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Fourteen seed lots of winter wheat were tested for Microdochium nivale contamination using various methods. The seed lots tested were largely free from other fungal contaminants and M. nivale was both superficial and deep seated. No relationship between seed weight and M. nivale contamination was shown. Microdochium nivale contaminated seeds were evenly distributed by weight throughout the three seed lots tested and no relationship between seed appearance and contamination was shown. Seedling disease symptoms were greatest for M. nivale in cold dry conditions and for F. culmorum in warm dry soil conditions. Good linear relationships were shown between disease severity and the rate of seedling emergence for both artificially inoculated and naturally contaminated seed. Contamination by M. nivale affected seedling vigour as measured by the rate of emergence. Seedlings took longer to emerge as the percentage of M. nivale contaminated seeds increased. Microdochium nivale var. majus was shown to be the most common sub-group of M. nivale isolated from wheat seed. Of 91 M. nivale isolates tested 85 were identified as M. nivale var. majus and 6 as var. nivale, with the var. majus isolates being more pathogenic towards wheat seedlings. The efficacy of fungicide seed treatments was not affected by inoculum load as measured by the percentage of contaminated seed. However, reduced temperature did decrease the efficacy of one of the fungicides tested. In the field, effects on crop emergence and infection were observed following seed treatment at two sites. At one site disease control resulted in an increase in grain yield of 300%. It is clear that seedling disease will be severe when a seed lot with a high percentage of contaminated seeds is sown into conditions where seedling emergence will be slow. Under such conditions the use of a robust seed treatment is advised.

Agricultural soils have considerable potential to mitigate climate change by sequestering substantial amounts of atmospheric carbon as soil organic carbon (SOC). This research hypothesized that adding winter wheat to corn-soybean crop rotations increases fungal abundance and diversity and the amount of more stabilized SOC. Corn-soybean (CS) and corn-soybean-wheat (CSW) treatments were established in 2012 under a no-till system with a randomized block design at two separate locations, the Northwest and Western Agricultural Research Stations (NWARS and WARS, respectively). Soil samples were collected in fall 2020 after corn harvest at a depth of 0-10 cm. Total fungal biomass and enzyme activity were measured in conjunction with long-read genetic sequencing of the mycobiome to provide fungal taxonomic abundance and diversity. Soil carbon (C) was examined using a modified Walkley-Black method along with total C analysis after size and density separation and chemical oxidation. Total fungal biomass was higher under CSW than the CS rotation (26% at NWARS, 9% at NWARS) with greater diversity at WARS but not NWARS. Concentrations of oxidatively resistant SOC were higher under CSW than the CS rotation (0.68% at NWARS, 13.1% at WARS). This study showed that diversifying crops can impact soil fungi and potentially increase the amount of stable SOC, but farmers should be aware of how rotations affect their operations. As methods to monitor and increase SOC improve, C farming programs and markets will expand allowing yield uncertainty to be countered by generating sellable C credits.

