Cover Crop Mixtures Research Articles

Tillage and cover crop mixtures interseeded in maize–soybean in the upper Midwest

AbstractEcosystem benefits of winter‐killed annual cover crops are less studied than winter hardy annuals. The objectives of this study were to determine (1) the effects of tillage practices and cover crop mixtures on biomass and soil cover of cover crops seeded into nearly mature maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] and (2) if cover crop biomass can be estimated from soil surface coverage measurements. The study was conducted within two long‐term tillage trials from 2016 to 2018. Tillage included conventional—(CT), strip—(ST), and no‐till—(NT). Cover crops included annual ryegrass (AR; Lolium multiflorum L.); AR and crimson clover (CC; Trifolium incarnatum L.) mixture (ARCC); AR, CC, and forage radish (FR; Raphanus sativus L.) mixture (ARCCFR); and no‐cover (NC). Seeding rates for AR, ARCC, and ARCCFR were 28, 36, and 40.5 kg ha−1, respectively. The ARCCFR mix produced the most biomass (256 kg ha−1), followed by AR (174 kg ha−1) and ARCC (165 kg ha−1). Cover crop biomass was 260 and 136 kg ha−1 in maize and soybean; and 218, 201, and 177 kg ha−1 in CT, ST, and NT, respectively. Cover crop soil coverage between rows was 25% in maize and 14% in soybean. Cover crop biomass was associated with soil surface coverage (R2 = 0.841). Given that cover crop biomass drives ecosystem services associated with cover crops, limited biomass and ground coverage of winter killed cover crops seeded into nearly mature maize and soybean may not add ecosystem services in the upper Midwest.

Legume-based cover crop mixtures can overcome trade-offs between C inputs, soil mineral N depletion and residual yield effects

Cover crops can contribute to climate change mitigation through enhanced sequestration of atmospheric carbon dioxide into soil organic carbon. Few studies, however, have estimated the total carbon (C) input to soil, i.e. derived both from plant material (shoot and root) and phyllo- and rhizodeposition. Selection of cover crop species should account for multiple objectives, such as C inputs to soil, nitrate leaching reduction and positive residual effects on the following main crop. However, trade-offs between these objectives may occur. The aim of this study was to investigate the performance of the cover crop species winter rye, hairy vetch and oilseed radish, and to assess the ability of mixtures to overcome potential trade-offs. A randomized split-plot field trial was conducted to compare cover crop treatments and a weeded control under high and low soil nitrogen (N) availability. Multiple-pulse labeling with 14C-CO2 was carried out to trace net cover crop-derived rhizodeposition C. Soil mineral N was measured to 1.5 m depth in autumn, as well as grain and N yield in the subsequent spring barley.Cover crop species accumulated between 1250 and 2580 kg C ha−1, with significantly higher total C input (in shoot, root and phyllo- and rhizodeposits) for the mixtures compared with pure stands of either vetch or radish, while the results for rye were in between. The quantity of C lost via phyllo- and rhizodeposition (qClvPR) showed a significant positive correlation with root C and was highest for the mixtures and rye. The relative ClvPR ranged between 7% and 14% of total cover crop-derived C and tended to decrease under higher soil N availability. All cover crop treatments were able to decrease soil mineral N (0–1.5 m), with radish displaying the highest N leaching reduction potential. Despite substantial differences in cover crop total N uptake and C:N ratios, no significant differences were observed in the subsequent main crop grain or N yields. The mixtures showed the highest total C input and generally a higher or similar mineral N depletion potential than the average of the pure stands, suggesting that cover crop mixtures offer a realistic means for overcoming trade-offs among ecosystem functions.

