Winter Annual Cover Crops Research Articles

Use of N immobilization to tighten the N cycle in conventional agroecosystems

Soils in conventional agroecosystems are purposely held in a nitrogen (N)-saturated state to maximize crop yields. Planting winter annual cover crops when fields are usually fallow has been proposed to ameliorate N losses from soils. In this study we introduced winter annual cover crops into an N rate study with plots fertilized at 0, 34, 67, 101, 134, 168, and 202 kg N/ha in maize (Zea mays L.) to determine how winter annual cover crops affect yields, N2O and NO3- fluxes, and N pools. At the six-leaf stage and during flowering, incorporation of cover crop into soil resulted in a 30% reduction in maize biomass. Three weeks after fertilization, KCl-extractable soil mineral N was 75-87% lower in covercropped soils than in no-cover soils, indicating that N had been immobilized in the covercropped soils. At physiological maturity, there was no difference between cover and no-cover treatments in crop yield, which was maximized at 9 Mg/ha in 2006 and 7 Mg/ha in 2007. Where N rates exceed crop requirements, cover crop incorporation may reduce N exports as NO3- and N2O. Tighter N cycling in conventional agroecosystems could be fostered by matching N rates to the amount of N removed with grain and using N immobilization to retain N and support yields. If N immobilization is viewed as a means for efficient fertilizer N use rather than a process that decreases crop productivity, growers might be more willing to adopt cover-cropping practices.

Winter Annual Cover Crop Has Only Minor Effects on Major Corn Arthropod Pests

We studied the effects of downy brome, Bromus tectorum L., winter cover crop on several corn, Zea mays L., pests in the summer crop after the cover crop. An experiment was conducted that consisted of two trials with two levels of irrigation, two levels of weed control, and two levels of downy brome. Corn was grown three consecutive years after the downy brome grown during the winter. Banks grass mites, Oligonychus pratensis (Banks), twospotted spider mites, Tetranychus urticae Koch, and predatory mites from the genus Neoseiulus were present in downy brome at the beginning of the growing season. They moved into corn, but their numbers did not differ significantly across the treatments. Larval western corn rootworm, Diabrotica virgifera virgifera LeConte, feeding on corn roots was evaluated the second and third years of corn, production. Irrigation and herbicide treatments had no significant effects on rootworm injury levels. In one trial, rootworm injury ratings were significantly greater in treatments with a history of high versus low brome, but this effect was not significant in the other trial. Rootworm injury seemed to be similar across plots with different surface soil moistures. This suggests that the use of a winter cover crop such as downy brome will not have a major negative impact the arthropods studied.

Sweet corn production and efficiency of nitrogen use in high cover crop residue

In the humid, temperate mid-Atlantic area of the USA, crop production that leaves the soil uncovered can lead to undesirable soil and nutrient losses to the surrounding Chesapeake Bay watershed. To cope with this issue, winter annual cover crops could provide soil cover both during winter months and, as surface residue in no-tillage cropping systems, during summer months. Legume cover crops such as hairy vetch can produce abundant biomass and N by the time summer crops are planted in spring. Although N mineralized from a legume cover crop can contribute to meeting the N requirement of crops such as corn, it also may not be used efficiently by crops and could be lost into the local environment. This research was conducted to determine whether hairy vetch or a hairy vetch-rye mixture that was allowed to produce high levels of biomass with a high N content (200 to 250 kg/ha) could meet the N requirements of no-tillage sweet corn and to determine the efficiency of N use relative to that of fertilizer N. Our results show that marketable yield of sweet corn was approximately doubled by hairy vetch in 2 of 3 years compared to an unfertilized, no-cover crop control. However, in 2 of 3 years, hairy vetch and the vetch-rye mix reduced yield by 19 and 34%, respectively, compared to a no-cover crop control with fertilizer N. Reduced plant population that reduced the number of ears per ha accounted for the yield reduction by these cover crops compared to the fertilized no-cover crop control. Fertilizer N was 1.5 to 2 times more efficient than hairy vetch at producing sweet corn ear mass per unit of N input but combinations of fertilizer N with cover crops were less efficient than either alone. Results suggest that growing sweet corn without tillage in high biomass levels of cover crops can interfere with crop establishment, reduce the efficiency of crop production, and allow for potentially high N losses into the environment.