Agriculture is one of the main contributors to climate change and is also severely threatened by the consequences of the changing climate. To reduce the environmental pressure from agriculture, sustainable practices are urgently in need of evaluation and implementation. In croplands, organic farming and conservation tillage can reduce energy consumption, greenhouse gas emissions, and pollutant production as well as increase carbon sequestration, hence are considered more environmental-friendly and sustainable than conventional farming and intensive tillage. Moreover, organic farming and conservation tillage are shown to improve soil health such as physical structure, chemical conditions, and microbial functionalities. Therefore, these practices are also recommended as beneficial to mitigate climate change effects, such as crop drought stress. However, if organic farming and conservation tillage are truly climate-smart adaptations for cropping systems is still to be tested in different climate conditions. Extreme weathers, increasing in frequency and severity due to climate change, are posing extra challenges on food security in addition to the growing population. Drought as a top threat causes intense damage in agroecosystems, especially in rainfed agriculture. Crop water relations are highly responsive to drought stress, and directly linked to growth and productivity. Therefore, understanding crop water relations in response to drought can provide insights on assessing cropping systems for future climate. As introduced in Chapter 1, this thesis aims to bring insights on the effects of cropping systems and drought on plant water relations along the soil-plant-atmosphere continuum. This includes root water uptake patterns, stem xylem vulnerability and anatomy, leaf water status and physiological processes, phenology, growth, and yield. Combining different management practices, four cropping systems are studied: conventional intensive tillage, conventional no-tillage, organic intensive tillage, and organic reduced tillage. Simulated drought periods with portable shelters were carried out in Swiss rainfed cropland under temperate climate. During the 2018 growing season pea-barley mixture, an important fodder crop, was studied. Winter wheat, a globally important food source, was studied during 2019. Root water uptake depths of crops provide important information on drought response and therefore may provide insight based on differential outcomes in cropping systems under drought. The foci in Chapter 2 are on root water uptake patterns of pea and barley grown in a mixture under the targeted cropping systems and different water availabilities. The water uptake patterns of winter wheat are included in Chapter 4. Stable water isotopes were used to estimate the water uptake patterns of these three species with a Bayesian framework. In all cropping systems, when subjected to the experimental drought, both pea and barley shifted their water uptake patterns to shallower depths without niche differentiation, whereas winter wheat went for deeper water uptake. Moreover, due to the natural drought period in summer 2018, we also observed responses of pea and barley to this more moderate drought compared to our treatment, where only barley shifted up in water uptake depths, but pea did not. Plant hydraulics greatly determines water transport, and it is shown to be affected by environments including soil conditions. The hydraulic traits of pea and barley in response to cropping systems as well as their links to growth and productivity are presented in Chapter 3. Xylem vulnerability to cavitation of both species was evaluated with the cavitron technique, and percentage loss of conductivity derived with xylem water potential in situ was used to assess the drought stress of these two species. Once again, different species showed inconsistent responses. Although grown in a mixture, cropping systems only affected the hydraulic traits of barley but not pea. Crop growth and productivity are shaped by various physiological processes with great complexities among regulation and compensation responses. Integrating crop traits along the entire continuum into a trait space helps to draw a clear picture on changes responding to the environment and managements. Winter wheat traits about crop water relations are presented in Chapter 4. In the trait space, cropping systems only changed growth trait space, which differed between organic and conventional systems but not between conversation and intensive tillage systems. Meanwhile, the drought treatment dominated water trait space, irrelevant to cropping systems. Other than the traits investigated on individual plant, visual changes in crop phenology can also help reveal cropping system effects. PhenoCams were used to track phenology of pea-barley mixture and winter wheat. Crop phenology was not affected by cropping systems for pea-barley mixture, but for winter wheat, showing differences consistent with the trait space (i.e., differed between organic and conventional systems). Because I contributed to data collection and analysis as well as revising the manuscript, this work is included in the Appendix. Our results show that cropping systems can affect certain hydraulic, physiological, and growth traits, as well as phenology of crops, which could link to yield traits. However, the responses and outcomes largely depend on species. These results emphasise that using different cropping systems to alleviate drought stress for plants might not be as effective as previously assumed, at least in temperate areas, hence compromising the expectation to counteract or compensate the aggravating drought threats under the changing climate.

Low grain protein content in hard red winter (HRW) wheat (Triticum aestivum L.) has been a serious challenge for rainfed wheat growers, particularly in years with elevated grain yield. Proper nitrogen (N) management with adequate N rate and time of application will be critical for optimizing both grain yield and protein content. In addition, crop canopy reflectance sensors (CRS), which have been widely used for precision N management in corn in Nebraska and explored in winter wheat in some other states, are yet to be explored in Nebraska. This 2-yr experiment evaluated the effects of different N rates (0%, 25%, 50%, 75%, 100%, and 125% of recommended rate) and application timings (fall, spring, and split between fall and spring) on grain yield and protein of HRW wheat. Field experiments were conducted at four different sites across Nebraska under rainfed conditions in 2018/2019 (Year 1) and 2019/2020 (Year 2). Nitrogen fertilization significantly increased grain yield in a year with above-average precipitation (Year 1). There was an increase in grain protein with increasing N rates at all sites in both years and the highest grain protein was always with the 125% N rate. Spring and split applied N was effective over fall application in the site-year when there was a risk of applied N loss via leaching or denitrification. Ruth, as a semi-dwarf most recently developed variety for greater adaptation in Nebraska and neighboring states demonstrated potential to benefit from spring or split N application given no disease pressure. Normalized Difference Vegetation Index (NDVI) obtained from active CRS at different growth stages had significant positive relationship with applied N rate, grain yield, and protein at certain growth stages and site-years, indicating its potential use for in-season N management in winter wheat. The results of this study suggest that an effective N management strategy for winter wheat should account for and be adaptable to weather variability to optimize grain yield and protein content in winter wheat. Advisor: Bijesh Maharjan

The winter wheat double crop soybean rotation is an economically viable rotation for Kentucky farmers. Recent decreases in commodity prices has warranted the need to evaluate intensive management practices that can increase yields and profitability in this crop rotation. There were three goals of this dissertation: 1.) identify management practices that would decrease deoxynivalenol (DON) in harvested wheat grain and increase wheat heading and anthesis uniformity, 2.) evaluate double crop soybean planting timing and identify intensive management practices to increase seed yield, and 3.) determine the profitability of these management options. These studies were conducted in Princeton KY between 2016 and 2019. In-furrow phosphorus did not decrease DON or heading and anthesis uniformity. Increased seeding rate decreased the number of days to beginning anthesis (Zadoks 60) in late planted wheat, however did not decrease DON contamination. Harvesting wheat at 20 to 22% grain moisture increased grain quality, but also increased DON contamination compared to harvesting at 13 to 15% grain moisture. Harvesting at 20 to 22% grain moisture, enabled an earlier planting timing of double crop soybeans which resulted in soybean yield increase. Increased seeding rate and the use of prophylactic R3 foliar pesticide application increased double crop soybean yields respectively. The use of seed treatment did not increase seed yield. Partial budget analysis indicate that the wheat intensive management treatments had negative net benefits, and that only the increased seeding rate and the use of prophylactic foliar pesticide application had positive net benefits. Overall, intensive management options were identified that increase yield and profitability for Kentucky’s winter wheat and double crop soybean rotation.

