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.

<div>Increasing the capability of maize hybrids to use nitrogen (N) more efficiently is a common goal that contributes to reducing farmer costs and limiting negative environmental impacts. However, development of such hybrids is costly and arduous due to the repeated need for laborious field and laboratory measurements of whole-plant biomass and N uptake in large early-stage breeding programs. This research evaluated alternative in-season methodologies, including field-based physiological measurements and hyperspectral remote imagery, as surrogate or predictive measures of important end-of-season N efficiency parameters. </div><div><br></div><div>Differences in the genetic potential of 285 hybrids (derived from test crosses to a single tester) with respect to N Internal Efficiency (NIE, grain yield per unit of accumulated plant N) were investigated at two Indiana locations in 2015. The hybrids (representing both early and late maturity groups) were grown at one low N rate and a single plant density. Germplasm sources included USDA, Dow AgroSciences, and “control” checks. Various secondary traits (plant height, stalk diameter, LAI, green leaf counts, and SPAD measurements) were evaluated for their potential role as surrogate measurements for N metrics at maturity (R6) such as plant N content or NIE. Four band (RGB, NIR) multispectral airborne remote sensing imagery at R1 and R3/R4 was also collected. The key findings were: 1) identification of the 10 highest and 10 lowest ranked hybrids for each maturity group in both grain yield and NIE categories, 2) the discovery of 5 top performing hybrids which had both high NIE and high yield, 3) strong correlations of leaf SPAD (at R1 and R2/R3) to grain yield or plant N at R6, 4) none of the surrogate measurements were significantly correlated to NIE, and 5) vegetation indices (NDVI and SR) from the remote imaging were not predictive of hybrid differences in yields or whole plant N content at R6. From these results we concluded genetic potential exists among current maize germplasm for NIE breeding improvements, but that more in-depth investigations were needed into other surrogate measures of relevant N efficiency traits in hybrid comparisons. </div><div><br></div><div>Next, hyperspectral imaging was investigated as a potential predictor of agronomic parameters related to N Use Efficiency (NUE, understood here as grain yield relative to applied N fertilizer input). Hyperspectral vegetation indices (HSI) were used to extract the image features for predicting N concentration (whole plant N at R6, %N), Nitrogen Conversion Efficiency (biomass per unit of plant N at R6, NCE), and NIE. Images were collected at V16/V18 and R1/R2 by manned aircraft and unmanned aerial vehicles (UAVs) at 50 cm spatial resolution. Nine maize hybrids, or a subset, were grown under N stress conditions with two plant densities over three site years in either 2014 or 2017. Forty HSI-based mixed models were analyzed for their predictability relative to the ground reference values of %N, NCE, and NIE. Two biomass and structural indices (HBSI1_682,855 and HBSI2_682,910 at R1) were predictive of NCE values and capably differentiated the highest and lowest ranked NCE hybrids. The highest prediction accuracy for NIE was achieved by two biochemical indices (HBCI_8515,550 at both V16 and R1, and HBCI9_490,550 at R1). These also allowed for hybrid differentiation of the highest and lowest ranked NIE hybrids. From these results, we concluded that accurate end-season prediction of hybrid differences in NCE and NIE was possible from mid-season hyperspectral imaging (yet not for %N). Furthermore, the quality of the predictions was dependent on image timing, actual HSI, and the targeted N parameter at maturity. </div><div><br></div><div>One benefit to hyperspectral imaging is that it can provide greater discrimination of imaged materials through its narrow, contiguous bands. However, the data are highly correlated in some ranges. This problem was mitigated through the use of partial least squares regressions (PLSR) to predict the three N parameters from the field data described previously. Data were divided into train and test; then ten-fold cross validation was performed. The twelve models evaluated included those with 89 image bands of 5 nm widths and a selected, reduced set of hyperspectral bands as predictors. The key findings were that PLSR models based on V16 and R1 images provided accurate predictions for final whole-plant %N (R² = 0.73, CV = 11%; R² = 0.68, CV = 10%) and NCE at R6 (R² = 0.71, CV = 10%; R² = 0.73, CV = 12%) but not NIE. Additionally, accurate hybrid differentiation was possible with the combination of hyperspectral imaging and PLSR at R1 to predict %N and NCE values at R6 stage. </div><div><br></div><div>The PLSR and HSI results from this research showed that hyperspectral imaging has the potential for prediction of NUE parameters through non-destructive remote sensing at a broad scale. Additional validation is needed through the study of other genotypes and locations. Nevertheless, practical application of these methods through the integration into early stage breeding programs may allow the early identification of the highest and lowest ranked hybrids providing data-driven decisions for selecting genotypes. Implementation of improved imaging approaches may drive the increased development of maize hybrids with superior NUE. </div><div><br></div>

