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.

Transport of Heavy Metals between Soil and Rice in the Jiulong River River Basin

Diet is one of the main pathways for heavy metals to enter the human body,so studying the content of heavy metals in agricultural products and evaluating them is of great significance.When farmland soil is contaminated with heavy metals,the heavy metals accumulated in the soil will be absorbed by the roots of rice plants growing on it,and will migrate and transform between different tissues and organs of rice plants.There is a significant correlation between heavy metal pollution in soil and the content of heavy metals in rice.The migration and enrichment of heavy metals in the agricultural soil rice system is a complex process that is influenced by many factors,such as the physical and chemical properties of the soil,the content and occurrence forms of heavy metals in the soil,and the physiological characteristics of rice plants.In actual field environments,these influencing factors have significant spatial differences and are relatively complex.Therefore,it is necessary to conduct practical analysis of the various influencing factors in actual field environments.Based on actual data analysis,studying the heavy metal content in rice and the characteristics of heavy metal accumulation and migration in rice plants is of great significance for improving the food safety of rice.

Substitution of chemical fertilizer by Chinese milk vetch improves the sustainability of yield and accumulation of soil organic carbon in a double-rice cropping system

The double-rice cropping system is a very important intensive cropping system for food security in China. There have been few studies of the sustainability of yield and accumulation of soil organic carbon (SOC) in the double-rice cropping system following a partial substitution of chemical fertilizer by Chinese milk vetch (Mv). We conducted a 10-year (2008–2017) field experiment in Nan County, South-Central China, to examine the double-rice productivity and SOC accumulation in a paddy soil in response to different fertilization levels and Mv application (22.5 Mg ha^–1). Fertilizer and Mv were applied both individually and in combination (sole chemical fertilizers, Mv plus 100, 80, 60, 40, and 0% of the recommended dose of chemical fertilizers, labeled as F100, MF100, MF80, MF60, MF40, and MF0, respectively). It was found that the grain yields of double-rice crop in treatments receiving Mv were reduced when the dose of chemical fertilizer was reduced, while the change in SOC stock displayed a double peak curve. The MF100 produced the highest double-rice yield and SOC stock, with the value higher by 13.5 and 26.8% than that in the F100. However, the grain yields increased in the MF80 (by 8.4% compared to the F100), while the SOC stock only increased by 8.4%. Analogous to the change of grain yield, the sustainable yield index (SYI) of double rice were improved significantly in the MF100 and MF80 compared to the F100, while there was a slight increase in the MF60 and MF40. After a certain amount of Mv input (22.5 Mg ha^–1), the carbon sequestration rate was affected by the nutrient input due to the stimulation of microbial biomass. Compared with the MF0, the MF100 and MF40 resulted in a dramatically higher carbon sequestration rate (with the value higher by 71.6 and 70.1%), whereas the MF80 induced a lower carbon sequestration rate with the value lower by 70.1% compared to the MF0. Based on the above results we suggested that Mv could partially replace chemical fertilizers (e.g., 40–60%) to improve or maintain the productivity and sustainability of the double-rice cropping system in South-Central China.

Growth and Yield of Rice(Oryza sativa L.)Applied by Inorganic and Organic Fertilizer in Indonesian Tidal Soil

The aims of this study were to determine the dose of inorganic fertilizer of NPK combined with organic fertilizer from CM(Cow Manure)to grow paddy Inpara 8 variety planted in a tidal soil.This experiment was done in a green house and conducted from July to December 2020.This pot experiment used factorial completely randomized design with two factors and three replications.The first factor was NPK which consisted of two kinds of NPK fertilizers which were urea 200 kg/ha,SP-36100 kg/ha,KCl 100 kg/ha from recommended fertilization and urea 37 kg/ha,SP-3656 kg/ha,KCl 183 kg/ha from calculation of the specific location soil analysis(in situ data).The second factor was dosage of CM at 5,7.5 and 10 tons/ha respectively.The results showed that NPK fertilization from specific location combined with CM at 10 tons/ha was the best treatment for rice production in an infertile tidal swampland producing 2.20 tons/ha.

