Fallow Season Research Articles

Effect of the number of tillages in fallow season and fertilizer type on greenhouse gas emission from a rice (Oryza sativa L.) paddy field in Ehime, southwestern Japan

ABSTRACTAgricultural fields, including rice (Oryza sativa L.) paddy fields, constitute one of the major sources of atmospheric methane (CH4) and nitrous oxide (N2O). Organic matter application, such as straw and organic fertilizer, enhances CH4 emission from paddy fields. In addition, rice straw management after harvest regulates CH4 emissions in the growing season. The interaction of tillage times and organic fertilizer application on CH4 and N2O emissions is largely unknown. Therefore, we studied the effects of fallow-season tillage times and fertilizer types on CH4 and N2O emissions in paddy fields in Ehime, southwestern Japan. From November 2011 to October 2013, four treatments, two (autumn and spring) or one (spring) in the first year, or two (autumn and spring) or three (autumn, winter, and spring) in the second year times of tillage with chemical or organic fertilizer application, were established. Gas fluxes were measured by the closed-chamber method. Increasing the number of tillage times from one to two decreased succeeding CH4 emission and the emission factor for CH4 (EFCH4) in the rice-growing season, suggesting that the substrate for CH4 production was reduced by autumn and spring tillage in the fallow season. Higher EFCH4 [1.8–2.0 kg carbon (C) ha−1 d−1] was observed when more straw was applied (6.9–7.2 Mg ha−1) in the second year. Organic fertilizer application induced higher CH4 emission just after the application as basal and supplemental fertilizers, especially at a lower straw application rate. This indicated that EFCH4 in the organically managed fields should be determined individually. Organic fertilizer application with two tillage times induced N2O efflux during the rice-growing season in the second year, but N2O emissions were not affected by winter tillage. Although paddy fields can act as an N2O sink because of reduced soil conditions when straw application was high, application of organic C and nitrogen as fertilizer can enhance N2O production by the denitrification process during the growing season, especially in the ripening stage when soil anaerobic conditions became moderate. These results suggest that negative emission factors for N2O (EFN2O) can be applied, and EFN2O of organic fertilizer should be considered during the estimation of N2O emission in the paddy field.

Rice agriculture increases base flow contribution to catchment nitrate loading in subtropical central China

Base flow is recognized as an important hydrological pathway for NO3−–N export, however, the base flow contribution to NO3−–N loading in rice agriculture catchments remains unknown. In this study, stream discharge and NO3−–N concentration were observed in two contrasting rice agriculture catchments (named Tuojia and Jianshan) in subtropical central China between November 2010 and December 2013, to quantify the base flow contribution to NO3−–N loading and determine its relationship with rice agriculture. The results suggested that Tuojia produced more base flow (727.0 vs. 426.5mm) and had higher base flow contribution to stream discharge (41.9% vs. 28.4%) than Jianshan did during the observation period, due to the more groundwater recharge associated with the higher areal proportion of rice agriculture in Tuojia. The average flow-weighted NO3−–N concentration in the base flow was higher in Tuojia than in Jianshan (1.43 vs. 1.07mgNL−1), because rice agriculture could result in obvious N leaching into groundwater system. The NO3−–N loading via the base flow reached 0.27kgNha−1month−1 in Tuojia, which contributed 36.5% of the NO3−–N loading via the stream discharge. These values were much greater than 0.12kgNha−1 month−1 and 27.3% in Jianshan. The more NO3−–N loading and greater base flow contribution in Tuojia were attributed to the more base flow and higher NO3−–N concentration in base flow associated with the intensive rice cropping. Specifically, the base flow contribution to the NO3−–N loading was greater during the fallow seasons than during the rice-growing seasons, likely due to the NO3−–N “landscape memory” effects from previous rice cropping seasons. Therefore, NO3−–N reduction practices in the rice agriculture catchments should be applied to mitigate the base flow contribution to NO3−–N loading in subtropical central China.

Greenhouse gas emissions, soil quality, and crop productivity from a mono-rice cultivation system as influenced by fallow season straw management.

