Academic literature on the topic 'Hairy Vetch'

Hairy vetch was grown as a winter annual cover crop and evaluated for weed suppression when desiccated by paraquat or left alive until natural senescence in a 3-yr field experiment. Total weed density and biomass were variable in the desiccated hairy vetch treatment relative to a bare soil treatment but were consistently lower in the live hairy vetch treatment relative to the desiccated or bare soil treatments. An average of 87% of sites under live hairy vetch compared to 8% of sites under desiccated hairy vetch transmitted less than 1% of unobstructed sunlight. The red (660 nm) to far-red (730 nm) ratio of transmitted light was reduced by 70% under live hairy vetch compared to 17% under desiccated hairy vetch. Daily maximum soil temperature and diurnal soil temperature amplitude were reduced by live hairy vetch > desiccated hairy vetch > bare soil. Soil moisture content was greater under both live and desiccated hairy vetch compared to bare soil during droughty periods. Changes in light extinction, red to far-red ratio, and diurnal soil temperature amplitude were sufficient to explain greater weed suppression by live than desiccated hairy vetch.

Field studies were conducted in 1990 and 1991 to determine the effects of corn planting date and hairy vetch control method on the efficacy of fall-planted hairy vetch as a weedsuppressive cover crop for no-till corn. Glyphosate controlled hairy vetch when applied at the early bud growth stage (April), but hairy vetch residue provided no weed control compared to the weedy check. Mowing was not an effective means of suppressing hairy vetch at the early bud stage. Untreated hairy vetch reduced weed biomass 96% in 1990 and 58% in 1991 but reduced yield over 76% in April-planted corn. There was no competition of untreated hairy vetch with corn when corn planting was delayed until May or June (mid- or late-bloom growth stages of hairy vetch). Corn planted in May into untreated hairy vetch yielded similarly to corn planted in a no-cover weed-free check.

This study evaluated the effect of hairy vetch (Vicia villosa Roth) as cover crop on maize nutrition and yield under no tillage using isotope techniques. For this purpose, three experiments were carried out: 1) quantification of biological nitrogen fixation (BNF) in hairy vetch; 2) estimation of the N release rate from hairy vetch residues on the soil surface; 3) quantification of 15N recovery by maize from labeled hairy vetch under three rates of mineral N fertilization. This two-year field experiment was conducted on a sandy Acrisol (FAO soil classification) or Argissolo Vermelho distrófico arênico (Brazilian Soil Classification), at a mean annual temperature of 18 ºC and mean annual rainfall of 1686 mm. The experiment was arranged in a double split-plot factorial design with three replications. Two levels of hairy vetch residue (50 and 100 % of the aboveground biomass production) were distributed on the surface of the main plots (5 x 12 m). Maize in the sub-plots (5 x 4 m) was fertilized with three N rates (0, 60, and 120 kg ha-1 N), with urea as N source. The hairy vetch-derived N recovered by maize was evaluated in microplots (1.8 x 2.2 m). The BFN of hairy vetch was on average 72.4 %, which represents an annual input of 130 kg ha-1 of atmospheric N. The N release from hairy vetch residues was fast, with a release of about 90 % of total N within the first four weeks after cover crop management and soil residue application. The recovery of hairy vetch 15N by maize was low, with an average of 12.3 % at harvest. Although hairy vetch was not directly the main source of maize N nutrition, the crop yield reached 8.2 Mg ha-1, without mineral fertilization. There was an apparent synergism between hairy vetch residue application and the mineral N fertilization rate of 60 kg ha-1, confirming the benefits of the combination of organic and inorganic N sources for maize under no tillage.

Ten cultivars of processing tomatoes (Lycopersicon esculentum Mill.) grown in bare soil or on black polyethylene and hairy vetch (Vicia villosa Roth.) mulches were evaluated for yield, fruit processing quality, and leaf necrosis. Yields were higher, fruit was heavier, and leaf necrosis less in hairy vetch than in bare soil or black polyethylene mulch. With the exception of pH, yield and fruit quality component responses to mulch treatments were not cultivar-dependent. Fruit pH, soluble solids concentration, and color equaled values obtained using bare soil production practices. Percent solids was highest with black polyethylene and lowest in hairy vetch. The hairy vetch mulch delayed fruit maturity compared to the bare soil and black polyethylene. The hairy vetch cultural system has the potential to increase yield of processing tomatoes.

