Field Experiment for the Effects of Rice Straw Returning and Seeding Pattern on Wheat Seedling Emergence and Grain Yield

In order to study the effect of rice straw returning and seeding patterns on seedling emergence and grain yield, field experiment was conducted to investi- gate the effects of straw mechanized returning and different seeding patterns on e- mergence rate, emergence uniformity and yield traits of wheat after rice. The results were as follows： in rice straw removal treatments, the emergence rate of mechani- cal seeding in drill was lower than that of mechanical uniform planting and manual broadcast sowing, which were 51.84%, 90.89% and 88.87%, respectively; the emer- gence uniformity of manual broadcast sowing was inferior to mechanical seeding in drill and mechanical uniform planting, which were 0.49, 0.26 and 0.23, respectively. As for the treatments with rice straw returning to the field, the emergence rate and emergence uniformity all decreased in the three seeding patterns, of which mechan- ical seeding in drill dropped markedly with emergence rate decreased by 36.54%. The emergence rate and emergence uniformity affected grain yield by affecting pan- icle, grains per spike and 1 000-grain weight. The grain yield for the treatment with rice straw removal was 6 091.34 kg/hm2, while that with rice straw returning to field was 6 476.20 kg/hm2, and both were higher than the yields of the other two seed- ing patterns. Therefore, mechanical uniform planting was？recommended for its higher emergence rate, better emergence uniformity, which was conductive to increase grain yield in wheat after rice production with rice straw returning to field.

Status Quo of Collection and Utilization of Rice and Wheat Straw in Jiangsu Province and the Countermeasures

A case study of Jiangsu Province was conducted using questionnaires and field survey to explore the status quo of the collection and utilization of rice and wheat straw of the province. Problems in collecting the straw were analyzed taking into account meteorological data of the rice and wheat harvesting seasons in the region. Results show：（1） Currently, the main handling way of rice and wheat straw was directly returning to field. The peasant households of straw returning from investigated townships A and B respectively occupied 22.01% and 28.75% of investigation households, and both of the two townships had a considerable portion of the straw wasted or improperly disposed. In township B, over 50% of the farmer households surveyed failed to make sure of any of the straw, and as high as over55% of the straw was discarded or burnt.（2） During the rice and wheat harvesting seasons, the ten-day precipitation was among 7.21-87.28 mm, and the ten-day precipitation days were among 1.53-5.00 d. Such weather not only affected timely harvesting of rice and wheat, but also seriously impeded baling, transportation and storage of straw.（3） As the crops must be harvested in a relatively short and concentrated time period, large volumes of straw were turned out within a few days.Moreover, harvesting of the first crop often coincided with sowing, leaving little time available for straw collection.（4） Straw collection was very low in economic benefit.A farmer can only get 60-90 RMB per day from straw collection and transportation,which was much lower than what they can get by working as migrant workers in the city.（5） Machines designed for straw collection were rare and those now used in the operation were low in efficiency and needed to be improved technically,which directly affected the efficiency of straw collection. The above-listed findings indicates that time shortage, negative weather condition, low benefit and low mechanization level were major factors affecting straw collection. To solve the problems,the following proposals were brought forth, that is, improving the economic benefit of straw collection as a driving force, accelerating the research and development of rice and wheat sheaf-binding reaping machine, and setting up a long-term operational mechanism for straw recovery, in the hope that this study may provide some useful ideas to help solve the problems.

Effects of ground-level ozone (O_3) pollution on the yields of rice and winter wheat in the Yangtze River Delta

Effects of elevated O_3 on the yields of rice and winter wheat were studied by using open-top chambers(OTCs). Results showed that compared to the control treatment, 200 ppb, 100 ppb, 50 ppb treatments caused a 80.4%, 58.6% and 10.5% decrease in grain yields per winter wheat plant and a 49.1%, 26.1% and 8.2% decrease in grain yield per rice plant, respectively. According to the dose-response relation educed from OTCs experiment and the monitor data of O_3 concentrations in spots, it was estimated that the yield losses of rice and winter wheat resulted by O_3 pollution in the Yangtze River Delta region in 1999 were 0.599 million ton and 0.669 million ton, economic losses were 0.539 billion RMB Yuan and 0.936 billion RMB Yuan, respectively.

