Evaluation of Harvest Aid Chemicals for the Cotton-Winter Wheat Double Cropping System

Timing of harvest is critical for mechanical picking in cotton production, especially in those regions with double cropping system. Appropriate and safe harvest aids will improve timing and facilitate harvest of cotton in the double cropping system. Three defoliants （dimethipin, thidiazuron, and thidiazuron-diuron） and one boll opener （ethephon） were included in this research. They were evaluated for their effects on defoliation, boll opening, seedcotton yield, seed quality, and fiber quality of field grown cotton when used alone or as a mixture in 2009 and 2010. Defoliation and/or boll opening were increased by all three defoliants and ethephon, especially by mixtures of a defoliant and ethephon. First harvest of seedcotton was significantly increased with defoliant-ethephon mixtures. No significant adverse effects were observed on boll weight, lint percentage, seed quality, and fiber properties. It was estimated that tank mixes of ethephon and one of the three defoliants can improve the adjusted gross revenue. Boll opening can be used as an alternative indicator for the adjusted gross revenue, because, it was linearly and positively correlated with the relative adjusted gross revenue and convenient in measurements. Wheat seedling growth was not affected by thidiazuron, whereas its seedling emergence, root dry weight, relative water content, and electrolyte leakage were adversely affected by dimethipin and thidiazuron- diuron when concentration was above 340 and 100 g （a.i.） ha-1, respectively. 90% defoliation and 80% boll opening were observed with the high rate of thidiazuron-ethephon mixture, but no adverse effects on winter wheat. The results suggested that tank mixes of ethephon with thidiazuron can be used effectively and safely in the cotton-winter wheat double cropping system to improve yield without adverse effects on seed quality and fiber quality.

The microbial community,nutrient supply and crop yields differ along a potassium fertilizer gradient under wheat-maize double-cropping systems

Soil microorganisms play critical roles in ecosystem function.However,the relative impact of the potassium(K)fertilizer gradient on the microbial community in wheat-maize double-cropping systems remains unclear.In this long-term field experiment(2008-2019),we researched bacterial and fungal diversity,composition,and community assemblage in the soil along a K fertilizer gradient in the wheat season(K0,no K fertilizer;K1,45 kg ha^(-1) K_(2)O;K_(2),90 kg ha^(-1)K_(2)O;K3,135 kg ha^(-1)K_(2)O)and in the maize season(K0,no K fertilizer;K_(1),150 kg ha^(-1) K_(2)O;K_(2),300 kg ha^(-1)K_(2)O;K_(3),450 kg ha^(-1)K_(2)O)using bacterial 16S rRNA and fungal internally transcribed spacer(ITS)data.We observed that environmental variables,such as mean annual soil temperature(MAT)and precipitation,available K,ammonium,nitrate,and organic matter,impacted the soil bacterial and fungal communities,and their impacts varied with fertilizer treatments and crop species.Furthermore,the relative abundance of bacteria involved in soil nutrient transformation(phylum Actinobacteria and class Alphaproteobacteria)in the wheat season was significantly increased compared to the maize season,and the optimal K fertilizer dosage(K2 treatment)boosted the relative bacterial abundance of soil nutrient transformation(genus Lactobacillus)and soil denitrification(phylum Proteobacteria)bacteria in the wheat season.The abundance of the soil bacterial community promoting root growth and nutrient absorption(genus Herbaspirillum)in the maize season was improved compared to the wheat season,and the K2 treatment enhanced the bacterial abundance of soil nutrient transformation(genus MND1)and soil nitrogen cycling(genus Nitrospira)genera in the maize season.The results indicated that the bacterial and fungal communities in the double-cropping system exhibited variable sensitivities and assembly mechanisms along a K fertilizer gradient,and microhabitats explained the largest amount of the variation in crop yields,and improved wheat?maize yields by 11.2-22.6 and 9.2-23.8%with K addition,respectively.These modes are shaped contemporaneously by the different meteorological factors and soil nutrient changes in the K fertilizer gradients.

