reaches of the Yangtze River (MLRYZ) were subject to less severe stresses compared with that of the South China (SC). Yield anomaly varied among subregions for both early rice and late rice. A case study in Hunan province showed that extreme stresses threatened the yield of double rice system, and vapor pressure deficits changed yield by − 6.66% for the early rice and − 1.82% for the late rice. Thus, climate-smart practices are needed for the double rice cropping system in Southern China to mitigate the effects of extreme weather and stabilize double rice yield.

Producing more grain yield of rice with less ammonia volatilization and greenhouse gases emission using slow/controlled-release urea.

Ammonia (NH3) volatilization and greenhouse gas (GHG) emission from rice (Oryza sativa L.) fields contaminate the atmospheric environment and lead to global warming. Field trials (2013-2015) were conducted to estimate the influences of different types of fertilization practices on grain yield, NH3 volatilization, and methane (CH4) and nitrous oxide (N2O) emissions in a double rice cropping system in Central China. Results showed that grain yields of rice were improved significantly by using slow/controlled-release urea (S/C-RU). Compared with farmers' fertilizer practice (FFP) treatment, average annual grain yield with application of polymer-coated urea (CRU), nitrapyrin-treated urea (CP), and urea with effective microorganism (EM) treatments was increased by 18.0%, 16.2%, and 15.4%, respectively. However, the effects on NH3 volatilization and CH4 and N2O emissions differed in diverse S/C-RU. Compared with that of the FFP treatment, the annual NH3 volatilization, CH4 emission, and N2O emissions of the CRU treatment were decreased by 64.8%, 19.7%, and 35.2%, respectively; the annual CH4 and N2O emissions of the CP treatment were reduced by 33.7% and 40.3%, respectively, while the NH3 volatilization was increased by 18.5%; the annual NH3 and N2O emissions of the EM treatment were reduced by 6.3% and 28.7%, while the CH4 emission was improved by 4.3%. Overall, CP showed the best emission reduction with a decrement of 34.3% in global warming potential (GWP) and 44.4% in the greenhouse gas intensity (GHGI), followed by CRU treatment with a decrement of 21.1% in GWP and 31.7% in GHGI, compared with that of the FFP treatment. Hence, it is suggested that polymer-coated urea can be a feasible way of mitigating NH3 volatilization and CH4 and N2O emission from rice fields while maintaining or increasing the grain yield in Chinese, the double rice cropping system.

Greenhouse gas footprint of diversifying rice cropping systems: Impacts of water regime and organic amendments

Increasing water scarcity and Asia’s rapid economic and social development, specifically the growing demand for animal products and biofuels, is forcing farmers to transform their traditional lowland double-rice cropping systems [R-R] to mixed lowland-upland systems where upland crops such as aerobic rice [R-A] or maize [R-M] are grown instead of paddy rice during the dry period. Such changes have implications on the C and N cycling in the soil-plant system, including major shifts in soil greenhouse gas (GHG) emissions from CH4 to N2O once paddies are used for upland cropping. Moreover, soil organic carbon stocks are decreasing, thereby jeopardizing soil fertility. In this study, we investigated if straw residue incorporation and/or catch crop cultivation impairs the greenhouse gas footprint of diversifying rice cropping systems and thus, presents an alternative to open-field straw burning and intensive mineral N fertilization. For this, we calculate annual global warming potentials (GWP) and yield-scaled GWPs of three different rice systems (R-R: rice-rice, R-A: rice- aerobic rice, R-M: rice maize) without (control) or with additions of straw (+6 Mg ha−1 [S]) or + straw + mungbean as catch crop ([M + S]) on the basis of high-temporal-resolution GHG emissions (CH4 and N2O), and measurements of yield parameters. The field trial was carried out at the International Rice Research Institute (IRRI), Philippines, covering two full years. Although dry season N2O emissions increased twice- to threefold in the diversified systems (R-A, R-M), the strong reduction of CH4 emissions during this period resulted in significantly lower annual yield-scaled GWP as compared to the traditional R-R system. The same pattern was observed after application and incorporation of organic material (straw and mungbean), but led to higher substrate availability for methanogens during the following season. Therefore, the GWP was 9–39% higher in treatments including straw incorporation as compared to a control treatment without organic substrate amendments. Additional incorporation of mungbeans further increased GWPs, whereby the increment was highest in R-R rotation (88%) and lowest in R-M rotation (55%), with annual GHG emissions of 11.8 and 5.6 Mg CO2-eq ha−1, respectively. Our study shows that the yield-scaled GWP, as well as irrigation water demand, is lowest for rice-maize (R-M) cropping systems, followed by R-A and R-R systems. This ranking persists even with the incorporation of crop residues, a requirement for farmers as the ban of open-field burning is increasingly enforced. Our work also calls for a refinement of IPCC emission factors for lowland-upland rotations and the inclusion of the land-preparation period within the GHG balance of rice cropping systems.

