Economic Analysis of Diversified Rotational Cropping Systems in the Lateritic Belt of Lower Gangetic Plain of Eastern India

Economic analysis of different diversified rotational cropping systems under Farmers＇ package/practices and improved package/practices was conducted in Birbhum district, West Bengal, located in the red and lateritic belt of lower Gangetic plain of eastern lndia. Diversified triple cropping systems （peanut-brinjal＋brinjal, rice-potato-pumpkin, and cucumber-cabbage-basella） required higher cost for cultivation, but also produced higher rice equivalent yield, higher net return and higher return rupee1 invested in both management practices. Considering the resource-ability and risk-bearing capacity, and net return and return rupee^-1 （RPR） invested, these cropping systems can be recommended for resource-rich farmers. Rice-rapeseed-cowpea, rice-wheat-green gram and radish-tomato-amaranthus systems profitable. These cropping systems can be required less inputs for cultivation, were less risky, and economically viable and recommended for resource-poor farmers. Peanut-brinjal ＋ brinjal-okra-chilli ＋ chilli-cucumber-cabbage-basella system was the best among all the 3-year rotational systems in respect to RPR in both management practices. This rotational system will be suitable for resource-rich farmers. Vegetable-based rotational systems （ridge gourd-marigold-okra-black gram-pointed gourd ＋ pointed gourd-radish-tomato-amaranthus） or rice-based rotational system （rice-wheat-green gram-rice-rapeseed-cowpea-rice-potato-pumpkin） also found to be suitable to increase the profitability and system sustainability. These cropping systems can be recommended for all groups of farmers.

Weed Incidences and Their Effect on Crop Productivity under Diversified Rotational Cropping Systems in the Lateritic Belt of Lower Gangetic Plain of Eastern India

A field experiment was conducted from 2002-2005 on a sandy clay loam red and lateritic soil under irrigation in a farmer＇s field at Senkapur （Lat. 23°36.79′ N, Long. 87°38.14′E, Elev. 46 m AMSL）, Birbhum, West Bengal, India. The objective was to provide the temporal changes of weed diversity and density, ecology, and impact of rotational cropping systems on different crops under double and triple cropping systems with improved （IP） and farmer＇s packages （FP）. There was significantly higher weed density in FP than in IP on all years. Grasses and sedges were more in vegetable-based rotational systems; but grasses and broad leaf weeds （BLWs） were more in rice-based rotational systems. The lowest weed population was in vegetable-based systems. Grasses increased in rice-based systems but gradually decreased in vegetable-based systems in subsequent years. Sedge density was higher in vegetable- than in rice-based rotational systems. Density of BLWs was higher but that of sedges was lower in rice-based rotational systems as compared to vegetable-based systems. Density of BLWs gradually decreased in all rotational systems over the years in both packages. Density of weeds decreased gradually in subsequent years indicating the positive effect of rotational systems on suppression of weeds. Results indicate that the weed density can be reduced through judicious diversified rotational cropping systems. Peanut-brinjal＋brinjal, okra-chilli＋chilli and cucumber-cabbage-basella systems greatly reduced the weed density in both packages, and hence can be recommended for the lateritic belt of lower Gangetic plain of eastern India.

Nitrogen rhizodeposition from corn and soybean,and its contribution to the subsequent wheat crops