Increasing the appropriate seedling density for higher yield in dry direct-seeded rice sown by a multifunctional seeder after wheatstraw return

Dry direct-seeded rice(DDR) sown using a multifunctional seeder that performs synchronous rotary tillage and sowing has received increased attention because it is highly efficient,relatively cheap,and environmentally friendly.However,this method of rice production may produce lower yields in a rice–wheat rotation system because of its poor seedling establishment.To address this problem,we performed field experiments to determine the rice yield at five seedling density levels(B1,B2,B3,B4,and B5=100,190,280,370,and 460 seedlings m-2,respectively) and clarify the physiological basis of yield formation.We selected a representative high-quality rice variety and a multifunctional seeder that used in a typical rice–wheat rotation area in 2016 and 2018.The proportion of main stem panicle increased with increasing seedling density.There was a parabolic relationship between yield and seedling density,and the maximum yield(9.34-9.47 t ha-1) was obtained under B3.The maximum yield was associated with a higher total spikelet number m-2 and greater biomass accumulation from heading to maturity.The higher total spikelet number m-2 under B3 was attributed to an increase in panicle number m-2 compared with B1 and B2.Although the panicle numbers also increased under B4 and B5,these increases were insufficient to compensate for the reduced spikelet numbers per panicle.Lower biomass,smaller leaf area,and lower N uptake per plant from the stem elongation stage to the heading stage were partially responsible for the smaller panicle size at higher seedling density levels such as B5.The higher biomass accumulation under B3 was ascribed to the increases in the photosynthetic rate of the top three leaves m-2 of land,crop growth rate,net assimilation rate,and leaf area index.Furthermore,the B3 rice population was marked by a higher grain–leaf ratio,as well as a lower export ratio and transport ratio of biomass per stem-sheath.A quadratic function predicted that 260-290 seedlings m-2 is the optimum seedling density for achieving maximum yield.Together,these results suggested that appropriately increasing the seedling density,and thereby increasing the proportion of panicles formed by the main stem,is an effective approach for obtaining a higher yield in DDR sown using a multifunctional seeder in a rice–wheat rotation system.

Effects of Nitrogen Application on Photosynthetic Characteristics and Nitrogen Use Efficiency in Wheat after Rice

In the present study, appropriate nitrogen(N) application mode in Jianghan Plain was explored by investigating the effects of different N applications on the photosynthetic characteristics of flag leaves and nitrogen use efficiency(NUE) in a wheat cultivar Zhengmai 9023. Nitrogen was top-dressed before sowing, before winter, and during the jointing stage, at different ratios:1:1:0(N1), 1:0:1(N2), 2:1:1(N3), 1:1:1(N4), and 0:0:1(N5), under the same amount of total N(180 kg/hm^2) during the growing season. No nitrogen fertilizer was used in the control(N0). Results showed that the SPAD values and photosynthetic rate(Pn) of different treatments in flag leaves increased initially and then decreased around the anthesis stage. The two indices in N1 and N5 treatments decreased rapidly after flowering, whereas those in N2, N3, and N4 treatments maintained at high levels for a long period after anthesis. Thus, reasonable nitrogen application could retard the decline of SPAD and Pn after anthesis.N4 and N1 treatments showed large dry matter accumulation. In decreasing order of crop yield, the treatments were: N4 >N1 >N3 >N5 >N2 >N0. The effective panicle number and grain number per spike of N2 were significantly lower than those of other treatments, and there was no significant difference among other treatments. No significant correlation was found between nitrogen application and 1 000-grain weight in this experiment. The nitrogen accumulation, agronomic efficiency of nitrogen fertilizer,nitrogen uptake and use efficiency of above-ground parts, nitrogen uptake and use efficiency of grain of N4 treatment were higher than those of other treatments, but the nitrogen harvest index of N4 was at a low level. In summary, N4 treatment is the most suitable nitrogen application mode in wheat after rice.

