Grass Cover Crop Research Articles

The use of legume and grass cover crops induced changes in ion accumulation, growth and physiological performance of young olive trees irrigated with high-salinity water

Abstract The impact of intercropping with two different forage crops (legume and grass) on the shoot growth, ion accumulation and some physiological traits of 3-old year olive trees irrigated by high-salinity water (120 mM NaCl) was assessed under greenhouse conditions. Olive plants were subjected to one of the following treatments: TC (control); TG – olive plants intercropped with grass (Oats: Avena sativa L) and TL – olive trees intercropped with legume (Berseem Clover: Trifolium alexandrinum L). Results showed that sodium root:leaf ratio and nitrogen concentration in olive leaves were significantly increased in TL treatment. Olive shoot length and maximum quantum yield of photosystem II (Fv/Fm) were significantly improved by using Berseem Clover as a cover crop. Negative correlation was observed between the total chlorophyll content and the leaf Na+ concentration. On the other hand, polyphenol content was significantly increased in olive leaves when oats were used as cover crops, in relation to the high N-deficiency observed in olive leaves of TG treatment.

What do we know about cover crop efficacy in the North Central United States?

Recent meta-analyses about the efficacy of cover crops predict increased (a) soil organic matter (Poeplau and Don 2015), (b) arbuscular mycorrhizal fungi colonization (Bowles et al. 2017), and (c) nutrient conservation (Quemada et al. 2013; Kladivko et al. 2014; Han et al. 2017), all while improving (with legume cover crops), or at least not reducing (with grass cover crops), main crop yields (Tonitto et al. 2006; Marcillo and Miguez 2017). These analyses broadly support cover crop adoption, and both survey and satellite data suggest that cover crop use in the North Central United States is increasing (Conservation Technology Information Center et al. 2015; Hamilton et al. 2017; Seifert et al. 2018). However, many studies show no benefit of cover crops (Poeplau and Don 2015; Han et al. 2017), and economic analyses show greater expenses and risks with cover crops (Pratt et al. 2014; Roth et al. 2018), so it is critical to clarify what costs and benefits may be expected in varying circumstances. Rather than expecting global benefits to mirror mean effects, we should take into account differences in cropping systems and climate to predict cover crop efficacy and set growers confidently on the lowest-risk path to success (Snapp et…

Different Cover Crops Affect Nitrogen Fluxes in Mediterranean Vineyard

Core Ideas Burr medic cover crop supplied 125 kg ha–1 year–1 of fixed N to the vineyard. Twice the N needs of grapevine annual organs were satisfied by legume cover crop. Legume cover crop promoted + 25% of total N compared to grass cover crop. Compared to traditional soil tillage, the establishment of cover crops in Mediterranean vineyards has several advantages such as better soil fertility; however, vigor and N concentration of grapevine [Vitis vinifera (L.)] organs may be affected. A 3‐yr experiment was performed in Sardinia (Italy) to: (i) quantify the N fixation ability by burr medic [Medicago polymorpha (L.)] grown in a vineyard and its potential benefit for grapevines; (ii) compare the effects of different management systems (grass or legume cover crop vs. soil tillage) on grapevines. Total N fixed by burr medic was 125 kg ha−1 yr−1 and it was twice as high as the N contents of grapevine annual organs. Soil tillage promoted higher cluster and cane dry matter (+38% and +31%), compared to cover crop treatments. Legume cover crop induced higher N concentration in leaves and canes. The N content detected in grapevine annual plant growth with the legume cover crop reached 61 kg ha−1 yr−1. According to an indirect 15N dilution approach, the higher 15N enrichments detected in organs of grapevines, did not indicate that legume N was utilized by grapevine. However, lower 15N enrichment was occasionaly detected, indicating 6 and 13% of N derived from legume in clusters and canes, respectively. Compared to grapevines with grass cover, the N contribution from legume cover, estimated by the N‐difference method, induced 24, 24, and 31% of N increase in leaves, clusters, and canes, respectively. The increases corresponded to 10% of legume fixed N.