Radish-based cover crop mixtures mitigate leaching and increase availability of nitrogen to the cash crop

Radish-based cover crop mixtures mitigate leaching and increase availability of nitrogen to the cash crop

Interseeded cover crop mixtures influence soil water storage during the corn phase of corn-soybean-wheat no-till cropping systems

Interseeded cover crop mixtures influence soil water storage during the corn phase of corn-soybean-wheat no-till cropping systems

Effect of soil fertility level on growth of cover crop mixtures and residual fertilizing value for spring barley

The use of cover crops may play an important role in ecological intensification of farming systems through their impacts on cycling and the availability of essential nutrients. However, little is known about the effect of soil fertility on the performance of cover crops and consequent nutrient dynamics. We performed a two-year field trial to quantify the effect of two soil fertility levels (low and moderate) on the growth and nutrient content of different leguminous and non-leguminous cover crop species and their mixtures, and on their fertilizing value for the succeeding crop.Overall, the growth and shoot nutrient content of cover crops in autumn was influenced by the species, mixture choices and soil fertility level. The growth of some species was less affected by fertility level than others. Among the legumes, fertility levels had no effect on the growth of lupin. Among the non-legumes, buckwheat had the highest biomass production as well as C:N ratio at a low fertility level, and in the first year was affected least by soil fertility level. However, buckwheat and lupin grown as a single species or in mixtures did not lead to yield improvements in the subsequent crop. Generally, legumes produced more biomass than non-legumes in the mixtures at the low fertility level, whereas non-legumes produced more biomass at the moderate fertility level. Growing a mixture of vetch and radish achieved the best synergetic effect and highest shoot N content. In both years, the greatest improvements in barley yields were achieved after vetch grown as a single species and in a mixture with radish (by up to 46 %). Rye was less competitive in mixtures than radish and buckwheat, and in the second year it had a negative effect on barley yield at the low soil fertility level, presumably due to pre-emptive competition for nitrogen. Soil fertility level had a greater effect on barley yields than cover crop treatments, as yield increments at the moderate fertility level amounted to 48 % in the first year and 64 % in the second year compared with the low fertility level.These results demonstrate that the cultivation of winter-persistent legumes alone or in a mixture with oilseed radish offers a promising tool for improving the yields of subsequent crops through nitrogen input and nutrient cycling on farms where soil fertility level is low.

Assessing the Efficacy of Living and Dead Cover Crop Mixtures for Weed Suppression in Sweet Corn

Modern vegetable production systems are often characterized by monoculture fields and the intensive use of tillage and/or synthetic agrochemicals for managing weeds. A growing public interest in more sustainable and eco-friendly production practices has resulted in increased demand for crops to be produced with lower inputs. Field studies were conducted over three field seasons to investigate the use of conservation tillage in concert with an interplanted living mulch and/or cover crop residue for managing weeds in sweet corn as compared with the standard practice of using conventional tillage and pre-emergence residual herbicides. Whole plot treatments included: (1) conventional till, (2) no-till with cover crop residue, (3) living mulch + cover crop residue, and (4) living mulch + winter killed residue. The split-plot factor consisted of herbicide treatments: (1) at-planting application of residual herbicides or (2) no herbicide. The cover crop systems suppressed weeds as well as the standard practice throughout the cropping cycle in all three years. In addition, there was no significant improvement in weed suppression with the application of herbicides within the cover crop treatments. Crop development and yield were similar among treatments in year 2. However, reduced yields were encountered in all cover crop treatments during year 3 relative to the conventional tillage treatment.

Can relative sensitivity of cover crop species to chloroacetamide and pyrazole herbicides be exploited to design interseeding mixtures?

AbstractDrill-interseeding cover crops into standing corn (V3 to V5 growth stage) provides opportunities for increasing functional diversity in cropping systems by facilitating use of cover crop mixtures that include grass, legume, and brassica species. Designing herbicide-based weed control programs that negotiate tradeoffs between crop protection and environmental goals when interseeding mixtures remains a major challenge. The objective of this study was to use greenhouse-based dose-response assays to describe the relative sensitivity of 12 cover crop species that differ in traits, including taxonomic group and seed mass, to chloroacetamide (acetochlor, dimethenamid, S-metolachlor; Group 15 herbicides as categorized by the Weed Science Society of America) and pyrazole (pyroxasulfone; Group 15) herbicides. Nonlinear models were fit, and effective doses were estimated (ED50) to compare relative sensitivities of cover crop species to each herbicide. Brassica species (winter canola, Dwarf Essex rape, daikon radish) were less sensitive than small-seeded legumes (medium red clover, crimson clover) and grasses (annual ryegrass) in response to each chloroacetamide, but similar in response to pyroxasulfone. Austrian winter pea, a large-seeded legume, was less sensitive to each herbicide compared to other legumes (crimson clover, medium red clover, hairy vetch). Cereal rye and triticale were less sensitive to dimethenamid, S-metolachlor, and pyroxasulfone compared to annual ryegrass, but similar sensitivities were observed for acetochlor. These results suggest that relative differences in sensitivity to chloroacetamide and pyrazole herbicides could be exploited when designing cover crop mixtures for interseeding. It is imperative, however, to use these findings in conjunction with field-based observations of cover crop injury potential in interseeded systems.

