Crop Termination Research Articles

Simulating Soil-Plant-Climate Interactions and Greenhouse Gas Exchange in Boreal Grasslands Using the DNDC Model

With global warming, arable land in boreal regions is tending to expand into high latitude regions in the northern hemisphere. This entails certain risks; such that inappropriate management could result in previously stable carbon sinks becoming sources. Agroecological models are an important tool for assessing the sustainability of long-term management, yet applications of such models in boreal zones are scarce. We collated eddy-covariance, soil climate and biomass data to evaluate the simulation of GHG emissions from grassland in eastern Finland using the process-based model DNDC. We simulated gross primary production (GPP), net ecosystem exchange (NEE) and ecosystem respiration (Reco) with fair performance. Soil climate, soil temperature and soil moisture at 5 cm were excellent, and soil moisture at 20 cm was good. However, the model overestimated NEE and Reco following crop termination and tillage events. These results indicate that DNDC can satisfactorily simulate GHG fluxes in a boreal grassland setting, but further work is needed, particularly in simulated second biomass cuts, the (>20 cm) soil layers and model response to management transitions between crop types, cultivation, and land use change.

Narrow-row soybean and a cereal rye cover crop suppress glyphosate-resistant horseweed (Conyza canadensis)

AbstractAlternative strategies are needed for management of glyphosate-resistant (GR) horseweed in soybean. Integrating a cereal rye cover crop with soybean planted in narrow rows may improve control and reduce herbicide selection pressure for herbicide-resistant horseweed biotypes. Four site-years of experiments were conducted in Michigan to determine whether fall-planted cereal rye terminated with glyphosate 1 wk prior to (early termination) or 1 wk after (planting green) planting in combination with narrow-row soybean improved GR horseweed management. At postemergence (POST) herbicide application, horseweed biomass was reduced by 71% to 90% when soybean was planted into cereal rye, regardless of termination time, compared with no cover across all row widths. Planting green or narrow-row soybean suppressed horseweed through soybean harvest. When glyphosate was applied POST (noneffective), horseweed biomass was 36% to 46% lower when planting green compared with early terminated cereal rye and no cover. Similarly, planting soybean in 19- and 38-cm rows reduced horseweed biomass by 48% and 28%, respectively, compared with 76-cm rows. Cereal rye did not affect soybean yield pooled over 3 of 4 site-years; however, narrow row soybean yielded 11% to 18% higher than 76-cm rows. Soybean yield was 11% higher when an effective POST herbicide was applied. In conclusion, fall-seeded cereal rye or narrow-row soybean suppressed horseweed compared with no cover and 76-cm rows; however, the effects of early termination did not last throughout the growing season in most cases. Delaying cover crop termination by planting green reduced horseweed biomass and density through soybean harvest, but reduced yield in 1 site-year due to an increased incidence of white mold. These cultural practices have a positive influence on suppressing horseweed that should be part of an overall horseweed management strategy; however, the use of an effective POST herbicide is still needed for complete season-long horseweed management.

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.

Grape Tomato Growth, Yield, and Fruit Mineral Content as Affected by Rootstocks in a High Tunnel Organic Production System

Recently, so-called “vegetative” and “generative” rootstocks have been identified by seed companies as rootstock types that have different impacts on tomato scions. In this experiment of grafted grape tomato production in an organically managed high tunnel system, we characterized the effects of vegetative and generative rootstock cultivars on tomato yield components and fruit mineral contents. Grape tomato scions ‘BHN 1022’ (determinate) and ‘Sweet Hearts’ (indeterminate) were grafted onto ‘DR0141TX’ (vegetative), ‘Estamino’ (generative), and ‘Multifort’ (noncharacterized) rootstocks with self- and nongrafted scions as controls. Experiments were conducted twice with different transplanting dates (Expt. 1: 31 Jan. vs. Expt. 2: 9 Mar.) in 2018. No rootstock by scion interaction effects on whole-season fruit yield components were observed, indicating similar responses of determinate and indeterminate grape tomato scions to all rootstocks tested. For Expt. 1, the three rootstocks increased marketable fruit number, marketable yield, and total yield by 23.3%, 37.9%, and 34.4% on average, respectively, compared with the self- and nongrafted controls, primarily due to improved productivity during the peak and late harvest periods. For Expt. 2, the rootstocks did not significantly benefit any whole-season yield components. ‘DR0141TX’ and ‘Multifort’ increased stem diameter in both experiments, whereas ‘Estamino’ only increased stem diameter in Expt. 2 relative to the nongrafted controls. Consistent increase in aboveground dry biomass of rootstock treatments at crop termination in Expt. 1 corresponded to the greater yield of rootstock-grafted plants in that experiment. All rootstocks in both experiments consistently increased fruit P, K, Ca, Zn, and Fe contents on a dry weight basis at peak harvest regardless of the tomato scion used. Despite a relatively low level of root-knot nematode infestation, plants grafted with ‘DR0141TX’ or ‘Estamino’ tended to have lower root galling index ratings than scion controls and ‘Multifort’-grafted plants, which was more evident in Expt. 1. Given the different environmental conditions during the tomato production period between the two experiments conducted in high tunnels, our findings highlight the important influence of production environment on grafted tomato performance. This study on grafted grape tomatoes in high tunnel organic production systems also demonstrated that so-called “vegetative” and “generative” rootstocks had similar impacts on tomato scion yield components and fruit mineral contents.