Weed Suppression in Cover Crop Monocultures and Mixtures

Interest in planting mixtures of cover crop species has grown in recent years as farmers seek to increase the breadth of ecosystem services cover crops provide. As part of a multidisciplinary project, we quantified the degree to which monocultures and mixtures of cover crops suppress weeds during the fall-to-spring cover crop growing period. Weed-suppressive cover crop stands can limit weed seed rain from summer- and winter-annual species, reducing weed population growth and ultimately weed pressure in future cash crop stands. We established monocultures and mixtures of two legumes (medium red clover and Austrian winter pea), two grasses (cereal rye and oats), and two brassicas (forage radish and canola) in a long fall growing window following winter wheat harvest and in a shorter window following silage corn harvest. In fall of the long window, grass cover crops and mixtures were the most weed suppressive, whereas legume cover crops were the least weed suppressive. All mixtures also effectively suppressed weeds. This was likely primarily due to the presence of fast-growing grass species, which were effective even when they were seeded at only 20% of their monoculture rate. In spring, weed biomass was low in all treatments due to winter kill of summer-annual weeds and low germination of winter annuals. In the short window following silage corn, biomass accumulation by cover crops and weeds in the fall was more than an order of magnitude lower than in the longer window. However, there was substantial weed seed production in the spring in all treatments not containing cereal rye (monoculture or mixture). Our results suggest that cover crop mixtures require only low seeding rates of aggressive grass species to provide weed suppression. This creates an opportunity for other species to deliver additional ecosystem services, though careful species selection may be required to maintain mixture diversity and avoid dominance of winter-hardy cover crop grasses in the spring.

Starter Fertilizer for Managing Cover Crop‐Based Organic Corn

Core Ideas Grass and legume cover crops are combined for weed and fertility management. A cereal rye and hairy vetch mixture provided more than 7500 kg ha−1 biomass. Additional fertility is necessary to maximize cover‐crop based organic corn yield. Subsurface banding feather meal is an option to increase organic corn yield. If cover crop biomass is low, providing adequate N fertility is critical for yield. Grass and legume cover crops are combined in mixtures to provide both weed and N fertility management in organic production; however, additional N fertility may be required to maximize corn yield. The research was conducted in Beltsville, MD; Kinston, NC; and Salisbury, NC; from 2012 to 2014 to evaluate the effect of starter fertilizer source and application method on weed competition and grain yield in cover crop‐based, organic corn production. Fertility treatments included high rate broadcast poultry litter (Plant available nitrogen [PAN] = 160 kg ha−1), low rate broadcast poultry litter (PAN = 72 kg ha−1), subsurface banded feather meal (PAN = 80 kg ha−1), subsurface banded poultry litter (PAN = 12 kg ha−1), and no starter fertility. A cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) mixture was established in the fall and was terminated using a roller‐crimper before corn planting. Cover crop biomass more than 7500 kg ha−1 provided excellent weed suppression. In a combined analysis of five environments, corn N content and yield followed the same pattern of high rate broadcast poultry litter > low rate broadcast poultry litter = subsurface banded feather meal > subsurface banded poultry litter = no starter fertility. Results from this study indicate that starter fertilizer is necessary to maximize corn yield in cover crop‐based organic corn production and that decisions regarding additional fertility will need to be dynamic based on site history, cover crop biomass production, and the ability to broadcast poultry litter.

Growing Legumes in Orchard Alleys as an Internal Nitrogen Source

The drive alley in modern apple (Malus ×domestica Bork.) orchards often receives enough light to grow plants other than the typical perennial grass cover. By planting leguminous species in this area, it is possible to produce a portion of the nitrogen needs of the orchard by mowing the vegetation and blowing it onto the tree row where it mineralizes and releases available N over the tree roots. Four perennial legume species [alfalfa (Medicago sativa L.), ladino white clover (Trifolium repens L.), birdsfoot trefoil (Lotus corniculatus L.), kura clover (Trifolium ambiguum L.)] were compared with the resident grass cover crop in a mature apple orchard. All legumes were direct-seeded into the alley to avoid any soil disturbance and were successfully established. Legume biomass and tissue N were monitored, along with biweekly monitoring of tree row soil nitrogen with both soil sampling and ion exchange resins using Plant Root Simulator® probes. Four mowings of alfalfa contained ≈43 kg total N/ha that was added to the tree row during the second season (2009), with a dry matter C:N of 10.8. Economically, legume nitrogen appears to be less expensive than other sources of organic N and may be cost competitive with synthetic fertilizer N when prices are high.

