Soybean [Glycine max (L.) Merr.] seed cost has increased dramatically with the introduction and adoption of herbicide-resistant cultivars, generating interest from growers to reduce seeding rates to the lowest possible level that does not affect yield. Research indicates that greater seeding rates are needed to maximize yield under low-yielding environments and less seed is needed in high-yielding environments, but this has not been confirmed with recent research in Virginia. The objectives of this research was to 1) determine the yield response of soybean cultivars with differing growth habits and maturities grown in full-season and double-crop systems to seeding rate under different yield environments; and 2) compare two seeding rates in large on-farm strip-plots to determine if the growth environment within the field affects the yield response to seeding rate. For objective 1, small-plot research was conducted on Piedmont and Coastal Plain sites across Virginia from 2017 thru 2020. Maturity group (MG) 4 or 5 cultivars were planted in 46-cm rows at the following seeding rates: full-season soybean – 74,130, 148,260, 222,390, 296,520, 370,650, and 444,780 seed ha-1; and double-crop soybean – 197,680, 296,520, 395,360, 494,200, 543,620, and 593,040 seed ha-1. One cultivar per MG was used in 2017 and 2018, but the experiments were expanded to include two cultivars, differing in canopy structure, within each MG in 2019 and 2020. On-farm research compared a high and low seeding rate with a 100,000 seed ha-1 difference based upon grower current practices. To determine growth influence on the yield response, normal difference vegetative index (NDVI) was measured at 2-week intervals from late-vegetative to late-reproductive stages in small-plot and on-farm experiments. Double-crop soybean required an average of 205,000 more seed ha-1 than full-season soybean. Although yield response varied with site and year, MG 4 cultivars usually yielded more than MG 5 at higher seeding rates, but less at lower seeding rate. No differences between cultivar canopy structure were present in full-season systems; differences were revealed in double-crop systems but were not consistent over sites. To obtain 95% of maximum yield, 170,000 to 390,000 seed ha-1 were required in full-season soybean and 470,000 to 550,000 seed ha-1 were required in double-crop soybean. While the NDVI response to seeding rate generally reflected the yield response at most site-years, relationship between yield and NDVI was weak. In on-farm experiments, higher seeding rates yielded more at 3 of 6 sites, but differences varied within the field. The yield-NDVI relationship was stronger due to greater variability within the field, but these differences due to seeding rate could not be discerned. Growing environment, primarily amount and distribution of rainfall, greatly influenced these results; therefore, more exact site-specific seed rate recommendations will be difficult in Virginia's environment. / Master of Science / Soybean is one of the world's most important seed legumes and contributes a major portion of global protein concentrate for livestock feeding and oil for human consumption therefore, it is essential to continually and sustainably increase yield while maintaining profitability for growers. Through adoption of precision agriculture technology by Southeastern farmers, site-specific management using variable rate application and/or automatic section control of inputs are able to be utilized when field variability is assessed. Additionally, on-farm experiments validate small plot research with larger field-scale evaluations with proper technology and design. In this study various seeding rates on soybean yield in both small-plot and on-farm experiments, as influenced by variable growth and yield differences within the field, was determined. On-farm research allowed better observation of yield response to seeding rate for each field, allowing the evaluation of production practices under realistic growing conditions. Ultimately, it is expected that more early-season growth in areas of the field with greater productivity will result in greater yields using less seed per hectare. The utilization of vegetative indices as well as remote sensing technology contributed largely to the analysis of yield and varying seeding rates. Accordingly, measurements were correlated with one another to determine if remote sensing techniques can be substituted for ground measurements in predicting yields.

