Crop Mixtures Research Articles

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.

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.

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.

Forage Potential of Cereal–Legume Mixtures as an Adaptive Climate Change Strategy under Low Input Systems

Mixed cropping systems can constitute important agroecological adaptation strategies for enhancing crop growth and productivity in view of climate change, while reducing the need for synthetic fertilizers and providing important ecosystem services. The aim of this study was to investigate growth, competitiveness, and productivity of two forage mixtures combining triticale (X triticosecale Wittmack) to common vetch (Vicia sativa L.), and to fenugreek (Trigonella fœnum-græcum L.) in different mixture combinations (40% T–60% V vs. 60% T–40% V and 40% T–60% F vs. 60% T–40% F). Field results showed that both forage legumes were higher inside the different crop mixtures (+225% for vetch, +94% for fenugreek) than in monocropping. In regard to the competition ration (CR), triticale was the more dominant and competitive species in three out of four studied mixtures. Forage yield was higher in crop mixtures than for corresponding sole crops. Yield gain was greater for common vetch-based mixtures than fenugreek ones (+60% vs. +30%). The results show that using cereal–legume mixtures can provide important productivity increase for fodder yield compared to conventional pure crops. The method is an important adaptive agricultural strategy in view of climate change.

INVESTIGATION OF THE PROCESS OF DRYING SEEDS OF HERBS

The modern unsatisfactory state of livestock in Ukraine depends largely on the lack of high -use feed, especially on legumes. In turn, the lack of such feed is associated with insufficient amounts of high -yielding seeds. All studies aimed at increasing the production of herbs are relevant and require a priority solution. The deficiency of high -performance seeds of legumes is explained by several reasons. These are the agrotechnical and physical and mechanical properties of both the seeds and the components of the crop mixture, the weather conditions under which is harvested, etc. To a large extent, the amount and quality of seeds depends on the conditions and results of harvesting the seeds. In this regard, the development of new means for drying the crop mixture of herbs and the study of the impact of their structural and technological parameters to improve the energy and qualitative indicators of the technological process of work of drying equipment is an important task. Analysis of the technologies of collection of legumes of legumes shows that almost all methods of harvesting require additional treatment of crop mass on the hospital. It is thanks to bringing the crop mixture to the corresponding condition, especially by its humidity, that it is possible to significantly reduce the field loss of seed crop. Analysis of agricultural dryers in terms of suitability for drying the crop mixture was carried out. For the implementation of the process of drying of this material, the most suitable are dryers with a fixed layer. After all, the use of most types of dryers is impossible due to the specific features of the material. The scheme of the laboratory installation for the experimental determination of structural and mode parameters of the drying process is proposed. The laboratory installation allows you to adequately simulate the process of drying the thick layer of crop mixture with the possibility of reversible supply of the drying agent.

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.

Sustainable Agricultural Intensification and Climate Smart Agricultural Practices for Improved Food and Climate Security

The grand challenge of increasing production and access to nutritious and safe food to meet growing populations under threat to climate change and climate variability requires systems and transdisciplinary approaches towards agri-food systems. Sustainable agricultural intensification (SAI) focuses on increasing agricultural production from existing farmland without any adverse environmental impacts. There are three major components of SAI which include: (i) genetic intensification (e.g., focused on improving yields, resistance to pests and diseases, tolerance to abiotic stresses, increasing nutritional quality of food products, and using precision breeding, genetics, and genomics tools); (ii) ecological intensification (e.g., focused increasing diversification, farming, cropping and agroforestry systems, resource use efficiency, integrated water, nutrient and pest management); and (iii) socio-economic intensification (e.g., focused on markets, value addition, income generation, policy, creating enabling environment, and building social capital). Climate-smart agricultural (CSA) practices emphasize greenhouse gas emissions, water footprint, and focus on both adaptation and mitigation strategies. Few selected SAI and CSA practices include minimum and no-tillage; cover crops; crop diversity and genotypes selection for effective water use and stress tolerance; diversification (crop mixtures and rotations; perennials, agroforestry systems; forage crops; dual purpose crops); and nutrient recycling from livestock. Overall, developing adoption and scaling of these practices will require convergence of biophysical and social sciences, participatory approaches, public and private sector engagement and commitment of resources from all donor agencies for research and development, human and institutional capacity building.

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.