Influence of Recurrent Rolling/Crimping of a Cereal Rye/Crimson Clover Cover Crop on No-Till Bush Bean Yield

A no-till experiment was conducted in Auburn, AL U.S.A. to evaluate the effectiveness of an experimental two-stage roller/crimper in reoccurring rolling over the same area planted with a cereal rye/crimson clover cover crop mix and its influence on bush bean yield. Cover crop termination was much greater with rolling/crimping when compared to the non-rolled (untreated) control. During the three growing seasons, rolling three times had significantly higher termination rates compared to all other treatments, exceeding 90% in 2020. These results suggest that there may be an advantage to rolling/crimping three times so that planting of the cash crop could potentially be performed one week earlier, under favorable soil moisture conditions. However, for growing seasons 2018 and 2020 at three weeks after rolling, there were no differences between rolling treatments. In 2019, rolling three times over the same cover crop area was the only treatment that achieved above 90% termination rate indicating a clear advantage of recurring rolling/crimping in 2019. Rolling/crimping proved to be effective as yield was significantly higher compared to not rolled when averaged over all three growing seasons. This is possible due to the difficulty in planting into a standing cover crop which could have negative effects on seed to soil contact, but more importantly explained with the slight soil moisture advantage given to the rolled plots over the standing cover crop plots. Thus, optimum soil moisture when planting beans is key for successful germination and good main crop stand.

Grazing management effects on cover crop responses and cotton lint yield

AbstractGrazing cover crops can improve land‐use efficiency and diversification, making agricultural enterprises more resilient to market fluctuations. We investigated how grazing intensity affects cover crop forage responses and cotton (Gossypium hirsutum L.) lint yield. Cover crops were a rye (Secale cereale L.)–oat (Avena sativa L.) mixture managed as follows: no grazing + 34 kg N ha–1 (NG34), no grazing + 90 kg N ha–1 (NG90), heavy grazing (HG), moderate grazing (MG), and light grazing (LG), compared with a no cover crop control. All grazed treatments received 90 kg N ha–1. Average postgrazing herbage mass (HM) for HG, MG, and LG was 520, 1,350, and 2,120 kg dry matter ha–1, respectively. Herbage accumulation (HA) rate was greater for LG than HG, with MG being intermediate. Forage crude protein (CP) and in vitro digestible organic matter (IVDOM) concentrations decreased as the season progressed and were usually greater for HG than MG and LG. Stubble residue before cover crop termination was greatest for NG34 and NG90 in 2018 and 2020, however, in 2019 NG90 had greater stubble residue before termination than NG34 (7540 vs. 6650 kg dry matter ha–1). Heavy grazing resulted in greater weed proportion (17 vs. 6.5%) and lesser soil cover (49 vs. 70%) than nongrazed cover crops. Cotton lint yield was low and unaffected by treatment, reaching a maximum of 520 kg ha–1 in 2019. Although lint yield was not affected by cover crop fertilization or grazing during 3 yr, HG reduced soil cover and increased weed presence.

