Effects of mixed fertilizers formed by the compounding of two targeted controlled-release nitrogen fertilizers on yield,nitrogen use efficiency,and ammonia volatilization in double-cropping rice

One-time application of mixed fertilizer formed by the compounding of two controlled-release nitrogen fertilizers(CRUs)with targeted N supply during the periods from transplantation(TS)to panicle initiation(PI)and from PI to heading(HS)is expected to synchronize the double-peak N demand of rice.However,its effects on the yield and N use efficiency(NUE)of labor-intensive double-cropping rice were unknown.Two targeted CRU(CRU_(A)and CRU_(B))were compounded in five ratios(CRU_(A):CRU_(B)=10:0,7:3,5:5,3:7,and 0:10)to form five mixed fertilizers(BBFs):BBF1-5.A field experiment was performed to investigate the characteristics of N supply in early and late seasons under different BBFs and their effects on N uptake,yield,and ammonia volatilization(AV)loss from paddy fields of double-cropping rice.Conventional high-yield fertilization(CK,three split applications of urea)and zero-N treatments were established as controls.The N supply dropped significantly with the increased compound ratio of CRU_(B)during the period from TS to PI,but increased during the period from PI to HS.With the exception of the period from TS to PI in the late rice season,the N uptake of early and late rice maintained close synchronicity with the N supply of BBFs during the double-peak periods.Excessive N supply(BBF1 and BBF2)in the late rice season during the period from TS to PI increased N loss by AV.The effect of BBF on grain yield increase varied widely between seasons,irrespective of year.Among the BBFs,the BBF2 treatment of early rice not only stabilized the spikelets per panicle but also ensured a high number of effective panicles by promoting N uptake during the period from TS to PI and a high grain-filling percentage by appropriately reducing the N supply at the later PI stage,resulting in the highest rice yield.While stabilizing the effective panicle number,the BBF4 treatment of late rice increased the number of spikelets per panicle by promoting N uptake during the period from PI to HS,resulting in the highest rice yield.The two-year average yield and apparent N recovery efficiency of the BBF2 treatment during the early rice season were 9.6 t ha 1 and 45.3%,while those of late rice in BBF4 were 9.6 t ha 1 and 43.0%,respectively.The yield and NUE indexes of BBF2 in early rice and BBF4 in late rice showed no significant difference from those of CK.The AVs of BBF2 during the early rice season and of BBF4 during the late rice season were 50.0%and 76.8%lower,respectively,than those of CK.BBF2 and BBF4 could effectively replace conventional urea split fertilization in early and late rice seasons,ensuring rice yield and NUE and reducing AV loss in paddy fields.

Inter-provincial Differences in Rice Multi-cropping Changes in Main Double-cropping Rice Area in China: Evidence from Provinces and Households

Since the early 1980 s, the multi-cropping index for rice has decreased significantly in main double-cropping rice area in China, which is the primary double-cropping rice(DCR) production area. This decline may bring challenges to food security in China because rice is the staple food for more than 60% of the Chinese population. It has been generally recognized that rapidly rising labor costs due to economic growth and urbanization in China is the key driving force of the ‘double-to-single' rice cropping system adaption. However, not all provinces have shown a dramatic decline in DCR area, and labor costs alone cannot explain this difference. To elucidate the reasons for these inter-provincial distinctions and the dynamics of rice cropping system adaption, we evaluated the influencing factors using provincial panel data from 1980 to 2015. We also used household survey data for empirical analysis to explore the mechanisms driving differences in rice multi-cropping changes. Our results indicated that the eight provinces in the study can be divided into three spatial groups based on the extent of DCR area decline, the rapidly-declining marginal, core, and stable zones. Increasing labor cost due to rapid urbanization was the key driving force of rice cropping system adaption, but the land use dynamic vary hugely among different provinces. These differences between zones were due to the interaction between labor price and accumulated temperature conditions. Therefore, increasing labor costs had the greatest impact in Zhejiang, Anhui, and Hubei, where the accumulated temperature is relatively low and rice multi-cropping index declined dramaticly. However, labor costs had little impact in Guangdong and Guangxi. Differences in accumulated temperature conditions resulted in spatially different labor demands and pressure on households during the busy season. As a result, there have been different profits and rice multi-cropping changes between provinces and zones. Because of these spatial differences, regionally appropriate policies that provide appropriate subsidies for early rice in rapidly-declining marginal zone such as Zhejiang and Hubei should be implemented. In addition, agricultural mechanization and the number of agricultural workers have facilitated double-cropping; therefore, small machinery and agricultural infrastructure construction should be further supported.

