Winter Annual Cover Crops Research Articles

Cover cropping history affects cotton boll distribution, lint yields, and fiber quality

AbstractThere has been limited introduction of new cover crop species into cotton (Gossypium hirsutum L.) production within the last 30 years. Mounting evidence shows that traditional cover cropping species may be detrimental to cotton production, either by depleting soil fertility with crop removal, immobilizing minerals from high carbon residue, or excessive quantity of residue remaining at planting. The objective of this study was to determine the effects of growing a novel cover crop species, carinata (Brassica carinata A. Braun), as a winter annual cover crop for cotton rotation in the southeastern Coastal Plain. Over a 2‐year period, carinata, winter wheat (Triticum aestivum L.), and fallow covers were maintained over winter months, then rotated into cotton. Each year, seedcotton and lint yields were collected, along with subsamples for ginning and subsequent fiber quality analyses. Additionally, end‐of‐season plant mapping was conducted on plants from 1 m of row per plot to determine cover crop effects on boll formation, retention, and distribution, as well as canopy architecture. Results indicated that seedcotton and lint yield of cotton following carinata was greater than cotton following winter wheat, and lint yields of cotton following wheat were lower than cotton after fallow. Fiber quality was largely unaffected by preceding cover crop. End‐of‐season plant mapping indicated that cotton grown after carinata had more position 2 bolls, which correlated to greater lint yields. These results indicate that carinata can potentially serve as a new, more effective cover crop than winter wheat for cotton rotations in Coastal Plain soils.

Agronomic and economic implications of cover crop and phosphorus fertilizer management practices for water quality improvement.

Phosphorus (P) fertilization practices and winter cover crops are promoted to protect water quality yet can potentially influence crop yield and profitability. This study examined the impacts of three P fertilizer management practices (no P, fall broadcast P, and spring injected P) and winter annual cover crop use on yields, net returns, and water quality in a no-till corn-soybean rotation. Treatments were replicated in a 4-yr field study where sediment, total P, and dissolved reactive P (DRP) losses in edge-of-field surface runoff were continuously monitored. Production budgets were developed for each treatment and coupled with water quality data to identify optimal practices and opportunity costs for improving water quality. Applying P fertilizers increased crop yield regardless of application method or cover crop, but the response was more pronounced in corn than soybean. The cover crop reduced corn grain yield in 1 yr with high temperature and low precipitation but did not impact grain yield in the other corn year or either year of soybean. The most profitable treatment was fall broadcast P fertilizer with no cover crop, which also had the greatest total P and DRP losses and near greatest sediment loss. The lowest-cost methods of reducing total P, DRP, and sediment losses were, respectively, no P fertilizer without a cover crop ($47.56kg-1 total P), spring injected P fertilizer without a cover crop ($56.47kg-1 DRP), and spring injected P fertilizer with a cover crop ($0.16kg-1 sediment). Widespread adoption of these practices will likely require monetary incentives.

Impacts of Winter Annual Cover Crops and Neonicotinoid Seed Treatments on Arthropod Diversity in Mississippi Soybean.

Winter annual cover crops can be planted before soybean in Mississippi for many agronomic reasons. Incorporating winter annual cover crops into soybean production changes the seasonal hosts within fields. Some studies suggest that reducing tillage and using diverse species of cover crops can increase arthropod diversity and predator activity. Neonicotinoid seed treatments are often implemented to combat early season insect pests in soybean that follow cover crops, but negative effects on the environment such as reductions in biodiversity are often attributed to these compounds. We conducted an experiment to measure the effects on the diversity of the soybean epigeal and foliar communities when incorporating cover crops as well as insecticidal seed treatments into Mississippi soybean growing systems. Our results showed that legume cover crops had significant impacts on the epigeal community diversity of soybean planted behind them. These cover crops, especially hairy vetch, supported a more diverse foliar community before termination. To prevent increases in herbivorous arthropods, neonicotinoid seed treatments can be used without affecting epigeal predators such as beetles, ants, and spiders. The neonicotinoid seed treatments affected arthropod diversity, but the reductions were mainly caused by decreases in herbivorous pest insects that fed on treated soybean plants.