Straw management during fallow season may influence crop productivity, soil quality, and greenhouse gas (GHG) emissions from rice field. A 3-year field experiment was carried out in central China to examine the influence of different fallow season straw management practices on rice yield, soil properties, and emissions of methane (CH4) and nitrous oxide (N2O) from a mono-rice cultivation system. The treatments comprised an unfertilized control (CK), inorganic fertilization (NPK), rice straw burning in situ (NPK + RSB), rice straw mulching (NPK + RSM), and rice straw strip mulching with green manuring (NPK + RSM + GM). The maximum rice yield, soil organic carbon, soil total nitrogen, and available potassium were observed in NPK + RSM + GM treatment. Compared with NPK, the NPK + RSM + GM recorded 9% higher grain yield averaged across 3 years. However, NPK + RSM and NPK + RSB were statistically similar with NPK regarding grain yield. The NPK + RSM and NPK + RSM + GM recorded significantly higher CH4 emission during rice growing season as well as winter fallow; however, the response of N2O emissions was variable. The NPK + RSM and NPK + RSM + GM were statistically similar for annual cumulative CH4 and N2O emissions. The NPK + RSM + GM recorded 103 and 72% higher straw-induced net economic benefits and soil organic carbon sequestration rate, and reduced net global warming potential by 27% as compared with NPK + RSM. Considering the benefits of soil fertility, higher crop productivity, and environmental safety, the NPK + RSM + GM could be the most feasible and sustainable option for mono-rice cultivation system in central China.

Effects of water management practices on residue decomposition and degradation of Cry1Ac protein from crop-wild Bt rice hybrids and parental lines during winter fallow season

Rice is the staple diet of over half of the world's population and Bacillus thuringiensis (Bt) rice expressing insecticidal Cry proteins is ready for deployment. An assessment of the potential impact of Bt rice on the soil ecosystem under varied field management practices is urgently required. We used litter bags to assess the residue (leaves, stems and roots) decomposition dynamics of two transgenic rice lines (Kefeng6 and Kefeng8) containing stacked genes from Bt and sck (a modified CpTI gene encoding a cowpea trypsin inhibitor) (Bt/CpTI), a non-transgenic rice near-isoline (Minghui86), wild rice (Oryza rufipogon) and crop-wild Bt rice hybrid under contrasting conditions (drainage or continuous flooding) in the field. No significant difference was detected in the remaining mass, total C and total N among cultivars under aerobic conditions, whereas significant differences in the remaining mass and total C were detected between Kefeng6 and Kefeng8 and Minghui86 under the flooded condition. A higher decomposition rate constant (km) was measured under the flooded condition compared with the aerobic condition for leaf residues, whereas the reverse was observed for root residues. The enzyme-linked immunosorbent assay (ELISA), which was used to monitor the changes in the Cry1Ac protein in Bt rice residues, indicated that (1) the degradation of the Cry1Ac protein under both conditions best fit first-order kinetics, and the predicted DT50 (50% degradation time) of the Cry1Ac protein ranged from 3.6 to 32.5 days; (2) the Cry1Ac protein in the residue degraded relatively faster under aerobic conditions; and (3) by the end of the study (~154 days), the protein was present at a low concentration in the remaining residues under both conditions. The degradation rate constant was negatively correlated with the initial carbon content and positively correlated with the initial Cry1Ac protein concentration, but it was only correlated with the mass decomposition rate constants under the flooded condition. No Cry1Ac protein was detected in the soils surrounding the buried residue. Our results did not reveal any evidence that the stacked genes (Bt/CpTI) or the presence of the Cry1Ac protein influenced the decomposition dynamics of the rice residues. Furthermore, our results suggested that field drainage after residue incorporation would promote Cry1Ac protein degradation.

Estimating annual soil carbon loss in agricultural peatland soils using a nitrogen budget approach.

Around the world, peatland degradation and soil subsidence is occurring where these soils have been converted to agriculture. Since initial drainage in the mid-1800s, continuous farming of such soils in the California Sacramento-San Joaquin Delta (the Delta) has led to subsidence of up to 8 meters in places, primarily due to soil organic matter (SOM) oxidation and physical compaction. Rice (Oryza sativa) production has been proposed as an alternative cropping system to limit SOM oxidation. Preliminary research on these soils revealed high N uptake by rice in N fertilizer omission plots, which we hypothesized was the result of SOM oxidation releasing N. Testing this hypothesis, we developed a novel N budgeting approach to assess annual soil C and N loss based on plant N uptake and fallow season N mineralization. Through field experiments examining N dynamics during growing season and winter fallow periods, a complete annual N budget was developed. Soil C loss was calculated from SOM-N mineralization using the soil C:N ratio. Surface water and crop residue were negligible in the total N uptake budget (3 – 4 % combined). Shallow groundwater contributed 24 – 33 %, likely representing subsurface SOM-N mineralization. Assuming 6 and 25 kg N ha-1 from atmospheric deposition and biological N2 fixation, respectively, our results suggest 77 – 81 % of plant N uptake (129 – 149 kg N ha-1) was supplied by SOM mineralization. Considering a range of N uptake efficiency from 50 – 70 %, estimated net C loss ranged from 1149 – 2473 kg C ha-1. These findings suggest that rice systems, as currently managed, reduce the rate of C loss from organic delta soils relative to other agricultural practices.