Effects of long-term straw return on soil organic carbon fractions and enzyme activities in a double-cropped rice paddy in South China

Long-term straw return is an important carbon source for improving soil organic carbon(SOC) stocks in croplands, and straw removal through burning is also a common practice in open fields in South China. However, the specific effects of long-term rice straw management on SOC fractions, the related enzyme activities and their relationships, and whether these effects differ between crop growing seasons remain unknown. Three treatments with equal nitrogen, phosphorus, and potassium nutrient inputs, including straw/ash and chemical nutrients, were established to compare the effects of straw removal(CK), straw return(SR), and straw burned return(SBR). Compared to CK, long-term SR tended to improve the yield of early season rice(P=0.057), and significantly increased total organic carbon(TOC) and microbial biomass carbon(MBC) in double-cropped rice paddies. While SBR had no effect on TOC, it decreased light fraction organic carbon(LFOC) in early rice and easily oxidizable organic carbon(EOC) in late rice, significantly increased dissolved organic carbon(DOC), and significantly decreased soil p H. These results showed that MBC was the most sensitive indicator for assessing changes of SOC in the double-cropped rice system due to long-term straw return. In addition, the different effects on SOC fraction sizes between SR and SBR were attributed to the divergent trends in most of the soil enzyme activities in the early and late rice that mainly altered DOC, while DOC was positively affected by β-xylosidase in both early and late rice. We concluded that straw return was superior to straw burned return for improving SOC fractions, but the negative effects on soil enzyme activities in late rice require further research.

Heat Injury Risk Assessment for Single-Cropping Rice in the Middle and Lower Reaches of the Yangtze River under Climate Change

Under global warming,the risk of heat injury for crops increases,which leads to increasing instability in agricultural production.In this study,based on phenological observation data and yield data during 1981-2011 and daily meteorological data during 1961-2011 in the middle and lower reaches of the Yangtze River（MLRYR）,the risk of heat injury for single-cropping rice in this area and its response to climate change were assessed and analyzed.The risk was decomposed into such elements as hazard,exposure,vulnerability,and disaster prevention/mitigation capacity,in accordance with natural disaster risk assessment theory and the formation mechanisms of agrometeorological disasters.First,a hazard assessment model was established to identify spatiotemporal variations of the heat injury in the MLRYR during 1961-2011,and the relationship between heat injury hazard and air temperature was analyzed to identify the response of hazard to climate change.It was found that the heat injury hazard of single-cropping rice was positively correlated with the mean and maximum temperatures during the rice heading period of 20 days,with the hazard increasing sharply when the mean temperature exceeded26.5℃ and the maximum temperature exceeded 31℃.Then,exposure,vulnerability,and disaster prevention/mitigation capacity were also quantitatively examined.The results show that vulnerability and hazard were the two most important factors in the heat injury risk assessment for single-cropping rice at most stations in the MLRYR.The risk assessment considering only the first three natural elements produced high-risk values（〉 0.46）mainly in the northeast of the study area.By adding the regional capability in disaster prevention/mitigation into account,the risk assessment produced high-risk values in a much smaller area in the northeast but somewhat larger areas in the southwest of the study domain.In general,the risk of heat injury differed greatly within the MLRYR.Particular rice varieties should be adopted for specific regions,according to the local risk features quantified by this study.Under the warming climate,the risk of heat injury for single-cropping rice is likely to continue to increase.

Reconstructing rice phenology curves with frequency-based analysis and multi-temporal NDVI in double-cropping area in Jiangsu, China

Crop phenology retrieval in the double-crop- ping area of China is of great significance in crop yield estimation and water management under the influences of global change. In this study, rice phenology in Jiangsu Province, China was extracted from multi-temporal MODIS NDVI using frequency-based analysis. Pure MODIS pixels of rice were selected with the help of TM images. Discrete Fourier Transformation （DFT）, Discrete Wavelet Transformation （DWT）, and Empirical Mode Decomposition （EMD） were performed to decompose time series into components of different frequencies. Rice phenology in the double-cropping area is mainly located on the last 2 IMFs of EMD and the first 2-3 frequencies of DFT and DWT. Compared with DFT and DWT, EMD is limited to fewer frequencies. Multi-temporal MODIS NDVI data combined with frequency-based analysis can retrieve rice phenology dates with on average 79% valid estimates. The sorting result for effective estimations from different methods is DWT （85%） 〉 EMD （80%） 〉 DFT （74%）. Planting date （88%） is easier to estimate than harvesting date （70%）. Rice planting date is easily affected by the former cropping mode within the same year in a double-cropping region. This study sheds light on under- standing crop phenology dynamics in the frequency domain of multi-temporal MODIS data.