The PROTEOLYSIS 6 (PRT6) branch of the N-end rule pathway is a well-characterized negative regulator of flooding and low oxygen tolerance in plants. This study investigated the role of this pathway in adaptation to salinity stress in Arabidopsis and maize via physiological and molecular characterization of Arabidopsis prt6-1 and maize prt6 MU insertion mutants, respectively. Our study demonstrated that the loss of function mutation of prt6 in Arabidopsis activated hormonal and transcriptional responses associated with adaptation to salinity stress, enhancing high salt tolerance at seed germination, seedling, and adult plant stages. Our data also indicated that salinity tolerance conferred by the prt6 mutation is attributed to increased mRNA abundance of key transcriptional factors in ABA-dependent (AREB/ABFs) and independent (DREBs) pathways, together with the dominant expression of downstream dehydrins. Furthermore, this study revealed that the prt6 mutation enhances ethylene and brassinosteroid responses, resulting in restricted Na+ accumulation in roots and shoots as well as increased expression of dehydrin genes such as RD29A and RD29B. Maize prt6 mutant plants, contrary to our observation in Arabidopsis, showed lower seed germination, primary root elongation, and shoot biomass growth along with increased malondialdehyde (MDA) accumulation under high salt. Moreover, maize prt6 mutants exhibited reduced grain yield and yield-related components under high salt. These results indicate that PRT6 functions as a negative regulator for salinity tolerance in Arabidopsis, whereas this gene plays a positive role in salinity tolerance in maize. In wheat, we compared two genotypes with contrasting nitrogen-use-efficiency (NUE), VA08MAS-369 and VA07W-415, to dissect physiological and molecular mechanisms underlying NUE regulation. Our agronomic data revealed that line 369 maintained yield and yield-related parameters and exhibited greater NUE indexes relative to line 415 under N deficient conditions. Furthermore, our analyses suggested that the significantly higher nitrogen use efficiency (NUE) in line 369 could be attributed to the greater N uptake efficiency in this genotype. In fact, line 369 was able to maintain the development of root systems under N limitation. Consistently, genes encoding high-affinity nitrate transporters such as TaNRT2.1 and TaNRT2.2 were expressed more abundantly in the roots of line 369 than line 415 at limited N. Overall, the results of this study characterized physiological and molecular phenotypes associated with high N uptake efficiency in line 369. This is useful information for the development of new wheat accessions with improved NUE. / Doctor of Philosophy / In coastal areas, sea-level rise increases the chances of saltwater intrusion into cultivable lands, making a hostile environment for crop growth and production by imposing flooding and salinity stresses simultaneously. Identification of central regulators that regulate the adaptation to both flooding and salinity is a critical step for the development of new crop genotypes with enhanced tolerance to these stresses. Previous studies have characterized the function of the PROTEOLYSIS 6 (PRT6) gene in adaptation to flooding stress in plants. This study assessed whether this gene is involved in adaptation to salinity stress in Arabidopsis and maize by evaluating the growth and survival of their respective prt6 mutants under high salt. Consistent with the flooding tolerance data, our study showed that the PRT6 gene also functions as a negative regulator of salinity stress tolerance in Arabidopsis. The prt6 mutation in Arabidopsis activated the key transcriptional and hormone response pathways associated with adaptation to both salinity/osmotic stress and sodium toxicity, expressed as enhanced tolerance to excess salt at seed germination, seedling, and adult plant stages. In maize, disruption of the PRT6 gene decreased seed germination, primary root elongation, and shoot biomass growth under high salt, which is opposite to our observations in Arabidopsis. Additionally, the maize mutant plants encountered more oxidative stress, as demonstrated by the higher accumulation of malondialdehyde (MDA) under high salt. Moreover, maize prt6 mutants exhibited reduced grain yield under high salt. Overall, these results indicate that disruption of the PRT6 gene confers increased tolerance to high salt in Arabidopsis, whereas it conversely reduced salinity tolerance in maize. In wheat, we compared two genotypes with distinct nitrogen use efficiency (NUE), VA08MAS-369 and VA07W-415, to determine critical traits involved in NUE regulation. Our study showed that grain yield and yield-related parameters were significantly higher in line 369 than line 415 under low N. Moreover, high NUE in line 369 was attributed to efficient N uptake in this genotype under limited N. Our root architecture analysis demonstrated that line 369 was able to maintain root depth, volume, and thickness even under N limitation. Consistently, line 369 highly induced expression of genes associated with nitrogen transport at low N. Altogether, this study identified key traits involved in high NUE in wheat, facilitating the breeding of new wheat genotypes with enhanced NUE.