Effects of Inorganic-organic Incorporation on Productivity and Soil Fertility of Rice Cropping System in Red Soil Area of China

Results from ten-year (1990 - 1999) field experiments indicated that the productivity and the soil fertility of rice cropping system were significantly influenced by the fertilization system adopted in red soil area of China. Contrasting with no-fertili/er treatment (CK), yield-increase rate of organic matter cycling, chemical NPK and inorganic-organic fertilizer incorporation treatments were 56.5% , 62.5% and 80.7% , respectively. In the case of optimum fertilization system, the largest contribution of inorganic fertilizer to the yield was 38.5% while that of inorganic-organic fertilizer incorporation was 44.7%. The content of soil organic matter changed in tendency from decrease to equilibrium with heightened the extent of N, P and K incorporation while that of inorganic-organic fertilizer incorporation could be enhanced further. After N, P and K entered into the rice cropping system and maintained organic matter cycling in the system, the pools of total N, P and K could be strengthened.

Soil carbon sequestration under long-term rice-based cropping systems of purple soil in Southwest China

Carbon sequestration in agricultural soils is a complex process controlled by farming practices, climate and some other environment factors. Since purple soils are unique in China and used as the main cropland in Sichuan Basin of China, it is of great importance to study and understand the impacts of different fertilizer amendments on soil organic carbon（SOC） changes with time. A research was carried out to investigate the relationship between soil carbon sequestration and organic carbon input as affected by different fertilizer treatments at two long-term rice-based cropping system experiments set up in early 1980 s. Each experiment consisted of six identical treatments, including（1） no fertilizer（CK）,（2） nitrogen and phosphorus fertilizers（NP）,（3） nitrogen, phosphorus and potassium fertilizers（NPK）,（4） fresh pig manure（M）,（5） nitrogen and phosphorus fertilizers plus manure（MNP）, and（6） nitrogen, phosphorus and potassium fertilizers plus manure（MNPK）. The results showed that annual harvestable carbon biomass was the highest in the treatment of MNPK, followed by MNP and NPK, then M and NP, and the lowest in CK. Most of fertilizer treatments resulted in a significant gain in SOC ranging from 6.48 to 2 9.13% compared with the CK, and raised soil carbon sequestration rate to 0.10–0.53 t ha–1 yr-1. Especially, addition of manure on the basis of mineral fertilizers was very conducive to SOC maintenance in this soil. SOC content and soil carbon sequestration rate under balanced fertilizer treatments（NPK and MNPK） in the calcareous purple soil（Suining） were higher than that in the acid purple soil（Leshan）. But carbon conversion rate at Leshan was 11.00%, almost 1.5 times of that（7.80%） at Suining. Significant linear correlations between soil carbon sequestration and carbon input were observed at both sites, signifying that the purple soil was not carbon-saturated and still had considerable potential to se questrate more carbon.

Modeling Methane Emission from Rice Paddy Soils:Ⅱ.Model Validation and Application

A simulation model developed by the authors (Huang et al., 1999) was validated against independent field measurements of methane emission from rice paddy soils in Texas of USA, Tuzu Of China and Vercelli of Italy.A simplified version of the simulation model was further validated against methane emission measurements from various regions of the world, including italy, China, Indonesia, Philippines and the United States. Model validation suggested that the seasonal variation of methane emission was mainly regulated by rice growth and development and that methane emission could be predicted from rice net productivity, cultivar character, soil texture and temperature, and organic matter amendments. Model simulations in general agreed with the observations. The comparison between computed and measured methane emission resulted in correlation coefficients r2 values from 0.450 to 0.952, significant at 0.01-0.001 probability level.On the basis of available information on rice cultivated area, growth duration, grain yield, soil texture and temperature, methane emission from rice paddy soils of China's Mainland was estimated for 28 rice cultivated provinces/municipal cities by employing the validated model. The calculated daily methane emission rates, on a provincial scale, ranged from 0.12 to 0.71 g m-2 with an average of 0.26 g m-2. A total amount of 7.92 Tg CH4 per year, ranging from 5.89 to 11.17 Tg year-1, was estimated to be released from Chinese rice paddy soils. Of the total, 45% was emitted from the single-rice growing season, and 19% and 36% were from the early-rice and the late-rice growing seasons, respectively. Approximately 70% of the total was emitted in the region located at latitude between 25°and 32°N. The emissions from rice fields in Sichuan and Hunan provinces were calculated to be 2.34 Tg year-1, accounting for approximately 30% of the total.

