Years Of Continuous Cropping Research Articles

Crop type and management are key filtering factors of functional traits in the weed communities of regions with contrasting soils and climates

AbstractQuestionsWeed community composition responds to the interactions between environmental and management factors at different scales. The aim of this study was to disentangle the relative contributions of factors defining the composition of weed communities through crop type and agronomic management at the field scale, and climate and soil factors at the regional scale.LocationThe study was carried out in croplands in the phytogeographic provinces of Espinal and Pampas in central Argentina.MethodsThe floristic and functional compositions of weed communities in maize and soybean crops were characterized and compared using permutational multivariate analysis of variance and non‐metric multidimensional scaling in the two regions. The Espinal and the Pampas differ in soil and climatic characteristics, but crops are grown with similar management strategies due to the widespread use of no‐tillage and agrochemicals.ResultsYears of continuous cropping, previous crop and sowing date were the most important factors modulating the species composition of both crops at field scale. Perennials and exotics were more abundant in the Pampas, whereas natives were more abundant in the Espinal. Moreover, mechanically dispersed species were more abundant in maize crops in the Pampas. Annuals and barochoric species were closely related to the years of continuous cropping in maize. In soybean, more monocotyledonous species were observed in fields previously cropped with maize, whereas more dicotyledonous and C3 species were observed in fields previously cropped with soybean.ConclusionsDifferences in species composition depend mainly on climatic and biogeographical factors. In contrast, the functional composition of the weed communities in maize and soybean is mostly determined by local factors at field level, which are mostly related to crop identity and agronomic management. The effects of farming practices determine the functional composition of weed communities, which makes crop rotation and thorough cleaning of harvester machines key strategies in the development of weed management.

Analysis of Differential Metabolites and Bacterial Community Structure in Soils of a Pineapple Orchard in Different Continuous-cropping Years

Analysis of Differential Metabolites and Bacterial Community Structure in Soils of a Pineapple Orchard in Different Continuous-cropping Years

Effects of Rhizophagus intraradices on Plant Growth and the Composition of Microbial Communities in the Roots of Continuous Cropping Soybean at Maturity

Soybean is the major food and oil crop in the world. However, soybean continuous cropping can significantly reduce soybean yield. In this study, the effects of Rhizophagus intraradices on soybean growth and the composition of microbial communities in soybean roots under different continuous cropping regimes were investigated at maturity. The results showed that the mycorrhizal colonization rate was affected by R. intraradices and soybean continuous cropping. The mycorrhizal colonization rate was the highest in the inoculated soybean plants under 1 year of continuous cropping. Inoculation of R. intraradices significantly increased soybean plant growth. The greatest biomass parameters were obtained from the soybean plants inoculated with R. intraradices under 0 years of continuous cropping. Bacterial diversity was decreased by soybean continuous cropping, while the opposite result occurred for fungal diversity. Moreover, inoculation of R. intraradices could increase and decrease the diversity of bacteria and fungi in soybean roots, respectively. It also indicated that R. intraradices and soybean continuous cropping had significant effects on the composition of microbial communities in soybean roots. Proteobacteria and Ascomycota were the most dominant bacterial and fungal phylum in all samples, respectively. It would contribute to developing a biocontrol strategy to alleviate the soybean continuous cropping obstacles.

Effects of Different Continuous Cropping Years on Bacterial Community and Diversity of Cucumber Rhizosphere Soil in Solar-Greenhouse.

The rhizosphere soils from 1, 3, 5, and 7years of cucumber continuous cropping in solar-greenhouse were used as the research objects. The region of bacterial 16S rRNA was analyzed by Illumina MiSeq high-throughput sequencing technology. The effect of continuous cropping years on the microbial community structure and diversity in cucumber soil in the greenhouse was investigated. The physical and chemical properties of soil and the activities of urease and catalase were determined. The results showed that cucumber crop succession for different years affected the community composition of the bacteria at the phylum level, and the abundance of Proteobacteria, Chloroflexi, Gemmatimonadetes, Patescibacteria and Firmicutes gradually increased, while Actinobacteria in the soil significantly decreased. Among the top 15 significantly different genera, with the extension of successive years, the relative abundance of most genera in bacteria decreased after a small increase in year 3. The diversity results indicated that soil samples from continuous cropping for 7years had the lowest community diversity. PICRUSt analysis showed a decreasing trend in soil bacterial function as the cucumber crop succession age increased. In environmental factor clustering analysis, the soil bacterial community was significantly correlated with pH, available nitrogen (AN), soil urease (SUR) and available phosphorus (AP), and the effect on the bacterial community was expressed as SUR > AP > AN > pH.