Seed Priming of Winter Annual Cover Crops Improves Germination and Emergence

Enhancing soil‐protecting living cover over the winter is an important challenge in temperate row crop production. This note reports on novel findings for cover crop seed priming, a process of controlled hydration and drying. The effects of seed priming over durations of 0, 2, 4, 8, 12, 24, and 36 h were evaluated for four species that varied in seed size and germination characteristics: cereal rye (Secale cereale L.), perennial ryegrass (Lolium perenne L.), hairy vetch (Vicia villosa Roth), and oriental mustard (Brassica juncea L.). A logistic function modeled response was used to quantify onset of germination, time to 50% germination (t50), maximum germination rate, final germination percentage (K), seedling emergence, and establishment in laboratory germination paper and soil core assays. Rye seed germinated rapidly regardless of priming treatment. Under the optimum environmental conditions of a laboratory germination assay, the smallest seeded cover crop, perennial ryegrass, was the only species to show a final germination response that was higher in primed (86%) than untreated seed (78%). However, seed germination rates of three species were influenced by priming: 50% germination was reached 8, 6, and 9 h earlier in hairy vetch, mustard, and perennial ryegrass, respectively. Compacted soil assays showed that priming (24 h) improved seedling emergence by 36% and 57% for hairy vetch and perennial ryegrass, respectively, compared with untreated seed. These results were consistent across experiment runs. Seed priming shows promise as a new technology for improving cover crop establishment in compacted soil.

Winter Cereal Cover Crop Removal Strategy Affects Spring Soil Nitrate Levels

ABSTRACT The use of winter cereal cover crops in no-till row crop systems has increased in the North Central Corn Belt. Timing of the cover crop removal can be managed to improve nitrogen availability for subsequently grown crops. Growers utilizing cover crop systems have several alternatives regarding the removal strategy for the winter cereal cover crop prior to seeding rotational corn (Zea mays L.) or soybean [Glycine max (L.) Merr.]. These alternatives include: herbicide burn-down; harvest of the winter annual cover crop as an early spring forage; or, allowing the winter cereal cover crop to mature as grain. The objective of this study was to evaluate the affect of winter cereal wheat (Triticum aestivum L.) and rye (Secale cereale L.) cover crop burndown or harvest strategies on spring soil nitrate levels. Experiments were established in 1999 through 2001 in East Lansing, Michigan. Each cover crop strategy evaluated had significantly lower or tended to have lower spring soil nitrate levels compared with a no-cover check treatment at all depths, especially in the mid (30–60 cm) and deep (60–90 cm) soil profile. The lower quantity of soil nitrate following the winter annual cereals can be attributed to the winter cereals scavenging soil nitrate over the fall and winter. The herbicide burndown strategies for terminating the winter cereals resulted in significantly greater spring soil nitrate levels in the upper soil profile than the forage or grain harvest removal strategies in 2001. The higher soil nitrate levels near the soil surface following the herbicide burndown strategies indicate the release of N from desiccation of plant material in the upper soil profile. The grain harvest removal strategy resulted in a tendency for less soil nitrate in the upper soil profile, probably due to the fact that the cover was still viable at the time of the spring soil sampling, preempting mineralization of N from plant residue and providing a longer residency time for the winter cereal to scavenge residual soil nitrates.

Contribution of ammonium to stimulation of smooth pigweed (Amaranthus hybridus L.) germination by extracts of hairy vetch (Vicia villosa Roth) residue

Hairy vetch is a leguminous winter annual cover crop that provides a significant contribution toward meeting the nitrogen requirement of succeeding crops. Hairy vetch residue is capable of suppressing weeds, but low levels of residue can intermittently stimulate the emergence of weeds, particularly smooth pigweed. This research was conducted to assess the inhibitory and stimulatory effects of hairy vetch extracts on two smooth pigweed lots with differing dormancy conditions under differing germination conditions (25 or 35°C in light or dark). Full‐strength extracts inhibited germination of both lots under all conditions, a result explained by the inhibitory osmotic potential of the full‐strength extract. At ≤ 0.1× proportions of the hairy vetch extract, there was a slight stimulation of germination above that of the control (average = 11%) of both lots of pigweed under all germination conditions, except for a large stimulation (87%) by the more dormant lot at 25°C in light. A similar response to ammonium hydroxide solutions was observed, in which germination stimulation averaged 7% for all conditions except for germination of the dormant pigweed lot that was stimulated 115% by 15 p.p.m. of ammonium ( ) at 25°C in light. As the concentration in the hairy vetch extract was similar to that in the ammonium hydroxide solutions that promoted the largest stimulation of germination, and because there was a high correlation between the degree of germination stimulation by hairy vetch extracts and by ammonium hydroxide, appears to be the principle ingredient in the extract responsible for stimulation of smooth pigweed germination.

