Soil microbial community composition by crop type under rotation diversification.

BACKGROUND: Crop rotation is an important agricultural practice that often affects the metabolic processes of soil microorganisms through the composition and combination of crops, thereby altering nutrient cycling and supply to the soil. Although the benefits of crop rotation have been extensively discussed, the effects and mechanisms of different crop combinations on the soil microbial community structure in specific environments still need to be analyzed in detail. MATERIALS AND METHODS: In this study, six crop rotation systems were selected, for which the spring crops were mainly tobacco or gramineous crops: AT (asparagus lettuce and tobacco rotation), BT (broad bean and tobacco rotation), OT (oilseed rape and tobacco rotation), AM (asparagus lettuce and maize rotation), BM (broad bean and maize rotation), and OR (oilseed rape and rice rotation). All crops had been cultivated for > 10 years. Soil samples were collected when the rotation was completed in spring, after which the soil properties, composition, and functions of bacterial and fungal communities were analyzed. RESULTS: The results indicate that spring cultivated crops play a more dominant role in the crop rotation systems than do autumn cultivated crops. Crop rotation systems with the same spring crops have similar soil properties and microbial community compositions. pH and AK are the most important factors driving microbial community changes, and bacteria are more sensitive to environmental responses than fungi. Rotation using tobacco systems led to soil acidification and a decrease in microbial diversity, while the number of biomarkers and taxonomic indicator species differed between rotation patterns. Symbiotic network analysis revealed that the network complexity of OT and BM was the highest, and that the network density of tobacco systems was lower than that of gramineous systems. CONCLUSIONS: Different crop rotation combinations influence both soil microbial communities and soil nutrient conditions. The spring crops in the crop rotation systems had stronger dominating effects, and the soil bacteria were more sensitive than the fungi were to environmental changes. The tobacco rotation system can cause soil acidification and thereby affect soil sustainability, while the complexity of soil microbial networks is lower than that of gramineous systems. These results provide a reference for future sustainable applications of rotation crop systems.

Root-exuded benzoxazinoids can alleviate negative plant-soil feedbacks.

Plants can suppress the growth of other plants by modifying soil properties. These negative plant-soil feedbacks are often species-specific, suggesting that some plants possess resistance strategies. However, the underlying mechanisms remain largely unknown. Here, we investigated whether benzoxazinoids, a class of dominant secondary metabolites that are exuded into the soil by maize and other cereals, allow maize plants to cope with plant-soil feedbacks. We find that three out of five tested crop species reduce maize (Zea mays L.) performance via negative plant-soil feedbacks relative to the mean across species. This effect is partially alleviated by the capacity of maize plants to produce benzoxazinoids. Soil complementation with purified benzoxazinoids restores the protective effect for benzoxazinoid-deficient mutants. Sterilization and reinoculation experiments suggest that benzoxazinoid-mediated protection acts via changes in soil biota. Substantial variation of the protective effect between experiments and soil types illustrates context dependency. In conclusion, exuded plant secondary metabolites allow plants to cope with plant-soil feedbacks. These findings expand the functional repertoire of plant secondary metabolites and reveal a mechanism by which plants can resist negative effects of soil feedbacks. The uncovered phenomenon may represent a promising avenue to stabilize plant performance in crop rotations.

Field evaluation of oil crop rotations for cadmium remediation and safe vegetable oil production across five sites with varying contamination levels.

Oil crops have the potential to remediate cadmium (Cd)-contaminated farmland while producing safe vegetable oil. However, it is currently unknown whether different oil crops can remediate varying levels of Cd contamination in farmland. This study assessed agricultural fields in southern China contaminated with Cd levels ranging from 0.42 to 10.3 mg/kg. Three representative oilseed crops winter rape, oil sunflower, and peanut were selected for field experiments under two rotation systems. The effects of different rotation systems on remediating various Cd contamination levels were compared to evaluate the feasibility and potential of a two oil crop rotation system. All three crops showed good tolerance to Cd without signs of biomass deficiency. The biomass produced by the rape-oil sunflower and rape-peanut rotation systems was 33.44-459.00 g/ha and 30.64-281.40 g/ha, respectively. The Cd concentration in the oil products obtained complied with existing national and international standards (0.05 mg/kg). The remediation efficiency of the rape-oil sunflower and rape-peanut rotation systems was 1.98-7.37 % and 1.21-4.94 %, respectively. However, the remediation efficiencies and enrichment capacities of both rotation systems were somewhat inhibited by heavy Cd contamination (10.3 mg/kg). Therefore, the agricultural model of rotating two oilseed crops can be implemented in Cd-contaminated farmland at all levels but is more suitable for light to moderate Cd contamination.