Effect of Continuous Application of Controlled Release Nitrogen Fertilizer in Various Types of Soil in Dong-Ting Lake Region under Double Rice Cropping System

[Objective] This study aimed to explore the effects of continuous application of controlled release nitrogen fertilizer under double rice cropping system. [Method] By modeling three types of paddy soils in Dong-Ting Lake area, four treatments as no fertilizer （CK）, urea, controlled release nitrogen fertilizer （CRNF） and 70% controlled release nitrogen fertilizer （70% CRNF） were designed in the micro-plot trials from 2005 to 2008. [Result] The rice yield in treatment CRNF at N 150 kg/hm2 was increased by 10.3%, 8.0% and 2.4% compared with treatment of urea, in alluvial sandy loamy paddy soil （ALS）, purple calcareous clayey paddy soil （PCS）, and reddish yellow loamy paddy soil （RYS）, respectively; and the yield in treatment of 70% CRNF was increased by 6.1%, 2.6% and -0.8%, respectively. The ranking order of nitrogen uptake amount by plant in early rice and late rice was CRNF 70% CRNF urea CK in all three types of soil. Nitrogen utilization efficiency of CRNF in above three types of soil was 60.7%, 59.6% and 56.3%, increased by 23.8%, 19.4% and 16.3% compared with that in treatment of urea, respectively. Nitrogen utilization efficiency of CRNF in early rice was increased year by year, and was higher than that of 70% CRNF during the whole experiment stage, while that in late rice was increased first and then decreased from the 3rd year. [Conclusion] Continuous application CRNF could alleviate the decreasing of soil nitrogen fertility and organic carbon especially in ALS, increase rice yield and nitrogen utilization efficiency in double-rice cropping system.

Model construction for field operation machinery selection and configuration in wheat-maize double cropping system

In order to scientifically and reasonably select the field operation machinery in the wheat-maize double cropping system,first,the selection evaluation index system was constructed through the existing national standards and industry standards.Then the selection evaluation model was established based on the improved fuzzy comprehensive evaluation method.And the method of subjective weight and objective weight was used to overcome the drawbacks of the previous single weighting method that could not take into account the subject and object information of each indicator,and the weight value of each index was obtained in the evaluation system.Finally,the tillage process was used as an example,the field experiment was carried out to obtain the evaluation index value,and the model of selection evaluation was verified.The selection results of moldboard plough and rotary cultivator were as follows:the order of the comprehensive evaluation results of the moldboard plough results was ranked from high to low as 1LFK-435(IIM),1LFK-535(IM),1LF-342(IIIM),1LFT-445(IVM),1LFT-545(VM),and the best machine type of the moldboard plough was IIM;the order of the comprehensive evaluation results of the rotary cultivator was ranked from high to low as 1GQKGN-240(IIIR),1GKNSM-250(IVR),1GKN-230K(IR),1GKN-250K(IIR),1GQKGN-220(VR),and the optimal model of the rotary cultivator was IIIR.The experimental results showed that the results obtained by the evaluation model were in agreement with the local actual situation.The evaluation model will provide a scientific method for the selection of wheat and maize double cropping field operation machinery.

Soil physical properties,nutrients,and crop yield with two-year tillage rotations under a winter wheat-summer maize double cropping system

Winter wheat and summer maize were planted from 2015-2017 to study the effects of different rotational tillage patterns on soil physicochemical properties,crop yield,water content,and fertilizer utilization.The tillage treatments were designed as wheat subsoiling-maize no tillage(WS-MN),wheat rotary tillage-maize subsoiling(WR-MS),wheat subsoiling-maize subsoiling(WS-MS),and conventional wheat rotary tillage-maize no tillage(WR-MN)as a control.Among the four treatments,WS-MN and WR-MS were single-season subsoiling treatments,and WS-MS was a two-season subsoiling treatment.The average soil bulk density decreased by 7.6%in the single-and double-season subsoiling groups compared to the WR-MN group,and the total porosity and noncapillary porosity increased by 10.7%and 12.2%,respectively.Single-or double-season subsoiling treatment was not conducive to water storage in the 0-20 cm soil layer but increased the water content of the 20-140 cm soil layer,and the average soil water content of the 0-140 cm layer was increased by 11.6%in the two-growing season treatment groups compared with the WR-MN group.In WS-MS and WS-MN groups compared with the WR-MN group,the soil ammonium nitrogen content was increased by an average of 18.6%in 0-20 cm soil and 16.8%in 20-100 cm soil;soil nitrate-nitrogen content was decreased by 13.5%in 0-100 cm soil;total organic carbon and microbial carbon contents in the 15-30 cm soil were increased by 18.1%and 12.7%,respectively;and soil urease,catalase,and alkaline phosphatase activities were increased by 46.1%,15.2%,and 23.1%,respectively.Annual crop yield and water use efficiency increased by 8.9%and 15.0%,respectively,in both the single-and double-season subsoiling treatment groups.This study demonstrated the advantages of subsoiling tillage and suggested that it is suitable for crop cultivation in the Haihe Plain,China.