Long-term effects of NPK fertilizers and organic manures on soil organic carbon and carbon management index under a double-cropping rice system in Southern China

ABSTRACT The effects of manure and chemical fertilizer on soil bulk density, soil organic carbon (SOC), and the role of carbon management index (CMI) in soil quality evaluation were studied under a double-cropping rice system in a long-term experiment. The experiment included five fertilizer treatments: without fertilizer input (CK), chemical fertilizer alone (MF), rice straw residue plus chemical fertilizer (RF), 30% organic matter plus 70% chemical fertilizer (LOM), and 60% organic matter plus 40% chemical fertilizer (HOM). RF, LOM, HOM treatments increased SOC content relative to MF treatment in the paddy fields at 0–20 cm. RF, LOM, HOM treatments were more effective for increasing CMI, lability index, lability of C, and SOC stocks, as compared with MF treatment. Based on rice grain yield and carbon storage, integrated fertilization of chemical fertilizer and organic manure proved to be the most effective practices for improving crop productivity and SOC sequestration.

Winter tillage with the incorporation of stubble reduces the net global warming potential and greenhouse gas intensity of double-cropping rice fields

Tillage with the incorporation of stubble is a common practice in rice cultivation, but its effect on the net global warming potential (GWP) and greenhouse gas intensity (GHGI) is poorly documented. A three-year field experiment in a double-cropping rice system was conducted to investigate the rate of sequestration of soil organic carbon, CH4 and N2O emissions, the net GWP and the GHGI. Two timings of tillage with three amounts of stubble incorporation were prepared: winter tillage (tillage after the harvest of late rice) and spring tillage (tillage before the transplantation of early rice) with no (0 t ha−1), low (3.5 t ha−1) and high (5.2 t ha−1) amounts of stubble incorporation. The results showed that the rates of sequestration of soil organic carbon with the incorporation of stubble were 0.85–1.06 t C ha−1 yr−1 for winter tillage, 67–429% higher than for spring tillage. Winter tillage significantly increased CH4 and N2O emissions in the winter fallow season relative to spring tillage, whereas it tended to decrease both emissions in the early and late rice seasons, thus playing a small part in the annual emissions. The total CH4 and N2O emissions averaged 106.5–198.2 kg ha−1 yr−1 and 114.4–229.4 g N ha−1 yr−1, respectively. Significant decreases in the net GWP (46–82%) and GHGI (49–84%) were observed when changing the tillage practices with the incorporation of stubble from spring to winter. Compared with high levels of stubble incorporation, winter tillage with low levels of stubble incorporation significantly decreased both the net GWP and the GHGI. The total grain yield was 13.0–13.3 t ha−1 yr−1 for winter tillage, 3–5% higher than for spring tillage. These findings suggest that tillage with the incorporation of stubble in the winter fallow season, particularly with 3.5 t ha−1 stubble, is an effective strategy to mitigate the net GWP and GHGI while maintaining a high grain yield in the double-cropping rice system.