Strip-tillage and Zonal Cover Cropping Effects on Organic Squash Production

Zonal management of cereal–legume cover crop mixtures may help address weed and nitrogen management challenges common in organic reduced tillage systems. During a field study conducted over 3 years in Michigan, we evaluated the effects of cover crop management, tillage, and supplemental mulch on organically produced acorn squash (Cucurbita pepo). During the fall season before squash production, rye (Secale cereale L.) and vetch (Vicia villosa Roth) cover crop mixtures were sown in two distinct spatial arrangements: a “mixed planting,” in which seeds were sown in the same rows, and a “zonal planting,” in which vetch was planted only in the in-row zone and rye was planted only in the between-row zone of the subsequent squash crop. During the following spring season, cover crops were mowed, and four tillage and cover crop management combinations were established: full-width tillage with the mixed planting of rye–vetch (full-till mixed); strip-till with the same mixed planting (strip-till mixed); strip-till with the rye–vetch zonal planting (strip-till zonal); and strip-till with the zonal planting and additional rye mulch added between crop rows immediately after crop establishment (strip-till zonal plus rye). The strip-till mixed treatment resulted in yields equivalent to those of the full-till mixed treatment despite lower available nitrogen and greater early weed competition in some cases. Within strip-till treatments, zonal planting of rye–vetch provided no benefits relative to full-width planting (treatment 2 vs 3) and resulted in lower total cover crop biomass, a higher density of escaped weeds, and lower squash yields during 1 of 3 years. Supplemental rye mulch improved weed suppression and yields in strip-till zonal treatments and resulted in yields equivalent to those of the full-till mixed treatment in all years, but it provided no benefits relative to strip-till mixed. Our results demonstrate that strip-till organic squash production can produce yields equivalent to full-till production in Northern climates, but that zonal planting and supplemental mulch have limited benefits for addressing ongoing weed and nitrogen management challenges. Growers must weigh costs associated with these challenges against potential benefits for soil and pest regulating ecosystem services before adopting these agricultural conservation practices.

A grass–legume cover crop maintains nitrogen inputs and nitrous oxide fluxes from an organic agroecosystem

AbstractLegume cover crops are central to an ecological nutrient management approach that can reduce nitrogen (N) losses from agriculture. Diversifying cropping systems with a legume–grass cover crop mixture could further reduce N losses by increasing soil N assimilation and synchronizing N mineralization with N uptake by the following crop. We established four winter cover crop treatments (crimson clover, cereal rye, clover–rye mixture, and weedy fallow control) in an organic grain agroecosystem that had been managed for 30 years with a legume cover crop as the only external N source. We hypothesized that the legume–grass mixture would provide similar inputs of biologically fixed N2 compared with the sole legume, while reducing N2O emissions during decomposition following tillage. We measured cover crop aboveground biomass C:N and clover N2 fixation, soil inorganic N and N2O fluxes throughout the corn growing season following cover crop tillage, and corn N assimilation at harvest. Even with a reduced clover seeding rate in mixture, the clover and mixture treatments had similar fixed N inputs, litter N and C:N, and no differences in cumulative N2O emissions. During the first peak flux, N2O emissions were 2–5 times higher in clover and mixture relative to rye and fallow, with no differences between clover and mixture. There were no treatment differences at the second N2O peak, which followed the first major rain event. We contextualized these findings by calculating a 6‐year partial N mass balance for this agroecosystem, which was slightly negative (−6.8 ± 0.8 kg N ha−1 year−1) when accounting for historical mean annual N2O emissions and nitrate leaching. Overall, N inputs and harvested N exports were approximately in balance for this legume‐based crop rotation, suggesting that the legacy of ecological nutrient management has promoted efficient N cycling. However, results from our field experiment indicate that short‐term N2O flux rates following cover crop incorporation can be high even for a legume–grass mixture. Additional strategies to reduce soil disturbance are therefore needed to further tighten N cycling in organic grain agroecosystems.