Host Range Characterization of Phytophthora sansomeana Across Corn, Soybean, Wheat, Winter Cereal Rye, Dry Bean, and Oats and an In Vitro Assessment of Seed Treatment Sensitivity.

Formally described in 2009, Phytophthora sansomeana is a pathogen of increasing interest in native, agricultural, and horticulturally important plant species. The objective of this study was to elucidate the symptomatic and asymptomatic host range of P. sansomeana on six agricultural crop species commonly used in field crop rotations in Michigan. In addition, sensitivity to oomicides commonly used in seed treatments, including oxathiapiprolin, mefenoxam, ethaboxam, and pyraclostrobin, was performed to aid in disease management recommendations. Plant biomass, quantity of P. sansomeana DNA in roots, and reisolations were used to assess pathogenicity and virulence of 18 isolates of P. sansomeana on each plant species using an inoculated seedling growth chamber assay. Isolates displayed varying levels of virulence to the hosts tested. Reisolations were completed for each plant species tested, and varying quantities of P. sansomeana DNA were found within all plant species root samples. Corn, wheat, soybean, dry bean, and winter cereal rye plants were symptomatic hosts with significant reduction observed in the total plant biomass. No significant reduction in total plant biomass was observed in oats, and oat roots harbored the least amount of P. sansomeana DNA. No P. sansomeana isolates were insensitive to the oomicide compounds tested with mean absolute inhibition (EC50) values of fungicide required for 50% growth inhibition values of 7.8 × 10-2 µg/ml for mefenoxam, 1.13 × 10-1 µg/ml for ethaboxam, 2.6 × 10-2 µg/ml for oxathiapiprolin, and 3.04 × 10-1 µg/ml for pyraclostrobin. These results suggest that common crop rotations in Michigan may not be a viable option to reduce soilborne inoculum accumulation and oomicide seed treatments could be considered for early-season management of P. sansomeana.

Cover Crop and Crop Rotation Effects on Tissue and Soil Population Dynamics of Macrophomina phaseolina and Yield Under No-Till System.

The effects of crop rotation and winter cover crops on soybean yield and colony-forming (CFU) units of Macrophomina phaseolina, the causal agent of charcoal rot (CR), are poorly understood. A field trial was conducted from 2011 to 2015 to evaluate (i) the impact of crop rotation consisting of soybean (Glycine max [L.] Merr.) following cotton (Gossypium hirsutum L.), soybean following corn (Zea mays L.), and soybean following soybean over a 2-year rotation and its interaction with cover crop and (ii) the impact of different cover crops on a continuous soybean crop over a 5-year period. This trial was conducted in a field with 10 subsequent years of cover crop and rotation treatments. Cover crops consisted of winter wheat (Triticum aestivum L.) and Austrian winter pea (Pisum sativum L. subsp. sativum var. arvense), hairy vetch (Vicia villosa Roth), and a fallow treatment was evaluated with and without poultry litter application (bio-cover). Tissue CFU of M. phaseolina varied significantly between crop rotation treatments: plots where soybean was grown following cotton had significantly greater tissue CFU than plots following soybean. Poultry litter and hairy vetch cover cropping caused increased tissue CFU, though this effect differed by year and crop rotation treatment. Soil CFU in 2015 was substantially lower compared with 2011. However, under some crop rotation sequences, plots in the fallow treatment had significantly greater soil CFU than plots where hairy vetch and wheat was grown as a cover crop. Yield was greater in 2015 compared with 2011. There was a significant interaction of the previous crop in the rotation with year, and greater yield was observed in plots planted following cotton in the rotation in 2015 but not in 2011. The result from the continuous soybean planted over 5 years showed that there were no significant overall effects of any of the cover crop treatments nor was there interaction between cover crop treatment and year on yield. The lack of significant interaction between crop rotation and cover crop and the absence of significant differences between cover crop treatments in continuous soybean planting suggest that cover crop recommendations for midsouthern soybean growers may need to be independent of crop rotation and be based on long-term crop needs.

Diversified crop rotations improve soil microbial communities and functions in a six-year field experiment.