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.

Desiccation of corn allows earlier direct seeding of winter camelina in the northern Corn Belt

AbstractIn the U.S. Upper Midwest where growing seasons are short, establishing winter annual cover crops following corn (Zea mays L.) is challenging. Winter camelina [Camelina sativa (L.) Crantz] shows promise as a winter annual cover crop that can be dual cropped with soybean [Glycine max (L.) Merr.] to help diversify the corn–soybean rotation. This 2‐yr field study in southern and western Minnesota evaluated desiccating corn with a preharvest aid to hasten its dry‐down and hence harvest so that camelina could be no‐till drilled in a timely manner. We hypothesized that direct drilling camelina following corn harvest would improve establishment and yields. Sodium chlorate was applied as a desiccant to corn at early (D1) and mid‐R5 (D2) and physiological maturity (D3) stages of development, including an untreated check. The D1 and D2 treatments hastened corn harvest by 1 to 3 wk compared with the check. Corn grain yields were unaffected by the D2 and D3 treatments, but significantly declined by 16% in D1. Camelina seed yield did not differ among desiccation treatments and averaged 815 kg ha−1 across both locations with an average oil content of 385 g ka−1. Desiccating corn hastened its harvest allowing more time to drill‐seed camelina, thus improving establishment. However, more work is needed to improve management and genetics of winter camelina for use as a cash cover crop in corn systems.

Corn yield and soil nitrogen following winter annual cover crops interseeded into soybean

AbstractNitrogen demand for corn (Zea mays L.) production is high, and winter annual cover crops (WCC) can be an alternative source of plant‐available N. Common corn–soybean [Glycine max (L.) Merr.] rotations in the Mid‐Atlantic region leave fields fallow after soybean, providing a niche for WCC. The objective of this research was to evaluate the effect of rye (Secale cereale L.), hairy vetch (Vicia villosa Roth subsp. Villosa), and rye–vetch mixture WCC interseeded into soybean on soil N, corn grain yield, and fertilizer N replacement from cover crops. Eight different field sites were seeded into standing soybeans in Virginia from 2012–2014. The experiment was a split‐plot design with WCC species as the main plot in a full factorial arrangement with N rate (0 or 45 kg N ha−1 as starter fertilization at planting, and sidedress rates of 0, 45, 90, 135, and 180 kg N ha−1) as subplots. Maximum corn grain yield following hairy vetch WCC was 0.7 and 0.6 Mg ha−1 higher than when following rye at 0 and 45 kg ha−1 starter N, respectively. At one site where hairy vetch biomass was >2 Mg ha−1, corn grain yield increased beyond levels attributable only to the addition of legume N. Instead of decreasing the sidedress N requirement, optimum N rates with hairy vetch were similar to other WCC, only with higher yields. Hairy vetch WCC generally resulted in higher soil N than other WCC at the V4 stage of corn, but no differences after corn harvest.

Establishing winter annual cover crops by interseeding into Maize and Soybean

AbstractThe limited time available for cover crop establishment after maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] harvest is one of the main reasons for low cover crop adoption in the upper Midwest. Therefore, a 2‐yr multilocation study was conducted to evaluate winter annual cover crops establishment, their effect on main crop grain yields, and soil water content when interseeded into standing maize and soybean. Treatments were three interseeding dates (broadcasting at R4, R5, and R6 growth stages for maize, and R6, R7, and R8 for soybean) and three cover crops (winter camelina [WC] [Camelina sativa L.], field pennycress [PC] [Thlaspi arvense L.], winter rye [Secale cereale L.] plus a no cover crop control). Cover crop establishment and growth varied with interseeding date across locations and seasons for both maize and soybean systems. Averaged over the years, rye produced more green cover and biomass than the oilseeds in spring. However, at the northern‐most site, the greatest (40%) green cover was recorded from pennycress and indicates its potential as a cover crop. Seeding date and cover crops did not negatively affect maize or soybean grain yields or soil water content. Generally, cover crop establishment and growth were better in the soybean system than maize due to better light penetration. Further research is needed to develop better suited cultivars and/or agronomic management practices for interseeding into maize. The results of this study indicate that producers could integrate these covers to diversify and add ecosystem services to soybean production practices.