Effects of different green manure treatments on soil apparent N and P balance under a 34-year double-rice cropping system

Although green manure rotation is often used to promote soil fertility and crop yield, the effects of this management practice on the nitrogen or phosphorus balance and the relationship between nutrient balance and the increase in soil nutrients have not been systematically studied. We investigated the apparent nitrogen and phosphorus balances and their associations with soil nitrogen and phosphorus increases, respectively, in a 34-year-old experimental site with various green manures and rice rotations using linear and logistic models. Cropping treatments included a rice-rice-winter fallow treatment as a control (RRW) and three green manure rotation treatments: rice-rice-ryegrass (RRR), rice-rice-oil rape (RRO), and rice-rice-Chinese milk vetch (RRC). We found that apparent nitrogen and phosphorus balances of RRR, RRO, and RRC were 164, 162, and 149 kg hm−2, which were all significantly lower than 200 kg hm−2 of RRW (P < 0.05). Moreover, the optimal fitted model of the relationship between cumulative nutrient balance and the increase in soil nutrients was different among treatments. Specifically, the correlation coefficients of cumulative nitrogen balance and soil nitrogen increase of RRR, RRO, and RRC in the linear model (0.49, 0.80, and 0.63) were all significantly lower than in the logistic model (0.81, 0.90, and 0.82). The correlation coefficients of cumulative phosphorus balance and increase in soil phosphorus of RRW in the linear model (0.81) were significantly lower than in the logistic model (0.91). Parameter analysis of the optimal fitted model revealed that RRC would increase the storage capacity of soil nitrogen and decrease the rate of soil phosphorus accumulation. Our results suggested that long-term rice-rice-green manure rotation could significantly change the apparent nitrogen and phosphorus balance and their association with soil nitrogen and phosphorus content, respectively. Our study highlights the importance of green manure rotation in an agro-ecological environment and soil fertility in a double rice cropping system in red paddy soil.

Effects of long-term fertilization practices on heavy metal cadmium accumulation in the surface soil and rice plants of double-cropping rice system in Southern China.

Fertilizer regime is playing an important role in heavy metal cadmium (Cd) accumulation in paddy soils and crop plant. It is necessary to assess the Cd accumulation in soils and rice (Oryza sativa L.) plants under long-term fertilization managements, and the results which help to assess the environmental and food risk in Southern China. However, the effects of different organic manure and chemical fertilizers on Cd accumulation in soils and rice plant remain unclear under intensively cultivated rice conditions. Therefore, the objective was to explore Cd accumulation in paddy soils and rice plant at mature stage under different long-term fertilization managements in the double-cropping rice system. Cd accumulation in the surface soils (0-20cm) and rice plant with chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), 30% organic matter and 70% chemical fertilizer (LOM), 60% organic matter and 40% chemical fertilizer (HOM), and without fertilizer input (CK) basis on 32years long-term fertilization experiment were analyzed. The results showed that the soil total Cd content was increased by 0.296 and 0.351mgkg-1 and 0.261 and 0.340mgkg-1 under LOM and HOM treatments at early and late rice mature stages, respectively, compared with the CK treatment. And the soil available Cd content was increased by 0.073 and 0.137mgkg-1 and 0.102 and 0.160mgkg-1 under LOM and HOM treatments at early and late rice mature stages, respectively, compared with the CK treatment. The bioconcentration factor of Cd across different parts of rice plant was the highest in root, followed by stem and grain, and the lowest in leaves. At early and late rice mature stages, the root Cd concentration of rice plant was increased by 0.689 and 0.608mgkg-1 with HOM treatment, the stem Cd concentration of rice plant was increased by 0.666 and 0.758mgkg-1 with RF treatment, and the leaf and grain Cd concentration of rice plant was increased 0.094 and 0.082mgkg-1 and 0.086 and 0.083mgkg-1 with LOM treatment, respectively, compared with the CK treatment. The soil Cd single-factor contaminant index (PCd) under different fertilization treatments was as the following HOM > LOM > RF > MF > CK. Meanwhile, the PCd with LOM and HOM treatments was higher than that of the MF, RF, and CK treatments, but there is no significant difference between that of MF and RF treatments. Therefore, long-term application of rice straw residue and chemical fertilizer had no obvious effect on the accumulation of Cd in paddy soils and grain, and soil Cd accumulation was increased as application of organic fertilizer.

