Assessment of CH_(4) flux and its influencing drivers in the rice-wheat agroecosystem of the Huai River Basin,China

To understand the CH_(4) flux variations and their climatic drivers in the rice-wheat agroecosystem in the Huai River Basin of China,the CH_(4) flux was observed by using open-path eddy covariance at a typical rice-wheat rotation system in Anhui Province,China from November 2019 to October 2021.The variations and their drivers were then analyzed with the Akaike information criterion method.CH_(4) flux showed distinct diurnal variations with single peaks during 9:00-13:00 local time.The highest peak was 2.15μg m^(-2)s^(-1)which occurred at 11:00 in the vegetative growth stage in the rice growing season(RGS).CH_(4) flux also showed significant seasonal variations.The average CH_(4)flux in the vegetative growth stage in the RGS(193.8±74.2 mg m^(-2)d^(-1))was the highest among all growth stages.The annual total CH_(4) flux in the non-rice growing season(3.2 g m^(-2))was relatively small compared to that in the RGS(23.9 g m^(-2)).CH_(4) flux increased significantly with increase in air temperature,soil temperature,and soil water content in both the RGS and the non-RGS,while it decreased significantly with increase in vapor pressure deficit in the RGS.This study provided a comprehensive understanding of the CH_(4) flux and its drivers in the rice-wheat rotation agroecosystem in the Huai River Basin of China.In addition,our findings will be helpful for the validation and adjustment of the CH_(4) models in this region.

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.

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.

A Field Study on Effects of Nitrogen Fertilization Modes on Nutrient Uptake,Crop Yield and Soil Biological Properties in Rice-Wheat Rotation System

Rational application of nitrogen （N） fertilizers is an important measure to raise N fertilizer recovery rate and reduce N loss.A two-year field experiment of rice-wheat rotation was employed to study the effects of N fertilization modes including a N fertilizer reduction and an organic manure replacement on crop yield,nutrient uptake,soil enzyme activity,and number of microbes as well as diversity of microbes.The result showed that 20% reduction of traditional N fertilizer dose of local farmers did not significantly change crop yield,N uptake,soil enzyme activity,and the number of microbes （bacteria,actinomycetes,and fungi）.On the basis of 20% reduction of N fertilizer,50% replacement of N fertilizer by organic manure increased the activity of sucrose,protease,urease,and phosphatase by 46-62,27-89,33-46,and 35-74%,respectively,and the number of microbes,i.e.,bacteria,actinomycetes,and fungi by 36-150,11-153,and 43-56%,respectively.Further,organic fertilizer replacement had a Shannon＇s diversity index （H） of 2.18,which was higher than that of other modes of single N fertilizer application.The results suggested that reducing N fertilizer by 20% and applying organic manure in the experimental areas could effectively lower the production costs and significantly improve soil fertility and biological properties.

Application of Micronutrients in Rice-Wheat Cropping System of South Asia

Rice-wheat cropping system (RWCS) is one of the most important cropping systems in South Asia. However, sustainability of this system is under threat owing to several factors, of which deficiency of micronutrients particularly zinc (Zn), boron (B) and manganese (Mn) is one of the major problems. Continuous rotation of rice and wheat, imbalanced fertilizer use and little/no use of micronutrient-enriched fertilizers induce deficiencies of Zn, B and Mn in the RWCS of South Asia. Here we review that (i) imbalanced fertilizer use and organic matter depletion deteriorate soil structure resulting in low efficiency of applied macro- and micro-nutrients in RWCS.(ii) The micronutrients (Zn, B and Mn) are essentially involved in metabolism of rice and wheat plants, including chlorophyll synthesis, photosynthesis, enzyme activation and membrane integrity.(iii) Availability and uptake of Zn, B and Mn from rhizosphere depend on the physico-chemical soil properties (which differ under aerobic and anaerobic conditions) including soil pH, soil organic matter, soil moisture and interaction of these micronutrients with other nutrients.(iv) Plant ability to uptake and utilize the nutrients is affected by several plant factors such as root architecture, root hairs, transport kinetics parameter and root exudates.(v) Crop management and application of these microelements can help correct the micronutrients deficiency and enhance their grain concentration.