The continuing population is placing unprecedented demands on worldwide crop yield production and quality. Improving genomic selection for breeding process is one essential aspect for solving this dilemma. Benefitted from the advances in high-throughput genotyping, researchers already gained better understanding of genetic traits. However, given the comparatively lower efficiency in current phenotyping technique, the significance of phenotypic traits has still not fully exploited in genomic selection. Therefore, improving HTPP efficiency has become an urgent task for researchers. As one of the platforms utilized for collecting HTPP data, unmanned aerial vehicle (UAV) allows high quality data to be collected within short time and by less labor. There are currently many options for customized UAV system on market; however, data analysis efficiency is still one limitation for the fully implementation of HTPP. To this end, the focus of this program was data analysis of UAV acquired data. The specific objectives were two-fold, one was to investigate statistical correlations between UAV derived phenotypic traits and manually measured sorghum biomass, nitrogen and chlorophyll content. Another was to conduct variable selection on the phenotypic parameters calculated from UAV derived vegetation index (VI) and plant height maps, aiming to find out the principal parameters that contribute most in explaining winter wheat grain yield. Corresponding, two studies were carried out. Good correlations between UAV-derived VI/plant height and sorghum biomass/nitrogen/chlorophyll in the first study suggested that UAV-based HTPP has great potential in facilitating genetic improvement. For the second study, variable selection results from the single-year data showed that plant height related parameters, especially from later season, contributed more in explaining grain yield. Advisor: Yeyin Shi

Genomic methods including genome wide association analysis (GWAS), genomic selection (GS) and RNA-seq allow for faster selection of superior breeding lines and for identification and resolution of candidate genes. A panel of 240 soft red winter wheat (Triticum aestivum L.) cultivars and breeding lines were subjected to soil waterlogging stress over two seasons at Stuttgart, AR and St. Joseph, LA, US. Total concentrations of P, K, Ca, Mg, Mn, Fe, Al, B, Cu, Na, S and Zn were determined in wheat shoots post-waterlogging using inductively coupled plasma spectroscopy. Yield components kernel number per spike (KNPS), kernel weight per spike (KWS) and thousand kernel weight (TKW) were measured at plant maturity. Negative correlations between TKW and KWS with aluminum and iron concentrations indicated the impact of elemental toxicity on grain production. A ten-fold cross-validation (CV) analysis and ridge regression BLUP (RR-BLUP) model found GS prediction accuracies (rgs) of micro and macronutrient concentrations to range from rgs = 0.06 to 0.52 and improved as more site-years were included in the analysis. The ratio of genomic to phenotypic prediction accuracy (rgs /H1/2) was greater than 0.50 for eight of the twelve elements, indicating the potential for using GS to select for shoot micro and macronutrient concentrations in the absence of phenotypic data. GWAS identified forty-seven highly significant (p < 0.00001), twenty-three very significant and consistent (p < 0.0005) and eight significant and consistent (p < 0.001) marker trait associations (MTA) for the twelve micro and macronutrients measured. Lastly, RNA-seq was used for transcriptome and gene expression analysis under waterlogged and non-waterlogged conditions in wheat cultivars ‘Pioneer Brand 26R61’ and ‘AGS 2000’. Around 300 million pair-end reads were developed, covering approximately 16 Gb of the wheat transcriptome. In total, 64,911 (AGS200) and 60,414 (26R61) were obtained and 58,753 expressed genes were observed across both cultivars and treatments. Overall, the results of this study have and will enable genomics assisted breeding for waterlogging tolerance within the University of Arkansas Wheat Breeding Program by allowing for selection of materials with reduced micro and macronutrient concentrations in new breeding lines in the absence of phenotypic data