Effects of biochar amendment on net greenhouse gas emissions and soil fertility in a double rice cropping system: A 4-year field experiment

A 4-year field experiment was conducted to investigate the effects of biochar amendment on the net greenhouse gas emission (NGHGE), greenhouse gas intensity (GHGI), soil fertility and crop yield in a typical double rice cropping system in the central subtropics of China, from April 2012 to April 2016. Three biochar treatments were studied in this experiment, with application rates of 0, 24 and 48 t ha−1 (named CK, LB and HB, respectively) using straw-derived biochar applied once at the beginning of the experiment. In each treatment, the fluxes of methane (CH4), nitrous oxide (N2O) and soil heterotrophic respiration (Rh) were measured using a static chamber/gas chromatography method. Major soil fertility properties were also determined throughout the experimental period. Biochar amendment was found to persistently decrease annual total CH4 emissions by 20 to 51% in the four years, but increased the annual total N2O emissions and Rh by 150 to 190% and 2 to 19% in the first year and the following three years, respectively. On a 4-year average, biochar addition significantly reduced annual NGHGE and GHGI by 156 to 264% and 159 to 278%, respectively (p < 0.05), with much higher reduction in the first year than those in the following three years (916 to 1911% vs 24 to 51%) due to soil carbon sequestration from biochar addition in the first year. The reduction of NGHGE and GHGI was mainly caused by the decrease of CH4 emissions (71 to 74% contribution), and the increase of soil carbon sequestration (25 to 29% contribution) in biochar treatments. Biochar amendment also significantly and persistently increased soil pH, total organic carbon (TOC), total nitrogen (TSN), and total phosphorus (TSP) by 6 to 14%, 33 to 61%, 11 to 15%, and 9 to 12%, respectively (p < 0.05), in the four years. Significant increases (p < 0.05) of microbial biomass carbon and nitrogen contents were found only in the first year after biochar amendment. Soil pH was also increased significantly (p < 0.05) with biochar amendment, but showed a declining trend in the four years. Annual grain yields for the biochar treatments were enhanced by 1 to 13%, with an average of 4 to 7% in the four years, compared to CK (p = 0.07–0.26). Compared to the LB treatment, the HB treatment significantly decreased average NGHGE and GHGI, and significantly increased average soil pH value and TOC content, but there was no significantly difference in average TSN, TSP, and yield between LB and HB treatments (p < 0.05). The gross margin analysis by considering the profit from rice grain, gain for NGHGE, and cost for biochar indicated that the economical profit for the LB treatment might be higher than that for the CK and HB treatments. Our results suggest that addition of biochar at 24 t ha−1 can be regarded as a consistently effective and economic measure for greenhouse gas emission mitigation, and soil fertility improvement, in the double rice cropping system.

Lime application lowers the global warming potential of a double rice cropping system

Liming is a common practice to alleviate soil acidification in agricultural systems worldwide. Because liming affects soil microbial activity and soil carbon (C) input rates, it can affect soil greenhouse gas (GHG) emissions as well. However, little is known about the effect of liming on GHG emissions from rice agriculture, one of the main sources of anthropogenic methane (CH4). Here, we report on the first experiment to measure the effect of liming on GHG emissions from rice paddy fields. We studied a double rice cropping system in an acid paddy for two years and measured the impacts of liming on GHG emissions and rice growth with or without straw incorporation. We found that liming reduced CH4 emissions in the early rice season, but it did not affect nitrous oxide (N2O) emissions. Over the two-year study, lime application reduced total CH4 emissions by 12.5% and 15.4% in plots without and with straw incorporation, respectively. Lime application significantly enhanced rice aboveground biomass, while reducing the area- and yield-scaled global warming potential of CH4 and N2O emissions. Lime application stimulated soil respiration during the fallow season and reduced the abundance of methanogens during the early rice growing season. Together, these results suggest that liming reduces CH4 emissions by promoting the decomposition of organic matter during the fallow season, thereby reducing C availability for methanogens. We conclude that in the short term, liming is an effective practice to reduce greenhouse gas emissions from acidic paddy soils.