Estimating daily actual evapotranspiration of a rice–wheat rotation system in typical farmland in the Huai River Basin using a two-step model and two one-step models

The objective of this study is to evaluate the performance of three models for estimating daily evapotranspiration(ET) by employing flux observation data from three years(2007, 2008 and 2009) during the growing seasons of winter wheat and rice crops cultivated in a farmland ecosystem(Shouxian County) located in the Huai River Basin(HRB), China. The first model is a two-step model(PM-Kc);the other two are one-step models(e.g., Rana-Katerji(R-K) and advection-aridity(AA)). The results showed that the energy closure degrees of eddy covariance(EC) data during winter wheat and rice-growing seasons were reasonable in the HRB, with values ranging from 0.84 to 0.91 and R2 of approximately 0.80. Daily ET of winter wheat showed a slow decreasing trend followed by a rapid increase, while that of rice presented a decreasing trend after an increase. After calibrating the crop coefficient(Kc), the PM–Kc model performed better than the model using the Kc recommended by the Food and Agricultural Organization(FAO). The calibrated key parameters of the R-K model and AA model showed better universality. After calibration, the simulation performance of the PM-Kc model was satisfactory. Both the R-K model and AA model underestimated the daily ET of winter wheat and rice. Compared with that of the R-K model, the simulation result of the AA model was better, especially in the simulation of daily ET of rice. Overall, this research highlighted the consistency of the PM-Kc model to estimate the water demand for rice and wheat crops in the HRB and in similar climatic regions in the world.

Seasonal and Interannual Variations of Carbon Exchange over a Rice–Wheat Rotation System on the North China Plain

Rice-wheat （R-W） rotation systems are ubiquitous in South and East Asia, and play an important role in modulating the carbon cycle and climate. Long-term, continuous flux measurements help in better understanding the seasonal and interannual variation of the carbon budget over R-W rotation systems. In this study, measurements of CO2 fluxes and meteorological variables over an R-W rotation system on the North China Plain from 2007 to 2010 were analyzed. To analyze the abiotic factors regulating Net Ecosystem Exchange （NEE）, NEE was partitioned into gross primary production （GPP） and ecosystem respiration. Nighttime NEE or ecosystem respiration was controlled primarily by soil temperature, while daytime NEE was mainly determined by photosythetically active radiation （PAR）. The responses of nighttime NEE to soil temperature and daytime NEE to light were closely associated with crop development and photosynthetic activity, respectively. Moreover, the interannual variation in GPP and NEE mainly depended on precipitation and PAR. Overall, NEE was negative on the annual scale and the rotation system behaved as a carbon sink of 982 g C m 2 per year over the three years. The winter wheat field took up more CO2 than the rice paddy during the longer growing season, while the daily NEE for wheat and rice were -2.35 and -3.96 g C m-2, respectively. After the grain harvest was subtracted from the NEE, the winter wheat field became a moderately strong carbon sink of 251-334 g C m-2 per season, whereas the rice paddy switched to a weak carbon sink of 107-132 per season.

Identification of radiation treatment of wheat (Triticum aestivum.L) and rice (Oryza sativa.L) samples using thermoluminescence of contaminating minerals

Food irradiation is gaining popularity worldwide and this technology is important to improve quality and reduce the post harvest losses of food.Because of the rapid commercialization of irradiated foods throughout the world,compliance of different regulations relating to use of technology in different countries and demand of consum- ers for clear labelling of irradiated foods,there is need for the development of analytical methods to detect radiation treatment of food.Among several methods studied so far,thermoluminescence (TL) is an important method that can be used to find out the irradiation history of food that contain even a very minute amount of dust particles.In this study,the irradiated and unirradiated wheat and rice samples were analyzed using the TL method.The samples were purchased from the local market of Peshawar and irradiated to radiation doses of 0.5 and 1.0 kGy using Co-60 gamma irradiator at the Nuclear Institute for Food and Agriculture (NIFA),Peshawar.The mineral contaminants were isolated by jet water,ultrasonic treatment,and density gradient.TL glow curves of the isolated minerals from irradiated and unirradiated samples were recorded between the temperature ranges of 50—500℃using a TL reader.Generally,the glow curves for irradiated samples showed much higher TL intensities (TL_1) than the unirradiated samples.The results were normalized by re-irradiation of mineral samples to gamma-ray dose of 1.0 kGy followed by determination of the second glow curves (TL_2).The ratio of the area of first glow curve to that of second glow curve (TL_1/TL_2) was calcu- lated for selected temperature intervals and compared with the recommended values for unirradiated and irradiated samples.Finally,the shapes of the glow curves for irradiated and unirradiated samples were also analyzed.On the ba- sis of these results (comparison of TL-intensities,TL_1/TL_2 ratios and shapes of the glow curves),all the irradiated and unirradiated samples of wheat and rice were unequivocally identified.