Impact of plastic film mulching on increasing greenhouse gas emissions in temperate upland soil during maize cultivation

Plastic film mulching (PFM) is an agricultural management practice that is commonly used to suppress weed growth. However, its effect on greenhouse gas (GHG) emissions has not been well evaluated. To investigate the effect of PFM on GHG emissions and crop productivities, black PFM and no-mulching plots were installed as the main treatment, and three sub-treatments, chemical fertilizer (NPK) and two green manures, were arranged within each main treatment. Two cover crops (hairy vetch and barley) with different carbon/nitrogen (C/N) ratios were cultivated in the two green manure treatments during the fallow season. The aboveground biomasses of vetch (23–25Mg fresh weight ha−1) and barley (10–11Mgha−1) were incorporated before maize seedling transplanting. Maize was cultivated without chemical fertilization in the two green manure treatments, whereas the recommended chemical fertilizers were applied in the NPK treatment. During two annual cropping seasons, the emission rates of methane (CH4) and nitrous oxide (N2O) gases were simultaneously monitored once a week using the closed-chamber method. Total global warming potential (GWP) was calculated as CO2 equivalents by multiplying the seasonal CH4 and N2O fluxes by 25 and 298, respectively. Irrespective of soil amendments, PFM significantly increased soil temperature and moisture content by a mean of 2°C and 0.04m3m−3 over no-mulching, respectively. Plastic film mulching increased grain productivity by 8–33% over no-mulching. However, PFM significantly decreased soil organic matter content and largely increased the two major GHG emissions. As a result, PFM increased the total GWP by 12–82% over no-mulching, irrespective of the soil amendments. In conclusion, more sustainable mulching systems should be developed that can sustain soil quality and minimize environmental impacts, including GHG emissions.

Does intensification of the rice cultivation cycle influence anuran diversity in rice fields?

The reduction in the amount of fallow time in rice production has occurred in the last years to increase the grain production and to sustain the global market. Some studies have shown environmental problems with reduced fallow time and it could influence negatively the pond anuran diversity. The present study tested three hypotheses: (1) amphibian richness and abundance will be greater in natural areas than rice fields; (2) rice fields with a fallow period will have greater amphibian richness and abundance than fields without this period; and (3) changes in the species composition between natural ponds and rice fields with and without a fallow period will be determined by community nestedness over the agricultural intensification gradient—natural ponds (no impact), fields with fallow period (medium impact) and fields without fallow period (greatest impact). Anurans were sampled from six rice fields cultivated under different levels of agricultural intensification (three fields with and three fields without a fallow season), and three natural ponds in southern Brazil. Although richness did not vary significantly between fields with and without fallow periods, there was a strong tendency in the results for the anuran community in the fields with fallow to be richer than that in the fields without fallow. Additionally, it is important to emphasize that the species composition of the fields with fallow were richer than the species composition of fields without fallow. Therefore, allowing the land to rest could be an important practice for the amphibian community, and rice farmers should manage some parcels of land in the agricultural matrix with resting practices in order to minimize the negative effects of rice production expansion on aquatic biodiversity in natural wetlands.