Nitrogen(N)is a key factor in the positive response of cereal crops that follow leguminous crops when compared to gramineous crops in rotations,with the nonrecyclable rhizosphere-derived N playing an important role.However,quantitative assessments of differences in the N derived from rhizodeposition(NdfR)between legumes and gramineous crops are lacking,and comparative studies on their contributions to the subsequent cereals are scarce.In this study,we conducted a meta-analysis of NdfR from leguminous and gramineous crops based on 34 observations published worldwide.In addition,pot experiments were conducted to study the differences in the NdfR amounts,distributions and subsequent effects of two major wheat(Triticum aestivum L.)-preceding crops,corn(Zea mays L.)and soybean(Glycine max L.),by the cotton wick-labelling method in the main wheat-producing areas of China.The meta-analysis results showed that the NdfR of legumes was significantly greater by 138.93%compared to gramineous crops.In our pot experiment,the NdfR values from corn and soybean were 502.32 and 944.12 mg/pot,respectively,and soybean was also significantly higher than corn,accounting for 76.91 and 84.15%of the total belowground nitrogen of the plants,respectively.Moreover,in different soil particle sizes,NdfR was mainly enriched in the large macro-aggregates(>2 mm),followed by the small macro-aggregates(2–0.25 mm).The amount and proportion of NdfR in the macro-aggregates(>0.25 mm)of soybean were 3.48 and 1.66 times higher than those of corn,respectively,indicating the high utilization potential of soybean NdfR.Regarding the N accumulation of subsequent wheat,the contribution of soybean NdfR to wheat was approximately 3 times that of corn,accounting for 8.37 and 4.04%of the total N uptake of wheat,respectively.In conclusion,soybean NdfR is superior to corn in terms of the quantity and distribution ratio of soil macro-aggregates.In future field production,legume NdfR should be included in the nitrogen pool that can be absorbed and utilized by subsequent crops,and the role and potential of leguminous plants as nitrogen source providers in crop rotation systems should be fully utilized.

Several Cotton Rotation and Intercropping Systems in Cotton Planting Area of Eastern Henan Province

In recent years,the area dedicated to cotton cultivation in eastern Henan Province has experienced a continuous decline.Developing efficient multi-cropping systems for cotton and increasing the multiple cropping index represent effective strategies to stabilize the cotton planting area and enhance the income of cotton farmers.This paper presents an overview of intercropping systems and the benefits associated with cotton rotation and intercropping practices.Specifically,it discusses the"early maturing cotton-wheat"rotation system,the"cotton-watermelon"intercropping system,the"cotton-Dutch bean"intercropping system,and the"early maturing cotton-peanut-garlic"intercropping system.

Characteristics of Nitrogen and Phosphorus Losses in Different Crop Rotation Systems in the North of Erhai Lake Basin

[Objective] Nitrogen and phosphorus losses of surface runoff in various crop rotation systems in the north of Erhai Lake basin were studied with the objective to provide references for risk evaluation of environmental pollution and formulating countermeasures to control the nonpoint source pollution from agriculture.[Method] Water samples collected in four typical crop rotation systems distributed in seven towns（townships） in the north of Erhai Lake basin were investigated,as well as the fertilizer input,to explore the dynamic change of nitrogen and phosphorus content in surface water of farmland and ditch water,and the correlation between fertilizer input and the concentrations of nitrogen and phosphorus in the surface water of farmland and in the ditch water.[Result] The results showed that nitrogen loss in surface water of farmland in different crop rotation systems differed greatly,and the risk of nitrogen loss was 38% lower in broad bean-rice crop rotation than that in garlic-rice crop rotation.The water soluble nitrogen was the primary form of nitrogen loss.The content of water soluble nitrogen was significantly higher in garlic-rice crop rotation than that in the other rotation systems,and the concentrations of nitrogen in the surface water of farmland in different crop rotation systems followed the sequence below：garlic-rice crop rotationryegrass-rice crop rotationbroad bean-rice crop rotationrape-rice crop rotation.The loss of phosphorus in the surface water of farmland was relatively low and phosphorus combined with silt was the primary form for phosphorus loss.There was no significant difference of the loss of various forms of phosphorus in different crop rotation systems.The contents of total nitrogen and total phosphorus in the surface water of farmland were higher than that in ditch water,with increasing rates of total nitrogen and total phosphorus in ditch water of 72% and 82%,respectively.Topdressing was the critical reason for the high concentrations of nitrogen and phosphorus in the surface water,which also caused the increasing load to the ditch water.[Conclusion] Both the nitrogen and phosphorus loss were the highest in garlic-rice crop rotation.Reasonable crop rotation systems should be established based on both the environmental and economic benefits.This study provided references for controlling the nonpoint source pollution of farmland and improving the water quality of Erhai Lake.