Identification of parameters of the separation process of safflower seed material on sieves

Separation of seed mixtures for the purpose of their purification or calibration by fractions is a mandatory technological operation in the processing of most crops. Due to its properties, the process of separation of seed mixtures of individual crops has undefined parameters or low efficiency of its flow. A similar seed material is safflower, the parameters of the purification process of which were determined in the work taking into account different methods of separation of the components of the mixture. The work involves determining the parameters of the holes of the sieves and the scheme of their installation during the separation of the seed mixture of safflower, provided the maximum quality of seeds. For this purpose, the dimensional characteristics of safflower seeds and characteristic impurities were determined, which allowed to determine the possibilities of their qualitative separation. As a result of experiments, variation curves of dimensional characteristics of safflower seed mixture components in thickness and width were established. To imitate hard-to-separate components, winter wheat and pea grains were added to safflower seeds. The efficiency of sieve separation was also determined taking into account different types of sieve openings. Studies of the process of purification of safflower seed mixture were performed both on traditional flat stamped sieves and on the proposed sieves with activators. A study on the separation of safflower seed mixtures on traditional sieves with round holes with a diameter of 5.0 mm and rectangular holes with a width of 3.0 mm has been carried out. For the first time, a sieve with five-petalled epicycloid and volume activators was used to clean the seed mixture, which, thanks to the innovative design, allows us to increase the efficiency of the separation process. For the first time, a well-grounded method of determining the coefficient, which comprehensively takes into account the parameters of holes and jumpers, can be used to optimize the parameters of seed and grain cleaning machines. The separation efficiency of the safflower seed mixture was determined both by the content of fractions and by the indicators of 1000 seed weight, germination energy and seed germination. It has been found that to increase the productivity and quality of separation, it is advisable to use sieves with sieve activators: the upper sieve with five-petalled epicycloid activators 5 mm, and the lower with elongated holes 3 mm wide as well as volume activators.

Feed management and health condition of Sumatran Elephant (Elephas maximus sumatranus) in Conservation Response Unit (CRU), Tangkahan, Langkat, North Sumatra

The present study investigates the feeding management and health condition of elephants through a descriptive and field observation approach by interviewing the mahouts and clinical workers in Tangkahan CRU, Langkat Regency, North Sumatra. The ex-situ conservation unit promoted two feeding strategies namely the natural or grazing activity in the forest and additional feed (food stocks) collected or purchased by the workers in the form of coconut fronds, elephant grasses, bananas, watermelons, and etc. In addition to the collected fruits or crops, the CRU workers also prepared concentrates or pudding made from a mixture of palatable crops including rice, sticky rice, green beans, sugars to increase the food supply for the elephants. The clinical workers in the form of Vesswic is a team of veterinarians, paramedics and administrative personnel who focus on animal health including the Sumatran elephants. The Tangkahan CRU was then proven to promote the welfare of elephants through a series of effective feeding and health management.

The effect of catch crops in spring barley on nitrate leaching and their fertilizer replacement value

Catch crops have been proven effective in reducing nitrogen leaching in cropping systems due to their uptake of post-harvest soil mineral N prior to the main percolation season in winter. Information on the residual effect of catch crops, and their nitrogen fertilizer replacement value is scarce. To determine nitrogen fertilizer replacement values for different catch crops a field experiment was conducted over a four-year period on a sandy soil in Denmark, involving different catch crops and catch crop mixtures with non-legume and legume species. The residual effect of the catch crops was measured in spring barley grown in the residual year. For comparison, winter rye was also included. Over the four-year period the spring barley/fodder radish showed significantly lower leaching compared with the other catch crops, and the winter rye had the highest leaching. Regarding the residual effect, fodder radish and ryegrass, were most valuable, with nitrogen fertilizer replacement values ranging from 13 to 41 kg ha-1, based on fertilizer recovery efficiency of 50%. The process based APSIM (Agricultural Production Systems sIMulator) model was used to simulate the spring barley/catch crop rotations and the winter rye, and showed good model performance regarding N leaching and, crop yield and N uptake. The model was then run over a period of 20 years, to determine variations in N leaching and residual effects due to environmental conditions. The simulations showed that catch crops reduced N leaching by 38–64% when grown every year, and by 21–39% when grown only every second year. Nitrogen fertilizer replacement values ranged on average from 28 to 44 kg N ha-1, but showed high inter-annual variability. The nitrogen fertilizer replacement values showed only a weak relationship with the N uptake of the catch crop prior to termination, likely due to long term effects of N mineralisation from catch crop residues and pre-emptive competition for N by the catch crop.

Crop mixtures outperform rotations and landscape mosaics in regulation of two fungal wheat pathogens: a simulation study

Crop mixtures outperform rotations and landscape mosaics in regulation of two fungal wheat pathogens: a simulation study

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.