No-till management for agronomic crop production is recognized as an effective practice to regain a portion of soil organic matter lost following decades of cultivation. Increasing soil organic matter sequesters C, conserves organic N and concomitantly improves soil quality. Objectives of this research were to: i) quantify C sequestration rate and N conservation with duration of continuous no-till; ii) measure C stratification with continuous no-till as an indicator of soil quality; and iii) evaluate the Illinois soil N test (ISNT) for its value to predict fertilizer N needs of corn in Virginia. Objectives i and ii were achieved by collecting soil samples from 63 production fields in the Virginia Coastal Plain that were managed using continuous no-till from 0 to 14 yrs. No-till management resulted in sequestration of 0.308 ± 0.280 Mg C ha⁻¹ y⁻¹ and conservation of 22.2 ± 21.2 kg N ha⁻¹ yr⁻¹ (0-15 cm). The C stratification ratio (0-2.5 cm: 7.5-15 cm) increased with increasing duration of continuous no-till (0.133 ± 0.056 yr⁻¹) due to the accumulation of organic matter at the soil surface indicating improved soil quality with continuous no-till management. Objective iii was addressed by conducting 29 on-farm fertilizer N response trials in major corn producing areas of Virginia with the duration of continuous no-till management ranging from 0 to 25 yrs. The ISNT values were significantly related to yield without fertilizer N (r² = 0.57; p<0.001) and relative yield (r² = 0.64; p<0.0001). We also found that the ISNT extracted a relatively consistent percentage of total soil N (16.3 ± 0.73 %) suggesting it is a poor indicator of labile N. Total soil N values did almost as well as the ISNT in predicting yield without fertilizer N (r² = 0.53; p = 0.0002), and equally well predicting relative yield (r² = 0.64; p<0.0001). Results do not suggest the ISNT is useful for measuring mineralizalbe N or improving fertilizer N recommendations in Virginia cropping systems. / Ph. D.

Development of winter wheat (Triticum aestivum L.) cultivars capable of more efficient uptake and utilization of applied nitrogen (N) has the potential to increase grower profitability and reduce negative environmental consequences associated with N lost from the plant-soil system. The first study sought to evaluate genotypic variation for N use efficiency (NUE) and identify lines consistently expressing high or low NUE under two or more N rates in a total of 51 N-environments. The results indicated that significant genotype by N rate interactions were frequently observed when trials utilized at least three N rates and identified wheat lines with high and stable yield potential that varied in performance under low N conditions. In addition, NUE was associated with above-ground biomass at physiological maturity were found to be both highly heritable across multiple N supplies. In the second study, two bi-parental mapping populations having a common low ('Yorktown') and two high (VA05W-151 and VA09W-52) NUE parents were characterized to dissect the genetics underlying N response. The populations were evaluated in eight N-environments and genotyped using single-nucleotide polymorphism data derived from a genotyping-by-sequencing protocol to identify quantitative trait loci (QTL) associated with high NUE. Six QTL for NUE were identified on chromosomes 1D, 2D, 4A, 6A, 7A, and 7D that were associated with N use efficiency. The QTL on 2D and 4A co-localized with known loci governing photoperiod sensitivity and resistance to Fusarium head blight (caused by the fungal pathogen Fusarium graminearum Schwabe), respectively. Three of the identified QTL (6A, 7A, and 7D) were associated with NUE in previous investigations, while the QTL on 1D was novel. The final experiment employed a small panel of soft red winter wheat lines to study the effects of photoperiod alleles on chromosome 1D (Ppd-D1) on yield-related traits under three or five N rates that were variably split over two growth stages in eight environments. The results validated the effect of a photoperiod sensitive allele (Ppd-D1b) that was associated with increased grain yield across N rates in half of the Virginia testing environments and under low N rates in all Ohio testing sites at the expense of grain N content. Yield advantages conferred by the Ppd-D1b allele were attributable to increased floret fertility and kernel number per spike. The findings from these studies have direct application for winter wheat breeding programs targeting NUE improvements. / Doctor of Philosophy / Wheat (Triticum aestivum L.) products account for a significant percentage of the total dietary calories and protein consumed globally. To meet production demands, wheat requires efficient nitrogen (N) management to ensure continued grower profitability and to reduce negative environmental impacts of N lost from agricultural systems. This dissertation sought to evaluate variation among wheat lines for N use efficiency (NUE), assess the performance of wheat lines under multiple N supplies, validate traits that are associated with NUE, investigate the role of photoperiod sensitivity genes on N response, and identify regions of the wheat genome associated with high N use efficiency. These studies were conducted using panels of winter wheat lines grown under two or more N conditions over a combined 32 location-years. Results of Chapter I identified variation in cultivar response to N rates was more frequently observed when a greater number of N rates were used in trials of wheat N response. The first chapter also identified variation among wheat lines for NUE and identified lines that consistently produce high grain yields over N-location-years. In addition, above-ground biomass at physiological maturity was found to be strongly associated with grain yield under all N rates and was highly heritable in both studies. Chapter II utilized a combination of genetic and observable trait data to perform genetic analysis in two bi-parental populations grown in eight Nlocation-years. The study identified reproducible and significant genetic markers associated with NUE for application in wheat breeding programs. Upon analysis of photoperiod sensitive versus insensitive wheat lines in Chapter III, photoperiod sensitive wheat lines had a significant yield advantage under N-limited conditions in Ohio and across N treatments in half of the Virginia testing location-years. This resulted from an increased number of kernels per spike and fertile florets in photoperiod sensitive wheat lines. Results from this dissertation suggest that active breeding and selection for N response may be achieved through the employment of high NUE genes and the continued identification of adapted high NUE wheat parental lines.