Soil Metagenomics Reveals Effects of Continuous Sugarcane Cropping on the Structure and Functional Pathway of Rhizospheric Microbial Community.

The continuous cropping of plants can result in the disruption of the soil microbial community and caused significant declines in yields. However, there are few reports on the effects of continuous cropping of sugarcane on the microbial community structure and functional pathway. In the current study, we analyzed the structural and functional changes of microbial community structure in the rhizospheric soil of sugarcane in different continuous cropping years using Illumina Miseq high-throughput sequencing and metagenomics analysis. We collected rhizosphere soils from fields of no continuous cropping history (NCC), 10 years of continuous cropping (CC10), and 30 years of continuous cropping (CC30) periods in the Fujian province. The results demonstrated that continuous sugarcane cropping resulted in significant changes in the physicochemical properties of soil and the composition of soil bacterial and fungal communities. With the continuous cropping, the crop yield dramatically declined from NCC to CC30. Besides, the redundancy analysis (RDA) of the dominant bacterial and fungal phyla and soil physicochemical properties revealed that the structures of the bacterial and fungal communities were mainly driven by pH and TS. Analysis of potential functional pathways during the continuous cropping suggests that different KEGG pathways were enriched in different continuous cropping periods. The significant reduction of bacteria associated with rhizospheric soil nitrogen and sulfur cycling functions and enrichment of pathogenic bacteria may be responsible for the reduction of effective nitrogen and total sulfur content in rhizospheric soil of continuous sugarcane as well as the reduction of sugarcane yield and sugar content. Additionally, genes related to nitrogen and sulfur cycling were identified in our study, and the decreased abundance of nitrogen translocation genes and AprAB and DsrAB in the dissimilatory sulfate reduction pathway could be the cause of declined biomass. The findings of this study may provide a theoretical basis for uncovering the mechanism of obstacles in continuous sugarcane cropping and provide better guidance for sustainable development of the sugarcane.

Effects of Funneliformis mosseae on the fungal community in and soil properties of a continuously cropped soybean system

Root rot leads to a substantial decline in the production and quality of soybean (Glycine max), particularly in continuous cropping systems. Therefore, it is important to explore methods and mechanisms for the biocontrol of root rot pathogens. In this paper, the fungal community structure in the roots and rhizosphere soil was determined by high-throughput sequencing technology under non-inoculated- and Funneliformis mosseae-inoculated conditions. Moreover, redundancy analysis (RDA) was used to analyse the effects of F. mosseae on the fungal community structure and the physical and chemical properties of the soil. In different samples (roots and rhizosphere soils), the fungal diversity index in HN48 was higher than that in HN66, while that without F. mosseae inoculation was slightly higher than that under inoculation with F. mosseae under different years of continuous cropping. Compared to those of non-inoculated plants, Fusarium oxysporum and Rhizoctonia solani were the dominant fungi in different root samples of soybean varieties. However, the predominant genera in the rhizosphere soil samples shifted with inoculation and comprised Fusarium, Mortierella, Cryptococcus, Guehomyces and Corynespora. Moreover, after inoculation with F. mosseae, the relative abundance of F. oxysporum and R. solani decreased in the roots and rhizosphere soils. Additionally, RDA showed that the rhizosphere soils showed significant differences depending on F. mosseae inoculation, continuous cropping year, and soybean variety. This study provides new insights into the interaction effects of arbuscular mycorrhizal fungi (AMF) and other fungi in continuously cropped soybean systems.

Identification and verification of rhizosphere indicator microorganisms in tobacco root rot