Influence of Biochar on Nitrogen Use Efficiency and Root Morphology of Rice-Seedling in Two Contrasting Paddy Soils

Biochar may affect the root morphology and nitrogen(N)use efficiency(NUE)of rice at seedling stage,which has not been clearly verified until now.To clarify it,we conducted a pot experiment regarding to two soil types(Hydragric Anthrosol and Haplic Acrisol),two biochar application rates(0.5 wt%and 1.5 wt%)and two rice varieties(common rice var.Xiushui134 and hybrid super rice var.Zhongkejiayou12-6)meanwhile.Seedling NUE of common rice Xiuhui134 was significantly increased(p<0.05)by 78.2%in Hydragric Anthrosol and by 91.4%in Haplic Acrisol following biochar addition with 1.5 wt%.However,biochar addition exerted no influence on seedling NUE of super rice Zhongkejiayou12-6 in both soils.Overall,0.09–0.10 units higher soil pH and 105–116%higher soil NH_(4)^(+)-N were observed in Xiushui134 growing two soils with 1.5 wt%biochar.In addition,improved root morphology(including longer root length,larger root surface area,bigger root volume,and more root tips)contributed to the higher seedling NUE of Xiushui134 in two soils.The soil pH and NH_(4)^(+)-N content,also the root morphology were influenced by biochar,which though could not thoroughly explained the NUE of Zhongkejiayou12-6.In conclusion,biochar application to paddy soil changed soil pH and NH_(4)^(+)-N content,root growth,and the consequent seedling NUE of rice,which effects are relative with rice cultivar,biochar addition rate,and soil type.

Modeling Methane Emission from Rice Paddy Soils:Ⅰ.Model Development

With an understanding of the processes of methane production, oxidation and emission, a semi-empirical model, focused on the contributions of rice plants to the processes and also the influence of environmental factors, was developed to predict methane emission from rice paddy soils. In the present model, the amount of methane transported from the soil to the atmosphere was determined by the rates of CH4 production and an emitted fraction. The rates of CH4 production in irrigated rice soils were computed from the availability of methanogenic substrates that are primarily derived from rice plaaes and added organic matter and the influence of soil texture, soil redox potential and temperature. The fraction of methane emitted was assumed to be modulated by the rice plants and declines with rice growth and development. TO make it applicable to a wider area with limited data sets, a simplified version of the model was also derived to predict methane emission in a more practical manner.

Enhancement of Cd Solubility and Bioavailability Induced by Straw Incorporation in Cd-Polluted Rice Soil

Of the factors affecting migration and bioavailability of toxic metals in heavy metal contaminated soil, DOC （dissolved organic carbon） provides binding sites for metal cations and reduces the fixation and adsorption of heavy metals by soil solid phase. Elevation of DOC level due to the direct incorporation of crop residues may lead to enhanced accumulation of toxic metals in crop body grown in polluted farmland. In this study, an incubation experiment and a pot experiment were conducted respectively to investigate the effects of wheat straw incorporation on DOC level, cadmium availability, and Cd accumulation in rice plant, and to establish the relation between Cd solubility and DOC level. A Cd-contaminated rice soil was used and incorporated with different rates （0%, 0.5% and 1%） of wheat straw in both experiments. Results showed that the change pattern of Cd in soil solution was very similar to that of DOC level. Wheat straw addition significantly elevated Cd and DOC level in soil solution while NH4NO3-extrated Cd was not affected. There existed a close linear correlation between soluble Cd and DOC level. Enhanced Cd accumulation in rice plant, grown in a Cd contaminated soil, induced by wheat straw incorporation was observed in this study.