成都平原水稻-小麦轮作系统NO排放及其主要影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 成都平原水稻-小麦轮作系统NO排放及其主要影响因素 DOI: 10.5846/stxb201308292169 作者: 作者单位: 山西师范大学城市与环境科学学院,中国科学院成都山地灾害与环境研究所,中国科学院成都山地灾害与环境研究所 作者简介: 通讯作者: 中图分类号: X511 基金项目: 国家自然科学基金青年基金项目(41301304); 中国科学院知识创新工程课题(KSCX2-YW-N-46-11) NO emission and its main impacting factors in rice-wheat rotation system in Chengdu Plain of Sichuan Basin Author: Affiliation: College of Urban and Environment Sciences of Shanxi Normal University,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:应用静态暗箱-化学发光氮氧化物分析法对成都平原水稻-小麦轮作系统进行了1.5个轮作周期的NO排放定位观测,分析了NO排放特征及施氮、土壤温度、土壤湿度和作物参与对NO排放的影响。结果表明:成都平原水稻-小麦轮作系统在不施氮情况下,表现为土壤NO负排放(吸收),而施氮(N150kg/hm2)时NO排放通量为(5.5±3.3)μg m-2 h-1,施氮能显著增加土壤NO排放量,并且其效应在水热条件较好的水稻季更明显。整个观测期NO排放量有56.1%来自水稻季,而2个小麦季和休闲期NO排放量分别占32.5%和11.4%,由于休闲期NO高排放主要是作物收获后的几次翻地引起的,因此,减少休闲期翻地次数可能会有效减少NO排放。土壤温度是影响NO排放的首要环境因素,并且两者呈线性回归关系,土壤湿度对NO排放的影响因土壤湿度本身状况而异,土壤湿度条件较差时,其增加有利于NO排放,而当土壤湿度较好时会抑制NO排放。此外,土壤水热条件还是造成NO负排放(吸收)和作物参与对水稻季和小麦季NO排放贡献有别的重要原因。 Abstract:Observation of NO emissions from a field under rice-wheat rotation was performed during the period from November, 2004 to May, 2006 using the static chamber method-chemiluminescence NO analyzer. Characteristics of the emissions and effects of the factors,such as N application, soil temperature, soil moisture and crops on the emissions were analyzed. Results show that in CK (No N applied) and in conventional fertilization (N was applied at rate of N150kg/hm2) the mean NO emission fluxes were (-0.8±2.1)μg m-2 h-1 and (5.5±3.3)μg m-2 h-1,respectively. N application increased NO emissions flux significantly,and increased more remarkablely in rice season than in wheat seasons because of better soil hydrothermal condition in the rice season. About 56.1% of the total amount of NO emission came from rice season during the total research period, and NO emission in two wheat seasons and fallow season accounted for 32.5% and 11.4% of the total amount, respectively. Due to the high NO emissions come mainly from a few times plough in fallow season after crop harvest, therefore, plough times reduction might reduce NO emissions effectively in fallow season. Soil temperature is the key factor of NO emission flux,and its were linearly regressioned. Soil moisture increase will promoted the NO emission in wheat seasons, while in rice season, soil moisture increase inhibited NO emissions. At the same time, soil hydrothermal condition were reasons of soil NO negative emissions (soil absorption) and the difference contribution of crops participation on NO emissions of between rice season and two wheat seasons. 参考文献 相似文献 引证文献

Contribution of greenhouse gas emissions during cropping and fallow seasons on total global warming potential in mono-rice paddy soils

Background and aims Temperate rice paddy fields are generally flooded for less than 100 days a year during the rice cropping season and are kept under dried soil conditions during the fallow season of over 200 days. The impacts of rice paddy soil on the global warming potential (GWP) are generally analysed during rice cultivation, without consideration of the fallow season, using only methane (CH4) and nitrous oxide (N2O) fluxes. To compare the impact of greenhouse gas (GHG) emissions during the flooded rice cultivation and the dried fallow seasons on the annual GWP in a mono-rice cultivation system, the emission fluxes of CH4, N2O and carbon dioxide (CO2) were evaluated under two different fertilization systems (NPK and NPK + Cover crop) for two consecutive years.

Life cycle greenhouse gas emissions in California rice production

The nexus of climate change and food security challenges currently facing humanity requires better understanding of how to balance food production needs with climate change mitigation. Life cycle assessment methods provide a way to quantify the climate impacts of a food product by accounting for all greenhouse gas (GHG) emissions associated with its production, including upstream and downstream from the farm. This study modeled life cycle GHG emissions for one kg of milled, unpackaged rice produced in California, USA, a state that achieves some of the highest rice yields in the world. The goal was to (1) provide an assessment of life cycle GHG emissions of a comparatively intensive production system, using local field emissions data, (2) identify emissions hotspots, and (3) create a model that elucidates the life cycle-wide consequences of potential changes in field management practices. Study parameters are based on an annual cropping cycle, with continuous flooding during the growing season and soil incorporation of straw post-harvest, and yields of 9.3Mtha−1 dried paddy rice. Field emissions (growing and fallow seasons) were estimated with empirical data while other emissions were calculated using an engineering model coupled with life cycle inventory datasets and vehicle emission models.The 100-year global warming potential (GWP, based on CO2, CH4 and N2O) was 1.47kgCO2-equivalent (CO2e)kg−1 of milled rice; of which field emissions contributed 69%. These results are relatively low when compared to life cycle studies in other parts of the world, due in large part to higher grain yields and lower field emissions. When using IPCC Tier 1 estimates of field emissions, the GWP increased to 3.60CO2ekg−1 rice, highlighting the importance of using direct field measurements as we have in this study. Due to their large contributions to life cycle GWP, reducing field CH4 emissions through different field management practices, optimizing N fertilizer use, and increasing fuel efficiency or reducing use of farm machinery present the greatest opportunities to reduce life cycle emissions. Because of high variability and uncertainty in estimating field emissions, they should also be targeted for improved measurement and modeling.