Targeted timing of hairy vetch cover crop termination with roller crimper can eliminate glyphosate requirements in no-till sunflower

No-till cropping systems with cover crops can improve soil health, but often rely on glyphosate, which is a contentious herbicide. In this study, we investigated whether a system based on the direct sowing of sunflower (Helianthus annuus) in the dead mulch of a roller-crimped hairy vetch (Vicia villosa) could be competitive with a system where glyphosate is also sprayed to terminate the cover crop and to control weeds. We hypothesized that optimum timing of roller-crimping would be key to eliminate glyphosate requirements while maintaining sunflower performance. In a 3-year on-farm experiment, we compared three vetch termination stages (early: pre-flowering; Intermediate: beginning of flowering; late: 70% flowering) and three glyphosate rates (Nil, half and full, i.e. 1440 g of active ingredient per hectare). Vetch biomass increased progressively from early to late termination stages, and ranged between 414 and 658 g m−2. Higher vetch biomass was correlated with lower weed biomass. Treatments had inconsistent effects on weed diversity and composition, largely determined by the interactions between treatments and seasonal (different years) or local factors (different fields). Glyphosate-based treatments seemed to select for aggressive weed species, but no clear species filtering effect based on ecological or functional traits was detected. Shannon H’ was positively correlated with sunflower grain yield below a weed dry biomass threshold of 150 g m−2. Crop yield with early termination stage was a failure without glyphosate application. However, crop yield with late vetch termination was acceptable, being at par or 15% higher (mean of first and second years) in no-glyphosate compared with glyphosate-based treatments. Crop gross margins showed the same trend (+33% for no-glyphosate compared with glyphosate-based treatments). This study, for the first time, shows that targeted timing of roller-crimped hairy vetch in no-till sunflower can result in equal agronomic and economic performances as addition of glyphosate.

Cover crops and preemergence herbicides: An integrated approach for weed management in corn-soybean systems in the US Midwest

Adoption of a fall established, high biomass cereal rye cover crop has potential to diversify weed management in corn and soybean production systems, reducing the selection pressure for resistance to postemergence herbicides. However, farmers and crop consultants express concern about limited weed suppression from an overwintering cover crop in areas where high biomass production is limited by cooler spring temperatures, such as in the Upper-Midwest U.S. Use of a preemergence herbicide, regardless of cover crop adoption, is a standard recommendation for improving early season weed control in corn and soybean. Field experiments were conducted at two sites in Wisconsin to assess the effects of six soil management practices (tillage, no-till, and four cereal rye cover crop termination timings/methods) with or without the use of a preemergence herbicide on weed suppression at the time of postemergence herbicide application and crop productivity. Results showed that cereal rye biomass increased > 6x between termination at the time of cash crop planting versus termination two weeks later. In corn and soybean, weed ground cover was lower for soil management with cereal rye cover crop terminated two weeks after cash crop planting (≤ 7% weed cover) compared to all other soil management practices (≥ 23% weed cover) when a preemergence herbicide was not used. Use of a preemergence herbicide resulted in low weed ground cover across treatments in corn (≤ 7% weed cover) and soybean (≤ 13% weed cover). Corn and soybean yield was not affected by preemergence herbicide treatments. Corn yield was lower at the south-central Wisconsin location for the soil management with a cereal rye cover crop terminated two weeks after cash crop planting (9.82 Mg ha-1) compared to all other soil management practices (≥ 12.07 Mg ha-1); at the southwest Wisconsin location, corn yield was greater for the conventional tillage treatment (14.28 Mg ha-1) compared to all other soil management treatments (≤ 10.89 Mg ha-1). Soil management did not affect soybean yield, although yields were different between locations with 3.44 Mg ha-1 at the south-central Wisconsin compared to 4.77 Mg ha-1 at the southwest Wisconsin location. These results indicate that in the absence of a high biomass cereal rye cover crop, preemergence herbicides are important for in-season weed control. Also, the inclusion of a late-terminated cereal rye cover crop in soybean should be considered as an effective management practice for reducing weed ground cover without affecting crop yield.