Responses of yield, CH 4 and N 2 O emissions to elevated atmospheric temperature and CO 2 concentration in a double rice cropping system

Abstract Elevated atmospheric temperature and CO2 concentration ([CO2]) can strongly affect yield, CH4 and N2O emissions in rice paddies. However, understanding of their response to combined temperature and [CO2] increases under field conditions is still limited. To study this issue further, an open-top chamber (OTC) platform was set up to simulate two levels of atmospheric temperature (ambient and 2 °C elevated) and two levels of [CO2] (ambient and 60 ppm elevated) during two rotations of double rice, including twelve independent OTCs and three un-chambered open field sites as trial plots. The experimental site is located in Hubei Province, Central China, which has a subtropical monsoon climate. In all four rice seasons, elevated CO2 induced an increment in grain yield by 11.4–19.7%, while also enhancing CH4 and N2O emissions by 19.8–52.6% and 102.4–140.0%, respectively, compared with ambient temperature and [CO2]. Elevated temperature enhanced CH4 emissions by 4.4–36.0%, and decreased N2O emissions by 1.5–10.5% in three rice seasons. Elevated temperature had different effects on grain yield, with a reduction of 1.0–3.2% in early rice and an increase of 6.3–9.2% in late rice. When elevated temperature and [CO2] were combined, there was a positive interaction that further enhanced CH4 emissions and yield of late rice, and an offsetting effect on N2O emissions and yield of early rice. Over the 2-year experiment, warming and CO2 enrichment caused an increase of 9.3–44.2% in greenhouse gas intensity, suggesting that more greenhouse gas emissions will be emitted to produce a unit mass of rice under projected global warming. These findings provide initial data for the estimation of CH4 and N2O emissions under elevated temperature and [CO2] in double rice cropping system, and stress the need for effective management practices that promote rice yield while reducing greenhouse gas emissions.

Impact of long-term fertilization practices on the soil aggregation and humic substances under double-cropped rice fields.

Soil organic matter (SOM) content and soil aggregation are essential components of soil structure, which plays an important role in soil quality and fertility. Also, the SOM content, aggregation, and humus substances in paddy field were affected by application of fertilization practices. However, there is still limited information about the effects of long-term different fertilization practices on soil aggregation and carbon content in the humic acid (C-HAF), fulvic acid (C-FAF), and humin (C-HUM) fractions under double-cropping rice (Oryza sativa L.) system in Southern China paddy fields. Therefore, the effects of long-term fertilizer application on soil aggregation and C-HUM, C-HAF, and C-FAF contents in 0-5-, 5-10-, and 10-20-cm soil depth under double-cropped rice fields in Southern China were investigated. The experiment located at NingXiang County in Hunan Province, China begins in 1986 and the experiment includes five treatments: without fertilizer input (CK), mineral fertilizer alone (MF), rice straw residues and mineral fertilizer (RF), 30% organic matter and 70% mineral fertilizer (LOM), and 60% organic matter and 40% mineral fertilizer (HOM). The results showed that the soil total organic carbon content in paddy soils with RF, LOM, and HOM treatments was significant higher (P < 0.05) than that of the CK treatment at early and late rice maturity stages. The different sizes of soil aggregates with different fertilization treatments were decreased as HOM > LOM > RF > MF > CK. The HOM treatment had the highest percentage of soil aggregates in each size class and the CK treatment had the lowest percentage of soil aggregates in each size class in 0-5-, 5-10-, and 10-20-cm soil depth at early and late rice maturity stages. The soil C-HAF, C-FAF, and C-HUM contents were increased by long-term combined application of manure with mineral fertilizer practices. Meanwhile, the results indicated that the soil C-HAF, C-FAF, and C-HUM contents with RF, LOM, and HOM treatments were significantly higher (P < 0.05) than that of the CK treatment at early and late rice maturity stages. As a result, the soil total organic carbon content, each size class of soil aggregates, and soil C-HAF, C-FAF, and C-HUM contents were increased by long-term combined application of manure with mineral fertilizer in double-cropped rice fields.

