The objectives of this research were: 1) to quantify the amount of supplemental nitrogen (N) to maximize organic broccoli (Brassica olearcea var. italica) on transition soils, 2) to evaluate the ability of leguminous cover crops lablab (Dolichos lablab L.), soybean (Glycine max L.), sunn hemp (Crotalria juncea L.) and a sunn hemp and cowpea mixture (Vigna sinensis Endl.) to supply N and suppress weeds and, 3) to compare the effect on N availability and broccoli yield potential of incorporating cover crops with conventional tillage (CT) or mulching cover crops with no-tillage (NT) practices. Broccoli was grown during the third year of organic transition in the spring and fall of 2006 at the Kentland Agricultural Research Farm in Blacksburg, VA. Supplemental N significantly increased broccoli yield up until 112 kg ha-1 with a quadratic correlation with leaf N. The NT treatment yielded no difference during the spring, but in the fall CT surpassed NT. On the other hand, N uptake, measured by leaf N, under NT conditions increased with supplemental N, which suggests NT has equivalent yield potential as CT when N is not limiting. Yields from leguminous residues did not differ, even though quality and quantity of cover crop biomass did. This suggests that N availability from cover crop legumes may be impacted other ecological process such as soil microbial activity. Also, cover crop residues differed in their ability to suppress weeds. The results from this study give organic growers in transition tools to maximize productivity and sustainability. / Master of Science

M.S.

Rye (<i>Secale cereale</i> L.) used as a winter cover crop was killed by paraquat or by mowing with a bushog. In subsequent no-till corn, early season armyworm, <i>Pseudaletia unipuncta</i> (Lepidoptera: Noctuidae) abundance was lower in the mowed treatment compared with the sprayed treatment. Total cumulative armyworm-days in the sprayed treatment were greater than in the mowed treatment and were significantly greater in the sprayed treatment in two fields. Lower armyworm populations may have resulted from a combination of mowing which physically destroyed some larvae, and predation by generalist predators attracted to the moist conditions provided by the mulch of mowed rye. Twelve species of parasitoids attacked armyworm. <i>Glyptapanteles 111ilitaris</i> (Walsh) (Hymenoptera: Braconidae) and <i>Periscepsia laevigata</i> (Wulp) (Diptera: Tachinidae) were the most abundant parasitoids. Seasonal parasitization rates ranged from 36-45%. Parasitism did not differ significantly between treatments. Mowing the cover crop was 40% less expensive than spraying. Corn silage yields did not differ significantly between treatments, but the average increase in net benefit from mowing compared to spraying was $91-113/ha. / Master of Science

Conservation tillage tobacco production has gained little producer acceptance since introduction in the late 1960's. Yield reductions, tobacco quality issues, unacceptable weed control, and inadequate planting equipment limited practice adoption and substantiated the need for continued research. The recent developments of a Subsurface Tiller-TransplanterTM and the herbicide SpartanTM renewed producer interest in conservation tillage and led to an investigation with both flue-cured and Virginia dark-fired tobacco. Flue-cured tobacco was transplanted into rye mulch on bedded rows and subsequently cultivated at various timings. Conservation tillage significantly reduced soil erosion approximately 92 percent and tobacco yield approximately 23 percent when row cultivation was not applied. Row cultivation significantly increased tobacco yield without increasing soil erosion. The yield of conservation tillage tobacco receiving a minimum of two cultivations was similar to conventional tobacco. The second study evaluated wheat, rye, crimson clover, and mixtures of crimson clover with either wheat or rye as cover crop mulches for conservation tillage production of Virginia dark-fired tobacco. Conservation tillage, regardless of cover crop, reduced dark-fired tobacco yields approximately 779 and 488 pounds per acre in 1996 and 1997, respectively. The removal of cover crop residue for hay did not lower tobacco yield compared to leaving residue on the soil surface. Row cultivation increased conservation tillage tobacco yield approximately 247 pounds in 1997 regardless of cover crop. The nitrogen contribution of crimson clover was minimal in both years of the study and did not affect tobacco performance. / Master of Science