The complex interaction of genetics, environment and management in determination of crop yields can interfere with selection progress in breeding programs. Specifically, the impact on selection for nitrogen use efficiency (NUE) in wheat (Triticum aestivum L.) under changing climatic conditions can be confounded by these interactions. Temperature increases for the southeastern United States are projected to range from 1-3°C by 2050 with nighttime temperatures increasing more rapidly than day temperatures. High temperatures are known to affect crop development and breeding for tolerance to heat stress is difficult to achieve in field environments. We utilized a multi-environment trial to assess variation in traits associated with NUE based on interactions of genotype x environment x management (G×E×M). All genotypes in the study responded favorably to lower than recommended nitrogen rates. Incremental application of N rates increased yield and post-anthesis N uptake significantly. Additionally, two multi-year studies investigating the effects of heat stress on soft red winter wheat varieties were conducted during the 2015-2016 growing seasons at the University of Kentucky Spindletop Research Farm in Lexington, KY. Thirty-six to 40 genotypes were chosen based on the combination of traits for vernalization and photoperiod sensitivity determined using marker analysis. Warmed environments were created through active and passive warming. Heading date, averaged across genotypes, shifted 1-5 days earlier in the actively warmed environment compared to the ambient environment across both years (p ≤0.05). Grain yield, averaged across genotypes, was significantly reduced in the actively warmed environment by 211.41 kg ha-1 (p ≤0.05) or 4.84%; however yield response to environment varied among genotypes with several genotypes displaying an increased yield in the warmed environment. Night temperature increases ranged from 0.27-0.75 °C above ambient temperature in the passively warmed environment. Grain yield, averaged across genotypes, was significantly reduced in the passively warmed environment by 224.29 kg ha-1 (p ≤0.05) or 6.44%; however, yield response to environment varied among genotypes with several genotypes displaying an increased yield in the warmed environment. Yield reductions are attributed to nitrogen utilization being reduced by 9.4% (p ≤0.001) under increased night temperatures.

An optimum planting date is important for winter wheat nitrogen (N) management as it dramatically changes the growing environment including temperature and moisture, ultimately affecting fertilizer efficiency and grain yield (GY). In Arkansas, high precipitation in the fall often forces farmers to delay planting and current Arkansas recommendations include the application of fall N when soft red winter wheat (SRWW) is sown later than optimum, despite the lack of data supporting this practice. This study evaluated the effect of rate and timing of N application on GY of SRWW sown at variable planting dates in Arkansas. Granular urea was split applied between the fall (F), late winter (LW) and/or early spring (ES) and compared to N only applied in the spring (LW, or LW + ES). Experiments were conducted at the Newport Research Station (NPRS), Pine Tree Research Station (PTRS), and Rohwer Research Station (RWRS), representing the diverse wheat growing regions in Arkansas. Wheat was sown at three planting dates and supplied with total N rates of 67, 101, 135, 169, and 202 kg N ha-1. Fall-N rates equal to 0, 34, 67 kg N ha-1 were applied after planting at Feekes 3 and spring-N rates equal to 67, 101, 135 and 169 kg N ha-1 were applied at Feekes stage 4 or 5. There was no statistical difference between spring (LW and ES) and split N applications at NPRS where there was low precipitation and the highest residual soil-N and thus decreased potential for volatilization and denitrification. A split fall and spring application was important for maximizing GY on the latest planting date at both PTRS and RWRS and increased mean GY by 1122 and 544 kg ha-1 compared to spring only application, respectively. Overall, results suggest that splitting fertilizer-N between fall and spring has the potential for increasing GY in late-planted wheat in fine-textured soils when there is high precipitation, which favors N loss.

Aphids (Hemiptera: Aphididae) are pests of multiple cropping systems, primarily due to the viruses they vector and direct crop damage that is exacerbated by their rapid population growth. In Kentucky, grain aphids (Rhopalosiphum padi and Sitobion avenae) cause significant yield loss to winter wheat as vectors of Barley Yellow Dwarf virus (BYDV), prompting the routine application of insecticides. Coupled with increasing human populations and decreasing arable land, it is increasingly evident that biological control services provided by natural enemies represent a viable long-term management option. Aphids are preyed upon by a diverse array of predators that can be exploited in conservation biological control. I designed a field experiment to monitor dispersal into and out of wheat fields, and how these movements were affected by the surrounding habitat. Analysis revealed there are significant movements of R. padi into the wheat in the fall, and S. avenae in spring, and that these movements are slowed down by forested edges. Natural, field-bordering weed strips were used as a conservation biological technique to enhance predator populations. Results showed that while weed strips did not affect the yield of the crop, aphid abundance, or BYDV incidence, it did significantly increase the abundance of natural enemies. Dominant predators included Coccinellidae, Anthocoridae, Chrysopidae larvae, and Braconidae. Using molecular gut-content analysis, I screened multiple species of predators and found strong trophic linkages between aphids and Orius insidiosus and multiple species of coccinellids, namely Coccinella septempunctata and Coleomegilla maculata. In aphidophagous systems, intraguild predation (IGP) can interfere with the biological control potential so I also screened coccinellids for IGP using newly designed primers. To identify intraguild prey DNA in coccinellids, I designed species-specific primers for C. maculata and C. septempunctata to use in PCR-based molecular gut-content analysis. Results revealed high frequencies of IGP between coccinellids that are significantly higher in weed strip plots. However, I observed no detectable impact on aphid predation during these increased times of IGP, suggesting it does not interfere with biological control of aphids in this system. I discuss the role of weed strips in winter wheat as part of an integrative pest management strategy.