Effect of No Tillage and Conventional Tillage on Wheat Grain Yield Variability: A Review

Conservation Agriculture(CA)covers more than 205 million hectares in the world.This made it possible to face and mitigate the challenges of climate change,reducing soil erosion and providing multiple ecosystem services.The first elementary factor influenced is the yield evaluation.It has a direct effect on farmers’choices for sustainable production.The present article records a review focused on wheat yield average positive change compared between conventional tillage(CT)and no tillage(NT)systems.The international database collected showed that NT is adaptable everywhere.The results of wheat yield differentiation showed the influence of crop rotation depending on stations located in different climatic zones.In more than 40 years of research,specialists have succeeded in demonstrating the importance of crop productivity like wheat.The whole integrates also experimentations where the initiation starts more than ten years.

A comprehensive analysis of the response of the fungal community structure to long-term continuous cropping in three typical upland crops

Certain agricultural management practices are known to affect the soil microbial community structure;however,knowledge of the response of the fungal community structure to the long-term continuous cropping and rotation of soybean,maize and wheat in the same agroecosystem is limited.We assessed the fungal abundance,composition and diversity among soybean rotation,maize rotation and wheat rotation systems and among long-term continuous cropping systems of soybean,maize and wheat as the effect of crop types on fungal community structure.We compared these fungal parameters of same crop between long-term crop rotation and continuous cropping systems as the effect of cropping systems on fungal community structure.The fungal abundance and composition were measured by quantitative real-time PCR and Illumina MiSeq sequencing.The results revealed that long-term continuous soybean cropping increased the soil fungal abundance compared with soybean rotation,and the fungal abundance was decreased in long-term continuous maize cropping compared with maize rotation.The long-term continuous soybean cropping also exhibited increased soil fungal diversity.The variation in the fungal community structure among the three crops was greater than that between long-term continuous cropping and rotation cropping.Mortierella,Guehomyces and Alternaria were the most important contributors to the dissimilarity of the fungal communities between the continuous cropping and rotation cropping of soybean,maize and wheat.There were 11 potential pathogen and 11 potential biocontrol fungi identified,and the relative abundance of most of the potential pathogenic fungi increased during the long-term continuous cropping of all three crops.The relative abundance of most biocontrol fungi increased in long-term continuous soybean cropping but decreased in long-term continuous maize and wheat cropping.Our results indicate that the response of the soil fungal community structure to long-term continuous cropping varies based upon crop types.

Estimation of USLE crop and management factor values for crop rotation systems in China

Soil erosion on cropland is a major source of environmental problems in China ranging from the losses of a non-renewable resource and of nutrients at the source to contamination of downstream areas. Regional soil loss assessments using the Universal Soil Loss Equation (USLE) would supply a scientiifc basis for soil conservation planning. However, a lack of in-formation on the cover and management (C) factor for cropland, one of the most important factors in the USLE, has limited accurate regional assessments in China due to the large number of crops grown and their complicated rotation systems. In this study, single crop soil loss ratios (SLRs) were col ected and quantiifed for 10 primary crops from past studies or re-ports. The mean annual C values for 88 crop rotation systems in 12 cropping system regions were estimated based on the combined effects of single crop SLRs and the percentage of annual rainfal erosivity (R) during the corresponding periods for each system. The C values in different cropping system regions were compared and discussed. The results indicated that the SLRs of the 10 primary crops ranged from 0.15 to 0.74. The mean annual C value for al 88 crop rotation systems was 0.34, with a standard deviation of 0.12. The mean C values in the single, double and triple cropping zones were 0.37, 0.36 and 0.28, respectively, and the C value in the triple zone was signiifcantly different from those in single and double zones. The C values of dryland crop systems exhibited signiifcant differences in the single and triple cropping system regions but the differences in the double regions were not signiifcant. This study is the ifrst report of the C values of crop rotation systems in China at the national scale. It wil provide necessary and practical parameters for accurately assessing regional soil losses from cropland to guide soil conservation plans and to optimize crop rotation systems.