Plant Ideotype at Heading for Super High-Yielding Rice in Double-Cropping System in South China

The newly released super high-yielding hybrid rice combinations, Yueza 122, Fengyou 428, Peiza 67, and the super high-yielding conventional cultivars, Guangchao 3 and Shengtai 1, were grown in both early and late seasons. The morphological characters of each population were investigated at the heading stage, and the data were analyzed by using ANOVY and other statistic methods. The plant ideal morphological characters at the heading stage were established as follows： 1 ） for the early-season cropping, 90-105 cm plant height; 11-12 tillers per plant; 35-40 em length and 2.1-2.2 cm width of flag leaf; 46-50 cm length and 1.8-2.1 cm width of the second leaf from the top （L2）; 59-64 cm length and 1.4-1.9 cm width of the third leaf from the top （L3）; 7°-14°, 18° and 200-33° for the ideal leaf angles of the flag leaf, L2 and L3, respectively; 2） for the late-season cropping, 90-100 cm plant height; 9-15 tillers per plant; 30-41 cm length and 1.8-2.0 cm width of flag leaf; 53-61 cm length and 1.3-1.8 cm width of L2; 52-58 cm length and 1.2-1.5 cm width of L3; 9°-19°, 15°-37° and 16°-49° for the ideal leaf angles of the flag leaf, L2 and L3, respectively. The main physiological characteristics of these varieties were also analyzed.

Phosphorus losses via surface runoff in rice-wheat cropping systems as impacted by rainfall regimes and fertilizer applications

Phosphorus（P） losses from agricultural soils contribute to eutrophication of surface waters. This field plot study investigated effects of rainfall regimes and P applications on P loss by surface runoff from rice（Oryza sativa L.） and wheat（Triticum aestivum L.） cropping systems in Lake Taihu region, China. The study was conducted on two types of paddy soils（Hydromorphic at Anzhen site, Wuxi City, and Degleyed at Xinzhuang site, Changshu City, Jiangsu Province） with different P status, and it covered 3 years with low, high and normal rainfall regimes. Four rates of mineral P fertilizer, i.e., no P（control）, 30 kg P ha^（–1） for rice and 20 kg P ha^（–1） for wheat（P_（30＋20））, 75 plus 40（P_（75＋40））, and 150 plus 80（P_（150＋80））, were applied as treatments. Runoff water from individual plots and runoff events was recorded and analyzed for total P and dissolved reactive P concentrations. Losses of total P and dissolved reactive P significantly increased with rainfall depth and P rates（P〈0.0001）. Annual total P losses ranged from 0.36–0.92 kg ha^–1 in control to 1.13–4.67 kg ha^–1 in P150＋80 at Anzhen, and correspondingly from 0.36–0.48 kg h^–1 to 1.26–1.88 kg ha^–1 at Xinzhuang, with 16–49% of total P as dissolved reactive P. In particular, large amounts of P were lost during heavy rainfall events that occurred shortly after P applications at Anzhen. On average of all P treatments, rice growing season constituted 37–86% of annual total P loss at Anzhen and 28–44% of that at Xinzhuang. In both crop seasons, P concentrations peaked in the first runoff events and decreased with time. During rice growing season, runoff P concentrations positively correlated（P〈0.0001） with P concentrations in field ponding water that was intentionally enclosed by construction of field bund. The relative high P loss during wheat growing season at Xinzhuang was due to high soil P status. In conclusion, P should be applied at rates balancing crop removal（20–30 kg P ha^–1 in this study） and at time excluding heavy rains. Moreover, irrigation and drainage water should be appropriately managed to reduce runoff P losses from rice-wheat cropping systems.