Flooding is a major environmental stress that damages agricultural production worldwide. Using the key regulator of submergence tolerance in rice, SUB1A, as a model, we have advanced our understanding of how plants coordinate transcriptional, hormonal, and metabolic responses to submergence. However, the contribution of SUB1A to recovery from sublethal submergence is still unknown. This study revealed SUB1A's additional role in the recovery phase: promotion of a rapid return to normal metabolic status upon desubmergence through quick recovery of photosystem II photochemistry and carbon fixation. We also investigated how SUB1A differentially regulates adaptive responses in two functionally distinct leaves, growing and mature leaves, under submergence. This study revealed that rice plants promote rapid carbohydrate and nitrogen remobilization and transport in mature leaves, supporting quick elongation growth of growing leaves. In the presence of SUB1A, these metabolic processes were suppressed in mature leaves, resulting in the avoidance of energy starvation in the source tissues. In growing leaves, SUB1A enhanced the accumulation of abscisic acid, but repressed the level of ACC, a precursor of ethylene, contributing to the restriction of elongation growth and leaf senescence in the sink tissues. Application of nitrogen fertilizers is a necessary step to maintain high grain yield in cereals, but plants absorb only 30-50% of supplied N. Wheat, one of the most widely grown crops in the world, requires a high level of nitrogen application to maintain grain yield and protein content. In this study, we investigated how nitrogen input affects the accumulation of major N and C compounds and expression of genes associated with N and C metabolism in flag leaves of wheat. We used two genotypes with distinct nitrogen use efficiencies (NUE), VA08MAS-369 and VA07W-415. VA08MAS-369 displayed higher grain yield, stover biomass, and stover N content at low N, which results from greater N-uptake efficiency in this genotype. Consistently, high N-uptake efficiency was reflected by increased mRNA accumulation of nitrate transporters and their transcriptional regulator, NAC2, in flag leaves at the post-anthesis stage. Overall, this study advanced our knowledge of the important mechanisms in plant response to flooding and N limitation in these key staple cereals. / PHD / Flooding is a serious natural disaster that damages agricultural production worldwide. Rice is a wetland plant that adapts to flooding conditions, but its tolerance to flooding varies in cultivars. Functional characterization of a submergence tolerance gene, SUB1A, has led to our understanding of various mechanisms that regulate flooding tolerance in rice and other plants. However, the role of SUB1A in plant recovery from mild submergence stress is still unknown. This study revealed that SUB1A contributes to the maintenance of photosynthetic performance and provides protection from sudden exposure to high light after floodwater subsides. These processes aid in a quick recovery from reduced metabolic activities. We also investigated the role of SUB1A in adaptive responses in growing and mature leaves of rice plants during submergence. Mature and growing leaves looked similar, but their functional importance was distinct. In general, mature leaves serve as energy production tissues through photosynthesis. The excess carbohydrate and nitrogen reserves produced in mature leaves are transferred to growing leaves that consume a large amount of energy for rapid growth. This study revealed that SUB1A restricted the consumption and transfer of energy reserves in mature leaves to avoid an energy crisis. In growing leaves, SUB1A suppressed elongation growth and leaf senescence through the proper regulation of key hormones controlling these processes. Nitrogen (N) fertilizer application is a necessary process to improve agricultural productivity in many crops. However, crops only take up 30-50% of applied N, resulting in water and air pollution and altered ecosystems. Improvement of plant N use efficiency (NUE) is one of the ways to address this issue. This study compared two soft red winter wheat lines with contrasting NUE under low and normal N supply. It was concluded that one line, VA08MAS-369, had higher grain yield and N uptake efficiency under low N supply. Our physiological and molecular study indicated that VA08MAS-369 significantly promoted N remobilization in leaves and N transport to grains after flowering under limited N. This study advanced our understanding of NUE mechanisms in winter wheat, which may aid the development of new cultivars with enhanced NUE through modern biotechnological approaches.