Increasing soil microbial biomass nitrogen in crop rotation systems by improving nitrogen resources under nitrogen application

Soil microbial biomass nitrogen(MBN)contains the largest proportion of biologically active nitrogen(N)in soil,and is considered as a crucial participant in soil N cycling.Agronomic management practices such as crop rotation and monocropping systems,dramatically affect MBN in agroecosystems.However,the influence of crop rotation and monocropping in agroecosystems on MBN remains unclear.A meta-analysis based on 203 published studies was conducted to quantify the effect of crop rotation and mono-cropping systems on MBN under synthetic N fertilizer application.The analysis showed that crop rotation significantly stimulated the response ratio(RR)of MBN to N fertilization and this parameter reached the highest levels in upland-fallow rotations.Upland mono-cropping did not change the RR of MBN to N application,however,the RR of MBN to N application in paddy mono-cropping increased.The difference between crop rotation and mono-cropping systems appeared to be due to the various cropping management scenarios,and the pattern,rate and duration of N addition.Crop rotation systems led to a more positive effect on soil total N(TN)and a smaller reduction in soil pH than mono-cropping systems.The RR of MBN to N application was positively correlated with the RR of mineral N only in crop rotation systems and with the RR of soil pH only in mono-cropping systems.Combining the results of Random Forest(RF)model and structural equation model showed that the predominant driving factors of MBN changes in crop rotation systems were soil mineral N and TN,while in mono-cropping systems the main driving factor was soil pH.Overall,our study indicates that crop rotation can be an effective way to enhance MBN by improving soil N resources,which promote the resistance of MBN to low pH induced by intensive synthetic N fertilizer application.

Varied previous crops on improving oilseed flax productivity in semiarid Loess Plateau in China

To investigate the effects of crop rotation on oilseed flax growth and yield,three season experiments were carried out in semi-arid area of Dingxi,Gansu from 2017 to 2019.The designed 6 rotational systems were FFF(flax-flaxflax),PFF(potato-flax-flax),WPF(wheat-potato-flax),FPF(flax-potato-flax),PWF(potato-wheat-flax)and FWF(flax-wheat-flax).Flax growth and yield investigation results showed that crop rotation increased leaf area duration,dry matter accumulation,seed nitrogen accumulation,water and nitrogen used efficiency,compared with continuous cropping of flax.Flaxseed yields in rotation systems were 22.23%–44.11%greater than those of continuous cropping system.Those in wheat and potato stubbles had higher tiller number(21.43%and 29.46%),more branches(14.24%and 6.97%),effective capsules(26.35%and 28.79%),higher water use efficiency(40.26%and 33.5%),higher nitrogen partial factor productivity(33.85%and 31.46%)and dry matter(41.98%and 25.47%)than those in oilseed flax stubble.It concluded that crop rotation system was an effective measure for oilseed flax productivity in semi-arid area by improving yield components and promoting biomass.

Effect of potassium on soil conservation and productivity of maize/cowpea based crop rotations in the north-west Indian Himalayas

Plots under conservation tillage may require higher amount of potassium(K) application for augmenting productivity due to its stratification in upper soil layers, thereby reducing K supplying capacity in a medium or long-term period. To test this hypothesis, a field experiment was performed in 2002-2003 and 2006-2007 to study the effect of K and several crop rotations on yield, water productivity, carbon sequestration, grain quality, soil K status and economic benefits derived in maize(Zea mays L)/cowpea(Vigna sinensis L.) based cropping system under minimum tillage(MT). All crops recorded higher grain yield with a higher dose of K(120 kg K2 O ha-1) than recommended K(40 kg K2 O ha-1). The five years' average yield data showed that higher K application(120 kg K2 O ha-1) produced 16.4%(P<0.05)more maize equivalent yield. Cowpea based rotation yielded 14.2%(P<0.05) higher production than maize based rotation. The maximum enhancement was found in cowpea-mustard rotation. Relationship between yield and sustainable indices revealed that only agronomic efficiency of fertilizer input was significantly correlated with yield. Similarly, higherdoses of K application not only increased the water use efficiency(WUE) of all crops, but also reduced runoff and soil loss by 16.5% and 15.8% under maize and 23.3% and 19.7% under cowpea cover, respectively. This study also revealed that on an average 16.5% of left over carbon input contributed to soil organic carbon(SOC). Here, cowpea based rotation with the higher K application increased carbon sequestration in soil. Potassium fertilization also significantly improved the nutritional value of harvested grain by increasing the protein content for maize(by 9.5%) and cowpea(by 10.6%). The oil content in mustard increased by 5.0% and 6.0% after maize and cowpea, respectively. Net return also increased with the application of the higher K than recommended K and the trend was similar to yield. Hence, the present study demonstrated the potential yield and profit gains along with resource conservation in the Indian Himalayas due to annual additions of higher amount of K than the recommended dose. The impact of high K application was maximum in the cowpea-mustard rotation.