Low N apparent surplus with higher rice yield under long-term fertilizer postponing in the rice-wheat cropping system

Nitrogen(N)fertilization increases rice yield,but inappropriate N fertilizer application increases N loss and the risk of environmental pollution.Short-term fertilizer postponing(FP)generally reduces N apparent surplus and increases rice yields,but the effects of long-term FP on N surplus and rice yields remain unknown.Our study was the first to investigate the impacts of long-term FP(11 years)on N apparent surplus and rice yields.FP effects in the short term(≤6 years)did not affect rice yields,whereas FP effects in the long term(>6 years)increased rice yields by 13.9%compared with conventional fertilization(CF).FP did not affect panicles per unit area,1000-kernel weight,and filled-kernel rate,but spikelets per panicle increased over time due to spikelet formation stimulation.FP also reduced the N apparent surplus over time more strongly than CF owing to higher N accumulation and N utilization efficiency.FP effects in the long term also significantly increased soil organic matter,total N,and NH4_(+)^(-)N content.Our results were supported by a pot experiment,showing that rice yields in soils with a history of FP were significantly higher than those for soils without a history of FP,indicating that FP increased rice yields more strongly in later years mainly because of soil quality improvement.Our findings suggest that longterm FP can reduce N loss while increasing rice yields by improving soil quality.

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.

Mechanized Transplanting of Rice(Oryza sativa L.)in Nonpuddled and No-Till Conditions in the Rice-Wheat Cropping System in Haryana,India

The common practice of establishing rice in the rice-wheat system in India is manual transplanting of seedlings in the puddled soil. Besides being costly, cumbersome, and time consuming, puddling results in degradation of soil and the formation of a hard pan, which impedes root growth of subsequent upland crops. In addition, decreased availability and increasing cost of labor have increased the cost of rice cultivation through conventional methods. Because of these concerns, there is a need for mechanized transplanting of rice which is less labor-intensive and can ensure optimum plant population under nonpuddled and/or no-till conditions. A large number of on-farm trials were conducted at farmers’ fields in Haryana, India, from 2006 to 2010 to evaluate the performance of the mechanical transplanted rice (MTR) under nonpuddled and no-till situations as compared to conventional puddled transplant rice (CPTR). Compared with CPTR, nonpuddled MTR produced 3%-11% higher grain yield in different years. Rice cultivars, viz. HKR47, HKR127, PR113, PR114, PB1, PB1121, CSR30, and Arize6129, performed consistently better under nonpuddled MTR as compared to CPTR. Performance of different cultivars (PR113, PR114, HKR47, and Pusa 44) was also better under no-till MTR as compared to CPTR. The “basmati” cultivar CSR30 performed equally in no-till MTR and CPTR systems. The results of our study suggest that rice can be easily grown under nonpuddled and no-till conditions with yield advantages over the CPTR system. Even in the case of similar yield between CPTR and MTR systems, the MTR system will help in reducing labor requirement and ultimately, will increase overall profits to farmers.

Yield Gap Analysis of Wheat in Rice-wheat Rotation Regions of Anhui Province,China

The present study was planned to analyze the yield gap of wheat and its production constraints in order to explore the approaches for narrowing the yield gap of wheat in different wheat-rice rotation regions of Anhui Province. The production status and limiting factors of wheat in three rice-wheat rotation regions which are named Region Ⅰ,Region Ⅱ and Region Ⅲ were surveyed by using participatory rural appraisal method. The personnel,who were engaged in wheat production in rice-wheat rotation regions of Anhui Province,mainly ageing from 41 to 60,accounted for 79% of the total personnel in the regions. There were significant differences in yield of wheat which was planted after rice in Anhui. The yield was ranging from 8 907. 00 to 2 700. 00 kg/ha from north to south with an average of 4 978. 5 kg/ha,and the rank of overall average yields at province level was Region Ⅰ( 5 685. 60 kg/ha) > Region Ⅱ( 5 600. 10 kg/ha) > Region Ⅲ( 3 048. 60 kg/ha). The average yield gap of wheat in wheat-rice rotation regions at province level was up to 2 637. 00 kg/ha,and the extreme yield gaps per hectare in the same region were 2 778. 00 kg( Region Ⅰ),2 502. 00 kg( Region Ⅱ) and 1 575. 00 kg( Region Ⅲ) respectively. The objective constraints were Fusarium head blight and pre-harvest sprouting;the subjective constraints were variety selection and layout,poor sowing quality and low seedling quality;social constraints were high cost,low market price and poor efficiency;and ecological constraints were poor soil texture,soil infertility and poor water-and-fertilizer retention. The yield gap of wheat in rice-wheat rotation regions can be effectively reduced by improving yield potential of low-and-medium-yielding fields. Selecting appropriate wheat varieties and layout,constructing disease forecast system,improving agricultural machinery and social service organizations of plant protection,and strengthening scientific training as well as technological training of new agricultural operators and agricultural machinery technicians are the core means to narrowing the yield gap of wheat in rice-wheat rotation regions at province scale.