Nitrogen use efficient (NUE) wheat varieties have potential to reduce input costs for growers, limit N runoff into water ways, and increase wheat adaptability to warmer environments. Previous studies have done little to explain the genetic basis for NUE and components, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE). Four studies were conducted to 1) determine genotypic stability of NUE under high and low N regimes and under warming 2) determine effect of warming on NUE 3) indentify QTL associated with NUE components 4) assess the utility of canopy spectral reflectance (CSR) as a high-throughput phenotyping device for NUE. Genotypic response to N stress or warming varied. Uptake efficiency was found to be more important than utilization efficiency to genotypic performance under high and low N environments and under warming. Selection under low N for NUpE and under high N for NUtE most efficiently identified NUE varieties. Uptake and utilization were lower under warming due to quickened development. No strong correlations between the CSR indices and NUE existed. No QTL were found to be significantly associated with NUE components. Further research into the mechanisms controlling NUE and to reveal plant response to N stress and under warming is necessary.

Fusarium head blight (FHB) or head scab, caused by Fusarium graminearum Schwabe [telomorph: Gibberella zeae Schwein.(Petch)], is one of the most destructive diseases of wheat (Triticum aestivum L.) worldwide. Numerous strategies for scab resistance breeding are in use, including phenotypic selection for low severity and marker-assisted selection for resistance QTL. The most destructive consequences of scab are evidenced through a reduction in grain quality, and the presence of mycotoxins, the most common of which is deoxynivalenol (DON). Thus, there is great interest among breeders in selecting for resistance to both of these traits. To this end, a study was devised as follows. In 2010, 20 bulk F3 SRW wheat populations with scab resistant parents in their pedigrees were harvested by population from unreplicated plots near Lexington, KY. The plots were affected by a naturally occurring mild-moderate scab epidemic. The grain was sorted on a USDA/ARS and National Manufacturing Seed Sorter System with color camera according to a calibration that reflected visual differences between asymptomatic grain and grain showing FHB symptoms. This process was repeated in 2011 using grain from plots that had conidial suspension applied at anthesis. In 2012, an unreplicated plot study of the C0, C1 and C2 cycles of selection, inoculated with grain spawn and conidial suspension, was evaluated for Fusarium damaged kernels (FDK) and DON concentration. An additional cycle of selection was conducted by running the bulk grain through the sorter. In October 2012, 4 selection cycles of the 20 populations were planted in a RCB experiment at Lexington and Princeton, KY. Bulk populations were planted in both scab nursery and plots, and C3 accepted and rejected of all populations and derived lines of 2 populations were planted in the scab nursery in Lexington, KY. Some populations had FDK and DON reduction with selection, and some derived lines had either numerical or significant reduction with selection. Although the accepted fraction had non-significant reduction compared with the rejected fraction over the populations, FDK and DON means were obviously lower in accepted than in rejected fractions.

In Nebraska, about 75% of the wheat production is in the western half of the state, and about 92% of the winter wheat acreage is in dryland production, where productivity is limited by low and/or uncertain rainfall. We have investigated the effects of water stress on few established winter wheat (Triticum aestivumL.) cultivars, which are known for their superior adaptation to either rainfed or irrigated wheat production systems in western Nebraska. We also began a study to investigate the variation in the root system architecture to confer drought tolerance in winter wheat. The objectives of this study were to investigate the effects of water stress on root and shoot growth of winter wheat cultivars, and also to characterize the root system architecture (RSA) traits of winter wheat cultivars in order to evaluate their drought tolerance under limiting water conditions. The root length, root dry matter, root-to-shoot length ratio and root-to-shoot mass ratio of the three cultivars were significantly greater in the water stress than well-watered conditions. Results from the water stress experiment showed that Goodstreak is a drought tolerant cultivar due to its longest root length and high root dry matter. Based on the RSA phenotyping of the 3-week old water-stressed plants, Goodstreak had the highest total root length, total root length density, projected area of roots and network root length distribution. Under water stress conditions, Harry demonstrated a shallow root system with low root and shoot dry matters but displayed the highest root-to-shoot length ratio. It appeared that Harry utilized less water and invested less energy into dry matter under water stress. Our findings support the fact that Wesley performed well in irrigated wheat production systems in Nebraska because of its high shoot and root biomasses. This study leads us to suggest that Wesley is a drought sensitive cultivar because it uses the available soil moisture at ‘uneconomical’ and ‘unsustainable’ rate compared to Harry and Goodstreak. Advisors: P. Stephen Baenziger and Harkamal Walia