Analysis of Optimized NPK Formulation and Topdressing on Increasing Yield in Double Cropping Rice of Hunan

The effect of different formula of NPK and twice topdressings on rice growth in typical double cropping rice area, which located at Kaihui, Ganshan, Matang and Xinqiang towns, were studied on field experiment in order to select the formula of compound fertilizer and top dressing mode for double cropping of rice production in Hunan. The results showed that the optimized formulated fertilizer treatment, which increased the proportion of phosphorus and potassium and reduced its nitrogen fertilizer by 7.5 kg/hm2 can ensure early rice stable. Fpr example, the yield of late rice increased by 187.5-378.0 kg/hm2 compared with the conventional complex fertilizer （N-PO5-K2O formula of 20-10-10 for early rice and 26-10-13 for late rice）. The N-P2O5-K2O formula 18-14-16 of optimized formulated fertilizer which was suitable for early rice production, and the other N-P2O5-K2O formula 18- 9-16 was suitable for late rice production. The rice yields for top-dressing at tiller- ing stage and booting stage can increased by 187.5-382.5 and 258.0-415.5 kg/hm2 for eady and late rice and the nitrogen use efficiency advanced 10.9-24.2 percent- age points （31.5%-51.1%） for eady rice and 8.3-13.4 percentage points （36.2%- 64.9%） for late dce compared with the top-dressing at tillering stage.

Effect of Different Seedling Age on the Growth and Yield of Double Cropping of Late Rice

The study aims to solve the problems of late transplanting rice with differ- ent seedling ages at the lower reaches of Yangtze River. We selected six varieties of different thermal and photo-response characteristics as the test material to study the effect of different seedling ages on growth and yield of rice. The results showed that growing period of thermal-response rice was delayed by long seedling age, but less affected by the impact of photo-response rice; the yield of later thermal-re- sponse varieties with 25 days and 30 days seedling ages was significantly reduced. In contrast, the yield of early thermal-response varieties and later photo-response varieties were significantly reduced with 30 days seedling age. The optimal trans- planting seedling age was 15 days of thermal-response rice, while photo-response rice was 20 days. The thermal-response rice should be selected as early maturing varieties, while the photo-response rice could be selected as late maturing varieties for high yield.

Cold Damage Risk Assessment of Double Cropping Rice in Hunan, China

Combined with remote sensing data and meteorological data, cold damage risk was assessed for planting area of double cropping rice （DCR） in Hunan Province, China. A new methodology of cold damage risk assessment was built that apply to grid and have clear hazard-affected body. Each station cold damage annual frequency and average annual intensity of cold damage was calculated by using 1951-2010 station daily mean temperature and simple cold damage identification index. On this basis, average annual cold damage risk index was obtained by their product. The spatial analysis models of cold damage risk index about double-season early rice （DSER） and double-season later rice （DSLR） were established respectively by the relation of average annual cold damage risk index and its geographic factors. Critical threshold of level of average annual cold damage risk index for DSER and DSLR were respectively divided by the correlative equation of cold damage annual frequency and average annual intensity of cold damage. 2001-2010 planting area of DCR, acquired by time series analysis of MOD09AI 8-d composite land surface reflectance product, was as target of assessment. The results show average annual intensity of cold damage is exponential function of cold damage annual frequency, average annual cold damage risk index is directly proportional to cold damage cumulant and cold damage annual frequency, and is inversely proportional to happen times of cold damage and the square of statistical time sequence length. Cold damage risk of DSER is higher than DSLR in Hunan Province. In the 10-yr stacking map, DCR planting in low risk area accounted for 11.92% of total extraction area, in moderate risk area accounted for 69.62%, in high risk area accounted for 18.46%. According to the cold damage risk assessment result, DCR production can be guided to reduce cold damage losses.