Experiences and Research Perspectives on Sustainable Development of Rice-Wheat Cropping Systems in the Chengdu Plain, China

The rice and wheat cropping pattern is one of the main cropping systems in the world. A large number of research results showed that successive cropping of rice and wheat resulted in a series of problems such as hindering nutrition absorption, gradual degeneration of soil fertility, decline of soil organic matter, and increased incidence of diseases and pests. In China, especially in the Chengdu plain where rice-wheat cropping system is practiced, productivity and soil fertility was enhanced and sustained. This paper reviews the relevant data and experiences on rice-wheat cropping in the Chengdu Plain from 1977 to 2006. The principal sustainable strategies used for rice-wheat cropping systems in Chengdu Plain included： 1） creating a favorable environment and viable rotations; 2） balanced fertilization for maintenance of sustainable soil productivity; 3） improvement of crop management for higher efficiency; and 4） use the newest cultivars and cultivation techniques to upgrade the production level. Future research is also discussed in the paper as： 1） the constant topic： a highly productive and efficient rice-wheat cropping system for sustainable growth; 2） the future trend： simplified cultivation techniques for the rice-wheat cropping system; 3） the foundation： basic research for continuous innovation needed for intensive cropping. It is concluded that in the rice-wheat cropping system, a scientific and reasonable tillage/cultivation method can not only avoid the degradation of soil productivity, but also maintain sustainable growth in the long run.

Effects of Crown Ether on Some Physiological Properties and Economic Characteristics of Spikes of Wheat and Panicles of Rice

The seeds of wheat and the young roots of rice were treated with SU15-C-5 and B15-C-5.The effects of crown ether on economic characters of the spike and some physiological properties in both crops were studied.The results showed that crown ethers could promote the growth of wheat seedling, improve the contents of chlorophyll (a+b), reduce the ratio of chlorophyll a to b in the leaves of rice,thus bring about good effects of economic characters of the spike. Especially, it suggests that SU15-C-5 showed better physiological effects than B15-C-5.

Improving the Nutritional Values of Wheat and Rice Crackers by Using Cauliflowers

The present study described the enhancement of the nutritional values of wheat and rice crackers by adding cauliflowers. The results showed that 25% - 75% cauliflower replaced in crackers increased the consumer acceptability, nutritional value, antioxidant activity, minerals, and anti-carcinogenic effect. Moreover, it also improved the functional properties and sensory quality. The results revealed that the raw samples of cauliflower recorded the highest value of moisture, ash, protein and fiber 89.29%, 7.68%, 19.04% and 10.18% on dry weight, respectively. The crackers formula of cauliflower: wheat 75%:25% and cauliflower: rice 75%:25% recorded the highest values in ash, protein, fat, and fiber. The data showed that increasing cauliflower percentage in crackers formula causing a parallel increase in all determined chemical composition. Cauliflower samples exhibited the highest antioxidant activity (92.94%). Also, crackers samples of cauliflower: wheat 75%:25% crackers, recorded 57.6% for antioxidant activity. The highest values of phenols and flavonoids for cauliflower cracker samples (cauliflower: wheat 75%:25% and cauliflower: rice 50%:50%) have increased up to (5.75 and 5.49) respectively. The results showed that the higher mineral content is the sulfur (635.96 mg/100g) in raw cauliflower, while (1.00 mg/100g, and 0.99 mg/100g sulfur content) in wheat and rice respectively. Moreover, the result found that as the cauliflower percentage increases, the minerals contents especially sulfur increase. Furthermore, the cauliflower displayed moderate activity for human hepatocellular carcinoma, colon cancer and intestinal epithelial barrier treatment, (IC50 = 183.4 ± 6.8, 175.8 ± 7.1 and 207.2 ± 8.5 μg/mL, respectively). There were significant differences in the taste property;the highest degree of acceptance of the taste was obtained to crackers samples which were replaced with cauliflower more than the control.