Projection of Heat Injury to Single-Cropping Rice in the Middle and Lower Reaches of the Yangtze River, China under Future Global Warming Scenarios

Based on simulation results from the 16 CMIP5 model runs under three Representative Concentration Pathways(RCP2.6, RCP4.5, and RCP8.5) in combination with the recent five years of growth-stage data from agrometeorological observation stations in the middle and lower reaches of the Yangtze River, changes in heat injury and spatial distribution patterns of single-cropping rice in China during the early(2016–35), middle(2046–65), and late(2080–99) 21 st century were projected by using quantitative estimations. Relative to the reference period(1986–2005), the occurrence probabilities of heat injury to single-cropping rice under different RCP scenarios increased significantly, showing a trend of mild > moderate > severe. The occurrence probabilities increased with time and predicted emissions, especially the average and maximum occurrence probabilities, which were ～48% and ～80%,respectively, in the late 21 st century under the RCP8.5 scenario. The spatial patterns of the occurrence probabilities at each level of heat injury to single-cropping rice did not change, remaining high in the middle planting region and low in the east. The high-value areas were mainly in central Anhui and southeastern Hubei provinces, and the areas extended to the northwest and northeast of the cultivation area over time. Under the RCP2.6, RCP4.5, and RCP8.5 scenarios, the total area of heat injury to single-cropping rice showed a significant linear increasing trend of 7.4 × 10~3, 19.9× 10~3, and 35.3 × 10~3 ha yr^(–1), respectively, from 2016 to 2099, and the areas of heat injury were greatest in the late21 st century, accounting for ～25%, ～40%, and ～59% of the cultivation area.

双季北缘地区水稻补偿超高产栽培研究

双季稻北缘地区生长季节短,温光资源不足;而常规高产栽培在品种选用、肥水运筹、群体结构及调控等方面均存在不足,产量不高不稳。补偿栽培采用生育期适中偏长优质品种;通过适当早播、拓展生长季节、增加温光利用,合理稀播培育壮秧、高效利用低位次分蘖成大穗;合理基本苗和群体结构,在大田早期迅速创建一个较大的叶面积指数、促进水稻群体尽早进入光合适期,生育中期壮秆强根、延长有效叶面积高值期,生育后期补充营养、湿润灌溉增强群体活力和抗逆性、减缓高效叶面积下降速率以补偿群体光合势,促进群体结构与光合功能高效协调,增强群体物质积累与转化能力而稳定高产。以生育期适中偏长、产量潜力高优质品种(或超级稻品种)为基础,培育多蘖壮秧、精确优化群体结构和肥料合理运筹为核心技术,配套湿润节水灌溉和病虫草害无害化防治,构建水稻补偿超高产栽培技术体系并成功示范。

Mapping rice-fallow cropland areas for short-season grain legumes intensification in South Asia using MODIS 250 m time-series data

