Annual Cropping Systems Research Articles

Are polycultures for silage pragmatic medleys or gallimaufries?

AbstractPolycultures, mixtures of different crop species in the same field, may provide both production and ecological benefits. Silage production in annual cropping systems may incorporate polycultures and take advantage of species’ niche partitioning, potentially stabilizing yield variation due to abiotic stress. Using maize (Zea mays L.) silage as the basis of our 3‐yr study, we tested the impact on crop and soil attributes of replacing a fraction of maize with soy [Glycine max (L.) Merr.], sorghum (Sorghum bicolor var. bicolor × bicolor and var. sudanense [unnamed hybrid]), or a medley of soy, sorghum, and sunflower (Helianthus annuus L.). Compared to maize monocultures and on average for the 3 yr, a replacement mixture of maize + soy lowered yields (1.57 vs. 1.87 kg m–2), but increased the N, P, and K concentration in the silage by 1.2x, 1.09x, and 1.03x, respectively. Maize + sorghum polycultures matched the biomass yields of maize monocultures (1.77 vs. 1.87 kg m–2) and increased K concentration (10.2 vs. 8.2 g kg–1). While random forest analysis revealed no change in post‐harvest soil mineral N with depth among treatments, there was a tendency for higher total mineral N left in the soil for soy‐containing vs. sorghum‐containing treatments (12.4 vs. 10.9 g m–2). Silage polycultures are a feasible alternative to maize silage monocultures and can improve silage nutrient concentration with no yield penalty if maize or sorghum dominate plant stands.

Monographs on invasive plants in Europe N° 5: Ambrosia trifida L.

ABSTRACT Ambrosia trifida L. (giant ragweed, Asteraceae) is native to the North American continent and was introduced into Europe and Asia at the end of the 19th century. In its native range, this tall annual species is common in riparian and ruderal habitats and is also a major weed in annual cropping systems. For nearly a century, A. trifida has also been of great concern in the U.S. for its highly allergenic pollen, necessitating targeted control measures to reduce its impact on human populations. Based on the distribution of A. trifida in North America and in its introduced range, riparian systems in the rest of the world may be particularly at risk to invasion, with potential negative consequences for their biodiversity. Currently, A. trifida has invaded Asia more widely than Europe, likely due to the more favourable local conditions in Asia. Throughout its introduced range, A. trifida is host to a limited number of invertebrates and pathogens and only a few biological agents are available for its control. The main impacts of A. trifida at a global level are on crop yield and human health, resulting in significant socio-economic impacts. The success of A. trifida invasion in areas in which it has been introduced is still unclear, but climate change may increase climate suitability, increasing the potential for A. trifida to spread. While effective management in cultivated fields seems potentially possible, the development and control of A. trifida in natural riparian habitats is of great concern due to the difficulty of management in these areas.

Weed–Insect Interactions in Annual Cropping Systems

Abstract Agricultural production is increasingly viewed as more than a source of food, feed, fiber and fuel, but also as a system of interdependent biotic and abiotic components that interact to produce ecosystem services and disservices. Weeds and insects are commonly viewed as non-desirable components of agroecosystems that should be managed. However, weeds can also provide benefits to cropping systems, such as providing resources and habitat to pollinators and other beneficial arthropods. This review on weed–insect interactions in annual cropping systems focuses on functional interactions within the context of regulating and supporting ecosystem services and disservices. Regulating services are those that act as regulators of the environment, such as weed–insect interactions that contribute to the regulating services of pollination and biological control, but also contribute to the disservices of crop and cover crop seed predation, and maintenance of insect pests and insect-transmitted phytopathogens. Supporting services include habitat and biodiversity that are necessary for the production and maintenance of the other types of ecosystem services. Here we review the impacts of weed–insect interactions as a component of biodiversity. We conclude by identifying some knowledge gaps that hinder our understanding of trade-offs when seeking to improve net positive ecosystem services in annual cropping systems.