Bird cherry-oat aphid is a common pest of Arkansas winter wheat. This aphid vectors barley yellow dwarf virus which may cause extensive crop damage and yield loss when wheat is infested by virulent aphids in the fall. Some suggest this damage may be avoided using insecticide seed treatments if growers are unable to delay planting, as is recommended. Field population dynamics of bird cherry-oat aphid during fall 2009 and 2010 was assessed through random sampling of whole plants and pan trapping methods to evaluate aphid immigration. The field plots were divided into four subplots treated with a systemic insecticide seed treatment (at the recommended rate of 0.148 liters of insecticide per 45 kilograms of seed or 5.0 fluid ounces per 100 lbs of seed) and four untreated plots. Aphids were counted twice weekly in ten 1 m row samples from plant emergence until the end of December. Aphids were classed as small or large nymphs and alates. Winged immigrants were also counted twice weekly in eight pan traps situated at equidistant points within the study fields. Aphid densities in untreated plots increased throughout the season and aphid densities were significantly lower in treated plots. In 2009 winged aphids in untreated fields were significantly higher (mean = 6.54 per meter-row) than in the treated fields (mean = 0.03 per meter-row) (t = 23.48, df = 639, P < .0001). Large aphids were greater in the untreated fields (mean = 5.17) than in the treated fields (mean = 0.43) (t = 10.6, df = 639, P

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.

Abstract: This research project gauges producer demand on the Canadian Prairies for the attributes of new hypothetical varieties of winter wheat. Data collected from a survey of producers in Western Canada is used to determine the values and attitudes of producers regarding new winter wheat variety traits with a focus on increased winter survival rates and increased waterfowl nesting habitat. Increased nesting habitat was found to have a small negative but significant impact on the decision to adopt hypothetical winter wheat varieties; however winter kill rates and gross profit had a large positive effect on its adoption and expansion. Other important drivers of the decision to adopt hypothetical winter wheat varieties are also analyzed. Policy implications include potential guidance of incentives for environmentally friendly farming practices, and the provision of information to winter wheat breeding programs about the needs of producers.

Abstract: This research project estimated economic costs and benefits of winter wheat production in the Canadian Prairies at a farm level. A combination of Net Present Value analysis and Monte Carlo simulation was used to build cash flow farm models by province and soil zone. The objective of this study was to examine the economic feasibility of winter wheat production on the Prairies. Results show that Prairie farmers will benefit from growing winter wheat if crop research further improves cold tolerance, yield, or quality of winter wheat. Incorporating winter wheat into crop rotations has potential to increase farmers’ wealth in the Canadian Prairies.

Abstract: Winter wheat fields provide upland nesting habitat for migrating birds. Duck nests built in winter wheat croplands experience lower probabilities of nest mortality due to farming practices compared to nests built in spring wheat croplands. Two dynamic optimization models are specified in order to measure economic (producer’s profit) and environmental benefits (mallard population) derived from increases in winter wheat acreage in the Prairies. The first model, maximizes the farmer’s revenue due to spring and winter wheat production, subject to mallard population dynamics. The second model uses a social planner point of view to maximize both the farmer’s revenue obtained from wheat production, and social benefit associated with mallard population. The connection between duck population and winter wheat is specified using a logistic growth function where the intrinsic growth rate is a function of winter wheat acreage, and carrying capacity sets the maximum numbers of ducks in a specific area.

Control of Italian ryegrass is important to Tennessee wheat producers. Control of Italian ryegrass has become more difficult over the years due to diclofop resistance. Italian ryegrass resistance to diclofop has been documented in several countries including the US. Tennessee producers have begun to notice that ryegrass escapes are becoming more prevalent than in years past. The purpose of this research was to use glasshouse methods to screen selected populations of Italian ryegrass for resistance to diclofop and to a more recent wheat herbicide pinoxaden and to utilize field experiments to develop herbicide programs for control Italian ryegrass in the field. Resistance to diclofop was found in eight TN populations. The eight populations did not show cross-resistance to pinoxaden. One population from Union County, NC (R1) was found to be resistant to both diclofop and pinoxaden. The level of resistance to pinoxaden of the R1 population was 14 x that of the susceptible population.Field experiments demonstrated preemergence (PRE) Italian ryegrass control with chlorsulfuron (71 to 94%) and flufenacet + metribuzin (84 to 96%). Italian ryegrass control with pendimethalin applied PRE or delayed preemergence (DPRE) was variable (0 to 85%). Postemergence control of Italian ryegrass was good with pinoxaden, mesosulfuron, flufenacet + metribuzin, and chlorsulfuron + flucarbazone (>80%). Timing of application and herbicide treatment had no effect upon wheat yield, except for diclofop and pendimethalin treatments where Italian ryegrass was not controlled. Pinoxaden is in the phenylpyrazolin herbicide family which offers control of Italian ryegrass but is not toxic to wheat. Pinoxaden has only been on the market for three years yet several wheat producers have suspected resistance in Italian ryegrass biotypes.An experiment was conducted to identify Italian ryegrass biotypes resistant to pinoxaden and to determine the mechanism of resistance using derived Cleaved Amplified Polymorphic Sequence (dCAPS) methods. Two populations were found resistant to pinoxaden, one from the state of Washington (R2) and the other from North Carolina (R1). The substitution of isoleucine by leucine at the 1781 ACCase residue was identified in the R1 biotype but not in the R2. The NC1 biotype is the first known pinoxaden resistant Italian ryegrass population to be documented having the 1781 target-site mutation.