Master of Science / Department of Agronomy / David B. Mengel / Nitrogen fertilizers play an essential role in agricultural production in Kansas, particularly in row crops such as corn (Zea mays L.) and grain sorghum (Sorghum bicolor (L.) Moench). A good portion of the corn and grain sorghum grown in Kansas is typically grown using no-till production systems. These systems leave a large amount of surface residue on the soil surface, which can lead to ammonia volatilization losses from surface applied urea-containing fertilizers and immobilization of N fertilizers placed in contact with the residue. Leaching and denitrification can also be a problem on some soils. Current nitrogen prices, as well as concerns over environmental stewardship, are forcing producers to make smarter choices in the fertilizer products used as well as when and how the materials are applied, to optimize their nitrogen use efficiency. A common practice throughout Kansas is to apply N fertilizers prior to planting, sometimes up to 6 month prior to planting. What affect does this practice have on nitrogen availability to the growing crop? Current Kansas State University (KSU) soil test fertilizer recommendations assume 50% nitrogen use efficiency. This means of every pound of nitrogen applied only half will be utilized by the plant and turned into valuable grain. Possible solutions to help increase nitrogen use efficiency are the use of nitrogen additives which are currently on the market and claim to reduce nitrogen loss through denitrification and volatilization as well as the use of timing and application of fertilizers to further increase nitrogen use efficiency. The objective of this study is to evaluate different N fertilizer products, as well as additives and application practices and determine whether specific combinations can improve yield and N use efficiency of no-till corn and grain sorghum. The long-term goal of this study is to quantify some of these relationships to assist farmers in selecting specific combinations that could enhance yield and profitability. In this study five tools for preventing N loss were examined: fertilizer placement, or placing N below the soil surface or in bands on the residue-covered soil surface to reduce immobilization and/or volatilization; use of a urease inhibitor Agrotain (NBPT) that blocks the urease hydrolysis reaction that converts urea to ammonia and potentially could reduce ammonia volatilization; the use of a commercially available additive, Agrotain Plus, that contains both a nitrification inhibitor (DCD) and a urease inhibitor to slow both urea hydrolysis and the rate of ammonium conversion to nitrate and subsequent denitrification or leaching loss; use of a commercial product NutriSphere-N, which claims urease and nitrification inhibition; and the use of a polyurethane plastic-coated urea to delay release of urea fertilizer until the crop can use it. The ultimate goal of using these practices or products is to increase N uptake by the plant and enhance yield. An important measurement that was developed for this research was the use of a greenleaf firing index which used the number of green leaves below the ear at pollination as a key measurement in determining the effectiveness of fertilizer placement, application method, application timing and the use of nitrogen additives. If significant differences in lower leaf nitrogen stress are found, the potential exists to further develop this index and correlate differences observed with key parameters of nitrogen uptake such as ear-leaf nitrogen concentration, total nitrogen uptake and grain yield. Results observed from this research show that the potential to increase nitrogen use efficiency and reduce nitrogen loss do exist with the use of certain nitrogen additives, application methods and application timing. When conditions are conducive for nitrogen loss the use of currently available tools to protect nitrogen from volatilization, immobilization and/or denitrification loss significantly increased yields in the corn experiments. Results from the grain sorghum research indicate that when N losses limit yield, the use of products and practices enhance yield. In locations where nitrogen loss is minimal or low yields limit nitrogen response, the use of these practices was not found to be helpful.

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.