Assessment of Long-Term Compost Application on Physical, Chemical, and Biological Properties, as Well as Fertility, of Soil in a Field Subjected to Double Cropping

The aim of this article was to assess the influence of long-term application of compost on the physical, chemical, and biological properties, as well as the fertility, of soil in a field subjected to double cropping (paddy rice and barley), mainly by integrating previous studies of the effects of compost and manure on soil qualities. Continuous compost application, especially at a high level (30 Mg·ha-1·y-1), into the double cropping soils increased the activities of organic C-, N-, and P-decomposing enzymes and the contents of organic C, total N, and microbial biomass N, as well as the cation exchange capacity, thereby contributing to the enhancement of soil fertility. Also, the compost application increased the degree of water-stable soil macroaggregation (>0.25 mm), which was correlated significantly (r > 0.950, p < 0.05) with the contents of hydrolyzable carbohydrates (with negative charge) and active Al (with positive charge), and resulted in the modification of soil physical properties. Furthermore, the application increased the amount of soil organic matter, including humic acid with a low degree of darkening and fulvic acid, and contributed to C sequestration and storage. Physical fractionation of soil indicated that about 60% of soil organic C was distributed in the silt-sized (2 - 20 μm) aggregate and clay-sized (<2 μm) aggregate fractions, while about 30% existed in the decayed plant fractions (53 - 2000 μm). The results obtained unambiguously indicate that long-term application of compost can improve soil qualities in the field subjected to double cropping, depending on the amount applied.

CLIMATIC RISK ZONING OF DOUBLE CROPPING SUPER RICE CULTIVATION IN HUNAN PROVINCE

Based on meteorological data including daily sunshine duration, temperature and precipitation from 97 meteorological stations in Hunan province during the period of 1981—2010, in combination with the field experiment in different places at different sowing dates, the precise climatic risk zoning of double cropping super rice cultivation has been studied by using the spatial interpolation method and other Geographical Information System(GIS)technologies. Three key climatic factors were selected including chilling in May, high temperature heat damage during July to early August and low temperature damage in autumn in this study. Furthermore, based on the analysis of climatic conditions suitable for double cropping super rice cultivation and climatic disasters, 8-22 ℃ active accumulated temperature, sunshine duration from late March to October, climatic risk index of the low temperature in autumn, and climatic risk index of chilling in May were selected as key climatic factors to study the precise agro-meteorological regionalization of double cropping super rice in Hunan province. The results showed that: the high-yielding zones of double cropping super rice in Hunan were mainly located in Zhuzhou, Hengyang, Yongzhou and Chenzhou City, the moderate-yielding zones were primarily located in the east and north reaches of Dongting Lake,together with most of Changsha, Zhuzhou and Xiangtan City, and other regions in Hunan were not suitable for double cropping super rice. These findings can provide valuable information for the large-scale cultivation of double cropping super rice in Hunan province.

Effects of Winter Planting Milk Vetch on Yield and PartialProductivity of Nitrogen Fertilizer of Machine-transplantedDouble-cropping Rice under Straw Returning to the Field

From 2017 to 2018,the effects of winter planting of milk vetch on yield and partial productivity of nitrogen fertilizer of machine-transplanted double-cropping rice under straw returning were studied in Ningxiang city,Hunan Province.The results showed that the dry matter accumulation,effective panicle,yield and partial productivity of nitrogen fertilizer in the stem,leaf,panicle and aboveground parts of early and late rice treated with winter planting milk vetch and straw returning were signi ficantly higher than those treated with straw returning only.Among them,the effective panicles of early and late rice increased by 2.58%,3.18%(2017)and 5.22%,6.32%(2018),respectively.Yield increased by 11.85%,10.07%(2017)and 12.42%,10.92%(2018),annual partial productivity of nitrogen fertilizer increased by 10.90%(2017)and 11.66%(2018),respectively.In conclusion,winter planting milk vetch under straw returning is beneficial to increase dry matter accumulation,rice yield and partial productivity of nitrogen fertilizer in mechanized double cropping rice.