AbstractThis study aimed to investigate the characteristics of the microbial community in the rhizosphere of tobacco (Nicotiana tabacum L.) and explore the potential microbiological indicators of tobacco root rot Rhizosphere soils of healthy and diseased tobacco over different continuous cropping years were sampled, and total DNA was extracted from the soils. Afterward, 16S rRNA combined with internal transcribed spacer gene sequencing was used to study the differences in microbial communities in the rhizosphere. A pot experiment was conducted to evaluate the effects of Paenibacillus polymyxa and Trichoderma harzianum on root rot, and the relative abundance of Fusarium, Rubrobacter, and Talaromyces spp. as the potential indicators of tobacco health were identified by sequencing data Bacterial and fungal diversity decreased with the increase in years of continuous cropping. The bacterial and fungal diversity in the rhizosphere with tobacco root rot was higher than that in the healthy rhizosphere. Rubrobacter and Talaromyces spp. were more abundant in the rhizosphere soil of healthy tobacco than in that of diseased tobacco. Paenibacillus polymyxa and T. harzianum treatment led to an increase in the relative abundance of Rubrobacter and Talaromyces spp., implying that this treatment could have a plant‐promoting effect Rubrobacter and Talaromyces spp. may serve as beneficial microbiological indicators of tobacco root rot, and P. polymyxa and T. harzianum may serve as antagonistic strains for the biocontrol of tobacco root rot.

Topsoil Bacterial Community Changes and Nutrient Dynamics Under Cereal Based Climate-Smart Agri-Food Systems.

Soil microorganisms play a critical role in soil biogeochemical processes, nutrient cycling, and resilience of agri-food systems and are immensely influenced by agronomic management practices. Understanding soil bacterial community and nutrient dynamics under contrasting management practices is of utmost importance for building climate-smart agri-food systems. Soil samples were collected at 0–15 cm soil depth from six management scenarios in long-term conservation agriculture (CA) and climate-smart agriculture (CSA) practices. These scenarios (Sc) involved; ScI-conventional tillage based rice-wheat rotation, ScII- partial CA based rice-wheat-mungbean, ScIII- partial CSA based rice-wheat-mungbean, ScIV is partial CSA based maize-wheat-mungbean, ScV and ScVI are CSA based scenarios, were similar to ScIII and ScIV respectively, layered with precision water & nutrient management. The sequencing of soil DNA results revealed that across the six scenarios, a total of forty bacterial phyla were observed, with Proteobacteria as dominant in all scenarios, followed by Acidobacteria and Actinobacteria. The relative abundance of Proteobacteria was 29% higher in rice-based CSA scenarios (ScIII and ScV) and 16% higher in maize-based CSA scenarios (ScIV and ScVI) compared to conventional-till practice (ScI). The relative abundance of Acidobacteria and Actinobacteria was respectively 29% and 91% higher in CT than CSA based rice and 27% and 110% higher than maize-based scenarios. Some taxa are present relatively in very low abundance or exclusively in some scenarios, but these might play important roles there. Three phyla are exclusively present in ScI and ScII i.e., Spirochaetes, Thermi, and Euryarchaeota. Shannon diversity index was 11% higher in CT compared to CSA scenarios. Maize based CSA scenarios recorded higher diversity indices than rice-based CSA scenarios. Similar to changes in soil bacterial community, the nutrient dynamics among the different scenarios also varied significantly. After nine years of continuous cropping, the soil organic carbon was improved by 111% and 31% in CSA and CA scenarios over the CT scenario. Similarly, the available nitrogen, phosphorus, and potassium were improved by, respectively, 38, 70, and 59% in CSA scenarios compared to the CT scenario. These results indicate that CSA based management has a positive influence on soil resilience in terms of relative abundances of bacterial groups, soil organic carbon & available plant nutrients and hence may play a critical role in the sustainability of the intensive cereal based agri-food systems.

31-year contrasting agricultural managements affect the distribution of organic carbon in aggregate-sized fractions of a Mollisol

Evaluation of soil organic carbon (SOC) dynamics is often limited by the complexity of soil matrix. Quantitative information on the distribution of SOC within aggregate hierarchy will help elucidate the carbon flow in soil matrix. However, this knowledge still needs to be documented. Soils were sampled from a surface Mollisol with plots under 100 years of continuous cropping, 31 years of simulated overgrazing to severely degraded bareland, and grassland restoration from cropped soil. A combined density and chemical fractionation procedure within water-stable aggregate was utilized to quantify the distribution of OC after long-term different land use patterns. Results showed that grassland significantly increased total SOC and mean aggregate associated OC compared to initial soil in 1985 with total SOC (g kg−1 soil) from 46.1 to 31.7 and mean aggregate associated OC (g kg−1 aggregate) from 31.6 to 44.7. Converting cropland to grassland also enhanced the formation of macroaggregates (>0.25 mm) (from 34.7% to 52.2%) and increased the OC concentrations in density and humic fractions by 48.3%-75.9% within aggregates. But the proportions of OC in density and humic fractions to SOC only increased in macroaggregates in grassland. Alternatively, converting cropland to bareland caused substantial depletion of total SOC, macroaggregates and their associated OC concentrations. The SOC (g kg−1 soil) and mean aggregate associated OC (g kg−1 aggregate) significantly decreased from 31.7 to 25.7 and from 31.6 to 26.2, respectively. While the OC concentration of density and humic fractions within aggregates in bareland did not show significant decreases. Principal component analysis demonstrated that the soils were developed by contrasting land use changes, with the grassland soil being more associated with labile OC fractions within macroaggregats and bareland soil more associated with recalcitrant OC fractions within microaggregates and silt-clay units. These findings highlighted the favorable preservation of plant-derived carbon within soil aggregates, particularly in the labile OC fractions within macroaggregates under high plant inputs with 31 years of grassland conversion. For the cropland and bareland soils without organic inputs, more OC was stabilized within fine aggregates via organo-mineral interactions, tending to be more recalcitrant.