Herbicide carryover to various fall-planted cover crop species

AbstractResidual herbicides applied to summer cash crops have the potential to injure subsequent winter annual cover crops, yet little information is available to guide growers’ choices. Field studies were conducted in 2016 and 2017 in Blacksburg and Suffolk, Virginia, to determine carryover of 30 herbicides commonly used in corn, soybean, or cotton on wheat, barley, cereal rye, oats, annual ryegrass, forage radish, Austrian winter pea, crimson clover, hairy vetch, and rapeseed cover crops. Herbicides were applied to bare ground either 14 wk before cover crop planting for a PRE timing or 10 wk for a POST timing. Visible injury was recorded 3 and 6 wk after planting (WAP), and cover crop biomass was collected 6 WAP. There were no differences observed in cover crop biomass among herbicide treatments, despite visible injury that suggested some residual herbicides have the potential to effect cover crop establishment. Visible injury on grass cover crop species did not exceed 20% from any herbicide. Fomesafen resulted in the greatest injury recorded on forage radish, with greater than 50% injury in 1 site-year. Trifloxysulfuron and atrazine resulted in greater than 20% visible injury on forage radish. Trifloxysulfuron resulted in the greatest injury (30%) observed on crimson clover in 1 site-year. Prosulfuron and isoxaflutole significantly injured rapeseed (17% to 21%). Results indicate that commonly used residual herbicides applied in the previous cash crop growing season result in little injury on grass cover crop species, and only a few residual herbicides could potentially affect the establishment of a forage radish, crimson clover, or rapeseed cover crop.

Assessment of In‐Season Soil Nitrogen Tests for Corn Planted into Winter Annual Cover Crops

Core Ideas The Solvita 1‐d CO2 mineralization test could be a new tool to improve in‐season N rate recommendations for corn. Solvita and soil NO3–N tests may be useful for predicting the level of early‐season N mineralization from winter cover crops (WCCs). Soil NO3–N collected at the V4 growth stage of corn at 0 to 15 cm was positively correlated (R2 = 0.45) with corn check yield. Neither the Solvita nor the presidedress nitrate test detected WCC N mineralization consistently enough to use them in rate recommendations. Environmental and economic goals encourage the use of soil N tests to improve fertilizer N (FN) management in corn (Zea mays L.). Recently, the Solvita 1‐d CO2 burst test, which proposes to estimate soil potentially mineralizable N (PMN), has been promoted as a tool for FN recommendations. We aimed to compare the Solvita test with the established presidedress nitrate test (PSNT) for estimating optimum sidedressed FN rates in a typical corn crop rotation in the Mid‐Atlantic United States that includes winter annual cover crops (WCCs). Research was conducted at eight locations from 2012 to 2014. Three WCC treatments [cereal rye (Secale cereale L.), hairy vetch (Vicia villosa Roth ssp. villosa) or a cereal rye–hairy vetch mix] were the main plots and 10 FN rates were the subplots. The WCCs affected preplanting (PP) Solvita results at one location, V4 NO3–N at 0 to 15 cm (PSNT15) at four locations, and V4 NO3–N at 0 to 30 cm (PSNT30) at two locations. Correlations between soil N test parameters and relative corn yields ranged from 0.31 to 0.13. Values for PSNT15 and PSNT30 correlated positively with corn check yields (r = 0.41 and 0.39 respectively). Solvita did not provide additional information to PSNT for predicting preplanting PMN, V4 PMN, or corn check yields. The advantages of the Solvita test were its simplicity, speed of analysis, and lower coefficient of variation relative to the PSNT. Neither method was consistently effective for predicting WCC effects on soil N or relative corn yield.