Studies on the Morphological Characters of South China Double Cropping Super Rice at the Active Tillering Stage

The morphological characters of the newly released super hybrid rice in South China, Yueza 122, Fengyou 428, Peiza 67, and super conventional varieties, Guangchao 3, Shengtai 1 at the active tillering stage in both early and late crops were investigated. Using the analysis of variance and other statistic methods, the ideal morphological characteristics of South China double cropping super-rice at the active tillering stage were determined. They are 55-60 cm in the early crop and 60-76 cm in the late crop for the ideal plant height, about 15 tillers in the early crop and 14-19 tillers in the late crop for the ideal tiller number per plant, 40-44 cm in the early crop and 42-60 cm in the late crop for the ideal length of the first leaf under the top leaf, 1.2-1.4 cm in the early crop and 1.2-1.3cm in the late crop for the ideal width of the first leaf under the top leaf, 39- 44 cm in the early crop and 37-43 cm in the late crop for the ideal length of the second leaf under the top leaf, 1.1-1.4 cm in the early crop and about 1.1 cm in the late crop for the ideal width of the second leaf under the top leaf, 22-58o in the early crop and 4- 12o in the late crop for the ideal top leaf angle at the active tillering stage. Based on these results, a new concept of “dynamic plant type structure” for South China double cropping super rice breeding was suggested.

Selection of Grape Varieties Suitable for Double Cropping a Year in Northern Greenhouse

With the development of the greenhouse grape cultivation area,the supporting greenhouse grape varieties appear to be single.At present,there are few researches on the selection of grape varieties suitable for two-harvest-a-year cultivation in greenhouses.In order to meet the needs of fruit growers for the diversity of greenhouse grape varieties,experimental studies had been carried out.Through three consecutive years of two-harvest-a-year production of six grape varieties of‘Jingxiangyu’,‘Ruidukemei’,‘Xiangfei’,‘Jingyan’,‘Zaomanao’and‘Hanxiangmi’,the first crop of greenhouse grapes matured from May to July,and the second crop matured during the New Year s Day and Spring Festival.Through the investigation and analysis of their phenological periods,fruit economic characteristics and economic benefits,it was found that the four varieties of‘Jingxiangyu’,‘Ruidukemei’,‘Xiangfei’and‘Jingyan’performed well under greenhouse cultivation conditions,and thus can be used as supporting fine varieties for large-scale promotion.

Effect of Different Winter Cover Crops on Carbon Dioxide Emission in Paddy Field of Double Cropping Rice Area in Southern China

In this study, a two-year experiment was conducted by suing a static chamber method to observe the effects of straw recycling of winter cover crops measure on CO2 emission fluxes in southern China. Three patterns of winter use were performed in the paddy field, including RRR （rice-rice-ryegrass （Lolium multiflorum L.） cropping system）, CRR （rice-rice-Chinese milk vetch （Astragalus sinicus L.） cropping system） and FRR （rice-rice cropping system with winter fallow）. During the winter, the average daily CO2 fluxes were greater （P 〈 0.05） in the RRR and CRR than the FRR. During the winter crop growing seasons, both the average daily CO2 fluxes and the total CO2 emissions were different as the following orders： RRR 〉 CRR 〉 FRR. The average CO2 fluxes during early rice and late rice season were similar. The highest CO2 flux was found at rice tillering stage with an order as the follows： RRR 〉 CRR 〉 FRR and CRR 〉 RRR 〉 FRR both in 2009 and 2010, respectively. The annual CO2 emissions of RRR and CRR were significantly higher respectively by 857.0 g.CO2-C.m2 and 607.4 g.CO2-C.m-2 than the FRR. The results show that straw recycling of winter cover crops measure may strongly influence the CO2 emission in paddy field in southern China.

Effects of Silicon Levels on Rice Grain Yield and Its Nitrogen Absorption

Pot experiments were conducted to investigate the influence of Si fertilizer on yield and N-uptake and use efficiency of double-season rice under the conditions of equal nitrogen, phosphorus and potassium nutrients. The results showed that along with the increase of Si fertilizer application, the yield of early and late rice increased firstly and then decreased within the range of SiO2 application rate of 0-0.8 g/kg soil. There was a significant parabolic correlation between the amounts of Si fertilizer application and rice grain yield （r= 0.931 2 and r= 0.973 3 in early-and late-rice season, respectively）. Results showed that efficient Si fertilizer application enchanced N contents in different plant components of early rice at maturity stages with increased nitrogen uptake of double cropping rice and nitrogen harvest index of late rice.