A aplicação de substâncias húmicas (SH) em misturas com ureia pode aumentar a eficiência do uso de N (EUN) em soqueiras e também melhorar a produtividade de cana-de-açúcar por favorecer a atividade de proteínas relacionadas ao processo de absorção de nutrientes. Neste sentido, experimentos de laboratório, casa-de-vegetação e de campo foram desenvolvidos com os seguintes objetivos: (i) Avaliar e caracterizar SH extraídas de turfa em misturas com soluções de N-ureia, quantificando teores de N-mineral e a volatilização de NH3. (ii) Quantificar a produtividade de colmos e atributos tecnológicos da cana-de-açúcar adubados com doses de SH, doses de ureia e misturas de doses ureia+SH em experimentos de campo. (iii) Estudar a eficiência de recuperação do 15N-ureia em misturas com SH e ácidos húmicos (AH) aplicados às folhas de cana-de-açúcar. (iv) Estimar a biomassa, acúmulo de nutrientes (N, P, K), particionamento (folhas secas, colmo e ponteiros) e a relação (N:P, N:K) destes nutrientes nas soqueiras de cana-de-açúcar com diferentes níveis de produtividade. Em experimento de laboratório, após a extração, purificação e caracterização das SH, foram preparadas as misturas com doses crescentes de ureia. Constatou-se a hidrólise de parte do N-amídico, transformando-o em N-NH4+ e que a concentração de ureia nas misturas pode interferir na hidrólise da mesma. A mistura da solução de ureia com SH (15% de N), com o pH corrigido (pH=7), possibilitou a redução nas perdas de NH3 por volatilização do solo. Em estudos de campo, com doses de N-ureia (0, 25, 50, 75 e 100 kg ha-1), doses de SH (0, 100, 200, 300 e 400 L ha-1) e mistura destas doses: ureia+HS, verificou-se que em três áreas estudadas, duas houve resposta aos fertilizantes nitrogenados ureia e misturas ureia+SH. Em geral, as doses de ureia+SH promoveram aumento significativo de 6% de rendimento de colmos (TCH) e incremento de 4,5% da produção de açúcar (Mg ha-1) comparando somente com a aplicação de doses de ureia. Em dois experimentos de casa-de-vegetação foram realizadas aplicações às folhas de cana-de-açúcar de ureia, ureia+AH e ureia+SH. Na média dos dois experimentos, a recuperação de 15N (EUN) foi maior para a ureia + SH (49%) em comparação com ureia + AH (43%) e apenas ureia (37%). A fertilização foliar com ureia + SH aumentou o valor total de proteína (7, 24, 17 e 93%) quando comparado com aplicação somente de ureia após 96, 192, 360 e 720 horas da aplicação foliar, respectivamente. O particionamento dos nutrientes (N, P e K) nos órgãos da cana-de-açúcar (folha seca, ponteiros e colmos) indicam que maiores produtividades de colmo foram obtidas com elevados acúmulos desses nutrientes no ponteiro e maior equilíbrio da relação de N:P (6:1) e N:K (0,5:1). A mistura de ureia com SH é uma estratégia viável que promove aumento de rendimento de colmos, maior produção de açúcar e ainda aumento da EUN. No entanto, para sistemas com altas produtividades é necessário observar a relação e o equilíbrio dos nutrientes principalmente nos componentes com alta atividade fotossintética (ponteiros de cana-de-açúcar). / Humic substances (HS) in mixture with urea can improve N use efficiency (NUE) and sugarcane yield when applied in ratoon. In this regard, lab experiments, greenhouse and field studies have been developed with the following goals: (i) Evaluate and characterize HS extracted from peat in mixtures with urea solutions, quantifying N-mineral content and NH3 volatilization. (ii) Quantify sugarcane yield and technological attributes of sugarcane ratoon fertilized with HS rates, urea rates and mixtures of the fertilizers: HS+urea on field experiments. (iii) Evaluate the recovery efficiency of 15N-urea mixture with HS and humic acid (HA) applied on sugarcane leaf. (iv) To estimate the biomass, nutrient uptake (N, P, K), partitioning (dry leaves, stem and tops) and the ratio (N:P,N:K) of these nutrients in the sugarcane ratoon with different levels of productivity. In the lab, after extraction, purification and characterization of HS, mixtures with rates of urea were performed. It was observed that this mixture was promoted by urea hydrolysis transforming into N-NH4+ and concentration of N-urea may interfere in the hydrolysis. The experiment to evaluate the volatilization was observed that the mixture of HS and urea solution with a fixed pH (pH = 7) led to the reduction in losses by volatilization of NH3. In field studies, N-urea rates (0, 25, 50, 75 and 100 kg ha-1), HS rates (0, 100, 200, 300 and 400 L ha-1) and mixing these doses: urea + HS. In two of the three studies there were response to the urea nitrogen fertilizers, urea and mixtures HS+urea. In general, urea doses + HS promoted significant increase of 6% yield of stalks (TCH) and 4.5% increase in sugar production (Mg ha-1) compared only with the application of urea. In greenhouse experiments applications were performed via foliar urea, urea+HA and urea+HS. The average of the two experiments, the recovery of 15N (NUE) was added to the HS + urea (49%) compared with HA+urea (43%) and only urea (37%). The foliar application of urea+HS increased the total protein value (7, 24, 17 and 93%) compared with the application of urea for only 96, 192, 360 and 720 hours following fertilizer application, respectively. In addition, there was a nutrient partitioning study (N, P and K) in the components of sugarcane (dry leaf, tops and stems). It was observed for nutrient partitioning process that dry leaves had lower nutrient content (N, P, and K) and broader N:P/N:K ratios when compared with tops and stalks. Greater sugarcane yield and narrowed N:P ratio (6:1) were documented for tops of sugarcane when increasing both N and P content. However, for high systems yields it is necessary check the ratio and balance of nutrients in the components with high photosynthetic activity (tops of sugarcane).