Continuous Cropping Affects Gross Nitrogen Transformations in Subtropical Acidic Soils Under Greenhouse Cultivation

Relationship between gross N transformation rate and continuous cropping years in the greenhouse soil is largely unknown. This study aimed to investigate the mechanism of the gross N transformation rate changes in greenhouse subtropical acidic soils under different continuous cropping years. The 15N isotope tracer method was used to study the effects of greenhouse soil under 4 years of continuous cropping (C4), 5 years of continuous cropping (C5), and 7 years of continuous cropping (C7) of lily (Lilium brownii), respectively, on soil N transformation with the N tracer model. The results showed that the main soil N transformation processes were N mineralization, autotrophic nitrification, and NO3−-N immobilization under the three continuous cropping years. After continuous cropping, the gross N mineralization rate, autotrophic nitrification rate, and NO3−-N immobilization rate increased with the increase of continuous cropping years. Specifically, the gross N mineralization rate was 0.62~0.85 mg N kg−1 day−1, the autotrophic nitrification rate was 1.08~3.24 mg N kg−1 day−1, and the NO3−-N immobilization rate was 0.30~0.62 mg N kg−1 day−1. Moreover, the positive difference between the autotrophic nitrification rate and immobilization rate of NO3−-N became greater with the increase of continuous cropping years, which might have been the main reason for the accumulation of NO3−-N in greenhouse subtropical soils. These findings contribute to the understanding of the mechanism of soil secondary salinization formation and provide ideas for prevention of secondary salinization under long-term continuous cropping.

Dynamics of soil properties and fungal community structure in continuous-cropped alfalfa fields in Northeast China

To compensate for the seasonal imbalance between livestock and forage yield in the cold region of Northeast China, alfalfa (Medicago sativa L.) continuous cropping has been widely employed in animal husbandry. However, the effects of continuous cropping of alfalfa on soil properties, including physical, chemical and biological properties, are poorly understood. In this study, we investigated the soil properties and fungal community composition of alfalfa fields under continuous cropping for different time periods (i.e., 1, 2, 6, 9, 12, 13 and 35 years). The results showed that soil moisture, total C, total N, NO3−-N and available K content decreased at less than 10 years of continuous cropping and then increased at more than 10 years of continuous cropping, but soil total P and available P content showed the opposite tendency. The soil fungal community composition determined using Illumina Miseq sequencing showed that continuous cropping increased the fungal alpha diversity and changed the fungal community structure. The relative abundances of Guehomyces and Chaetomium decreased, but the relative abundances of Phaeomycocentrospora and Paecilomyces increased with continuous cropping time. In addition, continuous cropping of alfalfa increased the relative abundances of some plant pathogens, such as Haematonectria haematococca and Cyphellophora sp. Soil total P and available P content were important soil factors affecting the soil fungal community diversity, fungal community structure and the relative abundances of specific fungi in this alfalfa continuous cropping system.