Aerial Interseeded Cover Crop and Corn Residue Harvest: Soil and Crop Impacts

Core Ideas Harvesting 71% of corn residue can increase wind erosion potential of a sandy loam soil. Corn residue harvest did not affect soil fertility and corn yields. Aerially interseeded winter rye cover crop tended to reduce wind erosion potential. Residue harvest can increase erosion potential but interseeded cover crop could partly offset this effect. Corn (Zea mays L.) residue is a forage source and a biofuel feedstock. Excessive residue harvest may, however, result in increased soil erosion risks and degraded soil properties. Aerial interseeding of a cover crop (CC) before harvesting corn may offset adverse effects of residue harvest. We studied the impacts of harvesting 71% of corn residue with and without aerially interseeded winter rye (Secale cereale L.) CC on wind and water erosion potential, soil organic carbon (SOC), nutrients, soil water content, and corn yields in a farmer's field under irrigated strip till continuous corn on a sandy loam in the western Corn Belt from 2013 to 2016. Interseeded CC biomass yield ranged from 0.2 to 3.4 Mg ha−1. Corn residue harvest reduced geometric mean diameter of dry soil aggregates and increased wind erodible fraction (<0.84 mm aggregates) by 0, 27, and 37% in the first, second, and third year, respectively, indicating that residue harvest increased the soil's susceptibility to wind erosion. Cover crop had no effect on geometric mean diameter and erodible fraction. Residue harvest reduced near‐surface water content but CC had no effect. Treatments did not affect fertility properties and corn yield. In spring, surface cover was 24.7% in residue‐harvested plots without CC and 65.3% in residue‐harvested plots with CC, indicating that CC provided soil protective cover. Overall. interseeded grass CC may not rapidly improve soil properties, but the added soil cover provided by the interseeded CC could partly offset the effect of residue harvest on wind erosion potential in sandy loam soils.

Herbicide Programs for the Termination of Various Cover Crop Species

The recent interest in cover crops as a component of Midwest corn and soybean production systems has led to a greater need to understand the most effective herbicide treatments for cover crop termination prior to planting corn or soybean. Previous research has shown that certain cover crop species can significantly reduce subsequent cash crop yields if not completely terminated. Two field experiments were conducted in 2013, 2014, and 2015 to determine the most effective herbicide program for the termination of winter wheat, cereal rye, crimson clover, Austrian winter pea, annual ryegrass, and hairy vetch; and cover crops were terminated in early April or early May. Visual control and above ground biomass reduction was determined 28 d after application (DAA). Control of grass cover crop species was often best with glyphosate alone or combined with 2,4-D, dicamba, or saflufenacil. The most consistent control of broadleaf cover crops occurred following treatment with glyphosate +2,4-D, dicamba, or saflufenacil. In general, control of cover crops was higher with early April applications compared to early May. In a separate study, control of 15-, 25-, and 75-cm tall annual ryegrass was highest with glyphosate at 2.8 kg ha−1or glyphosate at 1.4 kg ha−1plus clethodim at 0.136 kgha−1. Paraquat- or glufosinate-containing treatments did not provide adequate annual ryegrass control. For practitioners who desire higher levels of cover crop biomass, these results indicate that adequate levels of cover crop control can still be achieved in the late spring with certain herbicide treatments. But it is important to consider cover crop termination well in advance to ensure the most effective herbicide or herbicide combinations are used and the products are applied at the appropriate stage.

Vineyard Floor Management Influences ‘Pinot noir’ Vine Growth and Productivity More than Cluster Thinning

Vigor and crop level management are important practices for premium wine grape production. The implications of crop thinning ‘Pinot noir’(Vitis vinifera L.) vines of varying vigor were investigated in the Willamette Valley of Oregon in 2011 to 2013 to better understand the relationship between canopy size and yield within the framework of a cool-climate, premium production wine grape vineyard. To manipulate vigor, a competitive grass cover crop (Festuca rubra L.) was grown in both (Grass), alternating (Alternate), or neither side of the flanking alleyways (Tilled). Vines within each vineyard floor treatment had two crop levels applied, including cluster thinning to one cluster per shoot (Half Crop) or no crop thinning (Full Crop). Grass treatment had reduced leaf area and leaf nitrogen (N) concentrations during all years compared with Tilled treatments. Leaf photosynthesis was also lower in Grass treatments despite more light in the canopy interior. Grass treatments had lower yield than Tilled treatments in 2 of 3 years and lower yeast assimilable nitrogen (YAN) concentrations in fruit every year. There was limited impact of floor treatments on total soluble solids (TSS) and pH. Reduced yields through cluster thinning had limited impact on vegetative growth but increased TSS and pH, in 2 of 3 years. There were few floor management by crop level interactions in any year. Grass effectively reduced vegetative growth to moderate vigor levels with cane weights between 20 and 40 g. Using a competitive grass cover crop may be an effective strategy to reduce excessive vine growth and require less labor in canopy management and crop thinning without compromising basic fruit ripeness, although YAN levels need to be monitored.