Characteristics of Channeling Flow in Cultivated Horizon of Saline Rice Soil

By applying bromide ion as tracer, the channeling flow has been quantitatively described in saline rice soil and alkaline soil of Da＇an City, Jilin Province of China. Breakthrough curves of bromide ion in the saline rice soils after 1-year cultivation and 5-year cultivation and alkaline soil have been attained. Results show that the rice cultivation practice can improve the alkaline soil structure, however, it can accelerate the development of channeling flow pathway. Therefore, the channeling flow pathway has been developed widely in saline rice soil, but rarely in the alkaline soil. Three models of convection-dispersion equation （CDE）, transfer functional model （TFM） and Back-Progation Network （BP Network） were used to simulate the transportation process of bromide ion. The peaks of probability density function of saline rice soil are higher with left skewed feature compared with that of the alkaline soil. It shows that the TIM and CDE can simulate the transportation process of the bromide ion in saline rice soil after 5-year cultivation, however, some deviation exists when it was used to simulate transportation process of bromide ion in saline rice soil after 1-year cultivation and alkaline soil; BP network can effectively simulate transportation process of bromide ion in both saline rice soil and alkaline soil.

Effects of Nitrogen Dosage on the Yield and Nitrogen Use Efficiency of Machine Transplanted Rice Using Dry Soil Preparation in Rice Paddy Field

[Objective] The aim was to analyze the effects of nitrogen dosage on the yield and nitrogen use efficiency of machine transplanted rice using the technology of dry soil preparation in rice paddy field. [Method] With conventional Japonica rice cultivar Shengdao 18 as the study material, the effect of nitrogen dosage on stem and tillers dynamics, yield components and nitrogen use efficiency were investigated using the technology of dry soil preparation in rice paddy field. [Result] The highest yield was 10 957.20 kg/hm^2 as the nitrogen application was 315.00 kg/hm^2. Meanwhile, the roughness ratio, grain-straw ratio and nitrogen use efficiency remained at a higher level. Low nitrogen application could not obtain high yield. In contrast, high nitrogen application quantity led to a significant decline in nitrogen use efficiency. [Conclusion] The study could provide a scientific basis for the further promotion of the technology of dry soil preparation in rice paddy field.

Growth, Metabolism and Yield of Rice Cultivated in Soils Amended with Fly Ash and Cyanobacteria and Metal Loads in Plant Parts

Soil amendment with fly ash（FA） and combined supplementation with N_2-fixing cyanobacteria masses as biofertilizer were done in field experiments with rice. Amendments with FA levels, 0, 0.5, 1.0, 2.0, 4.0, 8.0 and 10.0 kg/m2, caused increase in growth and yield of rice up to 8.0 kg/m2, monitored with several parameters. Pigment contents and enzyme activities of leaves were enhanced by FA, with the maximum level of FA at 10.0 kg/m2. Protein content of rice seeds was the highest in plants grown at FA level 4.0 kg/m2. Basic soil properties, p H value, percentage of silt, percentage of clay, water-holding capacity, electrical conductivity, cation exchange capacity, and organic carbon content increased due to the FA amendment. Parallel supplementation of FA amended plots with 1.0 kg/m2 N_2-fixing cyanobacteria mass caused further significant increments of the most soil properties, and rice growth and yield parameters. 1000-grain weight of rice plants grown at FA level 4.0 kg/m2 along with cyanobacteria supplementation was the maximum. Cyanobacteria supplementation caused increase of important basic properties of soil including the total N-content. Estimations of elemental content in soils and plant parts（root and seed） were done by the atomic absorption spectrophotometry. Accumulations of K, P, Fe and several plant micronutrients（Mn, Ni, Co, Zn and Cu） and toxic elements（Pb, Cr and Cd） increased in soils and plant parts as a function of the FA gradation, but Na content remained almost unchanged in soils and seeds. Supplementation of cyanobacteria had ameliorating effect on toxic metal contents of soils and plant parts. The FA level 4.0 kg/m2, with 1.0 kg/m2 cyanobacteria mass supplementation, could be taken ideal, since there would be recharging of the soil with essential micronutrients as well as toxic chemicals in comparative lesser proportions, and cyanobacteria mass would cause lessening toxic metal loads with usual N_2-fixation.