Responses of Wheat Production, Quality, and Soil Profile Properties to Biochar Applied at Different Seasons in a Rice-Wheat Rotation

In the rice-wheat rotation system,biochar(BC)can be applied at the initiation of the rice or wheat season.Here,we compared the effects of BC that were applied at two different crop seasons on wheat production,quality,and soil profile properties in a rice-wheat rotation system with nitrogen(N)fertilizer applied at 280 kg/ha rate.Results showed that both wheat grain production and N recovery use efficiency were influenced by BC applied at two crop seasons.Biochar application did not affect the total non-essential amino-acid,but when applied during wheat season,BC significantly(p<0.05)increased total essential amino acid in grain by 12.3%,particularly for the valine(+48.2%),methionine(+43.8%),and isoleucine(+10.3%).We found that BC significantly(p<0.05)decreased the pH of soil at 0–6 cm and 20–30 cm by 0.14–0.18 and 0.05–0.08 units,respectively.The NH4+-N content of the whole observed soil profile were reduced by BC application,however,the effect of BC on NO3–-N content varied with the application season and profile depth.Interestingly,BC applied at wheat and rice season significantly(p<0.05)improved topsoil N contents by 48.4%and 19.7%,respectively.In addition,data suggested that BC applied during wheat season performed better in enhancing soil available phosphorus,potassium,and organic matter contents.In conclusion,we suggest that the optimum application time of BC for enhancing crop production and quality(take amino-acid content for example)and improving soil fertility is at the initiation of the wheat season.

不同秸秆还田模式对稻麦两熟农田稻季甲烷和氧化亚氮排放的影响

为了探讨不同秸秆还田模式下稻麦两熟农田稻季甲烷(CH4)和氧化亚氮(N2O)的排放规律,为评估该地区温室气体排放量与发展循环农业提供依据,在江苏省苏州市稻麦两熟农田进行了6年的田间定位试验,采用静态箱-气相色谱法开展了不同秸秆还田模式下水稻生长季田间甲烷和氧化亚氮排放监测试验,研究设计了稻麦季秸秆均不还田(CK)、麦季稻秸还田(R)、稻季麦秸还田(W)和稻麦季秸秆均还田(RW)4种秸秆还田模式。结果表明:不同秸秆还田模式对稻季CH4和N2O排放、总增温潜势(GWP)及单位产量的GWP有极显著影响,CH4稻季总排放量表现为RW(233.04 kg/hm2)>W(197.99 kg/hm2)>R(122.14 kg/hm2)>CK(97.07 kg/hm2),N2O稻季总排放量的顺序是R>W>RW>CK,依次为4.74 kg/hm2、2.66 kg/hm2、2.14 kg/hm2和1.07 kg/hm2。RW处理水稻产量(10.54 t/hm2)和R处理(10.36 t/hm2)较秸秆不还田对照显著增产,而秸秆还田处理(R、W和RW)的GWP以及单位产量的GWP均显著高于秸秆不还田对照。说明,秸秆还田增加了稻季CH4和N2O排放,小麦秸秆还田是增加稻季CH4排放的重要原因。

Environmental Effects of Returning Rice and Wheat Straw to Fields

Based on advances in returning rice and wheat straw to fields at home and abroad, environmental physical, chemical and ecological effects of returning rice and wheat straw to fields were analyzed. The results show that returning straw to fields can enhance soil porosity, reduce soil bulk density, and increase the ca- pacity of soil to preserve water, fertilizer and temperature. Besides, it can improve the content of organic matter, nitrogen, phosphorus and potassium in soil, of which the increase of potassium content is the most obvious. Meanwhile, it can provide energy and nutrients for microorganisms in soil and change the activity of soil enzymes, of which it affects invertase most greatly and enhances the activity of ure- ase but has no effect on neutral phosphatase. In addition, it can enhance the total quantity of microorganisms in soil obviously, and the increase correlates positively with the quantity of straw returning to fields. Finally, returning straw to fields can promote the sustainable development of agriculture.