Contribution of Promiscuous Soybean （Glycine max L.） to Upland Rice-based Cropping Systems in West Africa

A two-year on-farm study was carried out at Eglime in the moist savanna （MS） and Ouake in the dry savanna （DS） of Benin to evaluate the contribution of inoculation of dual-purpose soybean varieties to grain yield of upland NERICA rice fertilized with low N level. In 2005, four dual-purpose, promiscuous soybean varieties （cv. TGx1440-IE; TG×1448-2E; TG×1019-2EB; and TG×1844-18E）, and a popular improved variety （cv. Jupiter） were sown in 12 farmer fields with and without Bradyrhizobium japonicum inoculation. There was also land which was left fallow that acted as the control. In 2006, upland interspecific rice （NERICA 1） was sown in all the plots and supplied with 15 kg N haL. Dry matter yield, N accumulation, and net N-balance were significantly enhanced by over 40% with inoculation of cv. TG× 1844-18E than non-inoculation in the DS in comparison to other cultivars. There were no significant effects of inoculation of previous soybean cultivars on soybean grain yield and on the succeeding NERICA rice yield. Averaged over inoculation, previous cv. TG× 1019-2EB plots supplied with only 15 kg N hal gave the highest grain yield, more than twice the yield of control plots in the DS, possibly because of significant production of higher tillers, panicles and harvest index than the other cultivars; and it could be recommended for upland rice-based system for NERICA production.

Effect of Potash Application Patterns on Crop Yields Under Different Cultivation Systems

Three patterns of potash application were used in the corn-wheat and rice-wheat rotation experiments,which were conducted in the upland and wetland of Siyang County, northern Jiangsu Province, and the wetland of Liyang City, southern Jiangsu Province. The results of 5 cropping seasons (2 seasons/year)showed that the direct response of corn to K was larger than that of wheat, but no difference was found between rice and wheat in Siyang when the total annual amount of K was applied only in one cropping season. However, the response of wheat was much greater than that of rice in Liyang. If potash was applied in the preceding season, the residual effect of K on wheat was larger than that on rice both in Siyang and Liyang, but less than that on corn. The total effect (direct and residual effects) of K applied to corn or rice was greater than that to wheat in Siyang, but that to wheat was greater in Liyang. The direct and total effects of K application in the upland were larger than those in the wetland of Siyang; but for the wetland,the effects were larger in Liyang than in Siyang, especially in the wheat season. The results demonstrated that the most profitable practice to be recommended to the local farmers was to apply a limited amount of potash to only rice or corn but not to wheat. Equally applying half of the total annual amount of K to each of the crops may be advisable in order to lessen possible fertilization risks.

Land and Water Use in Rice-upland Crop Rotation Areas in Lower Ili River Basin, Kazakhstan

The lower Ili River Basin is located in semi-arid area, and the annual rainfall is 177mm. Therefore, the irrigation is inevitable for agriculture. Large-scale irrigated agriculture had been developed since 1960＇s in the lower parts of the river and the total irrigated area is about 32 000 hm2. In the project area, the paddy rice-upland crop rotation has been practiced. Due to the domestic water use for hydropower and agriculture as well as water use among riparian countries, the deficit of water for agriculture in the lower part has been concerned. The authors, therefore, conducted the field survey and water balance analysis of the Akdara irrigation project in the lower Ill River Basin in order to assess the land and water uses. Moreover, the impact of the water use on water environment to the basin was analyzed. The following results were obtained as following （1） the groundwater level in the irrigated district varied from 1.5 m to 3.5 m through year. （2） 1970＇s groundwater level was drastically raised from 8 m to 3 m and the groundwater had been recharged in this period. （3） Water use efficiency of agriculture, which is the ratio of total evapotranspiration to the total water withdrawal was as low as 0.23.