Diversified crop rotations can help mitigate the negative impacts of increased agricultural intensity on the sustainability of agroecosystems. However, the impact of crop rotation diversity on the complexity of soil microbial association networks and ecological functions is still not well understood. In this study, a 6-year field experiment was conducted to evaluate how six different crop rotations change the composition and network complexity of soil microbial communities, as well as their related ecological functions. Microbial traits were measured in six crop rotations with different crop diversity index (CDI) during 2016-2022, including winter wheat-summer maize (CDI 1, WM) as the control, sweet potato→winter wheat-summer maize (CDI 1.5, SpWM), peanut→winter wheat-summer maize (CDI 1.5, PWM), soybean→winter wheat-summer maize (CDI 1.5, SWM), spring maize→winter wheat-summer maize (CDI 1.5, SmWM), and ryegrass-sweet sorghum→winter wheat-summer maize (CDI 2, RSWM). The study findings indicated that diversified crop rotations significantly increased ASV richness of both bacterial and fungal communities after 6-year treatments, and the ß-diversity profiles of bacterial and fungal communities significantly distinguished at the year of 2022 from 2016. The relative abundance of Acidobacteria and Chloroflexi was significantly enriched in SpWM rotation at 2022, while Basidiomycota significantly declined in five diversified rotations compared to WM. Diversified crop rotations at 2022 increased the complexity and density of bacterial and fungal networks than 2016. SpWM and PWM rotations had the highest functional groups involved in chemoheterotrophy and saprotroph, respectively. Structural equation modelling (SEM) also revealed that diversified crop rotations increased soil nutrients through improving the composition of bacterial communities and the augmented intricacy of the interconnections within both bacterial and fungal communities. This research underscores the importance of preserving the diversity and ecological functions of soil microorganisms in the nutrient-recycling processes for efficient agricultural practices.

Crop diversification promotes soil aggregation and carbon accumulation in global agroecosystems: A meta-analysis.

Soil aggregation contributes to the stability of soil structure and the sequestration of soil organic carbon (SOC), making it an important indicator of soil health in agroecosystems. Crop diversification is considered a rational management practice for promoting sustainable agriculture. However, the complexity of cropping systems and crop species across different regions limits our comprehensive understanding of soil aggregation and associated carbon (C) content under crop diversification. Therefore, we conducted a meta-analysis by integrating 1924 observations from three diversification strategies (cover crops, crop rotation, and intercropping) in global agroecosystems to explore the effects of crop diversification on soil aggregates and associated C content. The results showed that compared to monoculture, crop diversification significantly increased the mean weight diameter and bulk soil C by 7.5% and 3.3%, respectively. Furthermore, there was a significant increase in the proportion of macroaggregates and their associated C content by 5.0% and 12.5%, while there was a significant decrease in the proportion of microaggregates as well as silt-clay fractions along with their associated C under crop diversification. Through further analysis, we identified several important factors that influence changes in soil aggregation and C content induced by crop diversification including climatic conditions, soil properties, crop species, and agronomic practices at the experimental sites. Interestingly, no significant differences were found among the three cropping systems (cover crops, crop rotation, and intercropping), while the effects induced by crop diversifications showed relatively consistent results for monoculture crops as well as additive crops and crop diversity. Moreover, the impact of crop diversification on soil aggregates and associated C content is influenced by soil properties such as pH and SOC. In general, our findings demonstrate that crop diversification promotes soil aggregation and enhances SOC levels in agroecosystems worldwide.

Regulation of wheat yield by soil multifunctionality and metagenomic-based microbial degradation potentials under crop rotations.

Crop rotation benefits soil fertility and crop yield by providing organic components including cellulose, lignin, chitin, and glucans that are mainly degraded by soil microbial carbohydrate-active enzymes (CAZymes). However, the impacts of crop rotation on soil microbial CAZyme genes are not well understood. Hence, CAZyme genes and families involved in the degradation of differentially originated organic components were investigated using metagenomics among distinct crop rotations. Crop rotation had a more significant effect on soil nitrogen than on carbon fractions with higher content in the complex rotation referring to alfalfa (Medicago sativa L.; 4 year)-potato (Solanum tuberosum L.; 1 year)-winter wheat (3 year; A4PoW3). The composition of soil microbial CAZyme genes related to the degradation of fungi-derived components was more affected by crop rotation compared with the degradation of plant- and bacteria-derived components. The total abundance of CAZyme genes and families was significantly higher in the complex rotation. Notably, CAZyme genes belonging to glycoside hydrolase and glycosyl transferase families had more connections in their network. Moreover, key genes including CE4, GH20, and GH23 assembled toward the middle of the network, and were significantly regulated by dominant soil nitrogen fractions including soil potential nitrogen mineralization and microbial biomass nitrogen. Soil multifunctionality was mostly explained by the composition and total abundance of CAZyme genes, but wheat grain yield was profoundly regulated by fungi-derived components degradation genes under effects of dominant nitrogen fractions. Overall, the findings provide deep insight into the degradation potentials of soil microbial CAZyme genes for developing sustainable crop rotational agroecosystems.