Tillage, crop residue, and nutrient management effects on.soil organic carbon in rice-based cropping systems： A review

Soil organic carbon （SOC） sequestration is one of the major agricultural strategies to mitigate greenhouse gas （GHG） emissions, enhance food security, and improve agricultural sustainability. This paper synthesizes the much-needed state- of-knowledge on the effects of tillage, crop residue, and nutrient management practices on SOC sequestration and identifies potential research gap, opportunities, and challenges in studying SOC dynamics in rice （Oryza sativa L.）-based cropping systems in South Asia, mainly in Bangladesh, Bhutan, India, Nepal, Pakistan, and Sri Lanka. Improved management prac- tices such as reduced- and no-tillage management, nitrogen （N） fertilizer and farmyard manure （FYM） application, and crop residue addition can improve SOC accumulation. Positive effects of no-tillage, crop residue addition, N addition through manure or compost application, and integration of organic and chemical fertilizers on SOC accumulation in rice-based cropping systems have been documented from South Asia. However, limited data and enormous discrepancies in SOC measurements across the region exist as the greatest challenge in increasing SOC sequestration and improving agricultural sustainability. More research on SOC as influenced by alternative tillage, crop residue, and nutrient management systems, and development of SOC monitoring system for existing long-term experiments will advance our understanding of the SOC dynamics in rice-based cropping systems and improve agricultural system sustainability in South Asia.

Composition of Wheat Rhizosphere Antagonistic Bacteria and Wheat Sharp Eyespot as Affected by Rice Straw Mulching

To assess the effect of rice straw mulching on changes of antagonistic bacteria and the incidence of wheat sharp eyespot, a multi-year field study was performed to compare unmulched plots and the plots mulched with rice straw for two or three years. Bacterial and fungal populations were evaluated in the cultures prepared from the wheat rhizosphere and bulk soils. Rice straw mulching increased the number of pseudomonas colony forming units in wheat rhizosphere and bulk soils. The proportion of total bacteria that were fluorescent pseudomonads was higher in mulched than in unmulched soil. Bacterial isolates antagonistic to Rhizoctonia cerealis were identified using an inhibition zone test. A series of these isolates were typed by partial sequencing of the 16S rRNA gene. Pseudomonads had higher antagonistic activity against R. cerealis than other species, and more than 80% of rhizosphere fluorescent pseudomonads were antagonistic to R. eerealis. The disease indices were lower in the mulched plots than in the unmulched control. These results suggest that rice straw mulching in a rice-wheat rotation increases the number of fluorescent pseudomonads. Additionally, these fluorescent pseudomonads may contribute to the control of wheat sharp eyespot.

Effects of Land Management Practices on Labile Organic Carbon Fractions in Rice Cultivation

A research trial with four land management practices, i.e., traditional tillage-fallow (TTF), traditional tillage-wheat (TTW), conservation tillage-fallow (CTF) and conservation tillage-wheat (CTW), was sampled in the 15th year after its establishment to assess the effects of different management practices on labile organic carbon fractions (LOCFs), such as easily oxidizable organic carbon (EOC), dissolved organic carbon (DOC), particulate organic carbon (POC) and microbial biomass carbon (MBC) in a typical paddy soil, Chongqing, Southwest China. The results indicated that LOCFs were significantly influenced by the combination of no-tillage, ridge culture and crop rotation. And, different combination patterns showed different effectiveness on soil LOCFs. The effects of no-tillage, ridge culture and wheat cultivation on EOC, DOC, POC and MBC mainly happened at 0-10cm. At this depth, soil under CTW had higher EOC, DOC, POC and MBC contents, compared to TTF, TTW and CTF, respectively. Moreover, the contents of LOCFs for different practices generally decreased when the soil depth increased. Our findings suggest that the paddy soil in Southwest China could be managed to concentrate greater quantities of EOC, DOC, POC and MBC.

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.

Long-term straw incorporation increases rice yield stability under high fertilization level conditions in the rice–wheat system

Straw incorporation is a global common practice to improve soil fertility and rice yield.However,the effect of straw incorporation on rice yield stability is still unknown,especially under high fertilization level conditions.Here,we reported the effect of straw returning on rice yield and yield stability under high fertilization levels in the rice–wheat system over nine years.The results showed that straw incorporation did not significantly affect the average rice yield of nine years.Straw incorporation reduced the coefficient of variation of rice yield by 25.8%and increased the sustainable yield index by 8.2%.The rice yield positively correlated with mean photosynthetically active radiation (PAR) of rice growth season and the effects of straw incorporation on rice yield depended on the PAR.Straw incorporation increased the rice yield by 5.4%in the low PAR years,whereas it did not affect the rice yield in the high PAR years.Long-term straw incorporation lowered soil bulk density but improved the soil organic matter,total N,available N,available P,and available K more strongly than straw removal.Our findings suggest that straw incorporation can increase rice yield stability through improving the resistance of rice plant growth to low PAR.