ABSTRACT WALL, DAVID PETER. Soil Tests for Winter Wheat Nitrogen Management in the Southeastern USA. (Under the direction of Randy Weisz). Developing a system where soil tests could be used for winter wheat (Triticum aestivum L.) nitrogen (N) management and to determine N-fertilizer requirements in the southeastern USA would have many environmental and economic benefits. The objectives of this study were to: (i) evaluate the effects of sampling time, sampling depth, crop rotation, and N fertilizer application on the amino sugar-N test (ASNT); (ii) determine appropriate and reliable sampling depths for the ASNT and soil mineral N tests; (iii) explore the relationships between these soil N tests and winter wheat N uptake; (iv) calibrate these soil N tests to predict optimum spring N rates (OptN) for winter wheat in North Carolina. Ten study sites were established, to assess changes in ASNT values with sampling depth, crop rotation, and N fertilizer application. A repeated measures experimental design was implemented whereby soil samples were taken from each of the 10 study sites at specific times and depths during the course of a 19-month period. Amino sugar-N (ASN), NO3-N, NH4-N, and soil organic matter (SOM) levels were evaluated at each sampling. At all sites, soil ASN decreased with depth and showed significant variation over time. Soil ASN was influenced by crop rotation and tillage but was not significantly affected by fertilizer applications. When all sites were considered together, soil ASN was well correlated with SOM, however, they were not correlated across time within sites. This suggests that the ASNT is measuring a nitrogenous fraction of SOM that behaves somewhat independently over time. These results indicate that sampling to 30 cm at a specific sampling time will be necessary to capture temporal variability in ASN. Sixty-nine winter wheat N response trials were conducted for three growing seasons over a wide range of soils, drainage and previous crop management practices. A randomized complete block design with five replications and seven growth-stage 30 (GS30) N-fertilizer rates ranging from 0 to 168 kg ha-1 was used. Each February, soil samples were taken over three depths (0-10, 0-20, and 0-30cm) and analyzed for ASN, NO3-N, NH4-N and SOM levels. In the wheat N uptake study, the relationships between these soil N tests and N uptake from the unfertilized check plots (NUPZero) were evaluated. Considering all the experimental locations, the soil tests had poor relationships with NUPZero. When only the well-drained locations (n=58) were considered, the data aggregated into two distinct groups: 1) locations with low residual N, and 2) locations with high residual N and elevated levels of NH4-N and ASN. For locations with low residual N, the ASNT was able to predict NUPZero and grain yield without spring fertilizer applied (YLDZero) and was therefore a good predictor of soil N supply through mineralization. A combination of soil tests (NH4-N, ASNT and SOM) was required to predict NUPZero for all well-drained locations (R2 = 80). In the N fertilizer response study, the ASNT by itself was a poor predictor of OptN for all well-drained locations, however the ASNT was correlated with N uptake at the optimum spring N fertilizer rate (NUPOpt) and N uptake at GS-30 (NUPGS30) for locations with low residual N. The ASNT could not satisfactorily predict OptN for these low residual N locations, but could be used to predict the NUPOpt and wheat yield at the optimum GS-30 N fertilizer rate (YLDOpt) for well-drained fields. A combination of soil tests was required to predict OptN for all locations (i.e., NH4-N and SOM with resultant R2 = 0.59). Soil NO3 tests showed no benefit for winter wheat N management in North Carolina.