A 2-yr field study was conducted from 2002 to 2003 on a Dundee silt loam soil at the Southern Weed Science Research Unit Farm, Stoneville, MS (33°26′N latitude), to examine the effects of hairy vetch cover crop (hairy vetch killed at corn planting [HV-K], hairy vetch killed in a 38-cm-wide band centered over the crop row at corn planting [HV-B], hairy vetch left alive [HV-L], and no hairy vetch [NHV]) and glyphosate postemergence (broadcast, banded, and no herbicide) application on weed control and yield in glyphosate-resistant corn. Two applications of glyphosate at 0.84 kg ae/ha were applied 3 and 5 wk after planting (WAP) corn. Hairy vetch dry biomass was higher in HV-L (4,420 kg/ha) and HV-B (4,180 kg/ha) than in HV-K (1,960 kg/ha) plots at 7 WAP. Hairy vetch reduced densities of pitted morningglory, prickly sida, and yellow nutsedge in HV-B and HV-L compared with NHV plots, but hairy vetch had no effect on densities of barnyardgrass, johnsongrass, and large crabgrass at 7 WAP regardless of desiccation. Total weed dry biomass at 7 WAP was lower in HV-B and HV-L than in HV-K and NHV plots. Corn yield was higher in HV-K (10,280 kg/ha) than in HV-B (9,440 kg/ha) and HV-L (9,100 kg/ha), and yields were similar between HV-K and NHV (9,960 kg/ha). Glyphosate applied broadcast resulted in the highest corn yield (11,300 kg/ha) compared with a banded application (10,160 kg/ha). These findings indicate that hairy vetch cover crop has the potential for reducing the density of certain weed species in glyphosate-resistant corn production systems; however, optimum weed control and higher yield were obtained when glyphosate was used.

Eight herbicide treatments per crop were evaluated for hairy vetch and crimson clover cover-crop control in no-till corn and cotton at two locations in North Carolina. Paraquat alone or combined with dicamba, 2,4-D, or cyanazine, and cyanazine alone, controlled clover the best in both crops. All herbicide treatments, except glyphosate alone, controlled at least 89% of hairy vetch in corn. However, only 2,4-D and cyanazine alone or combined with glyphosate controlled greater than 89% of hairy vetch in cotton. Except for poor control of hairy vetch and crimson clover by glyphosate alone, reduced legume control did not consistently decrease corn or cotton yield. Weed control was reduced in crimson clover treated with glyphosate alone, but control was similar among the remaining herbicide treatments. Effectiveness of legume control did not influence the N concentration of corn or cotton. Corn stand, height, and yield were greater in hairy vetch than in crimson clover. Seed cotton yield did not differ between vetch and clover.

Cover crops combined with conservation tillage practices can minimize chemical inputs and improve soil quality, soil water-holding capacity, weed suppression and crop yields. No-tillage production of sweet corn (Zea mays var. `Silver Queen') was studied for 2 years at the USDA Beltsville Agricultural Research Center, Md., to determine cover crop management practices that maximize yield and suppress weeds. Cover crop treatments were hairy vetch (Vicia villosa Roth), rye (Secale cereale L.) and hairy vetch mixture, and bare soil (no cover crop). There were three cover crop killing methods: mowing, rolling or contact herbicide paraquat. All plots were treated with or without atrazine and metolachlor after planting. There was a 23% reduction in sweet corn plant population in the rye-hairy vetch mixture compared to bare soil. Averaged over both years, sweet corn yield in hairy vetch treatments was 43% greater than in bare soil, whereas yield in the rye-hairy vetch mixture was 30% greater than in bare soil. There were no significant main effects of kill method or significant interactions between kill method and cover crop on yield. Sweet corn yields were not different for hairy vetch or rye-hairy vetch treatments with or without atrazine and metolachlor. However, yield in bare soil without the herbicides atrazine and metolachor were reduced by 63% compared to bare soil with these herbicides. When no atrazine and metolachlor were applied, weed biomass was reduced in cover crops compared to the bare soil. Regression analysis showed greater yield loss per unit of weed biomass for bare soil than for the vetch or rye-hairy vetch mixture. This analysis suggests that cover crops increased sweet corn yield in the absence of atrazine and metolachlor not only by reducing weed biomass, but also by increasing the competitiveness of corn to weeds at any given biomass.