Raised bed planting promotes grain number per spike in wheat grown after rice by improving spike differentiation and enhancing photosynthetic capacity

The yield of wheat in wheat–rice rotation cropping systems in the Yangtze River Plain, China, is adversely impacted by waterlogging. A raised bed planting(RBP) pattern may reduce waterlogging and increase the wheat yield after rice cultivation by improving the grain number per spike. However, the physiological basis for grain formation under RBP conditions remains poorly understood. The present study was performed over two growing seasons(2018/2019and 2019/2020) to examine the effects of the planting pattern(i.e., RBP and flat planting(FP)) on the floret and grain formation features and leaf photosynthetic source characteristics of wheat. The results indicated that implementation of the RBP pattern improved the soil–plant nitrogen(N) supply during floret development, which facilitated balanced floret development, resulting in a 9.5% increase in the number of fertile florets per spike. Moreover, the RBP pattern delayed wheat leaf senescence and increased the photosynthetic source capacity by 13.9%, which produced more assimilates for grain filling. Delayed leaf senescence was attributed to the resultant high leaf N content and enhanced antioxidant metabolism. Correspondingly, under RBP conditions, 7.6–8.6% more grains per spike were recorded, and the grain yield was ultimately enhanced by 10.4–12.7%. These results demonstrate that the improvement of the spike differentiation process and the enhancement of the leaf photosynthetic capacity were the main reasons for the increased grain number per spike of wheat under the RBP pattern, and additional improvements in this technique should be achievable through further investigation.

Influence of Mechanical Grinding on the Interface Characteristics of Rice/Wheat Straws

The mechanical grinding method was used to make rice and wheat straw flakes and the properties of the interface of straws before and after grinding were evaluated. The particle boards were prepared using two kinds of straw flakes, respectively and their physical and mechanical properties were investigated. The results showed that the rice straw was easier to be broken when compared with wheat straw and the inner surface of cells in grinded straws was exposed remarkably. The characteristic peaks of lignin and cellulose on the surface of wheat straw were more significant than rice straw. The free-radical concentrations of straws were increased dramatically after being grinded with heating in the range from I00 ~C to 200 ~C. The surface free energy of straws was also improved after being grinded and the value in wheat straw was higher than that of rice straw, which implies that wheat straw was easier to be bonded than rice straw. The physical and mechanical properties of two kinds of straw particle boards could achieve the requirements of Chinese National Standards of GB 4897.3-2003, while wheat straw particle boards had better properties than those made from rice straws.

Study on Environmental and Economic Benefits of Rice and Wheat Rotation with Swine Manure-Straw Returning

[Objective] The aim was to investigate the application effect of swine manure-straw returning and to determine the best mode. [Method] A field experiment under rice and wheat rotation with different swine manure-straw treatments was con- ducted to study the growth characters and output of rice and wheat, calculate the economic benefit and carbon dioxide emission reduction, and analyze the best mode of swine manure applying-straw returning. [Result] The swine manure-straw returning was conducive to the growth of crop, the highest outputs of rice and wheat were on the treatment of ＂30% swine manure and 20% straw and 50% chemical fertiliz- er＂, they were 7 874.57 and 6 427.00 kg/hm^2, and saved cost about 5 146.35 Yuan/hm^2, increased input 5 312.56 and 3 931.93 Yuan/hm^2, the greenhouse gas e- mission reduction was 1.30 t/hm^2 （calculated according to carbon dioxide on a dry basis）. [Conclusion] The treatment of ＂30% swine manure and 20% straw and 50% chemical fertilizer＂ was the best mode of swine manure-straw returning.

Fertilization and Soil Ploughing Practices under Changing Physical Environment Lead to Soil Organic Carbon Dynamics under Conservation Agriculture in Rice-Wheat Cropping System: A Scoping Review

Ploughing and fertilization practices in rice-wheat system have deteriorated the soil carbon (C) pools. Conservation agriculture (CA) based management approaches have proven to enhance C sequestration and reverse the loss of soil-organic-carbon (SOC), which further enhances soil fertility. Different fractions of SOC pools react to the alterations in management practices and indicate changes in SOC dynamics as compared to total C in the soil. Higher SOC levels in soil have been observed in case of reduced/no-till (NT) practices than conventional tillage (CT). However, between CT and zero tillage/NT, total SOC stocks diminished with an increase in soil depth, which demonstrated that the benefits of SOC are more pronounced in the topsoil under NT. Soil aggregation provides physical protection to C associated with different-sized particles, thus, the improvement in soil aggregation through CA is an effective way to mitigate soil C loss. Along with less soil disturbance, residual management, suitable crop rotation, rational application of manures and fertilizers, and integrated nutrient management have been found to be effective in not only improving soil C stock but also enhancing the soil health and productivity. Thus, CA can be considered as a potential method in the build-up of SOC of soil in rice-wheat system.