Monitoring daily evapotranspiration over two California vineyards using Landsat 8 in a multi-sensor data fusion approach

Abstract California's Central Valley grows a significant fraction of grapes used for wine production in the United States. With increasing vineyard acreage, reduced water availability in much of California, and competing water use interests, it is critical to be able to monitor regional water use and evapotranspiration (ET) over large areas, but also in detail at individual field scales to improve water management within these viticulture production systems. This can be achieved by integrating remote sensing data from multiple satellite systems with different spatiotemporal characteristics. In this research, we evaluate the utility of a multi-scale system for monitoring ET as applied over two vineyard sites near Lodi, California during the 2013 growing season, leading into the drought in early 2014. The system employs a multi-sensor satellite data fusion methodology (STARFM: Spatial and Temporal Adaptive Reflective Fusion Model) combined with a multi-scale ET retrieval algorithm based on the Two-Source Energy Balance (TSEB) land-surface representation to compute daily ET at 30 m resolution. In this system, TSEB is run using thermal band imagery from the Geostationary Environmental Operational Satellites (GOES; 4-km spatial resolution, hourly temporal sampling), the Moderate Resolution Imaging Spectroradiometer (MODIS) data (1 km resolution, daily acquisition) and the new Landsat 8 satellite (sharpened to 30 m resolution, ~ 16 day acquisition). Estimates of daily ET generated in two neighboring fields of Pinot noir vines of different age agree with ground-based flux measurements acquired in-field during most of the 2013 season with relative mean absolute errors on the order of 19–23% (root mean square errors of approximately 1 mm d − 1 ), reducing to 14–20% at the weekly timestep relevant for irrigation management (~ 5 mm wk − 1 ). A model overestimation of ET in the early season was detected in the younger vineyard, perhaps relating to an inter-row grass cover crop. Spatial patterns of cumulative ET generally correspond to measured yield maps and indicate areas of variable crop moisture, soil condition, and yield within the vineyards that could require adaptive management. The results suggest that multi-sensor remote sensing observations provide a unique means for monitoring crop water use and soil moisture status at field-scales over extended growing regions, and may have value in supporting operational water management decisions in vineyards and other high value crops.

Biomass and Nitrogen Content of Hairy Vetch–Cereal Rye Cover Crop Mixtures as Influenced by Species Proportions

The performance of legume–grass cover crop mixtures may be influenced by the species proportions in mixture. The objectives of this study were to: (i) evaluate total aboveground biomass and species biomass proportions resulting from different hairy vetch (legume; Vicia villosa Roth)/cereal rye (grass; Secale cereale L.) sown proportions, (ii) characterize aboveground N content and C/N ratios in response to species biomass proportions, and (iii) quantify biologically fixed nitrogen (BFN) in hairy vetch and the potential transfer of BFN to associated cereal rye. A gradient of six sown proportions ranging from 100% cereal rye to 100% hairy vetch was drilled in fall 2011 and 2012 at two sites in Beltsville, MD, and sampled for biomass, C and N content, and BFN the following spring. Hairy vetch monocultures produced less biomass than cereal rye monocultures, but biomass levels were similar between cereal rye monocultures and mixtures. Cereal rye was usually the dominant species in mixtures. Nitrogen content increased from 64 to 181 kg ha−1 and C/N ratio decreased from 83 to 16 as hairy vetch biomass increased from 0 to 100%. Nitrogen content was estimated to plateau when hairy vetch reached approximately 50% of the total biomass. Averaged across site‐years, BFN made up 63 and 86% of hairy vetch N in monoculture and mixture, respectively. For mixtures, a wide range of sown proportions produced >8 Mg ha−1 biomass, but achieving maximum N content and low C/N ratios required a hairy vetch/cereal rye seeding rate of 27:34 kg ha−1.