The Effect of Crop Rotation on Soil Nematode Community Composition in a Greenhouse

[Objective] The aim was to identify changes in a nematode community in response to crop rotation and to determine the appropriate catch crop for a greenhouse. [Method] The experiment was carried out in a typical 6-year-old greenhouse,in which cucumber crops were cultivated twice each year(in spring and autumn),and catch crops were planted in summer. The total number of nematodes was counted and nematode community indices were calculated after collecting soil samples in different stages. [Result] Total nematode abundance was decreased in the soils of catch crop in contrast with former crops(cucumber crops). The abundance of the nematode community was reduced in the treatment of crop rotation compared to the soils of catch crop. In addition, the number of nematode taxa was significantly reduced by the treatment of crown daisy compared to the treatments of following crops. Crop rotation regulated the functional composition of the nematode community by increasing the omnivores-predators functional group and decreasing the relative abundance of root herbivores. [Conclusion] These results indicate that crop rotation affects the nematode community in abundance, diversity and functional composition of the nematode community and crown daisy can be served as the most appropriate catch crop in the greenhouse.

Microbial Properties of a Ferric Lixisol as Affected by Long Term Crop Management and Fertilization Regimes in Burkina Faso, West Africa

We used an ongoing long-term field trial established since 1960 in Burkina Faso, to study the microbial properties of a Ferric Lixisol under various crop management and fertilization regimes. Microbial respiration rate, microbial biomass carbon (MBC) and soil bacteria’s number were assessed in soil samples taken at 0 - 20 cm depth. The crop management were continuous cropping of sorghum (Sorghum bicolor L.) (S/S) and rotation between sorghum and cowpea (Vigna unguiculata L.) (S/C), while the fertilization regimes were: 1) Control (te);2) Low rate of mineral fertilizer (fm);3) Low rate of mineral fertilizer + sorghum straw restitution (fmr);4) Low rate of mineral fertilizer + low rate of manure (fmo);5) High rate of mineral fertilizer (FM);and vii) High rate of mineral fertilizer + high rate of manure (FMO). The manure is applied every second year. The results indicate that sorghum/cowpea rotation significantly increase MBC and bacteria number as compared to continuous sorghum cropping. MBC ranged from 335.5 to 54.85 μg C g−1 soil with S/S and from 457.5 to 86.6 μg C g−1 soil with S/C. Application of high level of manure and mineral fertilizer increase microbial respiration rate and MBC. The highest MBC was observed with FMO and the lowest with the control. In general, the metabolic quotient (qCO2) was negatively impacted by the fertilization and cowpea rotation. For S/S rotation, qCO2 of the control was 1.5 to 2 times that of the treatments with low mineral fertilizer (fmr, fmo and fm) and 3 times that of the high rate of fertilization (FM and FMO). With S/C rotation, qCO2 of the control was 2 times of that fmr, FM and FMO and 0.8 times that of fmo and fm. Soil bacteria in the fmr were 63.6 and 12.4 times the control in the S/S and S/C rotations, respectively. In sum, combined application of manure and mineral fertilizer with crop rotation is the best management practices to improve in sustainable way microbial activities in tropical soil.

Effects of Direct Sowing under Mulch-Based Cropping System (DMC) on Cotton and Maize Yield and Chemical Characteristics of Ferruginous Soil (Lixisoil) in the South Sudan Area of Burkina Faso

To better understand the effects of direct sowing under mulch-based cropping system (DMC) in Burkina Faso’s cotton production systems, randomized blocks of Fisher experimental design were implemented at Farako-Ba research station from 2010 to 2019. The study was conducted on lixisoil to evaluate DMC effects on biomass production, crops yields and soil chemical properties in a maize and cotton rotation system associated with cover crop. Conventional tillage and direct seeding without cover crop were compared to DMC under B. ruziziensis (GERM. & EVRARD), DMC under B. ruziziensis + M. cochinchinensis mulch and DMC under C. juncea (L.) mulch used in association with maize. Biomass production, crop yields and soil chemistry were evaluated. Results showed that over 10 years, no-till with or without a cover crop provided cotton seed and maize yields that were statistically equivalent to the tillage commonly practiced by farmers. Cover crop has allowed increasing the biomass production compared to Conventional Tillage and Direct Seeding. Maize yield has not varied significantly with the cover crop. After 10 years of maize and cotton rotation, the improvement raised from +27% to +38% for organic matter and from +15% to +29% for nitrogen with DMC including legumes such as M. cochinchinensis and C. juncea compared to Conventional Tillage on 0 - 5 cm depth. No significant differences were found on soil pH like P2O5 and K2O content. Although DMC with C. juncea used as cover crop did not provide the best biomass production, it contributes to increase nitrogen and organic matter and presents better mineral balances in 10 years of rotation. The 5 - 10 cm and 10 - 20 cm were little influenced by DMC systems.