Designing multifunctional urban agroforestry with people in mind

AbstractUrban landscapes combining trees and crops—urban agroforestry (UAF) systems—may offer greater ecological and cultural benefits than annual cropping systems. Interest in UAF is growing, as evidenced by an increasing number of built projects and articles in the popular press and the academic literature on the subject. However, the practice of UAF appears to far outpace research on its scientific underpinnings or its design. Developing sustainable, resilient UAF sites can be challenging because of biophysical and sociocultural conditions unique to the city; however, cities offer opportunities not found in rural environments including the potential to close open nutrient loops between consumers and sites of food production. We argue that these biophysical and sociocultural challenges and opportunities can be best addressed through an evidence‐based approach to the design of UAF systems and a complex ecological aesthetic design language integrating theory, principles, and practices from urban agroecology and allied fields, environmental psychology, and landscape architecture. The resulting multifunctional UAF systems would be socially sustainable and equitable and promote the circular metabolism of the city. Drawing on a purposive review of literature from these disciplines, we propose a preliminary framework consisting of 14 guidelines and complementary principles and strategies for the design of multifunctional, culturally preferred UAF and offer recommendations for future research.

Effectiveness of Cover Crops for Water Pollutant Reduction from Agricultural Areas

HighlightsNitrogen loss reduction due to a cover crop tends to improve with increased cover crop biomass production.Mixed phosphorus loss reduction results in cold climates where freeze-thaw cycles occur and can increase dissolved phosphorus losses.Cereal rye was the primary cover crop studied and tended to provide the most water quality benefits.Abstract. Mitigating nutrient losses from agricultural fields retains these nutrients for subsequent crop production and reduces the risk to downstream water quality. This study evaluated the impact of cover crops, as part of an annual cropping system, on reducing nutrient losses and enhancing water quality. Cover crop literature focusing on water quality was reviewed to determine important factors regarding cover crop performance and cost. Results show that a grass-based cover crop and mixes with grasses tend to increase nitrate loss reduction (40%) compared to legumes (negligible). Biomass growth was also important, with early seeding or growth of a cover crop in areas with increased growing degree days enhancing performance. For phosphorus loss, benefits did not necessarily increase with increasing biomass. Further, dissolved phosphorus concentrations may increase due to freeze-thaw cycles (23%), although overall dissolved phosphorus losses tend to decrease due to less runoff (34%). Cover crop implementation costs ranged from a savings of $25 to $44 ha-1 year-1 before soybeans and corn, respectively, when implementing a cover crop for five straight years to a cost of $193 ha-1 year-1. Including a cover crop in annual crop rotations with adequate time in the fall for germination and growth can reduce nitrogen and phosphorus losses from production agriculture to help meet water quality goals across the U.S. Keywords: Catch crop, Nitrogen, NRCS, Phosphorus, Practice Code 340, USDA, Water quality.

Different responses of soil carbon chemistry to fertilization regimes in the paddy soil and upland soil were mainly reflected by the opposite shifts of OCH and alkyl C