Common Spectral Bands and Optimum Vegetation Indices for Monitoring Leaf Nitrogen Accumulation in Rice and Wheat

Real-time monitoring of nitrogen status in rice and wheat plant is of significant importance for nitrogen diagnosis, fertilization recommendation, and productivity prediction. With 11 field experiments involving different cultivars, nitrogen rates, and water regimes, time-course measurements were taken of canopy hyperspeetral reflectance between 350-2 500 nm and leaf nitrogen accumulation （LNA） in rice and wheat. A new spectral analysis method through the consideration of characteristics of canopy components and plant growth status varied with phenological growth stages was designed to explore the common central bands in rice and wheat. Comprehensive analyses were made on the quantitative relationships of LNA to soil adjusted vegetation index （SAVI） and ratio vegetation index （RVI） composed of any two bands between 350-2 500 nm in rice and wheat. The results showed that the ranges of indicative spectral reflectance were largely located in 770-913 and 729-742 nm in both rice and wheat. The optimum spectral vegetation index for estimating LNA was SAVI （R822, R738） during the early-mid period （from jointing to booting）, and it was RVI （Rs22, R73s） during the mid-late period （from heading to filling） with the common central bands of 822 and 738 nm in rice and wheat. Comparison of the present spectral vegetation indices with previously reported vegetation indices gave a satisfactory performance in estimating LNA. It is concluded that the spectral bands of 822 and 738 nm can be used as common reflectance indicators for monitoring leaf nitrogen accumulation in rice and wheat.

The Possible Effect of Climate Warming on Northern Limits of Cropping System and Crop Yield in China

Significantly increasing temperature since the 1980s in China has become a consensus under the background of global climate change and how climate change affects agriculture or even cropping systems has attracted more and more attention from Chinese government and scientists. In this study, the possible effects of climate warming on the national northern limits of cropping systems, the northern limits of winter wheat and double rice, and the stable-yield northern limits of rainfed winter wheat-summer maize rotation in China from 1981 to 2007 were analyzed. Also, the possible change of crop yield caused by planting limits displacement during the periods 1950s-1981 and 1981-2007 was compared and discussed. The recognized calculation methods of agricultural climatic indices were employed. According to the indices of climatic regionalization for cropping systems, the national northern limits of cropping systems, winter wheat and double rice, and the stable-yield northern limits of rainfed winter wheat-summer maize rotation during two periods, including the 1950s-1980 and 1981-2007, were drawn with ArcGIS software. Compared with the situation during the 1950s- 1980, the northern limits of double cropping system during 1981-2007 showed significant spatial displacement in Shaanxi, Shanxi, Hebei, and Liaoning provinces and Beijing municipality, China. The northern limits of triple cropping system showed the maximum spatial displacement in Hunan, Hubei, Anhui, Jiangsu, and Zhejiang provinces, China. Without considering variety change and social economic factors, the per unit area grain yield of main planting patterns would increase about 54-106% if single cropping system was replaced by double cropping system, which turned out to be 27- 58% if double cropping system was replaced by triple cropping system. In Liaoning, Hebei, Shanxi, Shaanxi, Gansu, and Qinghai provinces, Inner Mongolia and Ningxia autonomous regions, China, the northern limits of winter wheat during 1981-2007 moved northward and expanded westward in different degrees, compared with those during the 1950s-1980. Taking Hebei Province as an example, the northern limits of winter wheat moved northward, and the per unit area grain yield would averagely increase about 25% in the change region if the spring wheat was replaced by winter wheat. In Zhejiang, Anhui, Hubei, and Hunan provinces, China, the planting northern limits of double rice moved northward, and the per unit area grain yield would increase in different degrees only from the perspective of heat resource. The stable- yield northern limits of rainfed winter wheat-summer maize rotation moved southeastward in most regions, which was caused by the decrease of local precipitation in recent years. During the past 50 yr, climate warming made the national northern limits of cropping systems move northward in different degrees, the northern limits of winter wheat and double rice both moved northward, and the cropping system change would cause the increase of per unit area grain yield in the change region. However, the stable-yield northern limits of rainfed winter wheat-summer maize rotation moved southeastward due to the decrease of precipitation.