Hairy vetch (Vicia villosa Roth) is cultivated during the cold fallow season in paddy soils of temperate countries such as South Korea and Japan, mostly as animal feed and green manure. Information on the effect of ageing of hairy vetch incorporation in relation to greenhouse gas (GHG) emissions and global warming potential (GWP) is not available. Therefore, hairy vetch biomass of ages 183, 190, 197, and 204 days was incorporated in paddy soil to estimate GWP during rice cultivation. The emission rates of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) gases were monitored once a week by using the closed-chamber method. The net ecosystem carbon budget was used to estimate pure CO2 emission fluxes. Biomass production of hairy vetch was 6.5 Mg ha–1 at 204 days, which was similar to other treatments. The GWP was lower with the 204-day-old vetch biomass incorporation than with other treatments. High content of cellulose and lignin in 204-day-old hairy vetch might have affected decomposition rate and subsequently reduced GHGs emissions during rice cultivation. Our results suggest that hairy vetch can be allowed to grow for 204 days before incorporation at 3 Mg ha–1 without sacrificing rice yield, while maximising biomass production and minimising GWP during rice cultivation.

Hairy vetch (Vicia villosa Roth) as a soil amendment was evaluated for suppression of Fusarium wilt of watermelon and soil populations of Fusarium oxysporum f. sp. niveum in greenhouse, microplot, and field studies. When mixed at 1 or 5% (wt/wt) in a loamy sand soil that was artificially or naturally infested with race 2 of F. oxysporum f. sp. niveum, pulverized dry hairy vetch, crab shell, and urea provided the best suppression (53 to 87% reduction) of Fusarium wilt on watermelon seedlings among 13 plant and animal residues screened. Soil amended with hairy vetch at 0.25 or 0.5% (wt/wt) in microplots resulted in 54 to 69% decreased wilt incidence and 100 to 220% increase of watermelon plant biomass. Hairy vetch winter cover crop incorporated into field plots under black plastic provided 42 to 48% reduction of wilt incidence, 64 to 100% increase of plant biomass, and a 34 to 68% increase in weight of fruit, comparable to improvements achieved by the soil fumigants methyl bromide or 1,3-dichloropropene plus 35% chloropicrin. Soil amendment with hairy vetch also increased the sugar content of watermelon fruit 10 to 15%. Significant reductions in the populations of F. oxysporum f. sp. niveum were not observed in hairy vetch-amended soil in microplots and field plots, but were observed in greenhouse pot soil amended with 5% (wt/wt) hairy vetch, which was attributed primarily to increased levels of fungicidal ammonia produced during decomposition. Incorporating hairy vetch into mulched soil can be an alternative or supplement to cultivar resistance and crop rotation for management of Fusarium wilt of watermelon.

Influences of a hairy vetch cover crop and residual herbicides were examined in field corn in 1991 and 1992. Hairy vetch was seeded in mid-August and killed the following May with tillage, mowing, or glyphosate plus 2,4-D (no-till). These cover crop management systems were compared with a no-cover treatment. Residual herbicides including atrazine plus metolachlor applied PRE at three rates and nicosulfuron plus thifensulfuron applied POST at a single rate were compared within cover crop management systems. All cover crop management systems effectively controlled hairy vetch except mowing in 1992. The corn population was reduced in mow treatments containing uncontrolled vetch. Hairy vetch mulch suppressed some weeds in the no-till treatments in 1991, but more annual grass was noted late in the season with no-till into hairy vetch than with the no-cover treatments in 1992. Residual herbicide performance was similar across cover crop management systems, except for fall panicum control which decreased in some no-till systems. Unlike soil-applied herbicides, performance of POST herbicides was unaffected by cover crop management systems.