Distribution of the Si-deficiency rice soil in Hubei Province

There are about 1 million ha of Si-deficiency paddy soils in Hubei Province. Practically, it is essential to study the Si nutrient status in those Si-deficiency rice soil and its regional distribution before the application of Si-fertilizer. According to the analysis of 50 rice soil samples which collected from 20 counties/cities in Hubei Province, the available Si content in rice soils derived from different parent materials varied greatly. The Si content from high to low was in sequence of limestone, redpurplish sandy shale with carbonate, alluvium and lacustrine deposits, quaternary period red clay, granitic gneiss, and sandy shale. In addition, the Si content in rice soil was remarkably related with its pH. It seems that the pH 6.5 might be a demarcation line that divided the supplying Si ability of rice soils into the low and high categories (Table 1). Integrating the results with a critical soil Si-deficiency as 100 mg/kg, the evaluation index of soil Si supplying capability of a rice soil

Effect of nitrogen fertilizer on the uptake and utilization of potassium by various rice varieties in purple soil

Nitrogen and potassium are important nutrientelements for rice.Besides supplied by the or- ganic manure,potassium nutrition of ricecomes dominantly from purple soils in Sichuanbasin.Potassium exists abundantly in mineralforms in the purple soils.Availability of soilpotassium for crop depends on the potassiumforms,the uptake ability of crops,and fertiliz-er practices.A pot culture experiment wasconducted to study the kinetics of potassiumuptake in the purple soil(total N 22.64g·kg,total K 24.36g·kg,available N 102.6mg·kg,available K 140.6mg·kg,acidsoluble K 936.0mg·kg,and pH 6.8).Ma-terials used were three Fhybrid rices,Eryou

Long-Term No-Tillage Direct Seeding Mode for Water-Saving and Drought-Resistance Rice Production in Rice-Rapeseed Rotation System

To study the effects of long-term no-tillage direct seeding mode on rice yield and the soil physiochemical property in a rice-rapeseed rotation system, a comparative experiment with a water-saving and drought-resistance rice （WDR） variety and a double low rapeseed variety as materials was conducted under no-tillage direct seeding （NTDS） mode and conventional tillage direct seeding （CTDS） mode for four years, using the CTDS mode as the control. Compared with the CTDS mode, the actual rice yield of WDR decreased by 8.10% at the first year, whereas the plant height, spikelet number per panicle, spikelet fertility, 1000-grain weight, grain yield, actual yield, and harvest index increased with no-tillage years, which led to the actual yield increase by 6.49% at the fourth year. Correlation analysis showed that the panicle length was significantly related to the actual yield of WDR. Compared with the CTDS mode in terms of the soil properties, the pH value of the NTDS mode decreased every year, whereas the contents of soil organic matter and total N of the NTDS mode increased. In the 0-5 cm layer of the NTDS mode, the soil bulk decreased, whereas the contents of soil organic matter, total N, and available N increased. In the 5-20 cm layer of the NTDS mode, the available N and K decreased, whereas the soil bulk, contents of soil organic matter, and total N increased. In summary, the NTDS mode increased the rice yield, and could improve the paddy soil fertility of the top layer.

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.

土壤-水稻系统中硫代砷的研究进展

硫代砷是土壤-水稻系统中砷的重要形态之一,其形态转化对砷的生物地球化学循环具有重要意义,同时也对环境和人类健康构成潜在威胁.总结了近年来国内外有关水稻土中硫代砷的定量检测方法、存在形态、影响因素、生物地球化学过程与水稻吸收机制方面的研究进展,旨在为后续研究提供方法参考与理论依据.为减少在环境样品分析之前硫代砷的形态转化,可向样品中加入二乙基三胺五乙酸(DTPA),将样品快速冷冻后低温避光保存.离子色谱串联电感耦合等离子体质谱法(IC-ICP-MS)适用于环境样品中硫代砷的分离与定量检测.无机硫代砷与甲基硫代砷在形成条件、环境行为以及水稻吸收方面存在显著差异.水稻土中硫代砷的含量受pH、氧化还原环境以及还原态硫等因素的影响,环境条件的变化会驱使不同形态硫代砷之间以及硫代砷与非硫代砷之间的相互转化.相较于(亚)砷酸盐,硫代砷在铁矿物表面的吸附能力通常较弱,且在土壤氧化还原条件变化时表现出更高的不稳定性.硫代砷可被水稻吸收并在籽粒中积累,其中二甲基一硫代砷酸盐(DMMTA)具有高吸收、高转运和高毒性,广泛存在于全球水稻籽粒与商品大米中.目前尚未明确水稻对硫代砷的吸收、转运与解毒机制,值得进一步深入探索以准确评估硫代砷对水稻生长、食品安全与人类健康所带来的潜在风险.