Uticaj ozimih međuuseva i različitih jarih useva na strukturu zemljišta tipa černozem

The intensive form of agricultural production often leads to disruption of physical, chemical and biological properties of the soil. Therefore, in recent years there has been an increasing focus on research and finding ways to preserve the soil with management practices that support soil conservation. The research was conducted on the experimental field of the Institute for Field and Vegetable Crops Novi Sad on Rimski Šančevi. The experiment was set up as a randomized block design. The winter cover crops consisted of the combined intercrops: Triticale (×Triticosecale Wittm. ex A. Camus) and winter pea (Pisum sativum ssp. arvense L.) (T+P), solo winter fodder pea crop (Pisum sativum ssp. arvense L.) (P) and a control without winter cover crops (sole or mixtures)(Ø). The experiment with winter cover crops was divided into two blocks. In the first block, the winter cover crops were chopped and plowed, while treatments in the second block were mowed using a rotary mower and the fodder was removed for feeding ruminants. After ploughing and preparing the soil for sowing, sowing of spring crops (soybean, maize and sudan grass) was carried out on all varieties in the subsequent sowing period. This research aims to determine the influence of different types of winter cover crops and spring crops from subsequent sowing period on the physical properties of Chernozem with a special emphasis on soil structure. It was determined that values of MWD on the treatments where the mixture of cover crops (T+P plowed) ranged from 1.11 mm to 1.39 mm, which indicated a better aggregates stability compared to the control treatments where no cover crops were sown. Due to variable root morphology and water requirements, which may alter soil structure, it is required to pay more attention to the adaptation of management strategies through the use of cover crops as well as the selection of their mixes.

Weed control under increasing cover crop diversity in tropical summer and winter

Description of the subject. Weed pressure is a main biotic constraint in tropical agriculture. Cover crop mixtures have increased in popularity to limit weed growth through competition for resources, but the relationship between cover crop diversity and weed suppression is still under debate. Objectives. This study aimed to assess the impact of increasing cover crop diversity (one to four species) on weed control during two growing seasons (tropical summer and winter) in Reunion Island. Method. Weed control was expressed regarding ground cover by weeds and weed aboveground dry mass in the mixtures during four months of growth and its response to cover crop traits was tested using structural equation models. Results. While cover crops reduced weed ground cover and dry mass by 60% and 68% on average in summer and winter, respectively, a higher number of cover crop species within a mixture did not increase mean weed control. Nonetheless, weed control was influenced by the mixture composition and improved when including Guizotia abyssinica. Additionally, cover crop traits explaining weed control differed between growing seasons. In summer, weed control was mainly explained by the final cover crop aboveground biomass and leaf area (depletion strategy). In contrast, weed control was mainly explained by the cover crop rate of increase in ground cover (obstruction strategy) in winter. Conclusions. Using traits to characterize cover crop mixture enables us to identify mixtures of species and traits adapted to different growing conditions. Our study suggests that particular attention on species identity rather than diversity should be paid in mixture to improve weed control in tropical conditions.