Corn (Zea mays L.) and soybean (Glycine max L.) production in the Midwest US can result in significant nutrient leaching to groundwater and surface waters, which contributes to eutrophication and hypoxia in the Gulf of Mexico. A promising strategy to control nutrient leaching and sediment runoff loss during winter fallow period is the use of cover crops (CCs). In southern Illinois, CCs are not widely adopted by farmers due to economic constraints and the lack of scientific data that supports benefits of incorporating CCs into the corn-soybean rotation. Therefore, this doctoral dissertation addresses the critical question of the feasibility of the use of CCs in southern Illinois and is divided into three overarching research studies with different objectives divided into six research chapters. Research study 1 was a field experiment conducted from 2013 to 2017 to examine the effect of CCs (CC vs noCC) under two tillage systems [(no-tillage (NT) and conventional tillage (CT)] on aboveground plant attributes [dry matter yield, C:N ratio and nitrogen uptake (N uptake)], crop yields, available soil N content and N leaching in the vadose zone. The experimental layout was a randomized design with three rotations including corn-noCC-soybean-noCC [CncSnc], corn-cereal rye (Secale cereale L.) –soybean-hairy vetch (Vicia villosa R.) [CcrShv], and corn-cereal rye-soybean-oats+radish (Avena sativa L. + Raphanus sativus L.) [CcrSor] and two tillage systems. Soil samples collected after corn or soybean harvest and CC termination were analyzed for standard soil fertility parameters. Pan lysimeters installed below the ‘A’ horizon with depth varying from 22 to 30 cm were used for measuring soil solution nutrient concentration on weekly or biweekly basis depending on the precipitation. In NT system, the corn yield was 14% greater with CcrShv compared to CncSnc, whereas no significant difference existed in corn yield due to CC treatments within CT. Both CC treatments under NT reduced soybean yield by 24 to 27% compared to noCC. The rotations CcrShv and CcrSor with hairy vetch and oats+radish as preceding CCs resulted in 89% (37.73 vs 19.96 kg ha-1) and 68% (33.46 vs 19.96 kg ha-1) more nitrate-N (NO3-N) leaching than the CncSnc during cash crop season 2015. During the CC season in spring 2016, cereal rye CC in CcrShv and CcrSor reduced the NO3-N leaching by 84% (0.68 kg ha-1) and 78% (0.63 kg ha-1) compared to the CncSnc, respectively, under the CT system. Overall, our results indicated that the CT system had greater N leaching losses compared to NT system due to higher N availability in the tilled soil profile. The goal of the second research study was to understand the mechanisms of N cycling by CCs. Therefore, we applied 15N labeled urea fertilizer (9.2% atom) to corn that followed hairy vetch and noCC in May 2017 to evaluate the contribution of fertilizer and soil organic matter to N leaching and quantify the 15N content of surface runoff after storm events. During the 2017 corn season, repeated soil samples were collected and analyzed for 15N fertilizer recovery in soil at three depths. 15N recovery was higher in the corn that had hairy vetch as the preceding CC than the corn that had noCC by 13.13 and 3.68 kg ha-1 on soil sampling events of 7 and 21 days after planting of corn, respectively, at the depth 15-30 cm. Overall, the cumulative loss of 15NO3-N during corn season 2017 was <2% of the applied fertilizer. The contribution of NO3-N from soil organic matter to leaching was 61% higher for the corn rotation with hairy vetch CC compared to corn rotation with noCC (1.12 vs 0.69 kg ha-1). Research study 3 evaluated the effects of CCs (cereal rye and hairy vetch) and topography (shoulder, backslope, footslope) on corn-soybean production, soil and water quality, nutrient and sediment export in agricultural headwater streams in a paired-watershed experimental design. The crop rotation followed in the CC-watershed was corn-cereal rye-soybean-hairy vetch whereas the rotation in the noCC watershed was corn-noCC-soybean-noCC. Use of hairy vetch CC increased N uptake at shoulder, backslope and footslope positions by 110.90, 85.02, and 44.89 kg ha-1, respectively, when compared to noCC treatment. The corn yield at the shoulder position was increased by 69% in CC-watershed compared to noCC watershed in 2017 likely by providing large N additions following decomposition. Cereal rye increased soybean yield by 17% and 8% at the shoulder and backslope position, respectively in 2016. Additionally, the effects of topography and CCs on soil N levels and N leaching in the watersheds were also evaluated. The NO3-N concentrations measured using suction cup lysimeters in CC-watershed were reduced by 2.54 mg L-1 (67%) when compared to noCC watershed. During the hairy vetch CC season, the reduction in NO3-N concentrations in soil solution was only seen at the footslope position. The excessive N at footslope positions may have been immobilized or denitrified due to soil waterlogging from higher water availability at the footslope. Forty-two and 18 storm events were collected during a 4-yr calibration period and CC-treatment period, respectively. Predictive regression equations developed from the calibration period were used for calculating TSS, NO3-N, NH4-N, and DRP losses of surface runoff for the CC-treatment watershed. The CCs reduced TSS and discharge by 33% and 34%, respectively in the CC-watershed during the treatment period. However, EMCs for NO3-N, NH4-N, and DRP did not decrease. Overall, CCs are a recommended conservation practice for farmers who want to enhance the long term profitability of their production systems, while building soil health and protecting downstream water quality. The CCs have the potential to reduce nutrient leaching, peak/total discharge, improve soil quality and crop yields. However, reduction in leaching will depend on the type of CC (legume vs non-legume crops) used in rotation, the time of termination of CCs, cover crop establishment and number of years under CCs. Synchronizing N availability from CCs to N uptake by cash crop is important for reducing nitrate leaching and increasing crop yields.