Spatial variation of technical efficiency of cereal production in China at the farm level

Rice, wheat and maize are the main staple food crops to ensure the food security in China with diversified climate condition, cropping system and environmental and socio-economic factors across provinces. Spatial variation of technical efficiency in farmers' field is helpful to understand the potential to improve farmers' yield given the inputs level and reduce the yield gap. The study is based on a large-scale farm household survey which covered 1 218 rice farmers, 3 566 wheat farmers and 2 111 maize farmers in the main producing areas. The results indicate that rice farmers are with very high technical efficiency level, nearly 0.9 on average, with little room to improve the efficiency of agricultural inputs. Similar results have been found in wheat and maize farmers' fields, although the technical efficiency levels are lower than that of rice farmers while still at a high level with obvious variation across regions. Farmers with higher yield level also achieve better technical efficiency in most locations. Both local environmental and socio-economic factors significantly affect farmers' technical efficiency. In the context of urbanization and economic development, improved and new agricultural technologies need to be prioritized and facilitated to improve cereal yield at farm level.

Carbon Dioxide, Methane, and Nitrous Oxide Emissions from a Rice-Wheat Rotation as Affected by Crop Residue Incorporation and Temperature

Field measurements were made from June 2001 to May 2002 to evaluate the effect of crop residue application and temperature on CO2, CH4, and N2O emissions within an entire rice-wheat rotation season. Rapeseed cake and wheat straw were incorporated into the soil at a rate of 2.25 t hm(-2) when the rice crop was transplanted in June 2001. Compared with the control, the incorporation of rapeseed cake enhanced the emissions of CO2, CH4, and N2O in the rice-growing season by 12.3%, 252.3%, and 17.5%, respectively, while no further effect was held on the emissions of CO2 and N2O in the following wheat-growing season. The incorporation of wheat straw enhanced the emissions of CO2 and CH4 by 7.1% and 249.6%, respectively, but reduced the N2O emission by 18.8% in the rice-growing season. Significant reductions of 17.8% for the CO2 and of 12.9% for the N2O emission were observed in the following wheat-growing season. A positive correlation existed between the emissions of N2O and CO2 (R-2 = 0.445, n = 73,p < 0.001) from the rice-growing season when N2O was emitted. A trade-off relationship between the emissions of CH4 and N2O was found in the rice-growing season. The CH4 emission was significantly correlated with the CO2 emission for the period from rice transplantation to field drainage, but not for the entire rice-growing season. In addition, air temperature was found to regulate the CO2 emissions from the non-waterlogged period over the entire rice-wheat rotation season and the N2O emissions from the nonwaterlogged period of the rice-growing season, which can be quantitatively described by an exponential function. The temperature coefficient (Q(10)) was then evaluated to be 2.3+/-0.2 for the CO2 emission and 3.9+/-0.4 for the N2O emission, respectively.

Integrated pest management programme for cereal blast fungus Magnaporthe oryzae

Magnaporthe oryzae,the causal agent of blast diseases,is a destructive filamentous fungus that infects many plants including most economically important food crops,rice,wheat,pearl millet and finger millet.Magnaporthe oryzae has numerous pathotypes because of its high host-specificity in the field.The Oryza pathotype(MoO)of M.oryzae is the most devastating pathogen of rice,causing 10–30%yield loss in the world.On the other hand,the Triticum pathotype(MoT)causes blast disease in wheat,which is now a serious threat to wheat production in some South American countries,Bangladesh and Zambia.Because of low fungicide efficacy against the blast diseases and lack of availability of resistant varieties,control of rice and wheat blast diseases is difficult.Therefore,an integrated management programme should be adopted to control these two diseases in the field.Here,we introduced and summarized the classification,geographical distribution,host range,disease symptoms,biology and ecology,economic impact,and integrated pest management(IPM)programme of both rice and wheat blast diseases.