Cropping System Diversification Influences Soil Microbial Diversity in Subtropical Dryland Farming Systems.

Conventional dryland cropping systems are characterised by low crop diversity and frequent fallows. This has significant impacts on soil microbes that underpin soil function. Diversifying crop rotations can potentially counter these effects; however, limited data exists on the impacts of diversified crop rotations on soil microbes in drylands. Using phylogenetic marker gene sequencing, we characterised soil microbial diversity in conventional and diversified dryland crop rotations in subtropical Australia. This included winter and summer dominant rotations. Conventional systems were cereal-dominant with a crop-fallow rotation. Diversified systems included greater crop diversity, double crops, cover crops, and a multi-year ley pasture. In summer rotations with increased crop diversity and cover crops, bacterial and fungal richness increased, and distinct communities were formed compared to fallow land. Often, these community shifts were associated with greater soil organic carbon (SOC) and nitrogen. All winter rotations had distinct fungal communities and ley pasture resulted in greater fungal diversity compared to other rotations. No effects of the winter rotations were evident on bacterial communities. Our results show that diversification of dryland crop rotations leads to significant shifts in soil microbial communities in both winter and summer cropping systems. Both summer and winter rotations incorporating cover crops and ley pasture had greater soil respiration and nitrogen, indicating increases in soil fertility. These rotations may offer an alternative to conventional crop-fallow rotations to counter ongoing declines in soil health.

The scale dependency of spatial crop species diversity and its relation to temporal diversity.

Increasing crop species diversity can enhance agricultural sustainability, but the scale dependency of the processes that shape diversity and of the effects of diversity on agroecosystems is insufficiently understood. We used 30 m spatial resolution crop classification data for the conterminous United States to analyze spatial and temporal crop species diversity and their relationship. We found that the US average temporal (crop rotation) diversity is 2.1 effective number of species and that a crop's average temporal diversity is lowest for common crops. Spatial diversity monotonically increases with the size of the unit of observation, and it is most strongly associated with temporal diversity when measured for areas of 100 to 400 ha, which is the typical US farm size. The association between diversity in space and time weakens as data are aggregated over larger areas because of the increasing diversity among farms, but at intermediate aggregation levels (counties) it is possible to estimate temporal diversity and farm-scale spatial diversity from aggregated spatial crop diversity data if the effect of beta diversity is considered. For larger areas, the diversity among farms is usually much greater than the diversity within them, and this needs to be considered when analyzing large-area crop diversity data. US agriculture is dominated by a few major annual crops (maize, soybean, wheat) that are mostly grown on fields with a very low temporal diversity. To increase crop species diversity, currently minor crops would have to increase in area at the expense of these major crops.

Effect of Crop Rotation on Fusarium Mycotoxins and Fusarium Species in Cereals in Sichuan Province (China).

The present study was performed to evaluate the effect of crop rotation on Fusarium mycotoxins and species in cereals in Sichuan Province. A total of 311 cereal samples were randomly collected and analyzed from 2018 to 2019 in Sichuan Province. The results of mycotoxin analysis showed that the major trichothecene mycotoxins in Sichuan Province were nivalenol (NIV) and deoxynivalenol (DON), and the mean concentration of total trichothecenes (including NIV, fusarenone X [4ANIV], DON, 3-acetyldeoxynivalenol [3ADON], and 15-acetyldeoxynivalenol [15ADON]) in wheat was significantly higher than that in maize and rice. The concentration of total trichothecenes in the succeeding crops was significantly higher than that in the previous crops. In addition, wheat grown after maize had reduced incidence and concentration of trichothecene mycotoxins compared with that grown after rice, and ratooning rice grown after rice had increased incidence and concentration of trichothecene mycotoxins. Our data indicated that Fusarium asiaticum with the NIV chemotype was predominant in wheat and rice samples, while the number of the NIV chemotypes of F. asiaticum and Fusarium meridionale and the 15ADON chemotype of Fusarium graminearum in maize were almost the same. Although the composition of Fusarium species was affected by crop rotations, there were no differences when comparing the same crop rotation except for the maize-wheat rotation. Moreover, the same species and chemotype of Fusarium strains originated from different crops in various rotations, but there were no significant differences in pathogenicity in wheat and rice. These results contribute to the knowledge of the effect of crop rotation on Fusarium mycotoxins and species affecting cereals in Sichuan Province, which may lead to improved strategies for control of Fusarium mycotoxins and fungal disease in China.

Effects of rotation and Bacillus on the changes of continuous cropping soil fungal communities in American ginseng.