Unintentional nitrogen (N) loss from agroecosystems produces greenhouse gases, induces eutrophication, and is costly for farmers; therefore, adoption of conservation agricultural management practices, such as no-till and cover cropping, has increased. This study assessed N loss via leaching, NH3 volatilization, N2O emissions, and N retention in plant and soil pools of corn conservation agroecosystems across a year. Three systems were evaluated: 1) an unfertilized organic system with cover crops Vicia villosa, Triticum aestivum, or a mix of the two; 2) an organic system with a Vicia cover crop employing three fertilization schemes (0 N, organic N, or a cover crop N-credit approach); 3) a conventional system with a Triticum cover crop and three fertilization techniques (0 N, urea N, or organic N). During cover crop growth, species affected N leaching but gaseous emissions were low across all treatments. During corn growth, cover crop and fertilizer approach affected N loss. Fertilized treatments had greater N loss than unfertilized treatments, and fertilizer type affected gaseous fluxes temporally and in magnitude. Overall, increased N availability did not always indicate greater N loss or yield, suggesting that N conserving management techniques can be employed in conservation agriculture systems without sacrificing yield.

Master of Science
Department of Biological and Agricultural Engineering
Philip L. Barnes
The world’s population has passed 7 billion and is expected grow to more alarming numbers by the year 2050. The increase in human life on the planet ushers the need to responsibly and sustainably grow more food. In order to meet the demand necessary, it is crucial that soil remains healthy and crop yields continue to increase in efficiency. Irresponsible or ill-informed practices can lead to depleted resources and degradation of fertile soils that may limit a producers’ ability to sustainably grow food. Cover crops are a tool that can be used to address issues the modern producer may face. Cover crops have been shown to increase cash crop productivity, improve soil health by improving soil physical and chemical properties as well as providing protection from soil erosion runoff or nutrient leaching. A study was conducted in 2014 to examine the short term effects associated with cover cropping systems. The effects of ryegrass, red clover and a cover crop cocktail (mixture of ryegrass, red clover and hairy vetch) compared to bare tilled and bare control plots were studied. The five treatments were replicated three times in a completely randomized study and analyzed. Soil physical health indicators such as bulk density and porosity were calculated. Soil and cover crop nutrient use, as well as, soil moisture content data was collected and analyzed using excel and ANOVA statistical procedures. In the short term, the study found that there was only statistically significant differences between cover cropping regimens, tilled and control plots in regards to biomass production and biomass nutrient concentrations (α=0.05). The cocktail mix provided more biomass, N and P than the ryegrass and clover plots alone. Observable differences in cover crop volumetric soil moisture and water used between plots demonstrated that cover crops utilize soil moisture in the short term, which must be considered in areas experiencing water stress. Although more long-term data is needed to truly quantify how cover crops effect various aspects of soil health, this study demonstrated how cover crops have the potential for providing numerous benefits such as increased erosion control, lower reliance on anthropogenically created nutrients and the reduction of weeds. Overall the benefits associated with cover crops are still being researched and while adoption of cover cropping systems has been slow, a push towards agricultural sustainability while increasing food production will increase the amount of producers utilizing cover crops in the coming years.