A critical analysis on multifaceted benefits of mixture of cover crops over pure stand

A critical analysis on multifaceted benefits of mixture of cover crops over pure stand

Cover crop mixtures versus single species: Water quality and cash crop yield

Cover crops promote environmental health and agricultural production, but most research in the Midwest focuses solely on winter cereal rye (<i>Secale cereal</i> L.) (CR). We evaluated cover crop mixtures compared to single species in terms of cover crop biomass (<i>n</i> = 32 site-years), cash crop yield (<i>n</i> = 32), and subsurface water quality (<i>n</i> = 17) spanning six sites and seven years in Iowa. Before soybeans (<i>Glycine max</i> [L.] Merr), the single species was CR and the mixture species were CR, radish (<i>Raphanus sativus</i>), and rapeseed (<i>Brassica napus</i>). Before corn (<i>Zea mays</i> L.), the single species was oats (<i>Avena sativa</i>) and the mixture species were oats, radish, and hairy vetch (<i>Vicia villosa</i>). Before soybeans, average fall growth of CR in the single species was significantly greater than or similar to the mixture. Fall growth before corn with oats was significantly less than or similar to the oat mixture. Before soybeans/during soybean growth, both cover crop treatments had significantly lower spring nitrate-nitrogen (NO₃-N) concentrations in soil pore water than the control, and single species had lower concentrations than mixtures. Even with mostly winterkill cover crops before corn, spring NO₃-N concentrations of soil pore water were significantly lower in the single species treatment than in the no cover treatment. Cover crop treatments had no influence on corn yield overall and slight negative influence on soybean yield at two of the sites. We propose the following to increase diversity of cover crops in the Midwest: CR before soybeans, oats and/or an oat mixture before corn, and introducing brassicas and hairy vetch in southern Iowa. In this project, these diverse species were possible after broadcast seeding in late August, and that would be our planting recommendation to promote fall growth.

Yield, soil Nitrogen content and weed control in six years of conservation agriculture on-farm field trials in Southwest Germany

Conservation Agriculture (CA) is a farming system that aims to protect soil resources by promoting minimum soil disturbance in combination with the maintenance of a permanent soil cover, and diversification of crop rotation. The aim of this study was to investigate the effects of no-till and shallow conservation tillage using a chisel plough and rotor tiller on loamy soils with high clay contents in combination with cover crop mixtures in rotations with at least three different crops. Crop yield, soil Nitrogen content and weed coverage were the main parameters measured. Experiments were performed in an on-farm approach in southwest Germany on 18 farms and two research stations over a period of 6 years. Yields of cereals, oilseed rape, maize, soybean and peas were slightly lower under no-tillage with 5.8–7.3 Mg grain yield equivalents ha−1 than under conservation tillage with 6.3–7.8 Mg grain yield equivalents ha−1. Cover cropping did not affect crop yields. Tillage and cover cropping had no influence on weed control in the subsequent main crop. Soil nitrate contents before winter in November were on average 11 kg N ha −1 lower in the cover crop treatments compared to the plots without cover crops. This study shows that CA with minimum tillage had slight advantages compared to the no-till system under Southwest Germany farming conditions.

Cropping system diversity and tillage intensity affects wheat productivity in Texas

AbstractWheat (Triticum aestivum L.) production in Texas depends heavily on conventional tillage (CT) and a long summer fallow period, which contributes to soil degradation. This study compared the impact of reducing tillage intensity (CT, no‐tillage, and strip‐tillage) combined with summer cropping to CT–summer fallow on wheat establishment, grain production, and herbage mass from 2016 to 2020 in three Texas ecoregions (Coastal Plains, Southern High Plains, and Blackland Prairie). Tillage and summer cropping resulted in variable impacts on wheat stand establishment, grain yield, and herbage mass across years and locations. At Beeville, in the Coastal Plains, wheat grain and herbage mass yields were not impacted by tillage. Sorghum (Sorghum bicolor [L.] Moench) cropping resulted in less wheat grain yield in 2020. In 1 yr at Lubbock in the Southern High Plains, wheat grain yield was greater with CT than reduced tillage. Sorghum summer cropping resulted in lower wheat grain yield than cover crop mixture or cowpea (Vigna unguiculata [L.] Walp.) in 2017, but yield was greater in 2020. At Thrall, in the Blackland Prairie, wheat stand establishment and yield with reduced tillage were greater than CT in 2016, whereas CT was greater in 2017 and 2020. Sorghum or cover cropping resulted in reduced wheat grain yield compared with fallow in 2018, but sorghum and sesame (Sesamum indicum L.) resulted in increased yield compared with fallow in 2019 and 2020. Summer cropping in wheat production systems rarely had a negative impact on wheat production compared with summer fallow in all three ecoregions.