Organic and conventional farmers differ in their perspectives on cover crop use and breeding

AbstractCover crops play an important role in agricultural sustainability. Unlike commodity cash crops, however, there has been relatively little cover crop breeding research and development. We conducted an online survey to evaluate: (a) the perspectives of organic and conventional farmers in the USA who use cover crops and (b) the specific cover crop traits that are important to farmers. We recruited participants from both organic and conventional agriculture networks and 69% of respondents reported that they farmed organic land. In addition to demographic data and information on management practices, we quantified farmer perspectives on four winter annual cover crops: (1) Austrian winter pea, (2) crimson clover, (3) hairy vetch and (4) cereal rye. Overall, respondents represented a wide range of states, farm sizes, plant hardiness zones and cash crops produced. Of the 417 full responses received, 87% of respondents reported that they used cover crops. The maximum amount farmers were willing to spend on cover crop seed varied by farmer type: 1% of conventional farmers versus 19% of organic farmers were willing to spend over US$185 ha−1(US$75 acre−1). Organic and conventional farmers differed in terms of the reasons why they grew cover crops, with organic farmers placing greater value on the ecosystem services from cover crops. More organic (63%) than conventional (51%) farmers agreed that participatory breeding was important for cover crop variety development (P= 0.047). Both groups shared strong support for cover crop research and considered many of the same traits to be important for breeding. For the legume cover crops, nitrogen fixation was considered the most important trait, whereas winter hardiness, early vigor, biomass production and weed suppression were the most important traits for cereal rye. Our results illustrate common interests as well as differences in the perspectives between organic and conventional farmers on cover crops and can be used to inform nascent cover crop breeding efforts.

Integrating Winter Annual Cereal Rye or Triticale into a Corn Forage Biofuel Production System

ABSTRACTIntegrating cover crops into the corn (Zea mays L.) forage-production system could enhance growers’ profitability and improve ecosystem services. Field plots were established at two locations in Michigan during 2012--2014 to evaluate ethanol production, estimate carbon and energy balance, and the economics of corn forage plus cover crop, cropping systems. In the 2012--2013 crop cycle, which was characterized by a summer drought, the cereal rye (Secale cereale L.), and triticale (Triticale hexaploide Lart.), winter annual cover crops increased cropping system biomass yield by 44%, and total ethanol yield by 28% relative to the no-cover control. During the 2012--2013 cycle, cover crops provided sufficient biomass (6.5 and 8.1 Mg ha−1, respectively, for cereal rye and triticale) to result in a profitable harvest as a biofuel feedstock. However, following a harsh winter, such as that experienced in the 2013--2014 cycle, cover crop yield (1.6 and 1.2 Mg ha−1, respectively, for cereal rye and triticale) was compromised to the point that harvest was not economically justified. Incorporating cover crops into a corn forage cropping system increased total biomass and potential biofuel yield and generated a very favorable net ecosystem carbon and energy balance.

Grazing Winter Rye Cover Crop in a Cotton No‐Till System: Yield and Economics

Winter annual cover crop use is limited in conservation management systems in the United States. Grazing cover crops could encourage cover crop adoption if returns offset establishment costs without reducing crop yields. A 4‐yr field experiment was conducted near Watkinsville, GA, in which a rye (Secale cereale L.) cover crop was grazed by cattle or roller‐crimped before planting cotton (Gossypium hirsutum L.). Cattle consumed about 2.4 Mg ha−1 of forage annually but amounts were variable due to weather conditions. Rye residue remaining at cotton planting averaged 6.7 Mg ha−1 for non‐grazed compared with 1.7 Mg ha−1 for grazed treatments. Cotton yields tended to be better in the non‐grazed treatment but were significantly different only in 2009 when yields were reduced in the grazed treatment due to soil compaction. Four‐year average lint yield was 120 kg ha−1 greater for the non‐grazed treatment. Cotton fiber quality parameters were generally better in the non‐grazed treatment but not enough to change crop price. Differences between grazed and non‐grazed returns ranged from $–26 to $355 and averaged $81 ha−1 when based on market year prices. The difference in average return increased to $110 ha−1 when based on 2012 market year prices. Although negative effects of soil compaction were observed the final year, returns from grazing have the potential to offset establishment costs of a rye cover crop and increase profits for cotton producers in the Southern Piedmont of the United States.