The supposition that cropping system might affect fertilization-induced changes in chemical composition of soil organic carbon (SOC) and microbial community composition has mostly derived from field experiments in different sites, which may have been disturbed by different climate conditions and parent materials. Here, two adjacent long-term field experiments were used, which contained similar four fertilization regimes of NPK, 2NPK, NPKOM, and an unamended control (Control), while contrasting annual cropping system of rice–rice and maize–maize, to investigate how fertilization-induced changes in SOC chemistry differ in paddy soil from upland soil, and whether they correlate with different bacterial taxa. The bacterial community composition of the paddy soil was mainly determined by NO3–-N and total N, and that of the upland was mostly explained by SOC. The NPK, 2NPK, and NPKOM treatments from the paddy soil increased CCH3, decreased OCH, and reduced CH/CH2, while those from the upland soil decreased CH/CH2, increased OCH, and raised CH/CH2, respectively, indicating opposite shifts of OCH and alkyl C (i.e., CCH3 and CH/CH2) in each paired fertilizer treatment of the two soils. In the paddy soil, the CCH3 from the NPK treatment showed no association with any bacterial taxa, the OCH from the 2NPK showed a negative association with NO3–-related species, and the CH/CH2 from the NPKOM showed a negative association with Proteobacteria and Bacteroidetes. In the upland soil, the CH/CH2 from the NPK negatively associated with Thermogemmatisporales and Acidobacteriaceae subgroup 1, the OCH from the 2NPK positively associated with Thermogemmatisporales, and the CH/CH2 from the NPKOM positively associated with copiotrophic bacterial taxa. Our results provided direct evidence that cropping system mediated the shift direction of specific functional group under specific fertilization regimes, and implied that completely opposite shifts of OCH and alkyl C in each paired fertilizer treatment of the paddy soil and upland soil can likely be attributed to different fertilization-induced shifts in the microbial community composition resulting from soil N change in the paddy soil and soil C change in the upland soil.

Can switchgrass increase carbon accrual in marginal soils? The importance of site selection

AbstractMost soil carbon (C) is in the form of soil organic matter (SOM), the composition of which is controlled by the plant–microbe–soil continuum. The extent to which plant and microbial inputs contribute to persistent SOM has been linked to edaphic properties such as mineralogy and aggregation. However, it is unknown how variation in plant inputs, microbial community structure, and soil physical and chemical attributes interact to influence the chemical classes that comprise SOM pools. We used two long‐term biofuel feedstock field experiments to test the influence of cropping systems (corn and switchgrass) and soil characteristics (sandy and silty loams) on microbial selection and SOM chemistry. Cropping system had a strong influence on water‐extractable organic C chemistry with perennial switchgrass generally having a higher chemical richness than the annual corn cropping system. Nonetheless, cropping system was a less influential driver of soil microbial community structure and overall C chemistry than soil type. Soil type was especially influential on fungal community structure and the chemical composition of the chloroform‐extractable C. Although plant inputs strongly influence the substrates available for decomposition and SOM formation, total C and nitrogen (N) did not differ between cropping systems within either site. We conclude this is likely due to enhanced microbial activity under the perennial cropping system. Silty soils also had a higher activity of phosphate and C liberating enzymes. After 8 years, silty loams still contained twice the total C and N as sandy loams, with no significant response to biofuel cropping system inputs. Together, these results demonstrate that initial site selection is critical to plant–microbe interactions and substantially impacts the potential for long‐term C accrual in soils under biofuel feedstock production.

High C input by perennial energy crops boosts belowground functioning and increases soil organic P content

C input to soil together with plant-microbial-soil organic matter (SOM) transformations are key ecological drivers for soil functioning in perennial cropping systems. In this study, we assessed the effect of three woody (poplar, black locust, willow) and three herbaceous (giant reed, miscanthus, switchgrass) perennial energy crops (PECs) on SOM pools, soil microbial biomass and metabolism and soil P forms distribution. After 9 y from plantation on a low-grade arable land, PECs significantly increased SOM content as much as 3.9 g kg−1 (+23 %) in the topsoil (0−30 cm). At the same time active C increased by 194 mg kg−1 (+ 43 %) and microbial biomass by 10.7 mg g−1 (+ 80 %). Microbial catabolic activity as measured respectively with twenty enzymes activities (EA) involved in C-, N-, P-, and S- cycling increased by 90 % and C substrate utilization profile (CSU - Microresp™) showed an increase of respiration rate by 13 % on average of all 16 substrates utilized. PERMANOVA and dbRDA analysis indicated that activity of microbial community associated with PECs differed significantly from that of arable land, with herbaceous PECs significantly increasing EA involved in C and N cycling while woody PECs increasing those involved in P-cycling. Interestingly, organic P forms content (monoester- and diester-P) along with its contribution to total NaOH-EDTA extractable soil P increased in all PECs, but more in woody than herbaceous ones. Functional diversity and evenness of microbial community resulted higher under herbaceous than woody PECs. Depth decay relationships of Bray Curtis similarity for EA patterns, more than CSU profile, was significantly smaller in woody and arable land than in herbaceous PECs, indicating a significant control of plant C inputs to soil from deep-rooting systems on proximate agents of belowground functioning. Our investigation highlighted the higher capability PECs, compared to annual cropping systems, in coupling nutrients cycling with C cycling, with the high C input being most probably the driving factor. Therefore, PECs might be ultimately considered not just as energy crops but also as a valuable strategy for revitalizing depleted soils by conventional agricultural practices.