Nitrogen enrichment regulates straw decomposition and its associated microbial community in a double-rice cropping system

Litter bag method was conducted to investigate the decomposition characteristics of rice straw (6000 kg ha−1) and its associated microbial community under different nitrogen (N) addition rates (0, 90, 180 and 270 kg N ha−1) under double-rice rotation. Generally, straw mass reduction and nutrient release of rice straw were faster in early stage of decomposition (0−14 days after decomposition), when easily-utilized carbohydrates and amines were the preferential substrates for involved decomposers. Straw-associated N-acetyl-glucosamidase and L-leucine aminopeptidase activities, which were higher under 180 and 270 kg N ha−1 addition, showed more activities in the early stage of decomposition. Gram-positive bacteria were the quantitatively predominant microorganisms, while fungi and actinomycetes played a key role in decomposing recalcitrant compounds in late decomposition stage. Straw residue at middle decomposition stage was associated with greater cbhI and GH48 abundance and was followed by stronger β-glucosidase, β-cellobiohydrolase and β-xylosidase activities. Although enzyme activities and cellulolytic gene abundances were enhanced by 180 and 270 kg N ha−1 application, microbial communities and metabolic capability associated with rice straw were grouped by sampling time rather than specific fertilizer treatments. Thus, we recommended 180 kg N ha−1 application should be the economical rate for the current 6000 kg ha−1 rice straw returning.

Carbon budget and greenhouse gas balance during the initial years after rice paddy conversion to vegetable cultivation

Rice paddy conversion to vegetable production is a common agricultural practice driven by economic benefits and shifting diets. However, little is known on the initial effects of this land-use conversion on net ecosystem carbon budget (NECB) and greenhouse gas (GHG) balance. Annual NECB and emissions of CH4 and N2O were measured from a native double rice cropping system (Rice) and a vegetable field recently converted from rice paddy (Veg) under no nitrogen (N) fertilization (Rice-N0 and Veg-N0) and conventional N fertilization (Rice-N+ and Veg-N+) during the initial four years upon conversion in subtropical China. Land-use conversion from rice to vegetable cultivation led to substantial C losses (2.6 to 4.5 Mg C ha−1 yr−1), resulting from strongly reduced C input by 44–52% and increased soil organic matter mineralization by 46–59% relative to Rice. The magnitude of C losses from Veg was highest in the first year upon conversion, and showed a decreasing trend over time. N fertilization shifted rice paddy from a slight C source in Rice-N0 (−1.0 Mg C ha−1 yr−1) to a significant C sink in Rice-N+ (1.1 Mg C ha−1 yr−1) and alleviated the impact of land-use conversion on C loss via increased C input from higher crop productivity. Land-use conversion greatly increased the global warming potential (GWP) from Veg by 116–395% relative to Rice in the first year, primarily due to increased C losses and N2O emission outweighing the decreased CH4 emission. However, the GWP did not show obvious difference between Rice and Veg in the following years. N fertilization and land-use conversion interactively increased GWP in the first year via increased N2O production. Concluding, NECB and GHG emissions in the first year after conversion are crucial and should be considered when evaluating the environmental consequences of land-use conversion.

Net global warming potential and greenhouse gas intensity as affected by different water management strategies in Chinese double rice-cropping systems

This study provides a complete account of global warming potential (GWP) and greenhouse gas intensity (GHGI) in relation to a long-term water management experiment in Chinese double-rice cropping systems. The three strategies of water management comprised continuous (year-round) flooding (CF), flooding during the rice season but with drainage during the midseason and harvest time (F-D-F), and irrigation only for flooding during transplanting and the tillering stage (F-RF). The CH4 and N2O fluxes were measured with the static chamber method. Soil organic carbon (SOC) sequestration rates were estimated based on the changes in the carbon stocks during 1998–2014. Longer periods of soil flooding led to increased CH4 emissions, reduced N2O emissions, and enhanced SOC sequestration. The net GWPs were 22,497, 8,895, and 1,646 kg CO2-equivalent ha−1 yr−1 for the CF, F-D-F, and F-RF, respectively. The annual rice grain yields were comparable between the F-D-F and CF, but were reduced significantly (by 13%) in the F-RF. The GHGIs were 2.07, 0.87, and 0.18 kg CO2-equivalent kg−1 grain yr−1 for the CF, F-D-F, and F-RF, respectively. These results suggest that F-D-F could be used to maintain the grain yields and simultaneously mitigate the climatic impact of double rice-cropping systems.