Soil bacterial community response to cover crops, cover crop termination, and predicted climate conditions in a dryland cropping system

Soil microbial communities are integral to highly complex soil environments, responding to changes in aboveground plant biodiversity, influencing physical soil structure, driving nutrient cycling, and promoting both plant growth and disease suppression. Cover crops can improve soil health, but little is known about their effects on soil microbial community composition in semiarid cropping systems, which are rapidly becoming warmer and drier due to climate change. This study focused on a wheat-cover crop rotation near Havre, Montana that tested two cover crop mixtures (five species planted early season and seven species planted mid-season) with three different termination methods (chemical, grazed, or hayed and baled) against a fallow control under ambient or induced warmer/drier conditions. Soil samples from the 2018 and 2019 cover crop/fallow phases were collected for bacterial community 16S rRNA gene sequencing. The presence and composition of cover crops affected evenness and community composition. Bacterial communities in the 2018 ambient mid-season cover crops, warmer/drier mid-season cover crops, and ambient early season cover crops had greater richness and diversity than those in the warmer/drier early season cover crops. Soil microbial communities from mid-season cover crops were distinct from the early season cover crops and fallow. No treatments affected bacterial alpha or beta diversity in 2019, which could be attributed to high rainfall. Results indicate that cover crop mixtures including species tolerant to warmer and drier conditions can foster diverse soil bacterial communities compared to fallow soils.

Beneficial and Pest Arthropod Responses to Tillage and Cover Crop Residues in Organic Cucurbits.

Reduced tillage methods such as strip tillage are often combined with cover crop mixtures to provide agronomic benefits which can support crop and soil health. However, reduced tillage and cover crop species/arrangements effects on arthropods is less understood and results of previous studies have varied. In this study, we examined how agriculturally relevant pest and beneficial arthropod species were impacted by tillage and cover crop methods in USDA-certified organic Cucurbita (L.) (Cucurbitales: Cucurbitaceae). Aphididae were the most observed foliar pests and abundance was highest in full tillage treatment plots while foliar herbivores overall, excluding Aphididae, were more abundant in strip tillage treatment plots regardless of cover crop arrangement. Formicidae was also observed more on foliage, flowers, and in pitfall traps in full tillage, similarly to Aphididae. Parasitica were the most observed foliar natural enemies with increased abundance in strip tillage treatments. Activity densities of several epigeal natural enemies were also higher in strip tillage compared to full tillage. No significant effects of tillage and cover crop treatments were observed on flower visitation rates of Eucera pruinosa (Say) (Hymenoptera: Apidae), an important pollinator of Cucurbita, while the highest visitation rates of Apis mellifera (L.) (Hymenoptera: Apidae) and Bombus spp. (Latreille) (Hymenoptera: Apidae) were in strip tillage treatments. These results suggest that reduced tillage methods can support greater abundances of natural enemies and possibly pollinators. This may lead to enhanced biological control and pollination, but impacts may vary for different arthropod species and crops.

Cover crops and N fertilization affect soil ammonia volatilization and N2O emission by regulating the soil labile carbon and nitrogen fractions