Master of Science / Department of Agronomy / Charles W. Rice / Agricultural lands receiving N inputs are considered the primary source of N2O, a potent greenhouse gas. N fertilizer management has shown variable effects on both N2O losses and corn grain yield. The objectives of this study were to assess the impact of N source and placement on N2O emissions, fertilizer-induced emission factor (FIEF), corn grain yield, yield-scaled N2O emissions (YSNE) and N fertilizer recovery efficiency (NFRE). The experiment was conducted from 2013 through 2014 at the Agronomy North Farm located at Kansas State University, Manhattan, KS. The soil was a moderately well-drained Kennebec silt loam. The treatments were broadcast urea (BC-Urea), broadcast urea ammonium nitrate (UAN) (BC-UAN), broadcast coated urea (BC-CU), surface-band UAN (SB-UAN), subsurface-band UAN (SSB-UAN), subsurface-band UAN + nitrification inhibitor (SSB-UAN+I) and a 0 N control. In 2013, SSB- UAN emitted significantly more N2O (2.4 kg N2O-N ha-1), whereas control (0.3 kg ha-1) and BC- UAN (0.6 kg ha-1) emitted the least. In 2014, most treatments emitted between 3.3 and 2.5 kg N2O-N ha-1. Only SSB-UAN+I (1.03 kg ha-1) and control (0.26 kg ha-1) were significantly lower. The use of a nitrification inhibitor decreased N2O emissions by 62% and 55% in 2013 and 2014, respectively. BC treatments had cumulative emissions significantly higher in 2014 compared to 2013. Only SSB-UAN+I had a significantly lower FIEF (0.4%), and 2013 FIEF (0.68%) was significantly lower than that of 2014 (1.38%). In 2013, banded treatments had significantly higher grain yields (from 9.1 to 10.5 Mg ha-1), whereas in 2014 fewer differences among N treatments were observed, ranging from 7.2 to 8.6 Mg ha-1. Banded treatments had significantly lower grain yields in 2014 compared to 2013. Only BC-UAN and SSB-UAN+I had significantly lower YSNE, and 2013 had lower YSNE than 2014. In 2013, SSB-UAN had the greatest NFRE, whereas BC treatments had the lowest. In 2014, N treatments did not differ in NFRE. SSB-UAN and SSB-UAN+I had significantly lower NFRE values in 2014 compared to 2013. Fertilizer source and placement have the potential to mitigate N2O emissions and promote high yields and NFRE in corn, however, the response is dependent on the rainfall pattern after fertilizer application. The option of banding UAN without any additive promoted higher N2O losses on a year when precipitation was well distributed, but also enhanced grain yield and NFRE. On the other hand, under the same precipitation conditions, broadcasting N fertilizer promoted lower N2O losses, grain yield and NFRE, but those were all improved in a wet year. Therefore, the subsurface band placement would be the best option under a normal year, whereas broadcasting fertilizer would be the best option under a wetter year. Further, the use of NI with subsurface band UAN provides the most sustainable option, since the NI decreased N2O losses compared to UAN alone in both years. Further research should evaluate N source and placement combinations under different environments in order to better understand how they impact crop performance and the negative environmental aspects of N fertilization. It is important to test those treatments under different precipitation scenarios and look for trends that indicate the best N management option at the local level.