Strategic double cropping on Vertisols: A viable rainfed cropping option in the Indian SAT to increase productivity and reduce risk

Our study suggests the possibility for transformational change in the productivity and risk profile of some of India's rainfed cropping systems. In the semi-arid regions of Southern India, farmers traditionally crop sorghum or chickpea on Vertisols during the post-rainy season, keeping the fields fallow during the rainy season. This practice avoids land management problems, but limits the potential for crop intensification to increase systems productivity. A long-term (15 year) experiment at ICRISAT demonstrated that cropping during the rainy season is technically feasible, and that grain productivity of double cropped sorghum+chickpea (SCP–SCP) and mung bean+sorghum (MS–MS) sequential systems were higher than their conventional counterparts with rainy season fallow, i.e. fallow+post-rainy sorghum (FS–FS) and fallow+post-rainy chickpea (FS–FCP). Without N application, mean grain yield of post-rainy sorghum in the MS–MS system was significantly greater (2520kgha−1 per two-year rotation) than in the FS–FS system (1940kgha−1 per two-year rotation), with the added benefit of the mung bean grain yield (1000kgha−1 per two-year rotation) from the MS–MS system. In the SCP–SCP system the additional grain yield of rainy sorghum (3400kgha−1 per two-year rotation) ensured that the total productivity of this system was greater than all other systems. Double cropping MS–MS and SCP–SCP sequential systems had significantly higher crop N uptake compared to traditional fallow systems at all rates of applied nitrogen (N).The intensified MS–MS and SCP–SCP sequential systems without any N fertilizer applied recorded a much higher median gross profit of Rs. 20,600 (US $ 375) and Rs. 15,930 (US $ 290) ha−1yr−1, respectively, compared to Rs. 1560 (US $ 28) ha−1yr−1) with the FS–FS system. Applying 120kg of Nha−1 considerably increased the profitability of all systems, lifting median gross profits of the sorghum+chickpea system over Rs. 60,000 (US $ 1091) ha−1yr−1 and the conventional system to Rs. 20,570 (US $ 374) ha−1yr−1. The gross profit margin analysis showed that nitrogen is a key input for improving productivity, particularly for the double cropping systems. However, traditional systems are unviable and risky without N application in the variable climates of the semi-arid tropics. Together, our results show that on Vertisols in semi-arid India, double cropping systems increase systems’ productivity, and are financially more profitability and less risky than traditional fallow post-rainy systems while further benefits can be achieved through fertilizer application.

Effects of biochar amendment on the net greenhouse gas emission and greenhouse gas intensity in a Chinese double rice cropping system

The impacts of biochar amendment on the net greenhouse gas emission (NGHGE) and greenhouse gas intensity (GHGI) of double rice cropping systems are not well examined. In this study, a field experiment was carried out to investigate the effects of biochar amendment on NGHGE and GHGI emissions in a subtropical double rice cropping system managed with intermittent flooding during two rice-growing seasons and drainage during a fallow season from April 2012 to April 2013. Three biochar treatments were studied, with application rates of 0, 24 and 48 t ha−1 (named CK, LC and HC, respectively). 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. Key soil properties related to greenhouse gas (GHG) emissions were also determined throughout an entire double rice cycle. The results showed that biochar amendment significantly reduced annual CH4 emissions by up to 40% compared with the CK treatment, possibly due to the soil pH increase after biochar amendment other than increased soil aeration. In contrast, annual N2O emissions significantly increased by 150% and 190% in the two biochar treatments, compared with the CK treatment, which may be related to the increase of soil dissolvable organic C or NH4+ in the biochar treatments. The cumulative Rh significantly increased by 19% in the HC treatment possibly due to the additional carbon dioxide (CO2) emissions from decomposition of the labile C within biochar, but showed no increase and even a decrease in the LC treatment throughout the study period. Annually, the global warming potential for CH4 and N2O emissions, NGHGEs, and GHGIs in the biochar amendment treatments were reduced by 31–36%, 1551–2936% and 1452–2894%, respectively (p < 0.05). Our collective data may suggest that as the rice grain yield was improved by the biochar amendment found in this study, the biochar application in paddy fields may be an effective measure for GHG emission mitigation in the subtropics.