Winter Annual Cover Crop Impacts on No‐Till Soil Physical Properties and Organic Matter

The inclusion of winter annual cereal cover crops (WCC) in grain crop rotations is a common management practice promoted to protect soil resources and enhance water quality. However, the effects of long‐term incorporation of WCC into no‐till grain crop rotations on soil physical properties are not well established. We evaluated the long‐term effects of WCC on soil physical properties after 13 yr of use at three locations in Maryland, USA. Continuous maize (Zea mays L.) was the summer grain crop. In the control treatment, maize was followed by winter fallow and in the WCC treatment, cereal rye (Secale cereal L.) was planted as a WCC in the off‐season. We examined aggregate stability, total and labile organic matter, soil bulk density (BD), air permeability (AP), water infiltration rate (WIR), and hydraulic conductivity (HC), during the growing and off‐season. Aggregate stability increased under the WCC treatment but there were no increases in total organic matter and labile organic matter. Only during the winter sampling season at the two Coastal Plain locations, soils under WCC displayed improved soil physical properties in comparison with the same soils under winter fallow. The heavier‐textured soils at the Piedmont location exhibited no consistent differences attributable to WCC.

Impact of winter cover crops on soil properties under soybean cropping systems

Agricultural systems in Uruguay exhibit a high frequency of soybean in crop rotations. This could adversely affect soil organic carbon (SOC) storage in the long term. The introduction of winter annual cover crops (CC) in these systems may improve SOC balance as well as reduce the impact of rainfall on soil erosion rates. The objective of this study was to evaluate the impact of the inclusion of CC on SOC storage and soil physical properties under continuous soybean (Glycine max [L.] Merr) cropping systems. A field experiment was established in 2003 in a vertic Argiudoll. A split plot design was used with CC and non CC as whole plot arranged in four randomized complete blocks. Cover crops were: oats (Avena sativa L)., annual ryegrass (Lolium multiflorum L.). Two termination dates comprised split plots: 60 or 30 days before soybean planting. Mean annual forage production over eight years was higher (P ≤ 0.05) in oats compared to annual ryegrass for both termination dates. The inclusion of CC increased SOC concentration at the 0-7.5 cm depth, and at the 7.5-15 cm depth in the annual ryegrass treatment. Oats and annual ryegrass had 60 and 80 % more particulate organic carbon (POC) concentrations at the 0-7.5 cm, respectively than no cover crop treatment. No significant differences among treatments were observed for mineral associated organic C-MAOM at any depth. Nitrogen mineralization potential under ryegrass had a three-fold increase compared to the no cover crop treatment. Both CC treatments showed a higher (P ≤ 0.05) percentage of macropores compared to the no cover crop treatment. In most of the years soybean grain yield was not affected by cover crops treatments. However, late termination dates often reduced soybean yields. The inclusion of CC in high frequency soybean cropping systems may enhance soil C storage, and improve related soil physical properties.