Effect of Irrigation with Diluted Winery Wastewater on the Performance of Two Grass Cover Crops in Vineyards

Pennisetum glaucum L. cv. Babala (pearl millet) established as a summer catch crop followed by Avena sativa L. cv Palinup (oats) established as a winter catch crop were irrigated with winery wastewater diluted to eight chemical oxygen demand (COD) levels ranging between 100 mg/L and 3 000 mg/L. The diluted wastewater treatments were compared to irrigation with river water. The dry matter production (DMP) of oats, if not preceded by pearl millet, tended to improve when irrigated with winery wastewater. Growth of pearl millet peaked during the period when 91% of the diluted winery wastewater was applied. Winery wastewater improved the DMP of pearl millet. No trends were observed in the nutrient levels of the above-ground growth of the two interception crops. However, Na levels increased over time. Using both species, too high levels of macro-nutrients were intercepted, but insignificant amounts of Na were removed. Irrigation with winery wastewater with COD levels between 1 500 mg/L and 2 500 mg/L may be sustainable if only pearl millet is employed as an interception crop. Fertiliser needed to maintain the nutrient balance in the soil resulted in an additional cost of approximately R2 800/ha/yr. However, the fodder may provide an income in excess of R15 000/ha/yr.

Identifying resource competition in maize-based soil conservation systems using 13C and 15N isotopic discrimination

Soil conservation measures such as establishing grass barriers or cover crops effectively control erosion but also provoke competition, which reduces yields of companion crops. We used 13C and 15N natural abundance profiles to identify the causes of competition of soil conservation measures on a field with 59% slope in Northwest Vietnam three years after establishment. Treatments were maize under farmer’s practice (T1, control), maize with Guinea grass barriers (T2), maize under minimum tillage (MT) with Pinto peanuts as cover crop (T3), and maize under MT and relay cropped with Adzuki beans (T4). A pretest using data from zero-N plots revealed that abundance of water and limited nitrogen availability induced low grain N concentrations, enriched leaf δ13C, and reduced maize grain yield. Similar low N leaf concentrations and elevated δ13C values were observed in maize growing close to frequently pruned grass barriers under positive water balance conditions, indicating that yield decline in these rows can be attributed mainly to N competition. Enriched δ15N values of maize from rows next to barriers indicated reliance on soil N rather than on 15N-depleted fertiliser N. Vigorous cover crop growth under MT resulted in maize yield decline due to N competition while relay-cropped legumes did not trigger inter-species competition having a similar maize yield, leaf N concentration, δ13C, and δ15N as the control.

Cover Crop Impacts on Soil Water Status

Water is a primary concern for producers in the Great Plains; as such, research is warranted to quantify how much cover crops affect the amount of soil water available to subsequent cash crops. Cover crop mixes have been marketed as a means to conserve water in no-till cropping systems following winter wheat (Triticum aestivum L.) harvest. The objectives of this study are to quantify changes in soil profile water content in the presence of different cover crops and mixtures of increasing species complexity, to quantify their biomass productivity and quality, and to quantify the impact of cover crops on subsequent corn (Zea mays L.) yields. We hypothesized the change in soil water brought on by the cover crop treatments would be correlated to the quantity of biomass produced and the species composition, rather than mixture complexity. Soil moisture was measured using a neutron probe to a depth of 9 ft. Results from 2013–14 showed no difference in water use between cover crop mixtures and single species. Cover crops depleted the soil profile by a maximum of 3.5 in. during growth, but fallow was able to gain 0.75 in. of water during the same period. At the time of corn planting, soil moisture under all cover crops had replenished to levels at cover crop emergence, except for the brassicas, which had extracted water from deeper in the profile. Corn yields were reduced following the grass cover crops and the six-species mix. Corn yields were more closely related to the carbon:nitrogen (C:N) ratio of the cover crop residue than to profile soil moisture at corn emergence. The fact that yields were similar for corn after fallow and for corn after brassica cover crops implied that water was not the cause of yield reductions after the other cover crops.