No‐Tillage Corn and Grain Sorghum Response to Cover Crop and Nitrogen Fertilization

No‐tillage cropping systems may benefit from the addition of winter annual cover crops through decreased soil erosion, accumulation of biologically fixed N, or increased crop yield. The objectives of this research were to assess the amount of cover provided by winter annual legumes and oat (Avena sativa L.) to quantify the fertilizer N equivalent value of each cover crop system and the effect of cover crop and N rate on corn (Zea mays L.) and grain sorghum [Sorghum bicolor (L.) Moench] grain yield. Two experiments, one in corn and one in sorghum, were conducted in 1997, 1998, and 1999. In each experiment, the main‐plot effect was cover crop treatment while the subplot effect was spring N rates of 0, 56, 112, and 168 kg ha−1. The addition of oat to the legume cover crop treatments increased fall ground cover but decreased total spring dry matter yield. Maximum spring dry matter yield was greatest in the hairy vetch (Vicia villosa Roth)‐alone treatment. Hairy vetch alone also produced the greatest mean fertilizer N equivalent value in the corn and sorghum experiments, 43.6 and 56.9 kg N ha−1, respectfully. These values, however, were variable among years. Corn and sorghum grain yield were greatest in the Austrian winter pea (Pisum sativum L.) and hairy vetch full seeding rate treatments, 5.19 and 7.06 Mg ha−1, respectfully. Our results indicate that winter annual cover crops provide several distinct benefits to no‐tillage corn and sorghum production systems and that cover crops should be selected based on specific grower needs.

An Economic and Environmental Tradeoff Analysis of Sustainable Agriculture Cropping Systems

ABSTRACT This study used the results of a 60-year simulation based on data from the Sustainable Agricultural Demonstration site at the USDA, ARS Beltsville Agriculture Research Center in Beltsville, Maryland, to analyze tradeoffs between profitability and environmental stewardship. Six grain cropping systems included two no-tillage rotations with recommended fertilizer and herbicide inputs, two no-tillage rotations with winter annual cover crops and reduced herbicide and nitrogen inputs, and two reduced-tillage organic rotations. Economic analysis showed that highest gross margins were attained by a cover crop-based system with zero nitrogen inputs (CCZ). Risk analysis showed that the organic systems had lower profit variability across years and, therefore, would be most attractive to risk averse farmers. Both the cover crop-based systems and organic systems had low erosion risks and no risk of herbicide contamination so there were no profit versus erosion or herbicide tradeoffs amongst these systems. All systems had nitrogen runoff that exceeded threshold levels in at least two-thirds of the simulation years. In addition, systems that were lowest in nitrogen runoff were highest in phosphorus losses. This resulted in tradeoffs for risk neutral farmers between higher profitability along with higher nitrogen runoff for the CCZ system versus lower profitability along with lower nitrogen runoff for the organic systems. In contrast, for risk averse farmers, there would be a tradeoff between lower economic risk along with higher phosphorus loss in the organic systems versus higher economic risk along with lower phosphorus loss for the CCZ system. Thus, control of nutrient losses while maintaining profitable production levels represents a major challenge to the design of sustainable cropping systems.

Phosphorus Bioavailability following Incorporation of Green Manure Crops

Incorporating green manure crops into soil may increase P bioavailability for succeeding crops. We conducted a greenhouse study to evaluate the effects of green manures on biomass and P utilization of a succeeding grain sorghum [Sorghum bicolor (L.) Moench] crop. Four perennial forages and four winter annual cover crops were grown in pots, killed, and incorporated into the soil before planting sorghum in the same pots. Sorghum P uptake was positively correlated with perennial forage P uptake. Among winter cover crops, sorghum P uptake following white lupine (Lupinus albus L.) was lower than in all other treatments, including the control (no previous cover crop), even though lupine biomass, N content, and P uptake were two to three times greater than those of the other winter cover crops. Phosphorus uptake differed slightly among the other three winter cover crops but sorghum P uptake was not correlated to winter cover crop P uptake. Thus, among winter cover crops, plant type rather than P uptake seemed to influence the subsequent sorghum crop's P uptake. However, sorghum biomass following the three winter cover crops other than lupine was greater than sorghum biomass in the control treatment, indicating that there was a beneficial cover crop rotation effect among these three winter cover crops. Soil samples were collected and analyzed for Bray-1 P when green manure crops were planted, when they were incorporated into the soil, when sorghum was planted and when sorghum was harvested. These data showed that the Bray-1 soil P test has little potential to predict differences in P uptake and release among different types of green manures and it has limited potential to predict P uptake by sorghum following incorporation of green manures.