INVESTIGATING COMPONENT SPECIES PROPORTIONS IN A CEREAL-LEGUME COVER CROP MIXTURE UNDER ORGANIC MANAGEMENT

ISHS XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on Organic Horticulture: Productivity and Sustainability INVESTIGATING COMPONENT SPECIES PROPORTIONS IN A CEREAL-LEGUME COVER CROP MIXTURE UNDER ORGANIC MANAGEMENT

Demographic and Management Factors Affecting the Adoption and Perceived Yield Benefit of Winter Cover Crops in the Southeast

The inclusion of cover crops in cropping systems brings direct and indirect costs and benefits. Farmers will adopt and utilize cover crops as long as the perceived benefit of using them is positive. This paper examines the demographic and management factors affecting the adoption and perceived benefit (in terms of improved crop yield) of using winter annual cover crops. A double selectivity model of cover crop adoption and perceived yield gain was estimated using survey data of Alabama farmers examining cover crop use and management. Results may help in understanding factors shaping farmers' perceptions, adoption, and retention of cover crops.

Nitrogen Delivery from Legume Cover Crops in No‐Till Organic Corn Production

Sixteen winter annual cover crop cultivars were grown in North Carolina to determine total N accumulation, biological N fixation (BNF) potential, and compatibility with a roller‐crimper‐terminated organic corn (Zea maysL.) production system. Cover crops and termination dates were tested in a stripped block design. Treatments included hairy vetch (Vicia villosaRoth), common vetch (Vicia sativaL.), crimson clover (Trifolium incarnatumL.), Austrian winter pea (Pisum sativumL.), berseem clover (Trifolium alexandrinumL.), subterranean clover (Trifolium subterraneumL.), narrow leaf lupin (Lupinus angustifoliusL.), and Balansa clover (Trifolium michelianumSavi.), as well as bicultures of rye (Secale cerealeL.), hairy vetch, and Austrian winter pea. Roller‐crimper termination occurred in mid‐April, early May, and mid‐May. Total biomass, N concentration, and C/N ratios were determined for cover crops at all roll times and natural15N abundance at the optimal kill date. Hairy vetch and crimson clover monocultures had the greatest overall biomass in 2009, and bicultures the greatest biomass in 2010. Crimson clover successfully terminated in late April, hairy vetch and Austrian winter pea in mid‐May, and berseem clover and common vetch in late May. All cover crops except lupin and subterranean clover derived between 70 and 100% of their N from the atmosphere. Corn response to cover crop mulches was significantly affected by the time of rolling, with poor stands resulting from competition with insufficiently terminated mulches. Crimson, Balansa, and subterranean clover mulches resulted in poor corn yields despite relatively high levels of total N. The highest corn yields were achieved in hairy vetch and rye plus hairy vetch bicultures.

Cover crop effects on nitrogen load in tile drainage from Walnut Creek Iowa using root zone water quality (RZWQ) model

Abstract Studies quantifying winter annual cover crop effects on water quality are mostly limited to short-term studies at the plot scale. Long-term studies scaling-up water quality effects of cover crops to the watershed scale provide more integrated spatial responses from the landscape. The objective of this research was to quantify N loads from artificial subsurface drainage (tile drains) in a subbasin of the Walnut Creek, Iowa (Story county) watershed using the hybrid RZWQ-DSSAT model for a maize ( Zea mays L.)-soybean [ Glycine max (L.) Merr.] and maize–maize–soybean rotations in all phases with and without a winter wheat ( Triticum aestivum L.) cover crop during a 25-year period from 1981 to 2005. Simulated cover crop dry matter (DM) and N uptake averaged 1854 and 36 kg ha −1 in the spring in the maize–soybean phase of the 2-year rotation and 1895 and 36 kg ha −1 in the soybean–maize phase during 1981–2005. In the 3-year rotation, cover crop DM and N uptake averaged 2047 and 44 kg ha −1 in the maize–maize–soybean phase, 2039 and 43 kg ha −1 in the soybean–maize–maize phase, and 1963 and 43 kg ha −1 in the maize–soybean–maize phase during the same period. Annual N loads to tile drains averaged 29 kg ha −1 in the maize–soybean phase and 25 kg ha −1 in the soybean–maize phase compared to 21 and 20 kg ha −1 in the same phases with a cover crop. In the 3-year rotation, annual N loads averaged 46, 43, and 45 kg ha −1 in each phase of the rotation without a cover crop and 37, 35, and 35 kg ha −1 with a cover crop. These results indicate using a winter annual cover crop can reduce annual N loads to tile drains 20–28% in the 2-year rotation and 19–22% in the 3-year rotation at the watershed subbasin scale over a 25-year period.