Fallow replacement cover crops impact soil water and nitrogen dynamics in a semi-arid sub-tropical environment

Conventional dryland cropping systems rely upon frequent and lengthy fallow periods to conserve soil water and mineral nitrogen to stabilize crop production. However, this is associated with depletion of soil organic matter and decreased fallow efficiency. Intensifying cropping systems by planting cover crops has been touted as a means to stem soil organic matter loss and improve fallow efficiency. We investigated whether the manipulation of cover crop functional trait diversity and sowing proportions (utilizing Poaceae, Fabaceae, and Brassicaceae) could provide complementary functions that improve soil water and mineral N management during fallow. Grass-legume mixtures represented the best compromise between biomass production (> 4000 kg DM ha˗1), N retention (142 kg N ha˗1), N supply via biological N fixation (35 kg N ha˗1) and maintained an additional 70 mm of water at the end of fallow period. Regardless of functional trait type, cover crops increased N retention but maintained similar soil mineral N content at the end of fallow period. However, soil water effects were functional trait-specific, and there were significant soil water deficits with brassica-dominated cover crops. Soil water accumulation post cover crop termination was significantly higher in cover crops compared with conventional fallows, but the overall fallow efficiency was higher in the conventional fallow. This study demonstrates that cover crops are not universally beneficial, and careful selection of cover crop functional traits in mixtures could enhance fallow soil water and N management in semi-arid sub-tropical drylands.

Soil Water Dynamics and Cotton Production Following Cover Crop Use in a Semi-Arid Ecoregion

Conservation management practices such as no-tillage and cover crops can decrease soil’s susceptibility to wind erosion, but adoption of these practices has been limited on the Texas High Plains (THP) where producers are concerned with cover crop water usage. The objective of this study was to evaluate the impact of no-tillage and cover crops on cotton (Gossypium hirsutum L.) lint yield and soil water content in a deficit irrigated cropping system. Soil water was observed bi-weekly in long-term, continuous cotton systems established in 1998 that included (1) conventional tillage, winter fallow, (2) no-tillage with rye (Secale cereale L.) cover, and (3) no-tillage with mixed species cover located in Lamesa, TX, USA. Results include observations from 2018–2020 (years 21–23 of the study period). The adoption of conservation practices did not significantly reduce cotton lint yield compared to conventionally tilled, winter fallow cotton. Soil water was initially depleted with cover crops but was greater throughout the growing season following cover crop termination. Throughout the soil profile, water depletion and recharge were more dynamic with conservation practices compared to the conventionally tilled control. There were no differences in cotton water use efficiency between treatments. Results from this study indicate cover crop water usage is likely not the cause of cotton lint yield decline in this deficit irrigated semi-arid production system.

Relationships between Soil Tillage Systems, Nematode Communities and Weed Seed Predation

Soil tillage is generally recognized as having a negative effect on soil health and weed seed predators. Recent advancements in conservation tillage practices allow for further comparison of how different levels of soil disturbances could influence soil food web communities. Field trials were conducted in 2017 and 2018 at two different sites to measure the effects of four cover crop termination treatments: conventional till (CT), no-till (NT), strip-till following roller-crimping (ST-RC), and strip-till with a living mulch between crop rows (ST-LM) on soil health using nematode community indices as soil health bioindicators. Following cover crop termination, the soil was monitored in the subsequent bell pepper (Capsicum annuum) crop over three sampling dates (June, August, and October). In the ST-RC treatment plots, soil nutrients were enriched (increased Enrichment Index, EI) and the soil food web structure was improved (higher Structure Index, SI) by the mid-season of the 2017 trial. In the 2018 trial, the ST-RC treatment enhanced fungal decomposition pathways (fungivore/fungivore + bacterivore ratio) throughout the bell pepper crop cycle and enhanced bacterial decomposition (abundance of bacterivorous nematodes) by the end of the cropping cycle compared to the no-till treatment, suggesting that the ST-RC treatment can further improve soil health conditions achieved by the NT treatment. Scatter plots of sampling points revealed that the treatments CT and NT had very distinct nematode-weed community assemblages in both trials, with the ST-RC and ST-LM treatments distributed closely with the NT treatment. Multivariate analysis among soil health bioindicators, weed pressure and weed seed predation explained 76.4 and 55.7% of the variance in the 2017 and 2018 trials, respectively. Weed pressure was consistently negatively related to (1) the SI, indicating soil disturbance would lead to more weed pressure; (2) the EI, indicating soil with higher weed pressure was linked to poor soil nutrient cycling, (3) cover crop residues left in the field from conservation tillage, or (4) how well the living mulch of red clover covered the ground. This study did not show that weed seed predation would lead to lower weed pressure but weed seed predation increased as weed biomass increased.