Carbon Dioxide and Nitrous Oxide Emissions Impacted by Bioenergy Sorghum Management

Modern bioenergy feedstocks, such as bioenergy sorghum [Sorghum bicolor (L.) Moench], are being developed to supply future cellulosic biofuel demands. How these cropping systems impact greenhouse gas (GHG) emission of CO2 and N2O from the soil is unknown and field research is necessary to elucidate the effects of agronomic management practices on soil trace gas emissions. We studied the effects of N fertilization (0 vs. 280 kg urea‐N ha−1), residue management (0 vs. 50% of sorghum biomass returned), crop sequence (corn [Zea mays L.]–sorghum vs. sorghum–sorghum), and their interactions on CO2 and N2O emissions from bioenergy production scenarios on a Weswood (fine‐silty, mixed, superactive, thermic Udifluventic Haplustept) silty clay loam soil in central Texas. Gas fluxes were measured approximately weekly throughout the 2010 and 2011 growing season and at a reduced rate during the fallow season with a photoacoustic gas analyzer integrated with a static chamber. Overall, CO2 and N2O fluxes were relatively higher than those observed by others in the United States despite drought conditions throughout much of 2010 and 2011. Highest emissions of both gases were observed during the growing season, often following a precipitation–irrigation event and shortly after N fertilization. Residue return increased cumulative CO2 emissions each year, probably due to increased heterotrophic microbial activity. Nitrogen addition significantly increased cumulative emissions of N2O both years but only impacted cumulative CO2 emissions in 2011. While crop rotation impacted biomass yield, it had no significant effect on cumulative CO2 or N2O emissions. Additional research is needed to identify the optimal N and residue application rates that provide high yields with minimal soil GHG emissions and aid in sustaining long‐term soil quality.

C and N accumulations in soil aggregates determine nitrous oxide emissions from cover crop treated rice paddy soils during fallow season

Combination of leguminous and non-leguminous plant residues are preferably applied in rice paddy soils to increase the rate of organic matter mineralization and to improve plant growth. However, organic matter addition facilitates methane (CH4) emission from rice paddy soil. Mineralization of organic nitrogen (N) increases NO3–N concentrations in soil, which are precursors for the formation of nitrous oxide (N2O). However, N2O is a minor greenhouse gas emitted from submerged rice field and hence is not often considered during calculation of total global warming potential (GWP) during rice cultivation. The hypothesis of this study was that fluxes of N2O emissions might be changed after removal of flooded water from rice field and the effect of cover crops on N2O emissions in the fallow season might be interesting. However, the effects of N-rich plant residues on N2O emission rates in the fallow season and its effect on annual GWP were not studied before. In this experiment, combination of barley (non-leguminous) and hairy vetch (leguminous) biomasses were applied at 9Mgha−1 and 27Mgha−1 rates in rice paddy soil. Cover crop application significantly increased CH4 emission flux while decreased N2O emissions during rice cultivation. The lowest N2O emission was observed in 27Mgha−1 cover crop treated plots. Cover crop applications increased N contents in soil aggregates especially in smaller aggregates (<250μm), and that proportionately increased the N2O emission potentials of these soil aggregates. Fluxes of N2O emissions in the fallow season were influenced by the N2O emission potentials of soil aggregates and followed opposite trends as those observed during rice cultivation. Therefore, it could be concluded that the doses of cover crop applications for rice cultivation should not be optimized considering only CH4, but N2O should also be considered especially for fallow season to calculate total GWP.

Seasonal assessment of greenhouse gas emissions from irrigated lowland rice fields under infrared warming

Rice fields are considered as one of the major sources of methane (CH4), and they also emit nitrous oxide (N2O). A field experiment was conducted at the International Rice Research Institute, Philippines, in 2010–2011 using a temperature free-air controlled enhancement (T-FACE) system. Our objectives were to assess (i) the suitability of the T-FACE system for flooded rice fields and (ii) seasonal variations in greenhouse gas emissions with and without experimental warming.This observation period included one wet season (WS), one dry season (DS), and a fallow season. The experimental warming, i.e., T-FACE system, was maintained by using six infrared heaters deployed in a hexagonal pattern over each plot (7.1m2). Set-point canopy temperatures of the warming treatment were 1.5 and 3.0°C higher than the reference plots during daytime and nighttime, respectively. Two warming treatments (i.e., heated and reference) were arranged in a randomized complete block design with three replications. Infrared warming increased rice canopy temperature by 1.1 and 2.6°C (0.4°C below the targeted set-point) during daytime and nighttime, respectively. On the other hand, only a marginal (0.4–0.5°C) increase was observed for both water and soil temperatures, likely because flood irrigation water flowed across the field. The warming (elevated canopy temperature) had no significant effects on CH4 or N2O emissions during the dry, wet, and fallow seasons. However, diel and seasonal variations in CH4 emissions were observed during the rice-growing and fallow periods. CH4 emissions were higher during the early afternoons, which was positively correlated with both soil and air temperatures. Similarly, CH4 emission rates increased with rice growth stage up to the reproductive stage. Moreover, cumulative CH4 emissions were 1.5 times higher in the 2011 DS than in the 2010 WS (50 and 34gCH4m−2, respectively). The 2-month fallow season (late May–early July 2011) under continuous flooding emitted 51gCH4m−2, which is similar to that in the 2011 DS. On the other hand, N2O emissions were not detected throughout the growing season, but an emission peak was observed after final drainage at maturity during the 2011 DS. Both rice-growing and fallow seasons were the major sources of CH4 emissions as long as the field was continuously flooded, while N2O was not detectable in continuously flooded soil. Infrared warming did not affect rice yields or yield components, probably because the general growing temperatures were near optimum, and the warming treatment was not sufficiently large to cause a significant effect.