Use of Winter Annual Cover Crops to Reduce Soil Nitrate Levels

ABSTRACT The scientific community and various environmental groups have been concerned about the leaching of nitrate (NO3) to ground water from various sources including crop fields where all the applied NO3 is not utilized by the primary crop. Experiments were conducted on two soil types in Alabama to investigate the use of winter cover crops to capture NO3 remaining after the harvest of corn, cotton and soybeans. In these experiments, harvest of the primary crops was so late that cover crop growth in the fall was insufficient to immobilize significant amounts of NO3. Soil testing the following spring showed that most of the soil NO3 was in the top 30 cm (12 in) of the soil profile. A subsequent cover crop planting date experiment showed that wheat planted after September 18 and rye planted after October 2 made insufficient fall growth to immobilized significant amount of NO3. Most spring growth occurred after late February when much of the winter rainfall had already occurred. It appears that judicious selection of nitrogen fertilizer rates is a better approach to reducing NO3 leaching.

Cover crops and living mulches

Cover crops and living mulches bring many benefits to crop production. Interest in winter annual cover crops such as winter rye and hairy vetch for ground cover and soil erosion control has been increasing in the last 30 yr in some areas. The integration of cover crops into a cropping system by relay cropping, overseeding, interseeding, and double cropping may serve to provide and conserve nitrogen for grain crops, reduce soil erosion, reduce weed pressure, and increase soil organic matter content (Hartwig and Hoffman 1975). Hairy vetch has increased availability of nitrogen to succeeding crops, increased soil organic matter, improved soil structure and water infiltration, decreased water runoff, reduced surface soil temperature and water evaporation, improved weed control, and increased soil productivity (Frye et al. 1988). More recent research with perennial living mulches, such as crownvetch (Hartwig 1983), flatpea, birdsfoot trefoil, and white clover (Ammon et al. 1995), has added a new dimension to the use of ground covers that eliminates the need to reseed each year. Cropping systems with the use of ground covers have been worked out for vineyards, orchards, and common agronomic crops, such as corn, small grains, and forages. Legume cover crops have the potential for fixing nitrogen, a portion of which will be available for high-nitrogen–requiring crops such as corn. In areas where excess nitrogen is already a problem, the use of ground covers may provide a sink to tie up some of this excess nitrogen and hold it until the next growing season, when a crop that can make use of it might be planted (Hooda et al. 1998). Even legumes tend to use soil nitrogen rather than fixing their own, if it is available. It is these possibilities that provide the incentive for looking at the effect of various kinds of cover crops on soil erosion, nitrogen budgets, weed control, and other pest management and environmental problems.

The Use of Winter Annual Legume Cover Crops in a Wheat-Grain Sorghum Rotation in South Central Kansas

ABSTRACT Winter annual legumes in humid regions of the country can have a positive effect on subsequent corn (Zea mays) and grain sorghum (Sorghum bicolor) crops, mainly through N contribution of the legume and, in some cases, soil improvement. However, water use by the cover crop in drier regions has the potential to reduce yields in subsequent crops. This study was initiated in central and south-central Kansas to look at both the agronomic and economic implications of adding a winter annual legume cover crop to a winter wheat (Triticum aestivum)-grain sorghum rotation. Experiments included researcher-managed on-station trials and cooperative (i.e., farmer-managed) trials with farmers using hairy vetch (Vicia villosa) and Austrian winter pea (Pisum arvense). Results showed that in good rainfall years, establishment of cover crop was adequate, and no significant difference occurred between sorghum yields following cover crops versus following wheat with fertilization. On-station trials showed a significant nitrogen (N) contribution from hairy vetch and benefits to sorghum. During years with low rainfall, cover crop establishment was poor, N contribution from the cover crop was low, and grain sorghum yields were reduced because of water use by the cover crop. Variable costs were similar between cover crop and fertilized treatments, but gross returns and, consequently, net returns were lower in the cover crop plots because of this yield reduction. For cover crops to be attractive options for farmers in this part of Kansas: they must be used also for livestock feed and/or for early spring grazing; other cultivars or management systems that use less water must be developed; experiments must be conducted to ascertain benefits of cover crops during the second rotation cycle; and the price of N fertilizer must increase to the point that use of alternative sources is economical. Also, the use of cover crops by farmers in regions of variable rainfall should not be “recipe driven” but “response driven”, using cover crops in years where rainfall is adequate, and not planting or destroying stands during dry years to conserve water for the cash crop.