A utilização de inibidores de nitrificação pode ser uma alternativa interessante para aumentar a eficiência do uso do fertilizante nitrogenado em diversas culturas, porém, essa alternativa vem sendo pouco estudada em condições de solo e clima do Brasil. Assim, objetivou-se com esse trabalho avaliar a eficiência do inibidor de nitrificação fosfato de 3,4-dimetilpirazol (DMPP) em três solos com gradiente textural, bem como avaliar o destino do nitrogênio (N-NO3-, N-NH4+ e 15N) no solo, a absorção e o uso do nitrogênio (N-total e 15N) nas plantas de algodão. Três experimentos foram montados e desenvolvidos. No primeiro foi efetuada a incubação do solo em condições de laboratório para avaliar a inibição da nitrificação pelo DMPP aplicado na forma de ureia e sulfonitrato de amônio (SNA) em três solos (Neossolo Quartzarênico - NQ, Latossolo Vermelho Amarelo - LVA, Latossolo Vermelho - LV). No segundo experimento plantas de algodão foram cultivadas em colunas de lixiviação com os mesmos solos, recebendo ureia e sulfonitrato de amônio, com e sem DMPP como fonte de N. Foram avaliados a produção de matéria seca, o acúmulo de nutrientes nas plantas, a eficiência de uso do N pelo algodoeiro, a lixiviação e a quantidade de N mineral no solo após o cultivo do algodão por 60 dias. No terceiro experimento, plantas de algodão foram cultivadas também em colunas lixiviação, porém, com um solo de textura média (Latossolo Vermelho Amarelo), o qual recebeu três doses de N em cobertura (50, 100 e 150 kg ha-1 de N) na forma de ureia marcada no isótopo 15N, com e sem DMPP. Foram avaliados a produção de matéria seca, teor de N e recuperação do N aplicado na planta, lixiviação de N, teor de N-total, nítrico e amoniacal no solo, e recuperação do N aplicado no solo após o cultivo do algodão, por 90 dias. Melhores resultados foram obtidos com a aplicação do DMPP em ureia em relação ao SNA. No experimento de incubação, o DMPP foi capaz de manter menor o teor de nitrato nos três solos analisados. A nitrificação do N na ureia foi mais rápida comparado ao SNA, o que permitiu melhor desempenho do inibidor na ureia em dois dos três solos estudados. O efeito do DMPP aumentou seguindo a seguinte ordem: NQ>LVA>LV. O inibidor foi mais eficiente nos solos com menor teor de argila e matéria orgânica. O uso do DMPP em ureia aplicada no solo arenoso (NQ) reduziu significativamente a lixiviação de N e aumentou a produção de matéria seca, a eficiência do uso do N e a absorção de fósforo pela planta. No solo de textura média (LVA), sob irrigação intensa, o DMPP reduziu significativamente as perdas de N do sistema e aumentou a recuperação do 15N aplicado na planta e no solo, o que, porém, não se traduziu em maior produção de matéria seca provavelmente pelo N não ter sido limitante, devido à mineralização da matéria orgânica. As atividades das enzimas redutase do nitrato e urease não diferiram entre tratamentos com e sem DMPP / The use of nitrification inhibitors may be an interesting alternative to increase nitrogen fertilizer use efficiency in different crops, although it has been little studied in soil and climate conditions of Brazil. This study aimed to evaluate the efficiency of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in three soils with textural gradient (represented by clay percentage), as well as to evaluate the fate of soil nitrogen (N-NO3-, N-NH4+ and 15N), nitrogen uptake, and N-use efficiency (total-N and 15N) by cotton plants. Three experiments were set and carried out in a controlled environment. In the first one, a laboratory incubation was performed to evaluate the inhibition of nitrification by DMPP applied to urea and ammonium sulfate nitrate (ASN) in three soils (Typic Quartzipsammnet - NQ, Typic Hapludox - LVA, Rhodic Hapludox - LV). In the second experiment, leaching columns with the same soils were planted with cotton receiving ammonium sulfate nitrate and urea with or without DMPP as nitrogen source. It were evaluated plant dry matter yield (shoot plus roots), nutrient uptake and nitrogen use efficiency by cotton plants, as well as the nitrogen leaching, and mineral nitrogen amount in the soil after cotton growth, for 60 days. In the third experiment, leaching columns with a medium textured soil (LVA) were planted with cotton and received three nitrogen rates in topdressing (50, 100 