Effect of long-term nutrient management practices on soil micronutrient concentrations and uptake under a rice–wheat cropping system

AbstractA field experiment was conducted to study the long-term effects of nutrient management practices on micronutrient concentrations in soil and their uptake by crops under a long-term rice–wheat cropping system. The treatments comprised different combinations of N, P, K, Zn and farm yard manure (FYM), used as nutrient management practices. After 25 years of continuous cropping, the higher grain yields and uptake of iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn) were obtained when FYM was applied along with mineral sources of nitrogen, phosphorus and potassium (NPK) when compared to mineral sources of NPK alone. The residual effect of FYM, applied to rice, on the yield of subsequent wheat was significant. The application of mineral NPK with FYM recorded higher diethylene triamine penta acetic acid extracted (DTPA)-Fe, Mn and Cu concentrations in the soil compared to any other treatment. The plots with Zn application showed higher DTPA-Zn concentration in the soil compared to any other treatments. The available Fe, Mn and Cu in the soil were higher than their critical limits and the soil was low in Zn where inorganic fertilizers were applied alone (without Zn). Integrated application of mineral NPK and FYM to the rice crop and mineral NPK to wheat was found to be the best nutrient management practice in producing higher yields of rice and wheat and improve long-term soil micronutrient concentrations.

Biochar Effects on Bacterial Community and Metabolic Pathways in Continuously Cotton-Cropped Soil

This study was purposely designed to understand the role of biochar in soil bacterial community structure and diversity over continuous cotton-cropping years. The research questions addressed were what was the bacterial taxonomic status, the microbial community diversity and the cluster distribution and prediction of microbial metabolic functions across the continuous cotton-cropping years (5, 10, 20, and 40 years) under different biochar treatment rates (0 t ha-1, 20 t ha−1, and 40 t ha−1)? High-throughput sequencing of the 16S and integrated bioinformatic analysis techniques was used. The result showed that biochar of 20 t ha−1 and 40 t ha−1 application rate of up to 20 years of continuously cotton-cropped soils significantly increased bacterial diversity. However, higher application rates of up to 40 years on continuously cropped soils did not significantly change bacterial diversity and richness as compared to the 20 years of continuously cropped soil. The study also established the optimum bacterial diversity to be at 20 years of continuous cotton cropping, and the value were highest at 20 t ha−1 and 40 t ha−1 of biochar application rates. In contrast to the 20 years of continuous biochar application in cropped soils, higher application rates of up to 40 years on continuously cropped soils did not significantly change bacterial diversity and richness. In conclusion, controlled biochar application positively influences soil bacterial community and metabolic pathways in continuously cropped cotton soils. This indicates the significance of biochar application under different years of continuous cotton cropping on soil bacterial community structure, diversity, cluster distribution, and metabolic functions.

Potassium supplying capacity of a red soil from eastern India after forty-two years of continuous cropping and fertilization

Fertilizer use in Indian agriculture is skewed towards nitrogen (N) and phosphorus (P), and farmers generally neglect potassium (K) input ignoring K requirement of crops. We, therefore, studied the long-term effect of imbalanced fertilization (i.e. without K) on K supplying capacity of a kaolinitic red soil (Typic Haplustalf) after 42 years of intensive cultivation. Soil samples (0–15 and 15–30 cm) were collected after the completion of 42 cropping cycles from an on-going long-term fertilizer experiment located at Birsa Agricultural University, Ranchi, India, from six treatments, viz. control (unfertilized), fertilizer N, NP, NPK, 150% NPK (1.5 times of NPK) and NPK + FYM (NPK + farmyard manure), along with adjacent uncultivated land. Soil K pools, clay minerals, quantity-intensity relationship and K release kinetics along with grain yield and K uptake of soybean and wheat were studied. Among the treatments, NP treated soils showed the lowest amounts of labile (KL) and non-exchangeable K (Knex). Equilibrium activity ratio (AReK) and non-specifically held K (−ΔK0) were also lowest under NP treatment. The gap between equilibrium exchangeable K (EK0) and minimum exchangeable K (EKmin) was minimum under NP. Cropping and fertilization-induced transformation in clay minerals was noticed wherein continuous neglect of K fertilizer led to a decrease in illite content with a concomitant increase in interstratified minerals. On the other hand, noticeably lower alteration in clay minerals and comparatively less depletion in overall K-supplying capacity of soil were recorded under K addition as compared to imbalanced fertilization (i.e. without K). Soybean showed a significant positive response to K application. The study thus underlined the necessity of adequate K input for the sustenance of soil health, inherent K-supplying capacity and crop productivity.