基于CERES-Rice模型的覆膜旱作稻田增温效应模拟

水稻覆膜旱作技术具有显著的节水、增温、防污和减排效应,是节水稻作技术体系的重要措施之一,将CERES-Rice模型用于覆膜旱作条件时,必须首先解决覆膜增温效应的准确模拟问题。该文拟应用热量传输理论及目前旱地作物生产系统中采用的覆膜增温效应模拟方法,来模拟水稻覆膜旱作生产体系中的增温效应,从而为完善CERES-Rice模型并使其能用于覆膜旱作水稻的生长模拟奠定基础。参数调校与模型检验验证通过2013、2014年在湖北房县开展的2 a水稻覆膜旱作田间试验来进行,共涉及淹水(对照)、覆膜湿润栽培和覆膜旱作共3个水分处理,分别对2个生长季、2个覆膜处理地表5 cm及地下10、20 cm处温度的变化过程进行了模拟,结果表明:经过参数调校后,所建立的覆膜增温模型可较好地模拟覆膜稻田地表和剖面上土壤温度的变化规律,地表5 cm处土壤温度模拟值与实测值的均方根差、相对均方根差分别低于1.8℃和10%,相关系数在0.89以上(P<0.01);尽管地下10、20 cm处的模拟误差稍大,也基本可满足要求,相应的均方根误差<3.2℃,相对均方根差<15%,相关系数>0.65(P<0.01)。

施氮量对川东南冬水田稻鱼共作系统下杂交稻产量和土壤养分的影响

【目的】利用川东南冬水田区连续多年稻鱼共作系统,研究施氮(N)量对免耕栽培杂交稻产量形成和土壤养分的影响,为制定稻鱼共作系统下免耕栽培杂交稻长期、合理的氮肥管理策略提供理论依据。【方法】于2018—2022年在川东南冬水田区开展了5年大田定位试验,供试杂交稻品种为蓉优1015和内6优103,耕作方式为免耕。设置N 0、45、90、135 kg/hm^(2)4个施氮水平,分别记作N_(0)、N_(45)、N_(90)、N_(135)。在水稻收获期,调查杂交稻产量及产量构成因素,分析0—20 cm土层土壤全量和速效氮、磷、钾含量,以及有机质含量和pH,通过回归分析,研究施氮量与水稻产量和土壤养分因子含量变化之间的关系。【结果】稻鱼共作系统下,年份、施氮量对杂交稻产量及产量构成的影响达极显著水平。5年间,杂交稻产量与施氮量均呈极显著正相关(r=0.9070^(**)~0.9720^(**)),与低氮量处理N_(45)相比,N_(90)和N_(135)处理杂交稻产量分别增加了6.37%~26.53%、9.11%~25.11%,单位面积有效穗数和每穗粒数也显著增加。而N_(90)处理杂交稻产量与N_(135)处理相当或更高。逐步回归分析结果表明,杂交稻产量构成(单位面积有效穗数、每穗粒数、结实率和千粒重)与产量的偏相关系数达显著或极显著水平(t=2.20*~9.17^(**))。通径分析结果表明,杂交稻单位面积有效穗数和每穗粒数对产量的直接贡献(分别为0.8754和0.4987)和总贡献(分别为0.6364和0.3598)较大,表明单位面积有效穗数和每穗粒数是影响产量的主要因素。在N_(0)、N_(45)处理下,土壤全氮、碱解氮含量随稻鱼共作年限的增加而下降,而在N_(90)、N_(135)处理下随稻鱼共作年限的增加而增加。土壤全氮、碱解氮含量随施氮量增加而提高,而全磷、全钾、速效磷、速效钾含量则随施氮量增加而下降。杂交稻产量与土壤养分含量呈极显著正相关,可见提高磷素、钾素供给能力是稻鱼共作系统杂交稻高产的重要基础。【结论】川东南冬水田区稻鱼共作系统下,年施氮90 kg/hm^(2)可以提高杂交水稻的单位面积有效穗数和每穗粒数,进而维持甚至提高水稻产量。连续施用中、高量氮肥还可以提升土壤有机质、全氮、全磷、全钾、碱解氮、速效磷和速效钾含量,且随稻鱼共作年限延长呈增加趋势;土壤pH值则随稻鱼共作年限延长呈下降趋势。