and 150 kg ha-1) as 15N-urea with and without DMPP. The production of dry matter, nitrogen content and recovery of applied N in the plant and soil, as well as the nitrogen leaching, total nitrogen, nitrate and ammonium in the soil were evaluated after cotton growth for 90 days. Best results were obtained with the application of DMPP to urea than in ASN. In the incubation experiment, the DMPP was able to maintain lower nitrate content in the three soils. The nitrification of nitrogen from urea was faster than the one from ASN, which allowed a better performance of the inhibitor in the urea in two out of three soils analyzed. The effect of DMPP increased in the following order: NQ> LVA> LV. The inhibitor was more effective in soils with lower clay and organic matter contents. The use of DMPP in urea applied on the sandy soil (NQ) significantly reduced N leaching and increased dry matter production, nitrogen use efficiency and phosphorus uptake by cotton plants. In a medium textured soil (LVA) under intense irrigation, DMPP significantly reduced N losses in the system and increased the recovery of applied 15N in plant and soil, which however did not translate into higher dry matter production because nitrogen was probably not limiting. The activity of the enzymes nitrate reductase and urease were not different between treatments with and without DMPP

A aplicação de substâncias húmicas (SH) em misturas com ureia pode aumentar a eficiência do uso de N (EUN) em soqueiras e também melhorar a produtividade de cana-de-açúcar por favorecer a atividade de proteínas relacionadas ao processo de absorção de nutrientes. Neste sentido, experimentos de laboratório, casa-de-vegetação e de campo foram desenvolvidos com os seguintes objetivos: (i) Avaliar e caracterizar SH extraídas de turfa em misturas com soluções de N-ureia, quantificando teores de N-mineral e a volatilização de NH3. (ii) Quantificar a produtividade de colmos e atributos tecnológicos da cana-de-açúcar adubados com doses de SH, doses de ureia e misturas de doses ureia+SH em experimentos de campo. (iii) Estudar a eficiência de recuperação do 15N-ureia em misturas com SH e ácidos húmicos (AH) aplicados às folhas de cana-de-açúcar. (iv) Estimar a biomassa, acúmulo de nutrientes (N, P, K), particionamento (folhas secas, colmo e ponteiros) e a relação (N:P, N:K) destes nutrientes nas soqueiras de cana-de-açúcar com diferentes níveis de produtividade. Em experimento de laboratório, após a extração, purificação e caracterização das SH, foram preparadas as misturas com doses crescentes de ureia. Constatou-se a hidrólise de parte do N-amídico, transformando-o em N-NH4+ e que a concentração de ureia nas misturas pode interferir na hidrólise da mesma. A mistura da solução de ureia com SH (15% de N), com o pH corrigido (pH=7), possibilitou a redução nas perdas de NH3 por volatilização do solo. Em estudos de campo, com doses de N-ureia (0, 25, 50, 75 e 100 kg ha-1), doses de SH (0, 100, 200, 300 e 400 L ha-1) e mistura destas doses: ureia+HS, verificou-se que em três áreas estudadas, duas houve resposta aos fertilizantes nitrogenados ureia e misturas ureia+SH. Em geral, as doses de ureia+SH promoveram aumento significativo de 6% de rendimento de colmos (TCH) e incremento de 4,5% da produção de açúcar (Mg ha-1) comparando somente com a aplicação de doses de ureia. Em dois experimentos de casa-de-vegetação foram realizadas aplicações às folhas de cana-de-açúcar de ureia, ureia+AH e ureia+SH. Na média dos dois experimentos, a recuperação de 15N (EUN) foi maior para a ureia + SH (49%) em comparação com ureia + AH (43%) e apenas ureia (37%). A fertilização foliar com ureia + SH aumentou o valor total de proteína (7, 24, 17 e 93%) quando comparado com aplicação somente de ureia após 96, 192, 360 e 720 horas da aplicação foliar, respectivamente. O particionamento dos nutrientes (N, P e K) nos órgãos da cana-de-açúcar (folha seca, ponteiros e colmos) indicam que maiores produtividades de colmo foram obtidas com elevados acúmulos desses nutrientes no ponteiro e maior equilíbrio da relação de N:P (6:1) e N:K (0,5:1). A mistura de ureia com SH é uma estratégia viável que promove aumento de rendimento de colmos, maior produção de açúcar e ainda aumento da EUN. No entanto, para sistemas com altas produtividades é necessário observar a relação e