A SMAF assessment of U.S. tillage and crop management strategies

The Soil Management Assessment Framework (SMAF) was developed to collectively assess biological, chemical, and physical soil health changes due to management practices. SMAF scoring curves were designed to be site-specific but were never validated at national scale. Our goal was to verify the national effectiveness of SMAF for detecting changes induced by conservation practices. Data from 456 articles representing the U.S. was compiled as input for a SMAF analysis. Soil organic-C (SOC), microbial biomass-C (MBC), β-glucosidase activity (BG), macroaggregate stability (AS), bulk density (BD), pH, soil-test P and K indices and an overall soil quality index (SQI) were computed. Measured, scored, and SQI values were used to evaluate tillage intensity [conventional (CT), reduced tillage (RT), no-till (NT), and zero disturbance (perennial systems; PER)] and soil cover [annual cropping systems without cover crops (ANCC), annual cropping systems with cover crops (ACC), and year-round soil cover (perennial systems; PER)]. Reducing tillage intensity and increasing soil cover increased topsoil SOC, MBC, BG, and AS values (measured and scored). SMAF scoring curves were sensitive to agronomic practice effects on soil function. The highest SQI values were associated with perennial systems (zero soil disturbance) and year-round living roots. Within annual cropping systems, cover cropping, and NT demonstrated better soil biological and physical functioning. However, SMAF scores underestimated the effects for SOC and BG and overestimated the effects for AS, suggesting the algorithms for those indicators should be reevaluated and improved. Overall, this national assessment confirmed the utility of SMAF and highlighted benefits of conservation practices. • Sensitivity of SMAF scoring functions to land use was assessed on a national scale. • Current SMAF algorithms generally detected soil health changes due to management practices. • Some SMAF scoring curves (SOC, aggregate stability, and β-glucosidase) need to be improved. • All soil health indicators used in SMAF react to conservation practices on a national scale.

Assessment of crop and weed management strategies prior to introduction of auxin-resistant crops in Brazil

AbstractA stakeholder survey was conducted from April through June of 2018 to understand stakeholders’ perceptions and challenges about cropping systems and weed management in Brazil. The dominant crops managed by survey respondents were soybean (73%) and corn (66%). Approximately 75% of survey respondents have grown or managed annual cropping systems with two to three crops per year cultivated in succession. Eighteen percent of respondents manage only irrigated cropping systems, and over 60% of respondents adopt no-till as a standard practice. According to respondents, the top five troublesome weed species in Brazilian cropping systems are horseweed (asthmaweed, Canadian horseweed, and tall fleabane), sourgrass, morningglory, goosegrass, and dayflower (Asiatic dayflower and Benghal dayflower). Among the nine species documented to have evolved resistance to glyphosate in Brazil, horseweed and sourgrass were reported as the most concerning weeds. Other than glyphosate, 31% and 78% of respondents, respectively, manage weeds resistant to acetyl-CoA carboxylase (ACCase) inhibitors and/or acetolactate synthase (ALS) inhibitors. Besides herbicides, 45% of respondents use mechanical, and 75% use cultural (e.g., no-till, crop rotation/succession) weed control strategies. Sixty-one percent of survey respondents adopt cover crops to some extent to suppress weeds and improve soil chemical and physical properties. Nearly 60% of survey respondents intend to adopt the crops that are resistant to dicamba or 2,4-D when available. Results may help practitioners, academics, industry, and policy makers to better understand the bad and the good of current cropping systems and weed management practices adopted in Brazil, and to adjust research, education, technologies priorities, and needs moving forward.