The diverse cropping system of eastern Virginia's coastal plain offers limited opportunity to establish winter annual cover crops (WCC) for nitrogen (N) scavenging. The winter fallow niche after double-crop or full-season soybean (Glycine max L. Merr.) encompasses the majority of acres left fallow. Our objective was to evaluate interseeded WCC N scavenging performance following soybean and N supplying capacity to subsequent corn (Zea mays L.). Field studies were conducted at four different locations in each of the two study years. The experimental design was split plot with cereal rye, hairy vetch, and RV mix WCC as main plots and ten fertilizer nitrogen (FN) rates in a factorial arrangement (0 and 45 kg FN ha-1 as starter; and 0, 45, 90, 135, and 180 kg FN ha-1 at sidedress) to corn as subplots. The highest N uptake for cereal rye at winter dormancy was 18 kg N ha-1, but the average was 6-7 kg N ha-1. At WCC termination average N uptake for cereal rye was 35 and 40 kg N ha-1 in 2013 and 2014, respectively. Average biomass dry matter (DM) at WCC termination for cereal rye, cereal rye + hairy vetch mix (RV mix), and hairy vetch was 2356, 2000, and 1864 kg ha-1 in 2013; and 2055, 2701, and 692 kg ha-1 in 2014, respectively. Average cereal rye N uptake was 35 kg N ha-1 in 2013 and 40 kg N ha-1 in 2014. Significant differences for residual soil nitrogen were most apparent for soil nitrate (NO3-N) at lower depths (15-30 and 30-60 cm) during WCC termination and in the upper 0-15 cm during corn growth stage (GS) V4 of both years. Corn grain yield plateau following hairy vetch WCC was 0.7 and 0.6 Mg ha-1 higher than when following cereal rye WCC at zero and 45 kg ha-1 starter FN, respectively. Average agronomic optimum FN rates (AONR) were 26 and 9 kg ha-1 lower following hairy vetch than cereal rye WCC at zero and 45 kg ha-1 starter FN, respectively. Estimated hairy vetch FN reductions by FN replacement and AONR difference methods were 48 and 18 kg FN ha-1 in plots receiving zero starter FN; and 58 and -43 kg FN ha-1 in plots receiving 45 kg ha-1 starter FN. In-season soil N tests did not offer adequate information in order to predict sidedress FN reductions. These findings suggest that cereal rye and RV mix have the potential to scavenge and conserve residual soil N and hairy vetch is more than capable to supply PAN to subsequent corn when interseeded into soybean.
Master of Science

After termination, cover crop residue can suppress weeds by reducing sunlight, decreasing soil temperature, and providing a physical barrier. Experiments were implemented to monitor horseweed suppression from different cover crops as well as two fall-applied residual herbicide treatments. Results suggest that cover crops, other than forage radish in monoculture, can suppress horseweed more consistently than flumioxazin + paraquat or metribuzin + chlorimuron-ethyl. Cover crop biomass is positively correlated to weed suppression. Subsequent experiments were designed to determine the amount of weed suppression from different cover crop treatments and if carbon to nitrogen (C:N) ratios or lignin content are also correlated to weed suppression or cover crop residue thickness. Results indicate that cereal rye alone and mixtures containing cereal rye produced the most biomass and suppressed weeds more than hairy vetch, crimson clover, and forage radish alone. Analyses indicate that lignin, as well as biomass, is an important indicator of weed suppression. While cover crops provide many benefits, integrating cover crops into production can be difficult. Hairy vetch, a legume cover crop, can become a weed in subsequent seasons. Multiple experiments were implemented to determine germination phenology and viability of two hairy vetch cultivars, Groff and Purple Bounty, and to determine when viable seed are produced. Almost all germination occurred in the initial cover crop growing season for both cultivars. Both cultivars had <1% of viable seed at the termination of the experiment. These results indicate that seed dormancy is not the primary cause of weediness.
Master of Science in Life Sciences