Master of Science / Department of Agronomy / Ignacio Ciampitti / Genotype by seeding rate interaction can play a critical role in wheat (Triticum aestivum L.) yield potential. The objectives of this study were to i) quantify wheat yield response and ii) early-season plant establishment related to the planting technology under diverse seeding rates and with contrasting varieties relative to their tillering ability. Four studies were established at two locations during two growing seasons (2015-16 and 2016-17) at Ashland Bottoms (dryland and conventional till in the first year and no-till in the second year) and at Topeka (irrigated and no-tillage for both years) field research stations (KS, US). Two winter wheat varieties were planted with two different planting systems (singulated and conventional drill) at four different seeding rates (45, 90, 135, and 180 kg ha⁻¹). Early-season measurements consisted of stand counts, canopy coverage (estimated via imagery collection via small-unmanned aerial vehicle systems - sUAVS), determination of early-season gaps within the stand of plants, and spacing between plants. Early season measurements (emergence progression, stand count, and canopy coverage) and biomass did not present differences among treatments. At Ashland, across 2-yrs, single factors seeding rate and genotype significantly impacted yields. Seeding rate factor positively affected yields, ranging from 4.7 to 5.4 Mg ha⁻¹ with seeding rates going from 45 to 135 kg ha⁻¹, respectively. For the genotype factor, the variety WB Cedar (high-tillering) presented an overall yield of 605 kg ha⁻¹ greater than WB 4458 (low-tillering). Across locations, the seeding system did not influence yields for both years of the study. At Topeka, the seeding system significantly influenced yields in 2017, with singulation outyielding the drill system, in 161 kg ha⁻¹. Further research is needed at a farmer-scale testing more winter wheat varieties and focusing on lower seeding rates to better understand the potential benefits of the implementation of this new technology.

3 pp. / Production practices for grain sorghum are discussed including hybrid selection, planting date, seeding rate, row configuration, irrigation, fertilization, pest control, and harvesting.

Current Virginia soft red winter wheat (Triticum aestivum L.) management strategies have been in place for over 20 years. A new advanced intensive management (AIM) system has been evaluated in order to improve Virginia wheat yields and attempt to bring state average wheat yields of 4288 kg ha⁻¹ more closely in-line with the maximum yield achieved in the Virginia Tech Official Soft Red Winter Wheat Trials of 7400 kg ha⁻¹. Increases in nitrogen (N) fertilizer application rates and splits, a chelated micronutrient blend, increased seeding rates, and a "no tolerance" pest control methodology were compared to current intensive management practices in this study. Additional fall N application and an increased seeding rate resulted in an increased number of tillers m-2 at growth stage (GS) 25 and biomass at GS 30. This increased number of tillers may lead to a greater amount of viable grain head production and increased wheat yields. Higher seeding and N application rate resulted in dramatically increased lodging in 2009 with resultant yield loss. Grain yield was significantly affected by management type in three of six instances. The number of heads m-2 was the yield component factor most influenced by factors tested in these studies. / Master of Science

2 pp. / Until the introduction of semi-dwarf wheat in the late 1960s, wheat varieties were typically one and a half to two times their current height. Most heirloom, traditional, or landrace varieties are considered standard-height wheat (e.g. Sonoran white); in general they are adapted to lower-input conditions, and cannot tolerate high-fertility environments without lodging. Lodging reduces grain yield, delays harvest, and increases harvesting costs. Standard-height wheat needs to be grown at a lower plant density and with less nitrogen and irrigation water than semi-dwarfs in order to prevent lodging, optimize yield, and make the most efficient use of resources.

Master of Science / Department of Agronomy / J. A. Dille / Weed control in grain sorghum has always presented a challenge to producers in the semi-arid Great Plains. Cultural control tactics such as narrowing of row spacings and increasing seeding rates can be effective control methods. The objective of this research was to determine the row spacing and seeding rates that maximizes yield while suppressing weeds. Grain sorghum row spacings of 25, 51, and 76-cm and seeding rates of 75,000, 100,000, 125,000, and 150,000 seeds ha[superscript]-1 were evaluated in Kansas at Beloit and Manhattan in 2013 and Beloit, Manhattan, and Hays in 2014. Grain sorghum growth and yield response were measured in response to natural weed communities. After evaluation, Beloit was considered a low weed pressure site while Manhattan and Hays were considered to be moderate and high weed pressure sites, respectively. Grain sorghum biomass was different while weed biomass was consistent across row spacings. Yield loss equations and profit functions were derived to determine the amount of grain yield and $ ha[superscript]-1 loss from each of the three locations. Yield and profit lost was greatest amongst weedy observations. Results indicated that grain sorghum grown on wide row spacings and seeding rates of 125,000 seeds ha[superscript]-1 out yielded all other treatments under a low weed pressure site (Beloit) and narrow row spacings out yielded wider spacings in moderate and high weed pressure sites (Manhattan and Hays). These results imply that a Kansas grain sorghum producer should evaluate potential weed pressure before determining a final row spacing and seeding rate.