Garlic Substrate Induces Cucumber Growth Development and Decreases Fusarium Wilt through Regulation of Soil Microbial Community Structure and Diversity in Replanted Disturbed Soil

Garlic substrate could influence plant growth through affecting soil microbiome structure. The relationship mechanism between changes in soil microbial communities, disease suppression and plant development, however, remains unclear, particularly in the degraded soil micro-ecological environment. In this study, garlic substrates as a soil amendment were incorporated with different ratios (1:100, 3:100 and 5:100 g/100 g of soil) in a replanted disturbed soil of long-term cucumber monoculture (annual double cropping system in a greenhouse). The results indicated that higher amount of C-amended garlic substrate significantly induced soil suppressiveness (35.9% greater than control (CK) against the foliar disease incidence rate. This inhibitory effect consequently improved the cucumber growth performance and fruit yield to 20% higher than the non-amended soil. Short-term garlic substrate addition modified the soil quality through an increase in soil organic matter (SOM), nutrient availability and enzymatic activities. Illumina MiSeq sequencing analysis revealed that soil bacterial and fungal communities in the garlic amendment were significantly different from the control. Species richness and diversity indices significantly increased under treated soil. The correlation-based heat map analysis suggested that soil OM, nutrient contents and biological activators were the primary drivers reshaping the microbial community structure. Furthermore, garlic substrate inhibited soil-borne pathogen taxa (Fusarium and Nematoda), and their reduced abundances, significantly affecting the crop yield. In addition, the host plant recruited certain plant-beneficial microbes due to substrate addition that could directly contribute to plant–pathogen inhibition and crop biomass production. For example, abundant Acidobacteria, Ascomycota and Glomeromycota taxa were significantly associated with cucumber yield promotion. Firmicutes, Actinobacteria, Bacteroidetes, Basidiomycota and Glomeromycota were the associated microbial taxa that possibly performed as antagonists of Fusarium wilt, with plant pathogen suppression potential in monocropped cucumber-planted soil.

Expression of N-cycling genes of root microbiomes provides insights for sustaining oilseed crop production.

Agricultural production is dependent on inputs of nitrogen (N) whose cycle relies on soil and crop microbiomes. Crop diversification has increased productivity; however, its impact on the expression of microbial genes involved in N-cycling pathways remains unknown. Here, we assessed N-cycling gene expression patterns in the root and rhizosphere microbiomes of five oilseed crops as influenced by three 2-year crop rotations. The first phase consisted of fallow, lentil or wheat, and the second phase consisted of one of five oilseed crops. Expression of bacterial amoA, nirK and nirS genes showed that the microbiome of Ethiopian mustard had the lowest and that of camelina the highest potential for N loss. A preceding rotation phase of lentil significantly increased the expression of nifH gene by 23% compared with wheat and improved nxrA gene expression by 51% with chemical fallow in the following oilseed crops respectively. Lentil substantially increased biological N2 fixation and reduced denitrification in the following oilseed crops. Our results also revealed that most N-cycling gene transcripts are more abundant in the microbiomes associated with roots than with the rhizosphere. The outcome of our investigation brings a new level of understanding on how crop diversification and rotation sequences are related to N-cycling in annual cropping systems.