The continuous cropping obstacle is the main factor in leading to difficulty in American ginseng replanting. The dormant microbiota in the soil may be the cause of American ginseng disease and eventually caused continuous cropping obstacles, but there are few studies on the dynamic changes of soil microenvironment after American ginseng planting. In this study, we tracked short-term variation in physicochemical properties, enzyme activities, and fungal communities over time-series in soils with continuous cropping obstacle under crop rotation and probiotic Bacillus treatments. Furthermore, we examined the relationships between the important fungal compositions and the soil properties. The results showed that sucrase, cellulase, urease and acid phosphatase activities were significantly increased, while catalase and dehydrogenase were decreased with treatments time. Rotation treatment significantly affected the diversity, dissimilarity degree and species distribution of soil fungal community with continuous cropping obstacle over a short-term. Moreover, beneficial fungal biomarkers such as Cladorrhinum, Oidiodendron, and Mariannaea were accumulated at 48 h under rotation treatments. Almost all fungal biomarkers were negatively correlated with hydrolases and positively correlated with oxidoreductases and acid phosphatase under crop rotation treatments. This study suggested that compared to probiotic Bacillus, crop rotation can significantly affect soil fungal community structure, especially the enrichment of specific potentially beneficial fungal species. Our findings provide a scientific basis for understanding the dynamic changes of fungal communities and soil properties with continuous cropping obstacle of American ginseng in initial stage of soil improvement.

Evaluation of a crop rotation with biological inhibition potential to avoid N2O emissions in comparison with synthetic nitrification inhibition.

Agriculture has increased the release of reactive nitrogen to the environment due to crops' low nitrogen-use efficiency (NUE) after the application of nitrogen-fertilisers. Practices like the use of stabilized-fertilisers with nitrification inhibitors such as DMPP (3,4-dimethylpyrazole phosphate) have been adopted to reduce nitrogen losses. Otherwise, cover crops can be used in crop-rotation-strategies to reduce soil nitrogen pollution and benefit the following culture. Sorghum (Sorghum bicolor) could be a good candidate as it is drought tolerant and its culture can reduce nitrogen losses derived from nitrification because it exudates biological nitrification inhibitors (BNIs). This work aimed to evaluate the effect of fallow-wheat and sorghum cover crop-wheat rotations on N2O emissions and the grain yield of winter wheat crop. In addition, the suitability of DMPP addition was also analyzed. The use of sorghum as a cover crop might not be a suitable option to mitigate nitrogen losses in the subsequent crop. Although sorghum-wheat rotation was able to reduce 22% the abundance of amoA, it presented an increment of 77% in cumulative N2O emissions compared to fallow-wheat rotation, which was probably related to a greater abundance of heterotrophic-denitrification genes. On the other hand, the application of DMPP avoided the growth of ammonia-oxidizing bacteria and maintained the N2O emissions at the levels of unfertilized-soils in both rotations. As a conclusion, the use of DMPP would be recommendable regardless of the rotation since it maintains NH4+ in the soil for longer and mitigates the impact of the crop residues on nitrogen soil dynamics.

A new Rothamsted long-term field experiment for the twenty-first century: principles and practice.

Agriculture faces potentially competing societal demands to produce food, fiber and fuel while reducing negative environmental impacts and delivering regulating, supporting and cultural ecosystem services. This necessitates a new generation of long-term agricultural field experiments designed to study the behavior of contrasting cropping systems in terms of multiple outcomes. We document the principles and practices of a new long-term experiment of this type at Rothamsted, established at two contrasting sites in 2017 and 2018, and report initial yield data at the crop and system level. The objective of the Large-Scale Rotation Experiment was to establish gradients of system properties and outcomes to improve our fundamental understanding of UK cropping systems. It is composed of four management factors-phased rotations, cultivation (conventional vs reduced tillage), nutrition (additional organic amendment vs standard mineral fertilization) and crop protection (conventional vs smart crop protection). These factors were combined in a balanced design resulting in 24 emergent cropping systems at each site and can be analyzed at the level of the system or component management factors. We observed interactions between management factors and with the environment on crop yields, justifying the systems level, multi-site approach. Reduced tillage resulted in lower wheat yields but the effect varied with rotation, previous-crop and site. Organic amendments significantly increased spring barley yield by 8% on average though the effect again varied with site. The plowed cropping systems tended to produce higher caloric yield overall than systems under reduced tillage. Additional response variables are being monitored to study synergies and trade-offs with outcomes other than yield at the cropping system level. The experiment has been established as a long-term resource for inter-disciplinary research. By documenting the design process, we aim to facilitate the adoption of similar approaches to system-scale agricultural experimentation to inform the transition to more sustainable cropping systems. Supplementary Information: The online version contains supplementary material available at 10.1007/s13593-023-00914-8.