Planting date (PD), seeding rate (SR), genotype, and row spacing (RS) influence hard red spring wheat (HRSW, Triticum aestivum L. emend. Thell.) and soybean [Glycine max (L.) Merr.] yield. Evaluating HRSW economic optimum seeding rates (EOSR) is needed as modern hybrids may improve performance and have different SR requirements than cultivars. Two cultivars and five hybrids were evaluated in five North Dakota environments at two PDs and five SRs ranging from 2.22-5.19 million live seeds ha-1 in 2019-2020. Planting date, SR, and genotypes have unique yield responses across environments. Hybrid yield was the most associated with kernels spike-1 (r=0.17 to 0.43). The best hybrid yielded greater than cultivars in three environments. The EOSR ranged from 4.08-4.15 and 3.67-3.85 million seeds ha-1 for cultivars and hybrids, respectively. Hybrids are economical if seed prices are within $0.18 kg-1 of cultivars. In soybean, individual and synergistic effects of PD, SR, genotype relative maturity (RM), and RS on seed yield and agronomic characteristics, and how well canopy measurements can predict seed yield in North Dakota were investigated. Early and late PD, early and late RM, and two SRs (457 000 and 408 000 seed ha-1) were evaluated in 14 environments and two RS (30.5 and 61 cm) were included in four environments in 2019-2020. Individual factors resulted in 245 and 189 kg ha-1 more yield for early PD and late RM, respectively. The improved treatment of early PD, late RM, and high SR factors had 16% yield and $140 ha-1 more partial profit greater than the control. When including RS, 30.5 cm RS had 7% more yield than 61 cm RS. Adding 30.5 cm RS to the improved treatment in four environments resulted in 26% yield and $291 ha-1 more partial net profit compared to the control. A normalized difference vegetative index (NDVI) at R5 was the single best yield predictor, and stepwise regression using canopy measurements explained 69% of yield variation. North Dakota farmers are recommended to combine early PDs, late RM cultivars, 457 000 seed ha-1 SR, and 30.5 cm RS to improve soybean yield and profit compared to current management trends.

Dormant bermudagrass (Cynodon dactylon) fairways become matted down and thinned out from winter traffic. This appears to be more of a problem on the coarser textured, winter hardy, improved varieties (e.g., 'Midiron' and 'Vamont') typically used in the colder regions of the upper transition zone. Winter overseeding with cool-season species can improve dormant bermudagrass winter and spring quality. However, bermudagrass persistence can decline in golf course fairways overseeded with ryegrasses (Lolium sp.) for winter quality if ryegrasses persist due to cool spring temperatures, use of persistent ryegrass varieties, and management practices that favor ryegrasses over bermudagrass. Winter overseeding practices that facilitate a reliable transition from overseeded species to bermudagrass would enable transition zone golf courses to overseed bermudagrass fairways for winter-spring quality while allowing the bermudagrass turf to persist without excessive competition from cool-season overseeded species. Studies were conducted to determine the effects of perennial ryegrass (L. perenne) and annual ryegrass (L. multiflorum) seeding rates on winter-spring quality and subsequent transition to bermudagrass in two transition zone locations. Studies were also conducted to determine the potential influence trinexapac-ethyl (TE), a plant growth regulator used by many professional turfgrass managers to suppress foliar growth, has on encouraging overseeded species to transition to bermudagrass. These studies demonstrated that higher overseeding rates (448 and 896 kg ha-1) can provide greater winter-spring quality but do not enhance transition to bermudagrass over lower overseeding rates (224 kg ha-1). This was especially evident in cooler transition zone climate, where higher overseeding rates delayed transition to bermudagrass. Annual ryegrass transitioned to bermudagrass better than perennial ryegrass, but the overseeded winter-spring quality of annual ryegrass was unacceptable. Perennial ryegrass varieties differed in transition. Some perennial ryegrass varieties were too persistent to fully transition to bermudagrass even with the onset of summer temperatures. Intermediate ryegrasses (L. multiflorum x L. perenne) appeared to be promising alternatives to overseeding perennial ryegrass in areas of the transition zone where summer reliance on bermudagrass turf is strongly preferred. Trinexapac-ethyl, when applied to overseeded perennial ryegrasses, did not enhance overseeded ryegrass transition to bermudagrass. Spring TE applications to overseeded perennial ryegrasses were found to reduce or delay their transition to bermudagrass. / Master of Science