Importance of drive-row vegetation for soil carbon storage in woody perennial crops: A regional study

Increasing the carbon (C) content of agricultural soils can help mitigate rising atmospheric CO2 concentrations, improve soil health and increase crop yield. Unlike annual cropping systems, soils planted to perennial woody crops, such as vineyards and orchards, are left undisturbed for many years making them particularly amenable to soil C storage. Here, we used a regional sampling campaign of over 80 commercially-managed sites across the Okanagan Valley, in the southern interior of British Columbia, Canada, to examine the spatial distribution of soil C under irrigated perennial woody crops. Using this living lab approach, we collected soils from the crop and drive rows of apple and cherry orchards, and vineyards subjected to a wide range of real-life management regimes (e.g., for weed and pest control, fertilizer application, etc.). Sites were selected with soils belonging to five surficial deposit classes, representing 40% of the mapped agricultural land area. Soil C was spatially heterogeneous across all the sites, with the surface soil (0–15 cm) of drive rows containing more C than the soil in adjacent crop rows. Clear differences emerged among cropping systems, despite the variation in management practices applied by individual growers. Drip-irrigated apple orchards showed the greatest spatial heterogeneity, with C concentrations of 2.9% in the drive row and 1.8% in the crop row, while vineyard and cherry orchard soils showed the least, with differences between crop and drive rows of approximately 0.3%. Higher C concentrations in the drive rows appeared to be the result of recently assimilated/less processed litter and fine root C inputs from the shallow-rooted understory vegetation. This was confirmed using stable isotope analysis: drive row soil C was significantly 13C depleted compared to the crop row soil, to a depth of 30 cm. Overall, cherry orchards contained the most C (70 Mg C ha−1 to a depth of 30 cm), vineyards the least (48 Mg C ha−1), and apple orchards were intermediate (66 Mg C ha−1). A recent land-use survey in 2015 determined that 8501 ha of agricultural land in the Okanagan Valley was planted to apples, cherries or grapes, and that large shifts in crop land area have occurred since the previous survey, conducted in 2006. We estimate that apple orchards currently hold approximately 199 Gg C, vineyards 188 Gg C and cherry orchards 110 Gg C. Marked differences in soil C storage between the cropping systems, despite the fact some were less than 10 years old, suggests that soils in this region are responsive to changes in crop and associated management practices over relatively short time periods. We conclude that the drive rows of vineyards offer the greatest scope for increased soil C storage among woody perennial horticultural cropping systems in the Okanagan Valley but that ‘long-term’ soil carbon storage may not be possible in these soils.

Soil nitrate leaching under grazed cool-season grass pastures of the North Central US.

Nitrate leaching from agricultural cropping systems contributes to widespread and devastating eutrophication of water bodies globally. In the North Central USA, this problem is acute, with millions of dollars spent annually in efforts to clean up recreational and drinking water. The frequent soil disturbance and exogenous nitrogen (N) amendments applied in annual cropping systems make them major sources of ground- and surface-water nitrate pollution. Perennial grasslands under managed livestock grazing have been touted for their ability to retain soils and nutrients while simultaneously providing milk and meat to society. The present study provides an evaluation of the peer-reviewed literature addressing nitrate leaching loads beneath corn, pasture and prairie in temperate humid and sub-humid regions of the US, with a focus on cool-season grass pastures. Inputs of exogenous N to these agroecosystems comes from wet and dry deposition, livestock manure from imported feed, biological fixation and inorganic N fertilizer. Nitrate loads were highest beneath corn and lowest beneath restored prairie and switchgrass managed for bioenergy. Cool-season grass pastures had relatively low levels of nitrate leaching loads where little or no N was applied. However, where grazed perennial grasslands had inorganic N applied, nitrate leaching loads rivaled those of corn in some cases. When producing milk and meat from livestock, grazed perennial cool-season grass pastures should reduce nitrate leaching loads compared to growing corn that is used to feed livestock in confinement. However, cool-season grass pastures can lose significant nitrate to leaching with moderate- to high-levels of exogenous N inputs. © 2020 Society of Chemical Industry.