Effects of planting of two common crops, Allium fistulosum and Brassica napus, on soil properties and microbial communities of ginseng cultivation in northeast China.

BACKGROUND: Long-term cultivation of ginseng can cause severe crop disorders and soil sickness. Crop rotation is an effective agricultural management measure to improve soil sustainability and decrease pathogens. However, the suitable ginseng rotation system and the changes in soil microbial community and soil characteristics under the rotation system need to be further explored. METHODS: To explore suitable ginseng crop rotation systems and improve soil utilization, Allium fistulosum and Brassica napus were planted on ginseng cultivation soil for one year. The effects of the two crops on the chemical properties and enzyme activities of the ginseng cultivation soil were evaluated by chemical analysis. In addition, amplicon sequencing targeting 16 s rDNA genes of bacteria and ITS of fungi has been used to characterize the functional and compositional diversity of microbial communities. RESULTS: The results elucidated that the levels of available phosphorus (AP) and available potassium (AK) in the soil increased significantly after one year of cultivation for both crops and Allium fistulosum cultivation may also have reduced soil salinity. In addition, the effects of the two crops on the activities of key soil enzymes were different. Catalase (CAT), urease (URE), and acid phosphatase (A-PHO) activities were significantly reduced and sucrase (SUC), and laccase (LAC) activities were significantly increased after Allium fistulosum planting. While A-PHO activity was significantly increased and LAC activity was significantly decreased after Brassica napus planting. Allium fistulosum significantly reduced the abundance of soil fungal communities. The cultivation of Allium fistulosum and Brassica napus significantly altered the composition of soil bacterial and fungal communities, where changes in the abundance of dominant microorganisms, such as Ascomycota, and Mortierellomycota, etc., were closely related to soil chemistry and enzyme activity. Moreover, both significantly reduced the abundance of the pathogenic fungus Ilyonectria. CONCLUSIONS: Our study clarified the effects of Allium fistulosum and Brassica napus on the microbial community and physicochemical properties of ginseng cultivated soil and provides a basis for the sustainable application of ginseng cultivation soil and the development of ginseng crop rotation systems.

Application of plant-soil feedbacks in the selection of crop rotation sequences.

Plant-soil feedback (PSF) can be a major driver of plant performance in communities, and this concept can be used in selecting crop rotation sequences to maximize agricultural yields. Potential benefits of using PSF in this context include nutrient use optimization, pathogen reduction, and enhancement of mutualisms between crops and microbes. Yet the contributions of these combined mechanisms are poorly understood. Here we investigated the relative contributions of these mechanisms using five major crops commonly cultivated in rotation (alfalfa, canola, maize, soybean, and wheat) under controlled conditions. We trained soil by growing each of the five crops in a "training phase," and then reciprocally planted the five crops in the trained soils in a "feedback phase." To tease out soil biota from nutrient effects, we established three treatments: "control" (trained unsterilized soil used in the feedback phases), "biota" (sterilized soil in the feedback phase inoculated with soil biota from the control treatment after the training phase), and "nutrient" (sterilized soils in both phases). Plant-soil feedback for each crop was calculated by comparing the total biomass of each crop grown in soils trained by each of the four other crops (i.e., in rotation) against total biomass in self-trained soil (i.e., monocropping). We found that PSF values varied among crop combinations in all the treatments, but such variation was the greatest in the nutrient treatment. Overall, soil biota feedback tended to be lower, whereas nutrient feedback tended to be greater compared to the unsterilized control soil, suggesting that effects of antagonistic biota outweighed those of beneficial microbes in the biota treatment, and that plants optimized nutrient uptake when the soil microbiome was absent in the nutrient treatment. Furthermore, soils in the nutrient treatment trained by the legume crops (alfalfa and soybean) tended to provide the greatest positive feedback, emphasizing the important legacy of N2 fixers in crop rotation. Taken together, our data demonstrate how nutrients and soil biota can be integral to PSFs among crops, and that assessing PSFs under controlled conditions can serve as a basis to determine the most productive crop rotation sequences prior to field testing.

Modeling the evolution of herbicide resistance in weed species with a complex life cycle.