After termination, cover crop residue can suppress weeds by reducing sunlight, decreasing soil temperature, and providing a physical barrier. Experiments were implemented to monitor horseweed suppression from different cover crops as well as two fall-applied residual herbicide treatments. Results suggest that cover crops, other than forage radish in monoculture, can suppress horseweed more consistently than flumioxazin + paraquat or metribuzin + chlorimuron-ethyl. Cover crop biomass is positively correlated to weed suppression. Subsequent experiments were designed to determine the amount of weed suppression from different cover crop treatments and if carbon to nitrogen (C:N) ratios or lignin content are also correlated to weed suppression or cover crop residue thickness. Results indicate that cereal rye alone and mixtures containing cereal rye produced the most biomass and suppressed weeds more than hairy vetch, crimson clover, and forage radish alone. Analyses indicate that lignin, as well as biomass, is an important indicator of weed suppression. While cover crops provide many benefits, integrating cover crops into production can be difficult. Hairy vetch, a legume cover crop, can become a weed in subsequent seasons. Multiple experiments were implemented to determine germination phenology and viability of two hairy vetch cultivars, Groff and Purple Bounty, and to determine when viable seed are produced. Almost all germination occurred in the initial cover crop growing season for both cultivars. Both cultivars had <1% of viable seed at the termination of the experiment. These results indicate that seed dormancy is not the primary cause of weediness.
Master of Science in Life Sciences

Current interest in cover cropping is focused on enhancing ecosystem services beyond soil conservation. Cover crop (CC) species function uniquely in their effects on ecosystem services when grown in monoculture or mixtures. This research integrated field experiments and a literature synthesis to evaluate the role of cover crops in improving nitrogen (N) management and simultaneously providing multiple ecosystem services. Legume CC fertilized with poultry litter (PL) could replace 101 to 117 kg N ha-1 of fertilizer in corn (Zea mays L.) production. Rye (Secale cereale L.) CC fertilized with PL had a negligible effect on corn production. Biculture fertilizer equivalence ranged between -12 to +75 kg N ha-1. Fertilizer equivalence of legume-containing treatments increased across time. Without CC, fall-applied PL failed to supply N to corn. Ecosystem services of CC and PL illustrate complex species functions. Bicultures produced more total biomass than monocultures in year 1 but less than rye in year 2. Bicultures were as effective in suppressing weeds as rye, produced corn yield similar to legume, and by the second year had similar amounts of available soil N as the legume. Poultry litter effects and interspecific effects cover crop species biomass differed. Rye yield increased, while legume yield decreased slightly in biculture. Poultry litter increased legume N content and a decrease in legume C:N, while rye N content and C:N were unaffected. The synthesis corroborates that mixed and biculture cover crops yield more than the individual component species. Overyielding was transgressive in 60% of cases studied. Mixture effects varied by species: rye and brassica yield increased, while legume decreased in mixtures. The effect of mixed CC on crop yields varied by crop species and management practices, though generally crops increased 8 to 18% overall. This work can be applied to the design of complex CC and PL systems that optimize individual species functions to enhance ecosystem services.
Ph. D.

Adequate residue management may enhance the benefits of cover crops on greenhouse tomato (Solanum lycopersicum L.) productivity, soil N pool, N cycling, and environmental quality. Regardless of management, cover crops may maintain or increase soil N storage at 10 cm depth compared with bare fallow. Cover crops may also enhance microbial biomass N, as a result, soil N availability may increase with cover crops, except rye (Secale cereale L.), more so with hairy vetch (Vicia villosa R.; HV) incorporation than HV mulch and the biculture of HV and rye. Residual inorganic N at surface soil may increase with cover crops, more so with HV and rye monocultures than the biculture. Tomato yield may increase more with the biculture than either HV incorporation or HV mulch because of an efficient residue-N use by tomatoes. The biculture may change the N release pattern from both cover crops: rye of the biculture may release more N than the monoculture, while HV may release a similar or more N in the late than in the early period of tomato growth. With adequate seeding HV/rye ratio (2/1), biculture may maintain or increase soil N storage, increase N cycling and tomato yield, and improve environmental quality.