Survey of weed flora and weed management practices in Florida strawberry fields

AbstractA survey of weed flora and basic weed management practices was conducted in commercial strawberry [Fragaria × ananassa (Weston) Duchesne ex Rozier ssp. ananassa] fields in central Florida during the 2019 to 2020 field season. Forty-one fields on 14 farms were surveyed, which represents a total of 907 ha or 23% of the acreage planted to strawberries in Florida. All conventional fields were fumigated, and combinations of chloropicrin and 1,3-dichloropropene were used on 72% of the fumigated acreage. Preemergence or postemergence herbicides were used in row middles on 100% of the conventional acreage, but preemergence herbicides applied under the plastic mulch were only used on 12% of the acreage. A total of 47 weed species were identified during the survey. The five weed species with the highest frequency were goosegrass [Eleusine indica (L.) Gaertn.], cutleaf evening primrose (Oenothera laciniata Hill), Carolina geranium (Geranium carolinianum L.), common ragweed (Ambrosia artemisiifolia L.), and eclipta [Eclipta prostrata (L.) L.] which occurred in 83%, 63%, 58%, 58%, and 46% of all fields surveyed, respectively. The five species with the highest overall relative abundance were E. indica, O. lanciniata, G. carolinium, A. artemisiifolia, and Brazil pusley (Richardia brasiliensis Gomes). The frequency and distribution of E. indica is of particular concern, because populations in strawberry fields are thought to be resistant to paraquat, which is the primary herbicide used for crop termination. Weed density tended to be low overall, which suggests the integrated weed management (IWM) programs adopted by most growers are effective. Mean weed density tended to be similar on conventional and organic fields and unaffected by fumigant applied the year of the survey or the number of years strawberries had been grown consecutively in a field. Weed management research moving forward should focus on the development of IWM programs for E. indica, O. lanciniata, G. carolinium, and A. artemisiifolia.

Benzoxazinoids in roots and shoots of cereal rye (Secale cereale) and their fates in soil after cover crop termination

Benzoxazinoids in roots and shoots of cereal rye (Secale cereale) and their fates in soil after cover crop termination

Legume Cover Crop Contributions to Ecological Nutrient Management in Upper Midwest Vegetable Systems

Cover cropping, especially with legumes, is a critical approach to ecological soil nutrient management as a means to meet Sustainable Development Goal (SDG) 2, addressing food security issues via sustainable agriculture approaches. However, cover cropping in some of the most intensified food production regions of the northern U.S. is challenged by short growing seasons and harsh winters with variable temperatures and increasingly erratic snowfall. In this study, we explore the potential of winter annual legume cover crops to augment soil organic carbon (C) and nitrogen (N) stocks within a horticultural cropping system under climate conditions that allow only modest cover crop biomass production. We compared hairy vetch, cereal rye, red clover, and a hairy vetch/rye biculture in a randomized complete block design at two sites (North Central and Southwest Research and Outreach Centers in Minnesota) over 2 years. Cover crops were established in fall and terminated in spring prior to sweet corn planting, and soils sampled both at pre-cover crop termination and 2 weeks post-termination. We determined several indicators of C and N dynamics, including microbial biomass C (MBC), permanganate-oxidizable C (POXC), particulate organic matter C and N (POMC and POMN, respectively), extractable soil N (EXTN), and potentially mineralizable N (PMN). Out of all treatments evaluated, vetch production increased soil EXTN the greatest after 2 weeks, contributing two to 11 times more EXTN to soils compared to non-vetch treatments, meeting N requirements for sweet corn in three out of four site-years. Overall, time of sampling, either pre-or post-termination, consistently impacted soil measurements, with p < 0.05 in 20 out of 24 soil parameter × site-year combinations. Study results suggest that cover crops planted in colder northern climates during winter fallow periods can supply valuable N following spring termination, but termination effects on labile C and N pools are mixed. Our findings advance understanding of how cover cropping can support SDG 2 outcomes by assessing cover crop legume systems under biophysical conditions that challenge cover crop integration in agroecosystems.