Carbon dynamics, potential and cost of carbon sequestration in double rice cropping system in semi arid southern India

Carbon dynamics, potential and cost of carbon sequestration in double rice cropping system in semi arid southern India

Response of CH4 emissions to straw and biochar applications in double-rice cropping systems: Insights from observations and modeling.

Paddy soil plays an essential role in contributing to the emission of methane (CH4), a potent greenhouse gas, to the atmosphere. This study aimed to demonstrate the effects of straw incorporation and straw-derived biochar amendment on CH4 emissions from double-rice cropping fields and to explore their potential mechanisms based on in-situ field measurements conducted for a period of three years (2012-2014) and model analysis. The results showed that the improved soil aeration due to biochar amendment resulted in low CH4 emissions and that sufficient substrate carbon availability in straw amendment treatments caused high CH4 emissions. The newly developed CH4 emission module for the water and nitrogen management model (WNMM), a process-based biophysical model, performed well when simulating both daily CH4 fluxes and the annual cumulative CH4 emissions under straw incorporation and biochar amendment. Results of our study indicate that the model has a great potential for upscaling and could benefit mechanism analyses about the factors regulating CH4 emissions. Application of biochar into paddy fields provides a great opportunity to reduce CH4 emissions, and the decrease in CH4 emissions following biochar amendment with repeated crop cycles would sustain for a prolonged period.

Liming and straw retention interact to increase nitrogen uptake and grain yield in a double rice-cropping system

Liming and straw retention are often applied to increase yield in rice cropping systems on acidic soils. Although these practices affect soil fertility and rice growth through different mechanisms, it is still unclear whether or how these two management practices interact. Here we report on the first experiment to study the interaction between liming and straw management practices on rice yield. We conducted a two-year factorial field experiment to investigate the interactive effect of liming and straw retention on rice yield and nitrogen (N) uptake in a double rice-cropping system in subtropical China. We found that straw retention significantly interacted with liming to increase rice yields; without liming, straw retention increased yield by 4.2% on average, whereas with liming, straw retention increased yield by 11.6%. Straw retention also significantly interacted with liming to improve N uptake, with a stronger response for late rice compared to early rice. Liming and straw retention increased soil N availability and the activities of soil enzymes involved in both carbon and N cycling, suggesting increased organic matter decomposition and enhanced N mineralization rates. Across treatments, rice yields significantly correlated with soil N availability. Therefore, we conclude that in this short-term experiment, liming and straw retention interacted to increase rice yield, likely due to their effect on soil fertility and plant N uptake.

Nitrogen losses, use efficiency, and productivity of early rice under controlled-release urea

Ammonia (NH3) volatilization and nitrogen (N) surface runoff from rice (Oryza sativa L.) paddies contribute to air and water pollution in China and everywhere else. The purposes of this study were to assess N losses through NH3 volatilization and surface runoff and to determine the grain yield and N use efficiency (NUE) of early rice in double rice cropping system in southern China. We implemented six treatments viz., control with 0kgNha−1 (CK), basal application and split application (1/2 at transplanting, 1/4 at tillering, and 1/4 at panicle stages) of urea (U), and basal applications of three controlled-release urea (CRU) sources (polyurethane-coated urea [CRU-1], degradable polymer-coated urea [CRU-2], and water-based polymer-coated urea [CRU-3]) all applied at 165kgNha−1. Results showed that CRU-1 and CRU-2 significantly reduced NH3 volatilization (23 to 62%) and N surface runoff losses (8 to 58%) compared with U. Precipitation and ammonium-nitrogen (NH4-N) concentration in surface water from rice paddy were predominant factors defining N losses through NH3 volatilization and surface runoff. Application of CRU reduced NH4-N concentration and pH of surface water and N losses through surface runoff. The CRU produced similar (−3 to 4%) or higher (5–16%) rice grain yields and increased NUE (3 to 34%) and N uptake (3–55%) compared with U. Polymer-coated urea can reduce environmental risks of N losses through volatilization and surface runoff while maintaining rice yield and N uptake, it also enhances NUE compared with urea in double rice cropping system in southern China.