Economic Analysis of Sustainable Agricultural Cropping Systems for Mid-Atlantic States

ABSTRACT This paper evaluates the profitability and economic risks associated with four cropping systems for the Sustainable Agriculture Demonstration site at Beltsville, Maryland, for the 1994–97 period. Each system follows a 2-year rotation of corn in the first year and winter wheat and soybean in the second year. The four systems are (1) a no-tillage system with recommended fertilizer and herbicide inputs, (2) a no-tillage system with crownvetch living mulch, (3) a no-tillage system with winter annual cover crop, and (4) a reduced tillage manure-based system without chemical inputs. The cover crop system is the most profitable ($238 in gross margin), closely followed by the no-tillage ($233) and the manure-based system ($217). Even though farmers desire a cropping system that maximizes profits, the variability of profits, or risks, can influence the desirability of the cropping system. In terms of risks, no-tillage is the most preferred rotation with the smallest coefficient of variation (1.14) followed by the cover crop system (1.24), the manure-based system (1.58), and the crownvetch system (5.45). The same ranking can be obtained using a “safety-first” criterion for risk-averse farmers, in which the gross margin of the no-tillage system would exceed $53 ha−1 in three out of four years, while the gross margin of the cover crop system would exceed $39 ha−1 in three out of four years. The manure-based system is an organic system and it was not profitable in 1996 and 1997 because of weed infestations. However, the manure-based system shows potential to be the most profitable if some methods can be found to control weeds without resorting to herbicides and its crops can be certified as organic and sold at premium prices.

Winter Annual Legumes for Use as Cover Crops in Row Crops in Northern Regions

Weed suppression is one of several benefits achieved by including a cover crop in a cropping system. A requirement for developing cover crop systems is to find species and cultivars which are adapted for the local climate and latitude, prevent weed infestation, and do not compete with the main crop. Two experimental series were established at three locations in Norway to evaluate the ability of different species for use as cover crops in vegetable production. The first series of experiments was with subclover (Trifolium subterraneum L.) cultivars sown at different dates throughout the summer and the second with different winter annual legume species sown in late summer. Winter hardiness, life cycle, growth characteristics, and weed suppression ability of winter annual legumes sown in the autumn were studied. The experiments showed the following ranking of winter hardiness: hairy vetch (Vicia villosa Roth.) (best), black medic (Medicago lupulina L.), crimson clover (Trifolium incarnatum L.), and subclover (poorest). Time of flowering and senescence, factors related to competition in cover crop systems, showed that subclover was the most promising species followed by crimson clover and hairy vetch–black medic. The winter annual legume species showed the ability for natural reestablishment in the second autumn. Hairy vetch showed the highest biomass production, the lowest regrowth ability after mowing, and the best weed suppression. Subclover showed a very promising life cycle for the use as living mulch; however, more winter hardy cultivars or species with similar growth characteristic are needed before common commercial use in northern regions. In conclusion, until more suitable species or cultivars are found or developed through plant breeding, hairy vetch is the most promising winter annual cover crop under Norwegian conditions.

Rate and Timing of Nitrogen Fertilization on Yield and Gross Revenue of Fresh Market Tomatoes Following a Winter Legume Cover Crop

ABSTRACT Using a winter annual legume cover crop to supply the N needs of fresh market tomatoes (Lycopersicon esculentum L.) can be beneficial to the long-term productivity of the soil and an efficient utilization of resources. Successful production is related to fruit size, quality, yield, and timing to market highs. Mineralization of N from legumes must occur at rates and timing corresponding to optimal fruit development of the crop. The objective of this study was to determine if successful vine-ripened fresh market tomato production could occur using a winter legume cover crop to the supply the N needs. A two-year study investigated the rate and timing effects of supplemental N on yield and revenue of tomatoes following an incorporated winter annual legume cover crop of Austrian winter pea (Pisium sativum subsp. arvense). Treatments consisted of 0, 67,134,202 and 246 kg N (mulched ha)−1 applied all preplant or preplant + two split N injections of 34 kg N (mulched ha)−1 each at early fruit set and 10 d...