Glyphosate Use in the European Agricultural Sector and a Framework for Its Further Monitoring

Monitoring pesticide use is essential for assessing farming practices and the risks associated with the use of pesticides. Currently, there are neither consolidated, public data available on glyphosate use in Europe, nor a standardized categorization of its major uses. In this study, data on glyphosate sales and use in Europe were collected from multiple sources and compiled into a dataset of the agricultural use of glyphosate from 2013 to 2017. The survey shows that glyphosate represented 33% of the herbicide volume sold in Europe in 2017. One third of the acreage of annual cropping systems and half of the acreage of perennial tree crops received glyphosate annually. Glyphosate is widely used for at least eight agronomic purposes, including weed control, crop desiccation, terminating cover crops, terminating temporary grassland and renewing permanent grassland. Glyphosate use can be classified into occasional uses—i.e., exceptional applications, triggered by meteorological conditions or specific farm constraints—and recurrent uses, which are widespread practices that are embedded in farming systems and for which other agronomic solutions may exist but are not frequently used. This article proposes a framework for the precise monitoring of glyphosate use, based on the identification of the cropping systems in which glyphosate is used, the agronomic purposes for which it is employed, the dose used and the rationale behind the different uses.

Systemic Colonization by Metarhizium robertsii Enhances Cover Crop Growth.

Fungi in the genus Metarhizium (Hypocreales: Clavicipitaceae) are insect pathogens that can establish as endophytes and can benefit their host plant. In field experiments, we observed a positive correlation between the prevalence of M. robertsii and legume cover crops, and a negative relationship with brassicaceous cover crops and with increasing proportion of cereal rye in mixtures. Here, we report the effects of endophytic M. robertsii on three cover crop species under greenhouse conditions. We inoculated seeds of Austrian winter pea (Pisum sativum L., AWP), cereal rye (Secale cereale L.), and winter canola (Brassica napus L.) with conidia of M. robertsii to assess the effects of endophytic colonization on cover crop growth. We recovered M. robertsii from 59%, 46%, and 39% of seed-inoculated AWP, cereal rye, and canola plants, respectively. Endophytic M. robertsii significantly increased height and above-ground biomass of AWP and cereal rye but did not affect chlorophyll content of any of the cover crop species. Among inoculated plants from which we recovered M. robertsii, above-ground biomass of AWP was positively correlated with the proportion of colonized root but not leaf tissue sections. Our results suggest that winter cover crops may help to conserve Metarhizium spp. in annual cropping systems.

Short-Term Dispersal and Long-Term Spatial and Temporal Patterns of Carabidae (Coleoptera) in Lowbush Blueberry Fields.

Carabidae (Coleoptera) are important natural enemies of many insect pests in various cropping systems. Their population dynamics and how they disperse determine how effective they are at carrying out the natural enemy function. There are robust patterns of community dynamics in annual cropping systems, but it is unclear if these would carry over into a relatively underexplored North American perennial crop. In Nova Scotia lowbush blueberry fields, we found that Carabidae diversity did not change with distance from field edge nor with time. Their activity density also did not change with time, but it did change with distance from field edge. We also found that the most abundant carabid of lowbush blueberry, Harpalus rufipes (De Geer) (Coleoptera: Carabidae), can disperse approximately 14.5 m/d. Our results shed more light on the community dynamics of Carabidae in lowbush blueberry fields and can help growers make informed decisions when it comes to incorporating natural enemies into their pest management practices.

Biological soil health indicators respond to tillage intensity: A US meta-analysis