Aerially seeding cover crops in the northern US Corn Belt: Limitations, future research needs, and alternative practices

I ncorporating cover crops into the two-year corn ( Zea mays L.)–soybean ( Glycine max L.) rotation can reduce soil erosion, increase soil organic matter, improve soil structure (Snapp et al. 2005), and reduce nitrate (NO3) leaching (Strock et al. 2004; Fisher et al. 2011). However, it is often difficult to establish winter cover crops in the cooler climate and shorter growing season of the northern Corn Belt. Miguez and Bollero (2005) reported that grass cover crops in the north central United States would only provide marginal benefits due to low biomass production. Through growth simulations, Baker and Griffis (2009) found that the main limitations are degree days and photosynthetically active radiation. Strock et al. (2004) suggested that based on average weather patterns in southwestern Minnesota, winter rye ( Secale cereal L.) would only be a successful cover crop in one out of four years. In these studies, however, temperatures were already cool when the cover crop was planted following harvest of the preceding crop. As another option, Frye et al. (1988) suggested that broadcasting seed into a standing crop can result in earlier crop growth than drilling the seed after harvest. Through growth simulations based on field experiments, Feyereisen et al. (2006) recommended…

ASSESSMENT OF THE AGRONOMIC VALUE OF SEWAGE SLUDGE COMPOST APPLIED ON WINE-GROWING SOILS

A study was conducted from November 2005 to November 2008, to determine the efficiency of sewage sludge compost, applied as mulch, in the prevention of runoff and erosion in wine-growing plots. The study was established in the vineyard of La Clape, located in the south of France in a Mediterranean-climate region. Three soil management treatments were compared: bare soil, grass cover crop and application of mulch. Measurements focused on quantities of runoff water and soil losses by erosion, physicochemical and biological status of the soil, and vine plants performances. Results highlighted the ability of the mulch of sewage sludge compost to reduce runoff and erosion as well as to improve the organic status of the soil and its biological activity. Grass cover also enabled to limit erosion in the same amounts as the mulch but its efficiency in terms of runoff was significantly reduced by the summer water stress which did not allow an optimal development of the sowed species.

Influencia de las coberturas en cultivos de cítricos sobre los hongos formadores de micorrizas arbusculares en Oxisoles del piedemonte llanero colombiano

Se identificaron morfológicamente hongos formadores de micorrizas arbusculares nativos asociados a coberturas de gramíneas y leguminosas, establecidas en suelos Oxisoles del piedemonte llanero (Meta, Colombia) y se evaluó su capacidad de colonización. El área experimental se estableció en las calles de un cultivo de naranja Valencia donde se sembraron especies de Arachis pintoi (CIAT 18744), Brachiaria brizantha cv. Toledo, B. dictyoneura cv. Llanero, Desmodium ovalifolium cv. Maquenque, Panicum maximum (CIAT 36000), Paspalum notatum, un testigo químico (glifosato) y un testigo mecánico con guadaña. Se utilizó un diseño de bloques completos al azar con ocho tratamientos y tres repeticiones, que se evaluaron en la época húmeda y en la seca. Se tomaron muestras de suelo rizosférico y raíces de las gramíneas y leguminosas para identificar morfológicamente hongos formadores de micorrizas arbusculares y cuantificar el número de esporas y el porcentaje de colonización. Se identificaron 26 morfotipos de dichos hongos, incluyendo Scutellospora heterogama, Acaulospora scrobiculata y A. morrowiae que representaron 65% de la población presente en las dos épocas. La colonización radical osciló entre 47% y 94% con un contenido de esporas entre 63 y 300/100 g de suelo seco. Las coberturas con mayor porcentaje de colonización y diversidad de hongos formadores de micorrizas arbusculares fueron B. brizantha, B. dictyoneura y P. notatum; el control mecánico y los tratamientos con glifosato presentaron una influencia negativa sobre el contenido de esporas y colonización radical de dichos hongos.

Annual Cover Crops Do Not Inhibit Early Growth of Perennial Grasses on a Disturbed Restoration Soil in the Northern Great Plains, USA

In agricultural, rangeland, and forest system revegetation projects, cover crops are used for competitive exclusion of weeds and to stabilize soil. Within revegetation projects, annual or short-lived perennial grasses are often sown at the same time as the perennial grasses that are the desired species for long-term landscape rehabilitation. When cover crops are utilized to control weeds, the same principle of competitive exclusion may apply to sown perennial grasses. In this project, we tested if an annual grass cover crop reduces the early stage performance of sown perennial grasses. We conducted four experiments to evaluate the effects of annual cover crops on perennial grasses. The experiments included ex situ growth chamber experiments in two soil types, an agronomic soil, and soil collected from a revegetation project in a trenched water pipeline in western North Dakota. We also performed two in situ experiments where the presence of annuals was manipulated. Annual cover crops only reduced perennial grass biomass ex situ in the agronomic soil. The disturbed pipeline soil was high in sulfur and sodium. Even when this soil was fertilized, annual cover crops did not reduce sown perennial performance. In stressful environments, or when there is natural microenvironmental variability, annual cover crops do not appear to be costly for the early-stage establishment of more long-term, desirable species.