Effect of Long-Term Fertilization on Organic Carbon and Nitrogen in a Subtropical Paddy Soil

A long-term experiment beginning in 1981 in Jinxian County of Jiangxi Province, subtropical China, was conducted in a paddy field under a double rice cropping system with four different fertilization regimes, including 1) no fertilizer as control (CK), 2) balanced chemical N, P, and K fertilizers (NPK), 3) organic manure using milk vetch and pig manure in the early and late rice growing season, respectively (OM), and 4) balanced chemical fertilizers combined with organic manure (NPKM). Samples (0-17 cm) of the paddy field soil, which was derived from Quaternary red clay, were collected after the late rice harvest in November 2003 for determination of total organic carbon (TOC) and total nitrogen (TN) and fractions of organic C and N. Results showed that TOC and TN in the NPKM and OM treatments were significantly higher than those in other two treatments (CK and NPK). Application of organic manure with or without chemical fertilizers significantly increased the contents of all fractions of organic C and N, whereas chemical fertilizer application only increased the contents of occluded particulate organic C (oPOC) and amino acid N. In addition, application of organic manure significantly enhanced the proportions of free particulate organic carbon (fPOC) and oPOC in total C, and those of amino sugar N and amino acid N (P < 0.01) in total N. In contrast, chemical fertilizer application only increased the proportions of oPOC and amino acid N (P < 0.05). There were no significant differences in either contents or proportions of soil organic C and organic N fractions between the NPKM and OM treatments. These indicated that organic manure application with or without chemical fertilizers played the most significant role in enhancing soil organic C and N quantity and quality in the paddy field studied.

Root characteristics and yield of rice as affected by the cultivation pattern of strong seedlings with increased planting density and reduced nitrogen application

To address the relationships between the amount of nitrogen fertilizer application and the yield of double cropping rice systems,we investigated the effects of a cultivation pattern of strong seedlings with increased planting density and reduced nitrogen application(SDN)on the morphological and physiological characteristics of double cropping rice.Our results indicated that the effects of SDN on the morphological characteristics of the single plant roots of double cropping rice were not significant,but the morphological characteristics of the population roots were largely different.Specifically,SDN significantly increased the morphological indexes of the root population such as root fresh weight,root volume,root number,root length and root dry weight.The effects of SDN on the total root absorption areas and root active absorption areas of the single plants were non-significant,but it dramatically enhanced the total root absorption areas and root active absorption areas of the plant population during the tillering,heading and mature stages.In addition,SDN significantly increased the root bleeding intensity and elevated the soluble sugar and free amino acid contents of root bleeding sap.Compared to the traditional cultivation pattern(CK),SDN significantly increased root bleeding intensity at the heading stage by 4.37 and 8.90% for early and late rice,respectively.Meanwhile,SDN profoundly enhanced the soluble sugar contents of root bleeding sap by 12.85 and 10.41% for early and late rice,respectively.In addition,SDN also significantly enhanced free amino acid content of root bleeding sap by 43.25% for early rice and by 37.50% for late rice systems compared to CK.Furthermore,SDN increased the actual yield of double cropping rice mainly due to the higher effective panicle number and the larger seedsetting rate.The actual yields of early rice under SDN were higher than CK by 9.37 and 5.98% in 2016 and 2017,and the actual yields of late rice under SDN were higher than CK by 0.20 and 1.41% in 2016 and 2017,respectively.Correlation analysis indicated that the significant positive correlations were observed between the majority of the root indexes and the actual yield across the four different growth stages.

Screening and Verification of Rice Varieties with Low Cadmium Accumulation

In order to improve the utilization efficiency of heavy metal pollution of farmland,the revitalization of Hunan rice brand,this research worked on 20142016 oriented social extensive collection of 285 varieties of rice,including 98 early rice varieties and 187 late rice varieties.Screening and veri fication of rice varieties with low Cadmium accumulation were studied in Changsha-Zhuzhou-Xiangtan of Hunan Province,and in other typical cadmium polluted area in Hunan Province.12 early rice varieties and 13 late rice varieties were selected as low Cadmium accumulation varieties.Field test showed that,through the screening of varieties(V),irrigation(I)and acidity adjustment(P),the content of cadmium in early rice is 0.064~0.233 mg/kg,and 0.143~0.246 mg/kg in late rice,basically to ensure the content of cadmium in rice to reach the national standard,and to ensure good food security.