Improving soil health in agricultural soils is vital as the effects of climate change and an increasingly affluent population are putting a strain on land resources. Conservation agricultural practices such as cover cropping and conservation tillage systems (e.g., strip tillage, minimal tillage, or no tillage) are implemented to improve soil properties, but soil health outcomes in Coastal Plain cropping systems have been inconsistent and may take decades or longer to occur. Improving soil health and agricultural prosperity in the region requires: a better understanding of the rate and magnitude of response in soil properties to different types of management; and a better understanding of the interaction between management types, soil health parameters, and crop yield. In this study, four tillage systems (in order of decreasing intensity: conventional tillage > strip tillage > minimal tillage > and no tillage) and three winter cover rotations (in order of decreasing expected biomass input: high-biomass cover crop > winter cash crop > and fallow) were tested in a split plot design. For the first objective of this study, bulk density, penetration resistance (as depth to root restrictive layer), total organic carbon, carbon stocks, saturated hydraulic conductivity, and yield were measured repeatedly over a seven-year period to better understand the longitudinal response of these properties to management. Bulk density and saturated hydraulic conductivity showed a greater temporal variation in the more intensive tillage practices (strip tillage and conventional tillage) in the top 5 cm. Depth to root restrictive layer was consistently highest in the deep tillage treatments (strip tillage and minimal tillage). The change in soil organic carbon concentration between 2018 and 2022 in the top 5 cm was numerically greater in the strip tillage (0.67%) and no tillage (0.68) than the conventional tillage was 0.18%. In 2022, the carbon stocks were significantly increased in all three conservation tillage treatments compared to conventional tillage. Yield was significantly increased by winter cover in the years that a legume/non-legume cover crop mix was implemented. For the second objective of this study, the effects of 6 years of management were evaluated for total organic carbon, active carbon, short-term carbon mineralization, aggregate stability, and crop yield. These parameters were then correlated to determine drivers in soil health outcomes. Total organic carbon was increased in the strip tillage treatment (1.13% in 2021 and 1.61 % in 2022) compared to conventional tillage (0.83% in 2021 and 1.09% in 2022) in the top 5 cm. In 2022, total organic carbon under cover crop (1.51 %) and cash crop (1.46 %) treatments were also significantly higher than the fallow (1.33 %) in the top 5 cm. Active carbon results followed a similar but weaker trend in both years. Percent aggregate stability was improved by minimal tillage (47%) in 2022 compared to conventional tillage (41%). The findings from the correlation analyses suggest that total organic carbon concentration, soil texture, and tillage were all prominent drivers in improving soil health outcomes. These results demonstrate the relatively slow response of many soil physical properties to management, highlight the need for consistent management to improve properties, and emphasize the need to take measurements at different times of the year. This information can be used to develop more sustainable and resilient cropping systems in the Coastal Plain. / M.S. / Centuries of intensive farming practices have degraded agricultural soils, which contributes to the challenge of feeding a growing and increasingly affluent global population. Therefore, understanding which farming practices reverse this degradation and improve soil health is vital for regions such as the southeastern Coastal Plain, where agriculture is a prominent industry. Soil health is defined as the ability of soil to support life sustainably. Conservation agricultural practices, such as planting crops over the winter and conservation tillage systems (where at least 30% of the soil surface is left undisturbed) are implemented to improve soil properties, but soil health outcomes in Coastal Plain farms have been inconsistent and may take decades or longer to occur. Therefore, the improvement of environmental health and agricultural prosperity in this region requires a better understanding of the patterns of change in soil properties in response to different types of management; and a better understanding of the factors that most influence soil health outcomes. This study evaluated the combination of four tillage systems of differing intensities, and three winter crop types on soil health outcomes. For the first objective of this study, soil physical properties, soil carbon, and crop yield were measured repeatedly over a seven-year period to quantify how these properties respond to management. The soil physical properties showed temporary improvement by more intensive tillage but reverted in the months after tillage. The soil carbon increased from 2018 to 2022 in the three least-intensive tillage treatments. Crop yield was significantly increased in years when there was a mix of crop species planted. For the second objective of this study, the effects of management on soil carbon, soil stability, and crop yield were evaluated after six years of management. These soil health parameters were then correlated to determine the most prominent factors influencing change in soil properties. Soil carbon and soil stability were both improved in least-intensive tillage treatments. The findings from the correlation analyses suggest that soil carbon concentration, soil texture, and tillage were all prominent factors in improving soil health outcomes. These results demonstrate the relatively slow response in many soil physical properties to management, highlight the need for consistent management to improve soil health, and emphasize the importance of taking measurements at different times throughout the year. Furthermore, this is information that can be used to develop more sustainable and resilient cropping systems in the Coastal Plain.

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.

Master of Science / Department of Agronomy / Johanna A. Dille / No-till producers can manage weeds by including cover crops during the fallow phase as part of an integrated weed management plan. Field experiments were conducted between 2007 and 2009 to quantify the influence of cover crops on weed emergence, biomass accumulation, and seed production. Field experiments were established near Garden City, KS with winter wheat or fallow as main plots and cover crop treatments as subplots including five spring- and five fall-sown individual or mixtures of crop species and a no-cover chemical fallow. Separate1-m2 quadrats were seeded with kochia or downy brome at 500 seed/m2. Kochia density was reduced by 75% and biomass reduced by 88% in fall-sown cover crops compared to chemical fallow across growing seasons. Spring-sown cover crop mixtures reduced kochia biomass in 2009 when kochia emergence was delayed. Downy brome biomass decreased exponentially as cover crop biomass increased. A second field experiment was established near Manhattan, KS with soybean, winter wheat, or grain sorghum phases of the rotation as main plots and six cover crop treatments as subplots sown after winter wheat harvest. Paired Palmer amaranth 1-m2 quadrats were seeded with 500 seed/m2 in each cover crop subplot. One quadrat was protected from any herbicide application made to the cover crop or to the grain sorghum. Combining burndown application with high biomass-producing cover crops reduced Palmer amaranth emergence and biomass. Influence of cover crop presence reduced early season Palmer amaranth emergence in the subsequent grain sorghum phase. Optimal seeding rate of forage soybean sown in winter wheat stubble and its impact on Palmer amaranth and downy brome emergence and growth were evaluated in field studies established near Manhattan and Hesston, KS in 2008 and 2009. Soybean was no-till drilled after wheat harvest at five rates ranging from 100,000 to 600,000 seeds/ha. A no-cover chemical fallow treatment was included. Separate 0.5-m2 quadrats were seeded with Palmer amaranth at 100 seed/0.5 m2 or with downy brome at 250 seed/0.5 m2. Three termination methods evaluated were killing frost, glyphosate application, or crop rolling. Palmer amaranth density was not affected by treatments but biomass decreased as soybean seeding rate and crop biomass increased. Downy brome emergence was less with rolled or sprayed termination methods in one site year as timing of termination was optimal. High biomass producing cover crops sown during the fallow phase of a crop rotation reduced weed emergence, density, and biomass accumulation. Cover crops can be part of an integrated weed management plan in Kansas.

Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2007. / This study forms part of an ARC Nietvoorbij research project on the long-term effect of different groundcover management practices in vineyards. This study concentrated on the root distribution of the vines after different groundcover practices were used for one decade. The vineyard on the research farm of the Agricultural Research Council at Robertson, South Africa, was divided into 56 equally distributed trail blocks, 14 treatments with four replicas each. For the study Chardonnay cultivar on 99 Richter rootstock was used. This study concentrated on only eight treatments. The eight different cover crop practices consisted of the mechanical treatment, chemical treatment, straw mulch treatment, permanent cover crop treatment and four annual cover crop treatments. The annual cover crop treatments consisted of triticale cover crop that was sprayed with an herbicide before bloom, a triticale cover crop that was left to die naturally, a grazing vetch cover crop that was sprayed with an herbicide before bloom and a grazing vetch cover crop that was left to die naturally. The vineyard was established in November 1992 while the different treatments started in April 1993. Root studies were conducted during the 2002/2003 season. In this study the auger method was used to determine root density (mm/cm³). The root density was correlated with data from the penetrometer studies, yield and shoot mass collected during the same season.

Thesis (PhD(Agric) (Agronomy))--University of Stellenbosch, 2007 / A selection of species suitable for cover crop management in the different wine grape regions is required to enable more producers to apply this environment friendly practice in a sustainable manner as part of an integrated production strategy. The correct management practice(s) to be applied to these species over both the short and long term in a cooler and warmer wine grape region needed clarification. The effect of seeding date on the dry matter production (DMP) and weed control efficacy of seven grasses and sixteen legumes, as well as varieties of three of these species, was determined during 1991 and 1992. The decomposition rate of the mulches was determined. In the cooler climate of Stellenbosch (33o55'S, 18o52'E), the Medicago species, subterranean clovers, pink Seradella and three Vicia species did not compete effectively with the winter weeds if the weekly precipitation from mid-March to mid-May (autumn) exceeded 18 mm. The two oat species, as well as rye and triticale produced more than five t/ha of dry matter if the precipitation exceeded 18 mm per week. The DMP of the above-mentioned species indicated that these species could be considered for cover crop management in Lutzville (31o35'S, 18o52'E), if full surface irrigation of 18 mm per week could be applied for 10 weeks directly after sowing, followed by 18 mm fortnightly. Seeding date had a significant effect on DMP in both regions. A highly significant correlation (r = 0.85, p ≤ 0.0001) existed between the decomposition rate of the mulches and the initial amount of dry matter present on the soil surface.

<p>Cover crop use, especially in no-till systems, is an evolving practice to maintain or improve soil health. There are many possible indicators of soil health, but this study focuses on the analysis of soil aggregate stability, soil active carbon, and soil organic matter. Soil aggregate stability is related to water infiltration and potential for soil erosion, while active carbon serves as an indicator of a readily-available food source for microbial activity, and soil organic matter serves as a mediator for the soil physical, chemical, and biological processes. The sites include: three Purdue Agricultural Centers, two soil and water conservation district sites, 12 farmer sites with conservation cropping systems, and seven conventional comparison sites. The treatments consisted of cover crop versus no cover crop use, or cover crop use with different tillage systems or nitrogen rates. In 2016 and 2017, soil samples were collected at a depth of 0-5 cm, air-dried, and separated into two soil size fractions: 0-2 mm and 2-8 mm. The wet sieve method was used to measure the mean weight diameter of the water stable soil aggregates from the 2-8 mm size fraction in both years. The potassium permanganate method was used to measure the soil active carbon from both size fractions in both years. The dry combustion method was used to measure the soil organic matter from both soil size fractions in 2017 only. Results showed relatively small improvements in soil active carbon and aggregate stability with the addition of three to four years of cover crops to the long-term no-till systems. However, these improvements were greater when comparing the cover crops plus no-till treatments to the conventional-till without cover crops. More work is needed to understand the dynamics of soil aggregate stability, soil active carbon, and soil organic matter in relation to soil health and cover crop use. Cover crops will likely have more impact on soil aggregate stability, active carbon, and organic matter with a longer duration of use.</p><p></p>