Correlation Between Soil Organic and Inorganic Carbon and Environmental Factors in Cotton Fields in Different Continuous Cropping Years in the Oasis of the Northern Tarim Basin

Studying the characteristics of soil organic carbon (SOC) and soil inorganic carbon (SIC), and their relationship with environmental factors is helpful for understanding soil ecological processes, and providing theoretical support for research on the global carbon budget. Based on the oasis in the northern margin of Tarim Basin, this study analyzed the characteristics of the soil carbon pool, and, combined with redundancy and path analyses, explored the relationship between SOC and SIC, and their environmental factors. The results showed that there was a significant difference (P<0.05) in SOC and SIC contents in cotton fields with different continuous cropping years (P<0.05). With an increase in continuous cropping years, the SOC content increased firstly and then decreased, while the SIC content decreased firstly and then increased (P<0.05). The SOC content was the highest in the 0-20 cm layer, while the SIC content was the highest in the 20-50 cm layer. The importance of environmental factors on the characteristics of the soil carbon pool was deduced by redundancy analysis. The order of importance was phosphatase activity > pH > sucrase activity > catalase activity > total N > available P > available K > soil moisture content > urease activity > electrical conductivity (EC); phosphatase activity, pH value, invertase activity, catalase activity, total nitrogen, available phosphorus, and available potassium showed significant correlation with SOC and SIC (P<0.01). Soil moisture and urease activity showed significant correlation with SOC and SIC (P<0.05). The path analysis showed that available P had a direct effect on the SOC content; it was the main factor affecting it. The urease activity had a direct effect on SIC; it was the main factor affecting it. This study of soil carbon pools in arid and semiarid regions is the basis for evaluating the "source/sink" effect of soil carbon in farmland ecosystems, and is of great significance for studying the global carbon budget and land carbon cycle mechanism.

Evaluating multiple resistance to major diseases in a core set of inbred lines of Brassica rapa at seedling stage

Years of continuous cropping of Brassica rapa crops in main producing areas in China lead to the outbreak of some diseases, such as downy mildew (DM), turnip mosaic virus (TuMV), black rot (BR), verticillium wilt (VW), and club root (CR), causing severe loss in yield and quality. Resistance to the aforementioned diseases of 302 inbred lines of Brassica rapa to DM, TuMV, BR, VW, and CR were evaluated under controlled conditions at seedling stage. Forty lines were identified to be highly resistant to DM, 13 to TuMV, 0 to BR, 30 to VW, and 24 to CR. Among the 302 lines, 121 exhibited high resistance to two diseases, 70 to three diseases, and eight to four diseases, but none of these lines showed comprehensive resistance to all the five diseases. Chinese cabbage lines XDYFX, 536S, 536Q, DY×T, and CR-C, and Pak choi lines DFAK×SH, NB, and SYHTC showed high resistance to four diseases and therefore represent elite materials in multiple-disease resistance breeding. In addition, different disease resistance tendencies were discovered in diverse Chinese cabbage groups which were classified in different ways, such as the ecotype, heading-type, and geographical origin.

Effect of 36 Years of Continuous Cropping and Fertilization on Productivity, Micro and Secondary Nutrient Status and Uptake by Maize-wheat Cropping System in Western Himalayas

Effect of 36 Years of Continuous Cropping and Fertilization on Productivity, Micro and Secondary Nutrient Status and Uptake by Maize-wheat Cropping System in Western Himalayas

Long-term effects of organic manure and inorganic fertilization on sustainability and chemical soil quality indicators of soybean-wheat cropping system in the Indian mid-Himalayas

A long-term field study was commenced in 1995-96 to assess the impact of continuous application of inorganic fertilizers and organic manure on sustainability, productivity and chemical indicators of soil quality in an irrigated soybean-wheat cropping system (SWCS). Six treatments comprised inorganic fertilizers (NPK) and manure (M) either alone or in combination. Soybean yield indicated declining trend −22.50, −56.0 and −25.0 kg ha−1 year−1 under unfertilized control, sole nitrogen and NPK treatments, respectively while addition of organic manure resulted in a positive yield trend. Plot receiving NPK had positive yield trend of 118 kg ha−1 year−1 in wheat crop. The highest positive yield trend was obtained with manure (M) and NPK treatment, values being 17.60 and 191 kg ha−1 year−1 in soybean and wheat, respectively. Significantly (p < 0.05) the highest grain yield was also observed under the MNPK treatment, soybean and wheat reporting 2.56 and 4.31 Mg ha−1, respectively which was ∼ 30 and 25% higher than NPK treatment, respectively. Significantly higher yield sustainability was observed in the plots receiving manure either alone (0.77 and 0.51) or in combination with N fertilizer (0.79 and 0.79) or with NPK, MNPK (0.89 and 0.92) compared to the treatment, which did not receive the manure in both soybean and wheat crops. Due to continuous cropping and fertilization over the years, available N increased from initial values in all the plots except CK (−3.89 and −3.59%) under 0–15 and 15–30 cm soil depths. Negative trends for available P were observed in all treatments except MNPK over the years of continuous cropping. A significantly decreasing trend for the available K was observed under CK, N, NPK and M treatments, whereas a significant accumulation was estimated under MN and MNPK treated plots in both soil depths. Significantly higher accumulation of available N, P and K were observed under MNPK treatment compared to the rest of the treatments. The treatment MNPK had the highest soil DTPA-extractable Fe, Mn, Zn and Cu after 21-years of cropping and fertilization. The sustainable yield index (SYI) values indicated that soybean yield was more sustainable compared to the wheat. The SYI and grain yield of soybean had significantly higher correlation with available N, P, Fe, Mn, Zn and Cu. Soil available N had significantly higher values of coefficient of regression (r2) for wheat (0.98; p = 0.001 and 0.97; p = 0.001) compared to soybean (0.74; p = 0.029 and 0.74; p = 0.027) under 0–15 and 15–30 cm soil depths, respectively. The SYI was strongly positively correlated with chemical indicators of soil quality. Hence, SYI could potentially be used for assessment of agricultural productivity and soil sustainability elsewhere.