Introducing cover crops in monocropping systems to improve soil health has been broadly adopted worldwide. However, the impacts of different cover cropping systems on soil emissions and related soil fractions and their regulatory mechanism remain elusive. In this study, four cropping systems, i.e., relay intercropping with Orychophragmus violaceus L./cotton (OvC), Vicia villosa Roth/cotton (VvC), a cover crop mixture (Ov and Vv)/cotton (MSC) and a fallow field–cotton (FFC) system, were combined with four N application rates in a two-rotation cycle (2019–2021) to evaluate the effects on soil greenhouse gases (GHGs) emission, ammonia (NH3) volatilization, and labile carbon (C) and nitrogen (N) fractions and their relationships. Compared with the FFC system, the cumulative NH3 volatilization and nitrous oxide (N2O) emissions of OvC are noticeably reduced 13% and 58%, respectively, and those of VvC are comparable, while those of MSC are markedly increased by 15% and 24%, respectively. N fertilization significantly affects soil NH3 volatilization and N2O emissions, and a higher N rate results in more gaseous N emissions. In addition, NH3 volatilization and N2O emission are positively correlated with the soil microbial biomass N (MBN), dissolved organic N (DON), NH4+-N and NO3--N but negatively correlated with microbial biomass C (MBC) and dissolved organic C (DOC). OvC system decreased gaseous N emission by high soil MBC/MBN ratio, Vv as cover crop indirectly promote soil N2O emission through increased soil MBN, DON and MBC content, while cover crop mixtures increase soil labile C and N fractions and enhance gaseous N emission ultimately. Overall, application of N fertilizer and cover crop mixture both promoted soil NH3 and N2O emissions; the relay intercropping nonlegume cover crop Ov noticeably mitigates N2O and NH3 emissions through an increase in the soil MBC and reduce in the labile N, while introduction of the legume cover crop Vv increases N2O emissions but reduces soil NH3 volatilization due to a lower soil MBC/MBN ratio.

Cover crops and soil ecosystem engineers

AbstractEarthworms are key to the engineering of soil ecosystem services. However, how cover crops (CCs) influence these ecosystem engineers has not been widely discussed. This paper reviews (a) CC effects on earthworm abundance, biomass, diversity, and related soil ecosystems services and (b) factors affecting CC effects on earthworms. A review of existing literature (through 29 May 2022) found 22 CC studies on earthworm abundance and 10 on earthworm biomass, but studies on earthworm diversity were few. Cover crops increased earthworm abundance in 13 of 22 studies, increased biomass in five of 10 and had no effect in the rest of studies compared with no CCs. The change (Δ increase) was 11 to 535 earthworms m–2 and 11 to 44 g of earthworm biomass m–2. Cover crop effects on earthworm diversity are mixed. Earthworm abundance was more responsive to CCs than soil C and physical properties, suggesting earthworm abundance should be included as a sensitive measurement in soil health status. Cover crops with low C/N under no‐till or reduced‐till systems promote earthworm abundance relative to CCs with high C/N under conventionally tilled systems. Cover crop mixtures do not increase earthworm abundance more than monocultures. Earthworm abundance generally increases with increasing precipitation (r = 0.45; p = .025) and temperature (r = 0.36; p = .10). Overall, CCs increase earthworm abundance but have mixed effects on earthworm biomass and diversity, although more data from different CC management scenarios and climates are needed for more robust conclusions.

Knowledge Mapping of the Extant Literature on the Environmental Impacts of Using Cover Crops—A Scientometric Study

This study examined the last four decades of the existing academic literature related to the environmental impacts of using cover crops in agricultural production systems. Data were collected from the Web of Science database, resulting in a sample of 3246 peer-reviewed articles published between 1980 and 2021. We combined two advanced scientometrics analysis software (i.e., CiteSpace 6.0.R1 and Gephi 0.9.2) to identify the trajectory of the literature, hotspots, and frontiers. We developed authorship-, institution-and country-levels networks to examine academic cooperation over the last forty years. Our findings revealed that the number of peer-reviewed outputs documenting the environmental effects of cover crops has consistently increased, with a notable rise in publications between 2015 and 2021. Eighteen salient research topics were identified in the literature, including winter cover crops’ effects on soil health, cover crops’ effects on nitrous oxide emissions, and the relationship between cover crops and nitrate leaching. Based on the citation-clustering analysis, the trajectory of the literature may be divided into three stages. Studies in Stage 1_A (1980–2000) mainly assessed the role of cover crops in nitrogen management. In Stage 1_B (2001–2010), the research evaluated the impact of using different cover crop mixtures on farming systems. In Stage 2 (2011–2021), studies primarily addressed the environmental impacts of cover crops, particularly their effects on physical and chemical soil properties. Finally, the countries with the most outputs were the United States, Brazil, and Spain. The U.S. Department of Agriculture-Agricultural Research Service was the main contributor to the literature on the environmental impacts of cover crops.