Winter annual grass-legume bicultures for efficient nitrogen management in no-till corn

Winter annual cover crops may be an effective tool for managing inorganic N in the sandy soils of the Atlantic Coastal Plain when summer droughts can result in relatively high residual fertilizer N levels. A field experiment was conducted from 1992 to 1994 on a Norfolk loamy sand to determine the effect of (1) previous corn fertilizer N rate (150 or 300 kg ha −1) on dry matter (DM) and N accumulation in rye, crimson clover, and hairy vetch monocultures and respective rye-legume bicultures; (2) the respective cover crops on residual soil inorganic N levels; and (3) cover crops on corn grain yield. Compared to the preplant corn N rate of 150 kg ha −1, the 300 kg N ha −1 rate resulted in greater profile soil inorganic N contents on subsequent sampling dates in both years. Concomitant with these greater residual soil N levels were increases in cover crop DM and N accumulation compared with low residual soil N levels. Averaged over 2 year, cover crop DM accumulation by April was in the order of rye > rye-vetch = rye-crimson clover > hairy vetch > crimson clover. The corresponding cover crop N content ranking was hairy vetch > rye-hairy vetch > crimson clover = rye-crimson clover > rye. Before corn planting in Apr, rye monoculture reduced soil inorganic N content an average of 62% in 1993 and 37% in 1994 compared to legume monocultures. Soil inorganic N content under the rye-legume bicultures was reduced an average of 44% and 15% for the same dates. Inadequate rainfall during both corn growing seasons resulted in poor corn yields (1.18 to 2.50 Mg ha −1) that were generally unaffected by cover crop or prior N rate. The results from this study demonstrated the ability of rye and rye-legume bicultures to scavenge residual soil inorganic N following a summer corn crop, thereby minimizing the leaching of N from the plant rooting zone.

Grass–Legume Bicultures as Winter Annual Cover Crops

AbstractGrass‐legume bicultures as winter annual cover crops may combine the N scavenging ability of grasses and the biological N2 fixation capacity of legumes to improve N management in crop production systems of the southeastern USA. A 3‐yr field experiment was conducted on a Norfolk loamy sand (fine‐loamy, kaolinitic, thermic Typic Kandiudults). The focus of this research was to examine the differences among legume monocultures and grass‐legume bicultures with regard to early spring dry matter (DM) and N accumulation, and related effects on soil inorganic N levels and subsequent corn (Zea mays L.) yield. Austrian winter pea [Pisum sativum L. subsp, sativum var. arvense (L.) Poir.], crimson clover (Trifolium incarnatum L.), commonve tch (Vicla saava L.), and hairy vetch (Vicla villosa Roth) were grown in monoculture and in bicultures with rye (Secale cereale L.), oat (Arena satira L.), and wheat (Triacum aestivum L.). Aboveground plant material was harvested in early March, late March, and mid‐April. Biomass was separated into component species and analyzed for total N and C concentrations. Averaged over 3 yr, legume component DM accumulation in monoculture and biculture ranged from 0.87 to 2.53 Mg ha−1, with a ranking of Austrian winter pea < hairy vetch < commonv etch < crimson clover. For the same period, the grass component DM accumulation ranged from 1.31 to 2.28 Mg ha−1, in the order rye = oat < wheat. Three‐year mean N accumulation values for the legume component followed the same relative ranking and ranged from 24 to 93 kg N ha−1. Grass factor N content ranged from 18 to 39 kg N ha−1 in the order rye < oat < wheat. For all bicultures, the average C:N ratio over the 3‐yr experiment was >30, suggesting that net N mineralization would occur from the decomposing cover crop residues. Profile soil inorganic N (0 to 90 cm) was greater in legume monoculture than in grass‐legume biculture treatments, indicating the ability of grasses to capture soil N. Corn yield was affected by the treatments in 1 of 3 yr, with greater yields following a legume monoculture than a grass‐legume biculture. Collectively, these results suggest that grass‐legume bicultures as winter annual cover crops have the potential to utilize residual soil NO3 and thereby minimize leaching while adding fixed N to cropping systems in the southeastern USA.