The potential for improved fertilizer nitrogen (N) use efficiency (NUE) and yield in winter wheat (Triticum aestivum L.) and maize (Zea mays L.) was tested using a new, controlled release urea formaldehyde polymer (UFP). This polymer was compared with conventional aqueous urea-ammonium nitrate (UAN) [(NH2)2CO—NH4NO3] fertilizer during a two-year field experiment in North Carolina from 2004 to 2006. The crops were grown on three soils: Candor (sandy, siliceous, thermic Grossarenic Kandiudult), Portsmouth (fine-loamy over sandy or sandy-skeletal, mixed, semiactive, thermic Typic Umbraquult) and Cape Fear (fine, mixed, semiactive, thermic Typic Umbraquult). The sandy soil was irrigated as needed to avoid drought stress. Treatments were N source (UAN and UFP) and N rate (0, 50, 78, 106, 134, 162, and 190 kg N ha-1 or 0, 45, 70, 95, 120, 145, and 170 lb ac-1 for wheat and 0, 39, 78, 118, 157, 196, and 235 kg N ha-1 or 0, 35, 70, 105, 140, 175, and 210 lb ac-1 for maize) arranged as randomized complete blocks with four replications. The UAN and UFP were applied as a split application for wheat, while maize received UFP at planting and split UAN. Timing of the materials was determined either by label (UFP) or prior experimental experience (UAN). Harvest biomass, grain, and mid-season soil sampling were performed to assess N availability. For both crops, UAN performed statistically similar to or better than UFP at both sites with regards to yields and NUE. Also, soil sampling and incubation results showed no consistent difference between N sources, implying the slow release properties of the UFP were not seen under the site and laboratory conditions. The release time for both sources at both sites was approximately 14 days (2 weeks). Since the cost of UFP is substantially greater than UAN and form did not significantly affect yield, UFP may not be as economical as UAN, depending on pricing of the different fertilizers.

The purpose of this research was to improve nitrogen (N) management for soft red winter wheat (Triticum aestivum L.) in North Carolina with three areas of focus: delayed harvest effects on grain quality, explaining grain protein variability caused by management practices, and developing N recommendations at growth stage (GS) 30 using aerial color infrared (CIR) photography. Delayed harvest significantly reduced grain yield and test weight in the majority of trials. Yield reductions were attributed to dry, warm environments, possibly due to shattering. Test weight reductions were attributed to the negative effects of wetting and drying cycles. Of the 20 quality parameters investigated, flour falling number, clear flour, and farinograph breakdown times were significantly reduced due to delayed harvest, while grain deoxynivalenol (DON) levels increased with a delayed harvest. Environment contributed to grain protein variability (23%), though the majority of that variability was attributed to N management (52%). It was found that as grain protein levels increased at higher N rates and with the majority of N applied at GS 30, the overall grain protein variability increased. The recommendations to reduce grain protein variability are; to reduce the range in N fertilizer rates used, to avoid over application of N beyond what is required to optimize yields, and to apply spring N at GS 25. Relationships between derived agronomic optimum N rates and three spectral bands and 39 indexes were weak, but after separating the data into two biomass classes (low < 1000 kg ha-1 and high > 1000 kg ha-1), the relationships of optimum N rates with a relative Red and Green bands (relative to a high N-status reference plot) had the best (quadratic) relationships (R2 = 0.80 and 0.81, respectively) for the high biomass class. These results indicate that agronomic optimum N rates at GS 30 can be estimated using aerial CIR photographs if areas of low and high biomass can be determined.

Despite a large number of experimental investigations, it remains difficult to predict, or even interpret, changes in soil structure under different cropping systems. The principal objective of this investigation was to devise and test a conceptual model which could provide a framework for the design and interpretation of experiments concerning the effects of cropping systems on soil structure. The model concentrates on processes that change E100 (the volume of pores > 100 µm in effective diameter per unit volume of total soil). The processes identified are tillage, slaking and slumping, earthworm activity as well as root growth and decomposition. A glasshouse experiment demonstrated that root growth and decomposition could significantly change E100 and soil transmission properties, but attempts to mathematically model these changes were unsuccessful. In addition, the presence of living roots of wheat and perennial ryegrass both helped to maintain pore stability, as indicated by the way in which saturated hydraulic conductivity changed with time. Field experiments were conducted at Lincoln College, Canterbury, New Zealand to provide sufficient data to apply the conceptual model in the form of a budget equation for the 5-15 cm soil depth. In one experiment, perennial ryegrass and winter wheat were managed identically within two cultivation systems (conventional cultivation and direct-drilling) on a silt loam initially in long term pasture. Many of the soil measurements indicated a deterioration in soil structure over the two years of the experiment, regardless of treatment. There was little indication of differences between the effects of winter wheat or perennial ryegrass on soil structure. Nevertheless, as in the glasshouse experiment, the presence of living roots helped to arrest the decline in soil structure. In another field experiment using rhizotrons, it was found that an instantaneous measurement of the maximum amount of root material present in the soil could underestimate the real amount returned over one season by as much as 60% of the harvested root dry weight. Visual observations indicated a half-life of 254 days for perennial ryegrass root decomposition under Canterbury conditions. Analysis of the field experiment results using the conceptual model suggested that tillage and slumping were primarily responsible for changes in E100, whereas the actions of roots and earthworms themselves were insufficient for causing appreciable short-term increases in E100. Tillage appears the only practical way to achieve a rapid increase in E100. This increase may be best achieved if tillage is carried out when a crop is established so that the effect of living roots on macropore stability will be utilised to its fullest extent. Development and application of the conceptual model has emphasised a major need for methods to estimate macropore stability.