The goal of this study was to map rainfed and irrigated rice-fallow cropland areas across South Asia,using MODIS 250 m time-series data and identify where the farming system may be intensified by the inclusion of a short-season crop during the fallow period.Rice-fallow cropland areas are those areas where rice is grown during the kharif growing season(June–October),followed by a fallow during the rabi season(November–February).These cropland areas are not suitable for growing rabi-season rice due to their high water needs,but are suitable for a short-season(≤3 months),low water-consuming grain legumes such as chickpea(Cicer arietinum L.),black gram,green gram,and lentils.Intensification(double-cropping)in this manner can improve smallholder farmer’s incomes and soil health via rich nitrogen-fixation legume crops as well as address food security challenges of ballooning populations without having to expand croplands.Several grain legumes,primarily chickpea,are increasingly grown across Asia as a source of income for smallholder farmers and at the same time providing rich and cheap source of protein that can improve the nutritional quality of diets in the region.The suitability of rainfed and irrigated rice-fallow croplands for grain legume cultivation across South Asia were defined by these identifiers:(a)rice crop is grown during the primary(kharif)crop growing season or during the north-west monsoon season(June–October);(b)same croplands are left fallow during the second(rabi)season or during the south-east monsoon season(November–February);and(c)ability to support low water-consuming,short-growing season(≤3 months)grain legumes(chickpea,black gram,green gram,and lentils)during rabi season.Existing irrigated or rainfed crops such as rice or wheat that were grown during kharif were not considered suitable for growing during the rabi season,because the moisture/water demand of these crops is too high.The study established cropland classes based on the every 16-day 250 m normalized difference vegetation index(NDVI)time series for one year(June 2010–May 2011)of Moderate Resolution Imaging Spectroradiometer(MODIS)data,using spectral matching techniques(SMTs),and extensive field knowledge.Map accuracy was evaluated based on independent ground survey data as well as compared with available sub-national level statistics.The producers’and users’accuracies of the cropland fallow classes were between 75%and 82%.The overall accuracy and the kappa coefficient estimated for rice classes were 82%and 0.79,respectively.The analysis estimated approximately 22.3 Mha of suitable rice-fallow areas in South Asia,with 88.3%in India,0.5%in Pakistan,1.1%in Sri Lanka,8.7%in Bangladesh,1.4%in Nepal,and 0.02%in Bhutan.Decision-makers can target these areas for sustainable intensification of short-duration grain legumes.

南方水稻复种指数变化对国家粮食产能的影响及其政策启示（英文）

Changes in rice production in Southern China are crucial to national food security.This study employed Landsat images to map the distributions of paddy rice-cropping systems in Southern China in 1990 and 2015.The impact of rice multiple cropping index changes on grain production capacity was then evaluated.Three important results were obtained for the 1990 to 2015 study period.First,the multiple cropping index for rice decreased from 148.3% to 129.3%,and 253.16×10^4 ha of land area was converted from double-cropping to single- cropping rice,termed “double to single”.The area with the most dramatic changes is in the Middle-Lower Yangtze Plain.The rice-cropping system distribution in Southern China showed a change from north to south with double-cropping rice shrinking and single-cropping rice expanding.Second,the “double to single” conversion led to a reduction of 6.1% and 2.6% in rice and grain production,respectively.Hunan and Jiangxi Provinces,located in the main rice producing areas,and Zhejiang,which has shown better economic development,exhibited large reductions in rice production due to the “double to single” conversion,all exceeding 13%.Third,the grain production capacity of converted “double to single” paddy fields is equivalent to that of 223.3 × 10^4 ha of newly reclaimed cultivated land,which is 54% of the total newly cultivated land reclaimed through the 2001–2015 land consolidation project.It is also 1.7 times the target goal for newly cultivated land in the national land consolidation plan for 2016–2020.Making full use of the converted “double to single” paddy fields can save 167.44 billion yuan in newly reclaimed cultivated land costs.Therefore,instead of pursuing low-quality new arable land,it is better to make full use of the existing high-quality arable land.Based on these results,the government should change the assessment method for cultivated land balance,and incorporate the sown area increased by improving the multiple cropping index into the cultivated land compensation indicator.

Effects of long-term fertilization with different substitution ratios of organic fertilizer on paddy soil

In recent years,the abuse of chemical fertilizers has caused numerous environmental problems,such as soil acidification and compaction.Replacing chemical fertilizers with organic fertilizers can effectively alleviate these problems.However,the effects of alternative organic fertilizers remain unclear.To explore the effects of organic fertilizer substitution on rice yield and paddy soil physicochemical properties and bacterial community structure,we conducted a 5-year experiment using different proportions of organic fertilizer substitution in a double-cropping rice field in Jiangxi,China.Our results showed that replacing chemical fertilizers with organic fertilizers can reduce soil acidification,increase soil organic matter content,nutrient contents,and enzyme activities,improve soil physicochemical properties and microbial community,and enhance soil metabolism.Appropriate organic substitution also had positive effects on rice production.These findings enhance our understanding of the effects of different alternative organic fertilization methods and have important theoretical significance for the promotion of the use of organic fertilizers in the future.