Impact of Crop Rotation on Pathotype and Genetic Structure of Phythophthora sojae in Fields

To estimate the impact of crop rotation on the pathotype and genetic structure of Phythophthora sojae in fields, 372 isolates of P. sojae were obtained from long-term localisation experimental fields in Heilongjiang Province of China. The hypocotyl inoculation method was used to characterize the virulence of P. sojae on 13 differential cultivars, and the amplified fragment length polymorphism（AFLP） technique was used to analyze difference in the genetic structure of P. sojae. The results indicated that an abundant diversity of genetic structures and pathotypes of P. sojae, a more uniform distribution of pathotypes and less dominance of pathotypes occurred in corn-soybean and wheat-soybean rotation fields than in a continuous soybean mono-cropping field. These findings suggested that P. sojae did not easily become the dominant race in rotation fields, which maintain disease resistance in soybean varieties. Therefore, the results of this study suggested that Phytophthora stem and root rot of soybeans could be effectively controlled by rotating soybeans with non-host crops of corn and wheat.

Visual Analysis of Crop Rotation Fallow Patterns in Recent 5 Years Based on CiteSpace

Based on the"Web of Science Core Collection"(SCIE database),this article used the visualization software CiteSpace to visualize and analyze the crop rotation fallow patterns in the past five years.It analyzed the countries,institutions,keywords and hot topics of related literature to explore their research characteristics and development,and to provide reference for crop rotation fallow research and practice.The research shows that:1)developed countries are the main research force in the field of crop rotation and fallowing,and the connection between the research of each country and each institution is not close;2)research hotspots can be mainly summarized as:crop growth and yield,greenhouse gas emissions and soil health analysis,and the research in this field is constantly refined,combining macro and micro;3)In recent years,there is a big gap between China and foreign countries in the field of crop rotation and fallow research.It is necessary to strengthen the cooperation with research institutions in developed countries in Europe and the United States,and to carry out cross-regional and interdisciplinary research cooperation to improve the quality of papers and scientific research level.

Effects of Root Growth of Deep and Shallow Rooting Rice Cultivars in Compacted Paddy Soils on Subsequent Rice Growth

Rice is often grown as multiple seasons in one year,alternating between flooded and upland systems.A major constraint,introduced from the flooded system,is a plough pan that may decrease rooting depth and productivity of follow-on upland rice.Roots penetrating the plough pan under flooded rice system can leave a legacy of weaker root growth pathways.Deeper rooting rice cultivars could have a bigger impact,but no direct evidence is available.To explore whether a deep rather than a shallow rooting rice cultivar grown in a flooded cropping cycle benefited deeper root growth of follow-on rice in an upland,reduced tillage cropping cycle,a simulated flooded paddy in greenhouse was planted with deep(Black Gora) and shallow(IR64) rooting cultivars and a plant-free control.Artificial plough pans were made in between the topsoil and subsoil to form different treatments with no plough pan(0.35 MPa),soft plough pan(1.03 MPa) and hard plough pan(1.70 MPa).After harvest of this ‘first season’ rice,the soil was drained and undisturbed to simulate zero-tillage upland and planted rice cultivar BRRI Dhan 28.The overall root length density(RLD),root surface area,the numbers of root tips and branching of BRRI Dhan 28 did not vary between plough pan and no plough pan treatments.Compared with the shallow rooting rice genotype,the deep rooting rice genotype as ‘first season’ crop produced 19% greater RLD,34% greater surface area and 29% more branching of BRRI Dhan 28 in the subsoil.In the topsoil,however,BRRI Dhan 28 had 28% greater RLD,35% greater surface area and 43% more branching for the shallow rather than deep rooting genotype planted in the ‘first season’.The results suggested that rice cultivar selection for a paddy cycle affects root growth of a follow-on rice crop grown under no-till,with benefits to subsoil access from deep rooting cultivars and topsoil proliferation for shallow rooting cultivars.