Shifting crop-pasture rotations to no-till annual cropping reduces soil quality and wheat yield

When crop-pasture rotations are converted to continuous no-till annual cropping systems, the grain yield of wheat crops in the rotation stagnates or declines in response to the number of years of continuous cropping (YCC). We studied the soil properties underlining the response of wheat yield to YCC in 80 on-farm trials during three growing seasons. We determined the frontier yield and the yield gap under limited (YF−, or best technical means) and unlimited nutrient supply (YF+, supplemental additions of nitrogen, phosphorus, potassium and sulfur). For each field, we assessed soil quality based on soil organic carbon (SOC), phosphorus (Bray I), soil texture, field water infiltration rate (INF), and potentially mineralizable nitrogen (PMN). We also calculated a climatological index (CI) that combines temperature, radiation and precipitation during both the spike and early grain growth phases. We estimated YF−and YF+using stochastic frontier production functions with CI, YCC and soil properties as predictor variables. The YF−and YF+ after a perennial pasture were 6.9 and 8.4 Mg ha−1, with the 1.5 Mg ha−1 yield gap attributable to nutrient supply limitations. However, while YF− declined by 0.12 Mg ha−1 y−1 from YCC = 1 to 10 (P ≤ 0.05), YF+ stayed at roughly the same level till YCC = 5, declining thereafter by 0.17 Mg ha−1 y−1 (P ≤ 0.05). Reduced soil nutrient supply capacity, partially quantified as PMN and amendable with supplemental fertilization, limited YF− during the first five years after pasture. The subsequent YF− decline could not be compensated by increased nutrient supply. After 10 years, the yield gap between YF+ for YCC = 1 and YF− for YCC = 10, increased to 2.6 Mg ha−1. Up to 40% of this gap was explained by a deterioration of the soil quality that was independent of the nutrient supply; the YF+ decline after five years of continuous cropping was best explained by INF. Thus, continuous annual cropping under no-till generated a progressive increase in the wheat yield gap associated to deterioration in soil quality that could be corrected with supplemental fertilization only in the first years after a pasture, but not thereafter, when soil physical properties seemed to degrade past a threshold that limited wheat yield and reduced nutrient use efficiency.

Arbuscular mycorrhizal fungal communities in the rhizosphere of a continuous cropping soybean system at the seedling stage.

Arbuscular mycorrhizae (AM) fungi play a crucial role in the growth of soybean; however, the planting system employed is thought to have an effect on AM fungal communities in the rhizosphere. This study was performed to explore the influence of continuous soybean cropping on the diversity of Arbuscular mycorrhizal (AM) fungi, and to identify the dominant AM fungus during the seedling stage. Three soybean cultivars were planted under two and three years continuous cropping, respectively. The diversity of AM fungi in the rhizosphere soil at the seedling stage was subsequently analyzed using polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE). The results showed that an increase in cropping years improved the colonization rate of AM in all three soybean cultivars. Moreover, the dominant species were found to be Funneliformis mosseae and Glomus species. The results of cluster analysis further confirmed that the number of years of continuous cropping significantly affected the composition of rhizospheric AM fungal communities in different soybean cultivars.