Weed Control in a Newly Established Organic Vineyard

Consumer demand for organic and sustainably produced products has increased the interest in organic wine grape (Vitis vinifera) production. However, organic production can be challenging, and weed management is a critical issue during the establishment of an organic vineyard. In 2009, the effectiveness of five cover crop treatments and cultivation regimes was evaluated for two years for weed control in a newly established organic vineyard of ‘Pinot noir précoce’ and ‘Madeleine angevine’ grape cultivars in northwestern Washington State. Alleyway management treatments were cultivation in alleyways with hand weeding in the vine row (control), grass cover crop which included perennial ryegrass (Lolium perenne ssp. perenne) and red fescue (Festuca rubra ssp. arenaria) seeded in the alleyway and in-row tillage with a specialty offset-type cultivator, winter wheat (Triticum aestivum) cover crop with in-row string-trimming, austrian winter pea (Pisum sativum ssp. sativum var. arvense) cover crop with in-row string-trimming, and winter wheat–austrian winter pea cover crop mix with in-row string-trimming. In 2009, weed dry biomass was lowest in the alleyway of the control (0.8 g·m−2) and offset cultivator treatments (6.3 g·m−2) on 3 Aug. and tended to be lowest in the alleyway of the control (4.8 g·m−2) and offset cultivator treatments (16.0 g·m−2) on 27 Sept. In the second year of establishment (2010), winter wheat and austrian winter pea were eliminated from the plots by mid-July, and white clover (Trifolium repens) and perennial ryegrass were the dominant weed species and accounted for a majority of the total weeds. On average over the two-year period, the control treatment required the most time for alleyway management (92 h·ha−1) followed by the offset cultivator treatment (64 h·ha−1), while the winter wheat, austrian winter pea, and winter wheat–austrian winter pea mixture required 32 to 42 h·ha−1. ‘Madeline angevine’ produced more shoot growth than ‘Pinot noir précoce’ in Sept. 2010 (42.3 and 25.9 cm respectively), and shoot growth of both cultivars in the control treatment was significantly longer (125.0 cm) than under any other treatment (55.4 to 93.0 cm), illustrating the importance of weed control during vineyard establishment. In this study, the most effective weed management regime, although also the most time consuming, included a vegetative-free zone around the vines (e.g., in-row) maintained by hand weeding and a cultivated alleyway.

Effect of legume or grass cover crops and nitrogen application rate on soil properties and corn productivity

Winter Cover Crops (WCC) into continuous agriculture in Uruguay could improve water erosion control, soil organic carbon, and crop productivity. On the other hand, could reduced soil water and nutrients interfering with cash crops. We conducted a four years field study on a clay loam (Typic Argiudol) in Uruguay to evaluate the effects of WCC on soil chemical properties, water content, soil N-nitrate with nitrogen variable rate at V6 on corn productivity. The six treatments consisted of Common Oat (Avena sativa L.), Annual Ryegrass (Lolium mutiflorum L.), Triticale (× Triticosecale wittmack), Egyptian clover (Trifolium alexandrinum L.), Pea (Pisum sativum L.), and no WCC. The highest corn yields were observed with no WCC (6.47 Mg ha-1), followed by legumes WCC (5.97 Mg ha-1) and grasses WCC (4.52 Mg ha-1). These differences were probably due to more soil water content at corn planting (35%) and soil NO3-N at corn planting and V6 (44 and 36%, respectively) in no WCC than overall WCC. The N yield response in V6 corn was highest in grass WCC (31%), followed by legume WCC (23%) and no WCC (7%). No soil organic carbon different were detected among treatments after four years with low risk of soil erosion. This result could be explained by similar carbon inputs (shoot and roots residue adding corn + cover crops) since the beginning of the experiment (averaged over treatments: 46.5 Mg ha-1). Farmers, who adopt use of WCC, could take disadvantage on low corn yield, therefore could increase cost by adding more N in corn.