A growing number of weed species have evolved resistance to herbicides in recent years, which causes an immense financial burden to farmers. An increasingly popular method of weed control is the adoption of crops that are resistant to specific herbicides, which allows farmers to apply the herbicide during the growing season without harming the crop. If such crops are planted in the presence of closely related weed species, it is possible that resistance genes could transfer from the crop species to feral populations of the wild species via gene flow and become stably introgressed under ongoing selective pressure by the herbicide. We use a density-dependent matrix model to evaluate the effect of planting such crops on the evolution of herbicide resistance under a range of management scenarios. Our model expands on previous simulation studies by considering weed species with a more complex life cycle (perennial, rhizomatous weed species), studying the effect of environmental variation in herbicide effectiveness, and evaluating the role of common simplifying genetic assumptions on resistance evolution. Our model predictions are qualitatively similar to previous modeling studies using species with a simpler life cycle, which is, crop rotation in combination with rotation of herbicide site of action effectively controls weed populations and slows the evolution of herbicide resistance. We find that ignoring the effect of environmental variation can lead to an over- or under-prediction of the speed of resistance evolution. The effect of environmental variation in herbicide effectiveness depends on the resistance allele frequency in the weed population at the beginning of the simulation. Finally, we find that degree of dominance and ploidy level have a much larger effect on the predicted speed of resistance evolution compared to the rate of gene flow.

Multi-year and multi-site effects of recurrent glyphosate applications on the wheat rhizosphere microbiome.

Glyphosate (N-(phosphonomethyl)glycine) is broad-spectrum herbicide that is extensively used worldwide, but its effects on the soil microbiome are inconsistent. To provide a sound scientific basis for herbicide re-review and registration decisions, we conducted a four-year (2013-2016) study in which we consecutively applied glyphosate to a wheat (Triticum aestivum L.)-field pea (Pisum sativum L.)-canola (Brassica napus L.)-wheat crop rotation at five sites in the Canadian prairies. The glyphosate rates were 0, 1, 2, 4 and 8 kg ae ha-1, applied pre-seeding and post-harvest every year. The wheat rhizosphere was sampled in the final year of the study and analysed for microbial biomass C (MBC), the composition and diversity of the microbiome, and activities of ß-glucosidase, N-acetyl-ß-glucosiminidase, acid phosphomonoesterase and arylsulphatase. Glyphosate did not affect MBC, the composition and diversity of prokaryotes and fungi, and the activities of three of the four enzymes measured in the wheat rhizosphere. The one effect of glyphosate was a wave-like response of N-acetyl-ß-glucosaminidase activity with increasing application rates. The experimental sites had much greater effects, driven by soil pH and organic C, on the soil microbiome composition and enzyme activities than glyphosate. Soil pH was positively correlated with the relative abundance of Acidobacteriota but negatively correlated with that of Actinobacteriota and Basidiomycota. Soil organic C was positively correlated with the relative abundances of Proteobacteriota and Verrucomicrobiota, but negatively correlated with the relative abundance of Crenachaeota. The activity of acid phosphomonoesterase declined with increasing relative abundance of Acidobacteriota, but increased with that of Actinobacteriota and Basidiomycota. The activity of N-acetyl-ß-glucosaminidase also increased with increasing relative abundance of Actinobacteriota but decreased with that of Mortierellomycota. ß-glucosidase activity also decreased with increasing relative abundance of Mortierellomycota. The core fungal species observed in at least 90% of the samples were Humicola nigrescens, Gibberella tricincta and Giberella fujikuroi. Therefore, this multi-site study on the Canadian prairies revealed no significant effects of 4-year applications of glyphosate applied at different rates on most soil microbial properties despite differences in the properties among sites. However, it is important to keep evaluating glyphosate effects on the soil microbiome and its functioning because it is the most widely used herbicide worldwide.

Carbon footprint and net carbon gain of major long-term cropping systems under no-tillage.