Intensifiering av jordbruket globalt har lett till förhöjda halter reaktivt kväve (Nr) i omlopp på jorden. Användningen av stora mängder av framförallt handelsgödselkväve har rubbat balansen mellan reaktivt kväve och icke reaktivt kväve i kvävecykeln, vilket orsakar stora problem i form av övergödning. För att motverka denna negativa miljöpåverkan är det viktigt att uppmärksamma både makthavare och konsumenter på problemen och redovisa vilken påverkan som sker vid produktion av olika livsmedel. Detta så att konsumenter har möjlighet göra hållbara val vid köp av livsmedel och så att ett hållbart jordbruk kan utvecklas. För att beräkna ett livsmedels påverkan på kvävecykel kan flera olika metoder användas. I denna studie analyseras indikatorerna kväveffektivitet (NUE), kvävefotavtryck samt övergödningspotential för att undersöka vilken av indikatorerna som lämpar sig bäst för konsumentvägledning. NUE definieras som Nut/Nin och beräknar hur stor andel av inflödet av N som kommer ut i slutprodukten. Kvävefotavtrycket beräknas som (Nin-Nut) per kg produkt och övergödningspotential som utsläpp av olika övergödande ämnen per kg produkt. Indikatorerna applicerades på olika svenska livsmedel samt sojabönor från Brasilien och resultatet visade på att högst övergödningspotential och kvävefotavtryck fås för kött från kyckling, gris och nötkreatur. För samma indikatorer beräknades lägst potential och fotavtryck för gurka, tomat och morot. NUE beräknades vara högst för gurka på 0,90 och lägst för hallon och jordgubbe på 0,05 samt 0,08. Vid jämförelse av indikatorerna fastställdes att kvävefotavtrycket är bäst lämpad för konsumentvägledning eftersom resultatet är lättförståeligt och det kan kopplas till specifika miljöproblem så som övergödning. Övergödningspotentialen är också en lättförståelig indikator men N som resurs analyseras inte. Indikatorn kräver också mycket data som kan vara svår att få tag på för produkter som produceras i andra länder. Resultatet av NUE är lite mer komplicerat och indikatorn kan passa bättre som ett mått på hur kväveeffektivt en gård eller land är och därav lämpar sig indikatorn bättre för bönder och makthavare än konsumenter. / The amount of reactive nitrogen in the environment has increased as food production has intensified. A disrupted balance between reactive and non-reactive nitrogen can lead to a destabilisation of the state that the earth system is currently in. In order to create a sustainable agriculture, it is important to inform politicians and consumers about the impact on the nitrogen cycle associated with different food products in order to enable sustainable food choices. The objective of this study was to find an indicator that present the effect on the nitrogen cycle in food production and can be used for consumer guidance. The indicators evaluated in this study were Nitrogen Use Efficiency (NUE), the nitrogen footprint and eutrophication potential. NUE is calculated by dividing Nout by Nin. The nitrogen footprint is defined as the amount of reactive nitrogen released to the environment per product unit and is calculated as (Nin-Nout) per kg product. The indicator eutrophication potential calculates the amount of substances that can lead to eutrophication and is expressed per kg product. The results show that chicken, pig and beef have the highest eutrophication potential as well as nitrogen footprint. The lowest eutrophication potential and nitrogen footprint was found for cucumber, tomato and carrot. The highest NUE was calculated for cucumber with a value of 0,90 and the lowest was found for raspberries (0,05) and strawberries (0,08). The indicator that is recommended for consumer guidance after analysis is the nitrogen footprint because it is easy to understand, and the result can connect to specific problems such as eutrophication. The eutrophication potential is also easy to understand, however the use of nitrogen as a resource is not considered and it could be a problem to find data for products produced in other countries. The result from NUE is a bit more complicated for consumers to understand and the indicator might be more useful for politicians and farmers than for consumer guidance.