Long-Term Monitoring of Rainfed Wheat Yield and Soil Water at the Loess Plateau Reveals Low Water Use Efficiency

Increasing crop yield and water use efficiency (WUE) in dryland farming requires a quantitative understanding of relationships between crop yield and the water balance over many years. Here, we report on a long-term dryland monitoring site at the Loess Plateau, Shanxi, China, where winter wheat was grown for 30 consecutive years and soil water content (0–200 cm) was measured every 10 days. The monitoring data were used to calibrate the AquaCrop model and then to analyse the components of the water balance. There was a strong positive relationship between total available water and mean cereal yield. However, only one-third of the available water was actually used by the winter wheat for crop transpiration. The remaining two-thirds were lost by soil evaporation, of which 40 and 60% was lost during the growing and fallow seasons, respectively. Wheat yields ranged from 0.6 to 3.9 ton/ha and WUE from 0.3 to 0.9 kg/m3. Results of model experiments suggest that minimizing soil evaporation via straw mulch or plastic film covers could potentially double wheat yields and WUE. We conclude that the relatively low wheat yields and low WUE were mainly related to (i) limited rainfall, (ii) low soil water storage during fallow season due to large soil evaporation, and (iii) poor synchronisation of the wheat growing season to the rain season. The model experiments suggest significant potential for increased yields and WUE.

Effects of over-winter green cover on soil solution nitrate concentrations beneath tillage land

There is a growing need to reduce nitrogen losses from agricultural systems to increase food production while reducing negative environmental impacts. The efficacy of vegetation cover for reducing nitrate leaching in tillage systems during fallow periods has been widely investigated. Nitrate leaching reductions by natural regeneration (i.e. growth of weeds and crop volunteers) have been investigated to a lesser extent than reductions by planted cover crops. This study compares the efficacy of natural regeneration and a sown cover crop (mustard) relative to no vegetative cover under both a reduced tillage system and conventional plough-based system as potential mitigation measures for reducing over-winter soil solution nitrate concentrations. The study was conducted over three winter fallow seasons on well drained soil, highly susceptible to leaching, under temperate maritime climatic conditions. Mustard cover crop under both reduced tillage and conventional ploughing was observed to be an effective measure for significantly reducing nitrate concentrations. Natural regeneration under reduced tillage was found to significantly reduce the soil solution nitrate concentrations. This was not the case for the natural regeneration under conventional ploughing. The improved efficacy of natural regeneration under reduced tillage could be a consequence of potential stimulation of seedling germination by the autumn reduced tillage practices and improved over-winter plant growth. There was no significant effect of tillage practices on nitrate concentrations. This study shows that over winter covers of mustard and natural regeneration, under reduced tillage, are effective measures for reducing nitrate concentrations in free draining temperate soils.

Seasonal dynamics of dissolved silicon in a rice cropping system after straw incorporation

Rice is an important staple for over half the world’s population, and silicon (Si) is a vital nutrient that helps to improve yields through its role in alleviating biotic and abiotic stresses. Despite Si being abundant in crustal materials, it is only slowly released to soil pore-waters through chemical weathering. However, biocycling of Si through plant material (i.e. phytoliths) and back into soil is comparatively rapid, and thus may exert a dominant control on the biogeochemical cycling of Si within soils and near-surface sediments in some environments. Despite the potential importance of this pathway, Si cycling is poorly resolved in cultivated systems, such as rice cropping. Here, we monitored seasonal trends of Si in pore-water, plants, and soil over a two-year period in a California rice cropping system where straw is incorporated into the soil during the fallow season. There was a clear seasonal trend of high pore-water Si concentrations during the winter fallow that approached predicted equilibrium with amorphous Si, followed by low concentrations during the growing season within the top 20cm of the profile. The seasonal change in Ge/Si ratios from low values during the winter fallow to high values—up to 36μmolmol−1—during the growing season was due to a greater change in Si concentrations rather than Ge concentrations. These data indicate a low-[Ge], high-[Si] source of Si during the winter fallow, which may be due to incorporation of rice straw (a low-[Ge], high-[Si] source) and subsequent phytolith dissolution. Our results suggest that incorporation of high-[Si] plant material (e.g. straw) releases additional Si to soil pore-waters that is available for plant-uptake during the growing season.