Cover crops may exacerbate moisture limitations on South Texas dryland farms

Cover crops are a sustainable management tool for mediating weed pressure, reducing soil erosion, and enhancing soil organic carbon (C) and nitrogen (N) levels. Yet, adoption rates across water-limited farms in Texas remain low, especially among producers without irrigation access, due to concerns that cover crop use of soil moisture will negatively impact subsequent cash crop yields. This three-year cover crop trial in a rain-fed sorghum (<i>Sorghum bicolor</i> L.) farm in Lyford, Texas, trialed different cover crop mixes and seeding rates and confirmed that cover cropping leads to significant soil moisture deficits and cash crop failure when rainfall is low between cover crop termination and cash crop planting (&lt;30 mm). In seasons one and three, moisture deficits contributed to significantly lower germination of post–cover crop sorghum compared to fallow control plots. In season two, increased precipitation during a longer moisture recharge period between cover crop termination and cash crop planting helped avoid sorghum yield drops. Length of recharge period, amount of rainfall, species selection, planting density, and termination method are major determinants of subsequent cash crop outcomes. Careful management can minimize some of the risks cover cropping poses to soil moisture, but without reliable rainfall at key points in the cropping cycle, cover cropping remains risky for farmers without irrigation access.

Growth, weed control, and nitrogen uptake of winter-killed cover crops, and their effects on maize in conservation agriculture

The utilization of winter-killed cover crops is increasing due to their benefits in intensive cropping systems based on summer cash crops. However, there is still a lack of knowledge about their management in temperate climates, where maize is planted early under conservation tillage techniques. For these conditions, here we document for the first time various agronomic effects of winter-killed cover crops under different management options. We evaluated the production, the nitrogen uptake, and the weed control of five pure winter-killed cover crop species, as well as the production of the subsequent maize and its nitrogen recovery, in four different sites. Several management options were compared (cover crop fertilization, sowing technique, and cover crop termination method). Legume cover crops (Trifolium alexandrinum L. and Vicia benghalensis L.) had a small above-ground biomass (on average 0.6 t DM ha−1 in November), while for non-legumes (Avena strigosa Schreb., Sinapis alba L., and Raphanus sativus L.) the production (on average 2.4 t DM ha−1, N uptake 89 kg N ha−1) was higher, as well as weed control and N uptake. The difference in the above-ground biomass between the two groups of cover crops was smaller at the end of winter (0.4 Mg DM ha−1), when in five out of eight site × year combinations, soil mineral N was significantly higher in a cover crop treatment compared to the no cover crop, presumably due to N release from cover crops. Cover crops did not increase maize production, and their residues did not hamper maize sowing and emergence. The recovery of cover crop N by maize was 86% for legumes and − 1% for non-legumes. We conclude that productivity, N uptake, and weed control of winter-killed cover crops (especially non-legume species) are encouraging, with no negative effects on maize yield.

Post-termination Effects of Cover Crop Monocultures and Mixtures on Soil Inorganic Nitrogen and Microbial Communities on Two Organic Farms in Illinois

Cover crops can continue to affect agricultural systems even after they have been terminated by influencing nitrogen dynamics and by altering soil microbial communities. These post-termination effects can influence soil fertility, weed pressure, and the dynamics of potential plant pathogens in the narrow window of time between cover crop termination and cash crop emergence. We evaluated the post-termination effects of 12 different spring-sown cover crop mixtures and monocultures on soil nitrogen and microbial communities on two different organic farms in Central Illinois (on Lawson silt loam soil) and Northern Illinois (on Virgil silt loam soil). In comparison to control plots with no cover crops, all cover crop treatments significantly reduced soil nitrate levels but increased the potentially mineralizable nitrogen pool following termination. Nitrate levels of cover crop plots approached those of controls after 2 and 4 weeks, respectively, but potentially mineralizable nitrogen levels in cover plots remained elevated for at least 4 weeks following termination. Monocultures of Brassica cover crops showed the greatest decrease in soil nitrate, while Brassicas and unplanted control plots containing high biomass of weeds showed the greatest increase in potentially mineralizable nitrogen in comparison to plant-free control plots. In contrast to their effect on soil nitrogen, cover crops had very limited impact on the composition of soil microbial communities. Overall microbial community composition varied across sites and years, and only soil fungi significantly responded to cover cropping treatments. Nevertheless, we found that some highly correlated groups of soil microbes showed significant responses to soil nitrate and to high plant biomass. Key members of these correlated groups included ammonia-oxidizing organisms and saprotrophic fungi. Our results suggest that cover crops may reduce the potential for springtime nitrogen leaching losses by retaining nitrogen in the soil organic pool, and they may also have impacts on the soil microbial community that are particularly relevant for nitrogen cycling and decomposition of plant residues.