As nitrogen (N) is a critical nutrient for plant growth, the development of synthetic N fertilisers dramatically changed agricultural production in the twentieth century. Improvement in N use efficiency (NUE) has been a focus of breeding for grain crop species, since protein is an important component of the harvested product. The study of NUE in sugarcane has lagged behind grain crops, mainly because N is not a component of sucrose, the primary product of the traditional sugarcane industry. Recently, improvement in NUE has become a focus of sugarcane breeding, due largely to environmental concerns regarding pollution from high N fertilisation, and the increasing cost of N fertilisers. This thesis aimed to gain an initial understanding of the genetic basis for variability in NUE in sugarcane. This was achieved through: (i) the screening of 168 sugarcane genotypes under limiting and non-limiting N supply in two glasshouse experiments; (ii) the mapping of marker-trait associations (MTA) for biomass and physiological traits under limiting and non-limiting N supply in a sugarcane mapping population; (iii) the analysis of expression of candidate genes encoding enzymes involved in the central processes of N assimilation and remobilisation in plants; and (iv) the mapping of candidate genes in a sugarcane genetic map. Genetic variation was identified for growth traits as well as physiological traits including %N, internal NUE (iNUE, g dry weight g-1 N) and leaf glutamine synthetase (GS) activity in a sugarcane mapping population. These traits were also analysed for linkage with genetic markers. Genetic variation in the screened genotypes was higher under limiting N supply, a finding that was reflected by the fact that marker-trait associations (MTA) for increases in iNUE were not identified under non-limiting N supply in the commercial parent of the mapping population. Contrary to findings in grain crop species, there was no link between GS activity and other traits, either through phenotypic correlations or co-location of MTA. The expression of candidate genes encoding GS, nitrate reductase (NR) and alanine amintotransferase (AlaAT) was quantified with Sequenom™ MassARRAY technology. Plants were grown under growth-limiting N supply, non-limiting N supply, or a N-pulse treatment, which consisted of growth-limiting N supply followed by non-limiting N supply 24 hours prior to sampling. Two genes, scAlaAT.d and scGS1.a, encoding AlaAT and GS respectively, were identified as non-responsive to changes in N supply, whereas scAlaAT.a, scGS1.b and scGS1.c had significantly (p<0.05) increased expression under a N-pulse, indicating an important role for these genes in the response of sugarcane to a sudden increase in N availability. The location of candidate genes associated with variation in NUE in a sugarcane genetic map were sought through restriction fragment length polymorphism (RFLP) markers. Twenty-two probes were screened, of which two generated single-dose markers, allowing the mapping of a single allele of scAspAT, encoding aspartate aminotransferase, and two alleles of scGS2, encoding plastidic GS. Because of the economic and environmental consequences of inefficient N fertiliser application, the development of sugarcane cultivars with improved NUE is essential. Since variation for NUE exists, especially in unimproved sugarcane varieties, this may be achieved through traditional breeding methods by screening existing breeding populations under limiting N supply. Additionally, an improved understanding of the genetic basis of variation for NUE in sugarcane should be pursued by further analysis of candidate gene response to changing N availability by screening widely varying cane species for differences in gene expression, enzyme activity and metabolite profiles. The further addition of candidate gene locations to sugarcane genetic maps will aid both future marker-assisted selection in breeding, and a fundamental understanding of genetic control of NUE variation. Through the development of sugarcane cultivars with improved NUE and an enhanced knowledge of the genetic control underpinning sugarcane N physiology, concerns regarding high N fertiliser applications may be mitigated and sustainability ensured.

The feasibility of using optical sensors and non-nitrogen limiting reference crops to determine post-emergent nitrogen fertilizer requirements of canola was evaluated. Normalized difference vegetation index was well suited for estimating yield potential and nitrogen status. Although sensor-based nitrogen management was generally agronomically feasible for canola, the economic benefits of doing so remain uncertain because of the added cost of applying post-emergent nitrogen. / February 2008

This thesis tested the hypothesis that nitrogen use efficiency of subirrigated potted chrysanthemum (Chrysanthemum morifolium Ramat.) can be improved by managing the NO3- status of the plant. Replacement of NO3- with water one week prior to flower development was the most effective method of reducing tissue NO3- content and improving the nitrogen usage index, as compared to various combinations of NO3- and Cl-. Shoot or flower dry mass and N content were unaffected and the medium electrical conductivity was reduced. Supplying N in the NH4+ form in combination with NO3- did not affect nitrogen use indices. Reducing N supply improved various indices of nitrogen use efficiency, with a slight loss of quality. Elimination of NO3- prior to flower development and reduction in N supplied are effective strategies for improving nitrogen use efficiency in subirrigated potted chrysanthemums without sacrificing quality. / Cecil Delworth Foundation

The feasibility of using optical sensors and non-nitrogen limiting reference crops to determine post-emergent nitrogen fertilizer requirements of canola was evaluated. Normalized difference vegetation index was well suited for estimating yield potential and nitrogen status. Although sensor-based nitrogen management was generally agronomically feasible for canola, the economic benefits of doing so remain uncertain because of the added cost of applying post-emergent nitrogen.

The feasibility of using optical sensors and non-nitrogen limiting reference crops to determine post-emergent nitrogen fertilizer requirements of canola was evaluated. Normalized difference vegetation index was well suited for estimating yield potential and nitrogen status. Although sensor-based nitrogen management was generally agronomically feasible for canola, the economic benefits of doing so remain uncertain because of the added cost of applying post-emergent nitrogen.

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.