Methanogenic Pathway and Fraction of CH4 Oxidized in Paddy Fields: Seasonal Variation and Effect of Water Management in Winter Fallow Season

A 2-year field and incubation experiment was conducted to investigate δ13C during the processes of CH4 emission from the fields subjected to two water managements (flooding and drainage) in the winter fallow season, and further to estimate relative contribution of acetate to total methanogenesis (Fac) and fraction of CH4 oxidized (Fox) based on the isotopic data. Compared with flooding, drainage generally caused CH4, either anaerobically or aerobically produced, depleted in 13C. There was no obvious difference between the two in transport fractionation factor (εtransport) and δ13C-value of emitted CH4. CH4 emission was negatively related to its δ13C-value in seasonal variation (P<0.01). Acetate-dependent methanogenesis in soil was dominant (60–70%) in the late season, while drainage decreased Fac-value by 5–10%. On roots however, CH4 was mostly produced through H2/CO2 reduction (60–100%) over the season. CH4 oxidation mainly occurred in the first half of the season and roughly 10–90% of the CH4 was oxidized in the rhizosphere. Drainage increased Fox-value by 5–15%, which is possibly attributed to a significant decrease in production while no simultaneous decrease in oxidation. Around 30–70% of the CH4 was oxidized at the soil-water interface when CH4 in pore water was released into floodwater, although the amount of CH4 oxidized therein might be negligible relative to that in the rhizosphere. CH4 oxidation was also more important in the first half of the season in lab conditions and about 5–50% of the CH4 was oxidized in soil while almost 100% on roots. Drainage decreased Fox-value on roots by 15% as their CH4 oxidation potential was highly reduced. The findings suggest that water management in the winter fallow season substantially affects Fac in the soil and Fox in the rhizosphere and roots rather than Fac on roots and Fox at the soil-water interface.

Analysis of seasonal change in paddy soil structure based on the elasto-plastic deformation model

Paddy soil, puddled and submerged for a few months every year, shows remarkable shrinkage when it dries, but cannot swell up to its original volume when it is submerged again. Such volumetric change induces desiccation cracks, which significantly affect the hydrological behavior of paddy fields. The present study aimed to reveal the basic behavior of cyclic shrinkage and swelling of clayey paddy soil with regard to water management during cultivation and precipitation in the fallow season. The study also aimed to examine the applicability of the elasto-plastic deformation model to the temporal changes in water retention and volume change of paddy soil. Undisturbed soil samples from a clayey experimental paddy were taken repeatedly from the top soil and hardpan layers in a rice monoculture paddy field and a rotationally cropped paddy field, both having clayey soil. Sampling was performed three times a year from July 2005 to April 2007: 1) at the end of two months of continuous flooding after puddling, 2) after drying by the release of poding water, and 3) after the wet fallow period in winter. The samples were subject to measurement of Water Retention Characteristics (WRCs) by multiple saturation and dehydration treatment in the laboratory. The samples were saturated first and dehydrated at 3.1, 10, 20, 40 and 80 kPa in a pressure chamber. They were then saturated again and dehydrated at 3.1 and 80 kPa. From the difference in the retained water at 3.1 kPa of suction between the first and second dehydration, the amount of pore volume subject to irreversible volumetric shrinkage was evaluated. The amount of water retained by puddled soil decreased irreversibly due to desiccation, which can be attributed to the plastic deformation of the pores. The water reduction due to drying was higher in the rice monoculture paddy field than in the rotationally cultivated paddy field. However, the continuous wet conditions after harvest induced restoration of 23% to 78% of the pores that evaluated as having been plastically compressed. These observations revealed the limitation of applying the elasto-plastic model to temporal changes in paddy soil structure. The mechanisms which cause time-dependency in shrinkage and swelling should be studied to obtain effective control of the mechanical and hydrological behavior of paddy soil. Application of alternative mechanical models that take into account the time-dependent behavior should also be explored.