Effects of long-term straw incorporation on nematode community composition and metabolic footprint in a rice–wheat cropping system

Soil nematode communities can provide valuable information about the structure and functions of soil food webs,and are sensitive to agricultural practices,including short-term straw incorporation.However,currently,such effects under longterm straw incorporation conditions at different fertility levels are largely unknown.Thus,we conducted a 13-year ongoing experiment to evaluate the effects of long-term straw incorporation on the structure and functions of the soil food web in low and high fertility soils through analyzing its effects on nematode communities,food web indices and metabolic footprints.Four treatments were included:straw removal(–S)under non-fertilized(–NPK)or fertilized(+NPK)conditions;and straw incorporation(+S)under–NPK or+NPK conditions.Soil samples from a 0–20 cm depth layer were collected when wheat and rice were harvested.Compared with straw removal,straw incorporation increased the abundances of total nematodes,bacterivores,plant-parasites and omnivores-predators,as well the relative abundances of omnivores-predators with increases of 73.06,89.29,95.31,238.98,and 114.61%in–NPK soils and 16.23,2.23,19.01,141.38,and 90.23%in+NPK soils,respectively.Regardless of sampling times and fertilization effects,straw incorporation increased the diversity and community stability of nematodes,as indicated by the Shannon-Weaver diversity index and maturity index.Enrichment and structure index did not show significant responses to straw incorporation,but a slight increase was observed in the structure index.The analysis of nematode metabolic footprints showed that straw incorporation increased the plant-parasite footprint and structure footprint by 97.27 and 305.39%in–NPK soils and by 11.29 and 149.56%in+NPK soils,but did not significantly influence enrichment,bacterivore and fungivore footprints.In conclusion,long-term straw incorporation,particularly under a low fertility level,favored the soil nematodes and regulated the soil food web mainly via a top-down effect.

A Process-based Model of N_2O Emission from a Rice-Winter Wheat Rotation Agro-Ecosystem:Structure,Validation and Sensitivity

In order to numerically simulate daily nitrous oxide （N2O） emission from a rice-winter wheat rotation cropping system, a process-based site model was developed （referred to as IAP-N-GAS） to track the movement and transformation of several forms of nitrogen in the agro-eeosystem, which is affected by climate, soil, crop growth and management practices. The simulation of daily N2O fluxes, along with key daily environmental variables, was validated with three-year observations conducted in East China. The validation demonstrated that the model simulated well daily solar radiation, soil temperature and moisture, and also captured the dynamics and magnitude of accumulated rice aboveground biomass and mineral nitrogen in the soil. The simulated daily N2O emissions over all three years investigated were generally in good agreement with field observations. Particularly well simulated were the peak N2O emissions induced by fertilizations, rainfall events or mid-season drainages. The model simulation also represented closely the inter-annuM variation in N2O emission. These validations imply that the model has the capability to capture the general characteristics of N2O emission from a typical rice-wheat rotation agro-ecosystem. Sensitivity analyses revealed that the simulated N2O emission is most sensitive to the fertilizer application rate and the soil organic matter content, but it is much less sensitive to variations in soil pH and texture, temperature, precipitation and crop residue incorporation rate under local conditions.

Field experimental study on optimal design of the rotary strip-till tools applied in rice-wheat rotation cropping system

The rice-wheat rotation system plays a significant role in Asian agriculture.The introduction of strip-tillage into the rice-wheat system for wheat planting offers a way to use conservation tillage practices to improve the seedbed quality,retain residue between rows and reduce energy input.A field experiment was conducted using an in-situ test rig.Three types of blade(bent C,straight and hoe)were evaluated in four tool configurations at four rotary speeds(180 r/min,280 r/min,380 r/min and 510 r/min)in a paddy soil.Furrow shape parameters,tillage-induced soil structures and energy consumption were assessed.Results showed that the straight blade configuration failed to create a continuous furrow at either 180 r/min or 510 r/min.The bent C blade configuration produced a uniform furrow profile but its furrow backfill was poor and unsuitable for seeding.The hoe blade configuration cut a continuous furrow and better tillage-induced soil structure,but it produced a much wider and non-uniform furrow shape.The mixed blade configuration(central hoe blades with two straight blades aside)provided a uniform furrow with good backfill and fine tilth by utilizing both the cutting effect of straight blades on the furrow boundaries and tensile fracturing of the furrow soil by the hoe blades.The torque of the mixed blade configuration was comparable with the bent C blade but was less than the hoe blades.Hence,a mixed blade configuration was recommended for rotary strip-tillage seeding using in rice-wheat system.