Nitrogen Release from Grass and Legume Cover Crop Monocultures and Bicultures

AbstractThe use of grass‐legume bicultures grown as winter annual cover crops may provide farmers with additional cover crop management options regarding the availability of cover crop residue N. A 2‐yr field experiment was conducted to determine dry matter (DM) accumulation, chemical composition, and N release from grass and legume cover crops grown in monoculture (rye, crimson clover, and hairy vetch) and biculture (rye‐crimson clover and rye‐hairy vetch). Air‐dried plant material was placed on the soil surface in 1‐mm mesh nylon bags for 1, 2, 3, 4, 6, 8, and 16 wk. Following retrieval, mesh bag contents were analyzed for total N, C, cellulose, hemicellulose, and lignin concentrations. The 2‐yr mean cover crop DM production was in the order of rye‐hairy vetch > hairy vetch > rye‐crimson clover > rye > crimson clover. The greatest cover crop N content (2‐yr mean) occurred with hairy vetch monoculture (154 kg N ha−1), compared with a low of 41 kg N ha−1 for the rye monoculture. When grown in biculture with rye, hairy vetch accumulated more DM and biomass N compared with crimson clover, both as a proportion of the biculture and as DM yield. In general, the order of N release rates (rapid to slow) was hairy vetch > crimson clover = rye‐hairy vetch > rye‐crimson clover = rye. Estimates of N (kg ha−1) released from cover crop residue after 8 wk of field decomposition, averaged over 2 yr, were 24 for rye, 60 for crimson clover, 132 for hairy vetch, 48 for rye‐crimson clover, and 108 for rye‐hairy vetch. Results of this study demonstrate only slight reductions in N release from grass‐legume bicultures compared with legume monocultures.

Winter Annual Cover crops for the Home Food Garden

Cover crops add organic matter, improve soil fertility, prevent soil erosion and compaction and suppress weeds, but they can be difficult to manage at the home garden scale. Because incorporating the entire cover crop into the soil with garden tools can be problematic, two alternative strategies were explored: 1. clipping and removing aboveground vegetation before spading. 2. killing winter annual cover crops by mowing after they flower. Seven winter annual grasses and one legume [hairy vetch (Vicia villosa Roth.)] were evaluated. Roots + stubble of winter rye (Secale cereale L.) were easy to spade in late spring once the top growth was removed. Italian ryegrass (Lolium multiflorum Lam.), field brome (Bromus arvensis L.) and 'Blando' Brome (Bromus mollis L.) gave better ground cover than rye but their roots + stubble were much more difficult to spade. Rye could be controlled by clipping close to the ground after it began to shed pollen in late May, whereas ryegrass, field brome, Blando brome and annual bluegrass all regrew. Triticale (Triticum X Secale) and five early varieties of winter wheat (Triticum aestivum L.) all shed pollen later than rye, which suggests that they could not be mow-killed as early in the season. Rye + hairy vetch mowed just prior to transplanting tomatoes (Lycopersicon esculentum Mill.) in May or early June provided a moisture-consering, weed-suppressing mulch through the growing season. Additional mowing between plants was needed to control rye regrowth, but a single late-spring cutting to a low (2-in) stubble height has prevented regrowth of rye + vetch in other studies at the same location. Early-season tomato yields were lower in mowed than in soil-incorporated rye + vetch, possibly because the mulch cooled the soil and delayed mineralization of nitrogen. However, the mulch did not significantly lower total yields, and it saved labor on weeding, conserved soil moisture, and possibly reduced fruit cracking.

Fresh-market Tomato Production in a Low-input Alternative System Using Cover-crop Mulch

A low-input sustainable agricultural system for the production of staked, fresh-market field tomatoes (Lycopersicon esculentum Mill.) is described. The system uses winter annual cover crops to fix N, recycle leftover nutrients, produce biomass, and prevent soil erosion throughout the winter and spring. Yields of tomato plants grown in hairy vetch (Vicia villosa Roth), crimson clover (Trifolium incarnatum L.), and rye (Secale cereale L.) plus hairy vetch mulches were higher than those grown in the conventional black polyethylene (BP) mulch system in 2 of 3 years. Fruit were heavier with the plant mulches than with BP mulch. Eight weeks after transplanting, N levels in tomato leaves were higher with plant than with BP mulch, although the plant mulch plots received only 50% of the N applied to the BP plots. The cover crops had no effect on populations of five phytoparasitic nematode species.