Tillage intensity affects soil microbiological activity in many ways, often driven by changes in soil organic C (SOC) content. The magnitude and direction of those changes, however, depends on inherent (e.g., soil type and texture), experimental (e.g., study duration and sampling depth) and agronomic factors (e.g., cropping system and crop residue management). This nationwide meta-analysis examines published effects of chisel plowing (CP), no-tillage (NT), and perennial cropping systems (PER) relative to moldboard plow (MP) on seven soil health indicators: SOC, microbial biomass C (MBC), microbial biomass N (MBN), soil respiration (Resp), active-C (AC), beta-glucosidase activity (BG) and soil protein (Prot) within four soil depth increments in 302 studies from throughout the United States (U.S.). Overall, converting from MP to CP primarily affected topsoil (0 to ≤ 15 cm) SOC, MBC, and Resp, whereas converting from MP to NT significantly increased all seven soil health indicators in the topsoil. Below the topsoil, NT had greater MBC, MBN, Resp, and BG relative to MP (i.e., 15 to 25-cm). The impact of NT was affected by latitude, soil order, time under NT, and cropping system. Among soil orders, management practices had the largest positive effects in Ultisols, Inceptisols, Alfisols, and Mollisols. Those effects were most noticeable at lower latitudes, in systems that included cover crops or residue retention, and in experiments conducted for at least three years. Perennial systems had a positive effect on all soil health indicators at all soil depths (0 to >40-cm). The positive response of PER systems compared to MP was enhanced at lower latitudes and in Alfisols, Inceptisols, Entisols, and Mollisols. Based on this meta-analysis, reducing tillage intensity, planting cover crop and/or minimizing crop residue removal within annual cropping systems can significantly improve soil biological health in the U.S. Finally, we demonstrate that SOC and many other biological indicators are sensitive to management practices, confirming their utility in soil health assessment.

Intensive fertilizer use increases orchard N cycling and lowers net global warming potential

Nitrogen (N) fertilizer use has simultaneously increased global food production and N losses, resulting in degradation of water quality and climate pollution. A better understanding of N application rates and crop and environmental response is needed to optimize management of agroecosystems. Here we show an orchard agroecosystem with high N use efficiency promoted substantial gains in carbon (C) storage, thereby lowering net global warming potential (GWP). We conducted a 5-year whole-system analysis comparing reduced (224 kg N ha−1 yr−1) and intensive (309 kg N ha−1 yr−1) fertilizer N rates in a California almond orchard. The intensive rate increased net primary productivity (Mg C ha−1) and significantly increased N productivity (kg N ha−1) and net N mineralization (mg N kg−1 soil d−1). Use of 15N tracers demonstrated short and long-term mechanisms of soil N retention. These low organic matter soils (0.3–0.5%) rapidly immobilized fertilizer nitrate within 36 h of N application and 15N in tree biomass recycled back into soil organic matter over five years. Both fertilizer rates resulted in high crop and total N recovery efficiencies of 90% and 98% for the reduced rate, and 72% and 80% for the intensive rate. However, there was no difference in the proportion of N losses to N inputs due to a significant gain in soil total N (TN) in the intensive rate. Higher soil TN significantly increased net N mineralization and a larger gain in soil organic carbon (SOC) from the intensive rate offset nitrous oxide (N2O) emissions, leading to significantly lower net GWP of −1.64 Mg CO2-eq ha−1 yr−1 compared to −1.22 Mg CO2-eq ha−1 yr−1 for the reduced rate. Our study demonstrates increased N cycling and climate mitigation from intensive fertilizer N use in this orchard agroecosystem, implying a fundamentally different result than seen in conventional annual cropping systems.

Impact of Cover Crops on the Soil Microbiome of Tree Crops.

Increased concerns associated with interactions between herbicides, inorganic fertilizers, soil nutrient availability, and plant phytotoxicity in perennial tree crop production systems have renewed interest in the use of cover crops in the inter-row middles or between trees as an alternative sustainable management strategy for these systems. Although interactions between the soil microbiome and cover crops have been examined for annual cropping systems, there are critical differences in management and growth in perennial cropping systems that can influence the soil microbiome and, therefore, the response to cover crops. Here, we discuss the importance of cover crops in tree cropping systems using multispecies cover crop mixtures and minimum tillage and no-tillage to not only enhance the soil microbiome but also carbon, nitrogen, and phosphorus cycling compared to monocropping, conventional tillage, and inorganic fertilization. We also identify potentially important taxa and research gaps that need to be addressed to facilitate assessments of the relationships between cover crops, soil microbes, and the health of tree crops. Additional evaluations of the interactions between the soil microbiome, cover crops, nutrient cycling, and tree performance will allow for more effective and sustainable management of perennial cropping systems.