Cover Crop and Floor Management Affect Weed Coverage and Density in an Establishing Oregon Vineyard

Five vineyard floor management treatments were evaluated for effects on weed control over two growing seasons in an establishing ‘Chardonnay’ (Vitis vinifera) vineyard in the Willamette Valley of Oregon. Four cover crop management treatments and an unplanted treatment were compared to assess the effects on vine row and alleyway weed coverage and densities of broadleaf and grass weeds. A winter annual cover crop was grown in alleyways of the cover-cropped treatments and was mowed in spring. The mowed residue was managed as follows: 1) residue transferred in-row as mulch representing the industry practice of “mow-and-throw,” 2) residue transferred in-row as mulch at three times the rate of the earlier treatment, 3) mowed residue incorporated into alleyways, and 4) removal of mowed cover crop residue from the vineyard. Weed coverage was assessed visually within a 1.0-m2 quadrat placed randomly in alleyways and vine rows, and densities of broadleaf and grass weeds were determined by counting and grouping individual weeds within each quadrat. Vine row weed coverage and densities were lower in treatments with residue mulch at each sampling date in 2009 and 2010, with nearly 100% in-row weed suppression by the heavier mulch treatment. Alleyway weed coverage was lowest when residue was incorporated and highest in the unplanted treatment at some sampling dates. Grass weed densities in alleyways were similar between treatments at all sampling dates. Results of this study indicate that in-row mulch of cover crop residues at fresh weight densities of 2.5–15.0 kg·m−2 provided effective weed control in a non-irrigated vineyard in western Oregon. Also, alleyway weed coverage may be reduced through incorporation of mowed cover crop residues.

Rolled Winter Rye and Hairy Vetch Cover Crops Lower Weed Density but Reduce Vegetable Yields in No-tillage Organic Production

Winter annual cover crops, winter rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth), can reduce weed density and build soil quality in organic production systems. There is interest in integrating cover crops and reduced tillage with organic vegetable production, but few studies have been conducted in regions with short growing seasons and cool soils such as the upper Midwest. We evaluated no-tillage production of tomato (Solanum lycopersicum L.), zucchini (Cucurbita pepo L.), and bell pepper (Capsicum annuum L.) planted into winter rye, hairy vetch, and a winter rye/hairy vetch (WR/HV) mixture that were mechanically suppressed with a roller–crimper at two locations in Minnesota. Average marketable yields of tomato, zucchini, and bell pepper in the rolled cover crops were reduced 89%, 77%, and 92% in 2008 and 65%, 41%, and 79% in 2009, respectively, compared with a no-cover control. Winter rye and the WR/HV mixture reduced average annual weed density at St. Paul by 96% for 8 to 10 weeks after rolling (WAR) and hairy vetch mulch reduced weeds 80% for 2 to 8 WAR, whereas at Lamberton, there was no consistent effect of cover treatments on weed populations. Winter rye and the WR/HV mixture had higher average residue biomass (5.3 and 5.7 Mg·ha−1, respectively) than hairy vetch (3.0 Mg·ha−1) throughout the season. Soil growing degree-days (SGDD) were lower in cover crop treatments compared with the no-cover control, which could have delayed early vegetable growth and contributed to reduced yields. All cover crop mulches were associated with low levels of soil nitrogen (N) (less than 10 mg·kg−1 N) in the upper 15 cm. Rolled winter annual cover crops show promise for controlling annual weeds in organic no-tillage systems, but additional research is needed on methods to increase vegetable crop yields in rolled cover crops.