As the Mississippi River Alluvial Aquifer declines, it is the duty of soybean producers to become more efficient irrigators. Research was established in 2012 and 2013 in the Mississippi Delta to evaluate plant development and yield of an indeterminate soybean variety with irrigation initiated at the R1 producer standard and compared to initiation timings at the R2, R4, and R5 growth stages once a 2” deficit was reached according to the FAO-56 Penman-Monteith model. Research was also conducted to evaluate seeding rates in irrigated and non-irrigated systems in Starkville and Stoneville, MS in 2013 and 2014. These data indicate that delaying irrigation initiation beyond R1 did not adversely affect yield, and in some instances even provided a small yield increase. Irrigation did show consistent yield benefit regardless of initiation timing over a non-irrigated system. No optimum seeding rate in terms of yield or net return was observed across site years.

Producers choosing to implement an early corn planting management strategy often experience several yield limiting biotic and abiotic factors. Field variability, flooding, sub-optimal soil temperatures which leads to poor nutrient uptake, delayed emergence and reduced root growth can limit grain production. Three separate experiments were conducted to address some of the negative effects associated with early corn planting. Experiment 1 evaluated flooding effects on several morpho-physiological traits including root system architecture during early crop development. Hybrids (DKC 6208, Pioneer 1197) were flooded at planting (V0) and growth stages V1, V2, V3 for 0, 6, 12, 24, 48, 96 hours. Plants flooded at V0 11% suffered the steepest decline in collar height. Plants flooded at V2 10% were more susceptible than plants flooded V1 4%. Overall, there was a linear decline in nutrient concentration if flooding occurred at planting. Tissue Na levels were the most affected by flood duration and K was the least affected. Experiment 2 evaluated biologic compounds developed to increase immobile nutrients P and K to improve fertilizer use efficiency and provide slow developing roots essential nutrients. The effectiveness of microbial products (B-300, QR, Mammoth, EM-1) with/without starter fertilizer influenced yield, emergence, plant growth, and nutrient uptake. Biologic seed treatments compared to the control, resulted in a positive yield advantage for all treatments. Yields ranged from 37 to 48% higher if biologic compounds were applied. On average, yields increased from 26 to 38% after starter fertilizer was added to the biologic compounds. Phosphorus levels at VT were significantly higher for QR and K content was higher for B300, SF-B300, QR, Mamm, and SF-Mamm compared to the control. Experiment 3 addressed soil physical/chemical properties affecting plant development and there yield plant density relationship. On average, yields significantly increased 40% as plant population increased from 49,400 to 103,740 plants ha−1. Based on the quadratic model agronomically yields would be highest at 61,360 plants ha−1. Correlation analysis among yield and soil physical and chemical properties revealed positive correlations for grain yield, sand% (r2 = 0.42), soil K (r2 = 0.17) soil Na (r2 = 0.46), and soil P (r2 = 0.49).