The concurrent assessment of agronomic, ecological and environmental variables enables better choice of agroecological service crop termination management

Abstract Although organic farming was originally promoted as an alternative farming system to address agronomic, environmental and ecological issues, its conventionalisation has led to an intensification and specialisation of production. In the light of this, several studies have questioned the environmental benefits of organic farming as well as its agronomic viability. Thus, there is a need to improve organic vegetable systems to reduce their environmental impact without affecting their productivity. To tackle this challenge, European farmers and researchers have recently started to focus on agroecological service crops (ASCs). However, few studies have simultaneously evaluated the agronomic, environmental and ecological aspects of ASC management under different European pedo‐climatic conditions. We evaluated effects of the ASC management strategies—no‐till roller crimping (NT‐RC) and green manuring (T‐GM) on cropping system performance using agronomic, environmental and ecological indicators—to exemplify the need for multidimensional analysis to understand management implications for addressing environmental and agronomic challenges. We combined the results from 11 organic vegetable field trials conducted in seven European countries over a period of 2 years to test for general trends. Our results provide solid evidence that NT‐RC management across different pedo‐climatic conditions in Europe enhances the activity density of ground and rove beetles and improves both the potential energy recycling within the system and weed control. However, in NT‐RC plots, lower cash crop yield and quality, energetic efficiency of production and activity density of spiders were observed compared to T‐GM. Synthesis and applications. Multidimensional analyses using agronomic, environmental and ecological indicators are required to understand the implications of agricultural management in agroecosystem functioning. Introducing agroecological service crops combined with the use of no‐till roller crimping is a promising strategy for improving agronomic performance (e.g. fewer weeds) and reducing environmental (e.g. increasing the potentially recyclable energy) and ecological (e.g. enhancing the activity density of beneficial taxa such as ground and rove beetles) impacts. However, our study also indicates a need for agronomic and environmental improvements while promoting a wider acceptance of this strategy.

Tile Drainage Flow Partitioning and Phosphorus Export in Vermont USA

Tile drainage (TD) has been identified as a potential non-point source of phosphorus (P) pollution and subsequent water quality issues. Three fields with TD in Vermont USA were monitored to characterize hydrology and P export. Fields were in corn silage and used minimal tillage and cover cropping practices. Preferential flow path (PFP) activity was explored by separating TD flow into flow pathway and source connectivity components using two hydrograph separation techniques, electrical conductivity end member unmixing, and hydrograph recession analysis. TD was the dominant P export pathway because of higher total discharge. Drought conditions during this study limited surface runoff, and possibly resulted in maximum PFP activity in the active clay soils. The non-growing season dominated annual P loading for two of the three study years. Peak P concentrations in TD occurred during events following manure injection in the fall, as well as in the spring post cover crop termination and post-planting. Intra-event analysis of rainfall pulses showed that TD flow and P concentrations were higher because of higher intensity pulses. This study highlights the impacts of current manure management, as well as the potential for climate change to increase P transport to TD.

Effectiveness of Cover Crop Termination Methods on No-Till Cantaloupe

In a no-till system, there are many different methods available for terminating cover crops. Mechanical termination, utilizing rolling and crimping technology, is one method that injures the plant without cutting the stems. Another popular and commercially available method is mowing, but this can cause problems with cover crop re-growth and loose residue interfering with the planter during cash crop planting. A field experiment was conducted over three growing seasons in northern Alabama to determine the effects of different cover crops and termination methods on cantaloupe yield in a no-till system. Crimson clover, cereal rye, and hairy vetch cover crops were terminated using two different roller-crimpers, including a two-stage roller-crimper for four-wheel tractors and a powered roller-crimper for a two-wheel walk-behind tractor. Cover crop termination rates were evaluated one, two, and three weeks after termination. Three weeks after rolling, a higher termination rate was found for flail mowing (92%) compared to lower termination rates for a two-stage roller (86%) and powered roller-crimper (85%), while the control termination rate was only 49%. There were no significant differences in cantaloupe yield among the rolling treatments, which averaged 38,666 kg ha−1. However, yields were higher for cereal rye and hairy vetch cover crops (41,785 kg ha−1 and 42,000 kg ha−1) compared to crimson clover (32,213 kg ha−1).