Due to increased contribution from agriculture sector to total greenhouse gas emissions, there is need to study the ability of no-tilled diverse cropping systems including crop sequences and bio-covers to mitigate C equivalent emissions. Thus, C-footprint was calculated for a long-term experiment at the University of Tennessee's Research and Education Center in Milan with six-crop sequences: continuous cotton (Gossypium hirsutum L.), cotton-corn (Zea mays L.), continuous corn, corn-soybean (Glycine max L.), continuous soybean, and soybean-cotton interacted with four bio-covers: poultry litter, hairy vetch (Vicia villosa), winter wheat (Triticum aestivum), and fallow control with three replicates in a strip-plot design. During the experiment duration (2002-2017), field inputs (fertilizers, pesticides, and machinery used for planting, chemical applications, and harvesting) and outputs (crop yield, aboveground, and belowground residue) were assessed for each crop sequence/bio-cover combination to calculate total C equivalence of inputs and outputs, net C gain, C footprint per kg yield, sustainability index, and nitrous oxide emissions. For continuous corn, C-based input emissions were significantly higher by 0.28-0.62 Mg CO2 eq. ha-1 yr-1 than all other sequences, however, a greater net C gain (5.4 Mg C eq. ha-1 yr-1) was also observed due to increased crop yield, aboveground and belowground residues. Poultry litter application resulted in lower C-footprint (1.59-2.09 kg CO2 eq. kg-1 yield) than hairy vetch, wheat, and fallow under all crop sequences. Hairy vetch also lowered C-footprint per kg yield (∼2-14%) when compared with wheat under continuous systems of corn, soybean, and cotton, and cotton-corn rotation. Poultry litter application increased sustainability index (23-45) of all cropping sequences compared with other bio-covers. Hairy vetch improved sustainability index of corn including cropping sequences as compared with wheat and fallow. Inclusion of soybean and cotton with corn significantly decreased nitrous oxide emissions by 20-25%. The major factor contributing towards C-based input emissions was N fertilizer with 68% contribution to total emissions on average. It is concluded that application of poultry litter can reduce per yield C-footprint and enhance production system sustainability compared with hairy vetch, wheat, and fallow for monocultures or rotations of corn, soybean, cotton. Additionally, hairy vetch can outperform wheat in reducing the per yield C-footprint for continuous corn/soybean/cotton, and cotton-corn rotation. Especially for corn production systems, hairy vetch can enhance sustainability index compared with wheat and fallow. In order to increase per hectare net C gain, reduce per yield C-footprint and enhance sustainability index simultaneously, integration of continuous corn or corn-soybean/cotton rotation with bio-cover poultry litter or hairy vetch may perform better than the monocultures of soybean or cotton integrated with bio-cover wheat or fallow control in the Mid-south USA.

Effect of Biofumigation on Population Densities of Pratylenchus spp. and Verticillium spp. and Potato Yield in Eastern Canada.

Biofumigation has been proposed as an alternative to soil fumigation to manage soil-borne diseases including potato early dying disease complex (PED). This study examined the potential of using brown mustard (Mustard juncea) biofumigation to manage PED under rain-fed potato production in New Brunswick, Canada in two trials between 2017 and 2020 in comparison with chloropicrin fumigation and a conventional barley rotation. Biofumigation increased yield in one trial, but not in a second trial where the potato crop experienced severe drought, whereas chloropicrin fumigation increased yield in both trials. Biofumigation was effective in suppressing root-lesion nematode (RLN, Pratylenchus spp.) counts in both trials, but was ineffective in suppressing V. dahliae population density. Chloropicrin fumigation was effective in suppressing RLN counts and V. dahliae population density only in the hill where injected, but the effect was short-lived as the population density of V. dahliae in the hill increased to the level of the control in one potato growing season. Biofumigation may be an alternative to chloropicrin fumigation in managing PED, particularly in fields with high RLN population but relatively low Verticillium population density. However, neither biofumigation nor fumigation used alone may be sustainable in the short-term potato rotations commonly used in New Brunswick, and additional beneficial practices are required to sustain productivity in the long-term.

La biofumigación se ha propuesto como una alternativa a la fumigación del suelo para manejar las enfermedades transmitidas por el suelo, incluido el complejo de enfermedades de muerte prematura de la papa (PED). Este estudio examinó el potencial del uso de la biofumigación de mostaza marrón (Mustard juncea) para manejar la PED bajo la producción de papa de secano en New Brunswick, Canadá, en dos ensayos entre 2017 y 2020 en comparación con la fumigación con cloropicrina y una rotación de cebada convencional. La biofumigación aumentó el rendimiento en un ensayo, pero no en un segundo ensayo en el que el cultivo de papa experimentó una sequía severa, mientras que la fumigación con cloropicrina aumentó el rendimiento en ambos ensayos. La biofumigación fue efectiva para suprimir los conteos del nematodo lesionador de la raíz (RLN, Pratylenchus spp.) en ambos ensayos, pero fue ineficaz para suprimir la densidad de población de V. dahliae. La fumigación con cloropicrina fue efectiva para suprimir los conteos de RLN y la densidad de población de V. dahliae solo en el lomo del surco donde se inyectó, pero el efecto fue de corta duración ya que la densidad de población de V. dahliae en el surco aumentó al nivel del testigo en un ciclo de cultivo de papa. La biofumigación puede ser una alternativa a la fumigación con cloropicrina en el manejo de la PED, particularmente en campos con alta población de RLN pero densidad de población de Verticillium relativamente baja. Sin embargo, ni la biofumigación ni la fumigación utilizadas por sí solas pueden ser sustentables en las rotaciones de papa a corto plazo comúnmente utilizadas en New Brunswick, y se requieren prácticas benéficas adicionales para mantener la productividad a largo plazo.