o equilíbrio dos nutrientes principalmente nos componentes com alta atividade fotossintética (ponteiros de cana-de-açúcar). / Humic substances (HS) in mixture with urea can improve N use efficiency (NUE) and sugarcane yield when applied in ratoon. In this regard, lab experiments, greenhouse and field studies have been developed with the following goals: (i) Evaluate and characterize HS extracted from peat in mixtures with urea solutions, quantifying N-mineral content and NH3 volatilization. (ii) Quantify sugarcane yield and technological attributes of sugarcane ratoon fertilized with HS rates, urea rates and mixtures of the fertilizers: HS+urea on field experiments. (iii) Evaluate the recovery efficiency of 15N-urea mixture with HS and humic acid (HA) applied on sugarcane leaf. (iv) To estimate the biomass, nutrient uptake (N, P, K), partitioning (dry leaves, stem and tops) and the ratio (N:P,N:K) of these nutrients in the sugarcane ratoon with different levels of productivity. In the lab, after extraction, purification and characterization of HS, mixtures with rates of urea were performed. It was observed that this mixture was promoted by urea hydrolysis transforming into N-NH4+ and concentration of N-urea may interfere in the hydrolysis. The experiment to evaluate the volatilization was observed that the mixture of HS and urea solution with a fixed pH (pH = 7) led to the reduction in losses by volatilization of NH3. In field studies, N-urea rates (0, 25, 50, 75 and 100 kg ha-1), HS rates (0, 100, 200, 300 and 400 L ha-1) and mixing these doses: urea + HS. In two of the three studies there were response to the urea nitrogen fertilizers, urea and mixtures HS+urea. In general, urea doses + HS promoted significant increase of 6% yield of stalks (TCH) and 4.5% increase in sugar production (Mg ha-1) compared only with the application of urea. In greenhouse experiments applications were performed via foliar urea, urea+HA and urea+HS. The average of the two experiments, the recovery of 15N (NUE) was added to the HS + urea (49%) compared with HA+urea (43%) and only urea (37%). The foliar application of urea+HS increased the total protein value (7, 24, 17 and 93%) compared with the application of urea for only 96, 192, 360 and 720 hours following fertilizer application, respectively. In addition, there was a nutrient partitioning study (N, P and K) in the components of sugarcane (dry leaf, tops and stems). It was observed for nutrient partitioning process that dry leaves had lower nutrient content (N, P, and K) and broader N:P/N:K ratios when compared with tops and stalks. Greater sugarcane yield and narrowed N:P ratio (6:1) were documented for tops of sugarcane when increasing both N and P content. However, for high systems yields it is necessary check the ratio and balance of nutrients in the components with high photosynthetic activity (tops of sugarcane).

Made available in DSpace on 2014-06-11T19:33:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-07-13Bitstream added on 2014-06-13T19:04:51Z : No. of bitstreams: 1 rocha_rjs_dr_jabo.pdf: 825439 bytes, checksum: 2af7dcdaa1a7cdb8311729451dfa2d74 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O nitrogênio é nutriente absorvido em maiores quantidades na cultura do milho e o que proporciona maiores produtividades de grãos, sendo seu uso no sistema solo-planta alterado pelo sistema de cultivo utilizado. Com o objetivo de avaliar o efeito de sistemas de cultivo e doses de nitrogênio na produção de matéria seca, nitrogênio na planta, nitrogênio foliar, produtividade de grãos e eficiência do nitrogênio no milho, foi implantado experimento de campo nos anos de 2008 e 2009, em um Argissolo Vermelho-Amarelo, distrófico, sob irrigação. Utilizou-se o delineamento experimental em parcelas subdivididas, com oito repetições. As parcelas foram constituídas pela semeadura direta (SD) e plantio convencional (PC). Nas subparcelas, foram aplicadas seis doses de N (0; 40; 80; 120; 160 e 200 kg ha-1) na forma de uréia. Em 2009 a fim de avaliar a velocidade de decomposição e liberação do nitrogênio do feijão utilizado como cobertura morta, esses resíduos foram acondicionados em sacolas de náilon, as quais foram dispostas sobre o solo nas parcelas correspondente a SD e o seu conteúdo analisado em intervalos de 25 dias, até 100 dias após sua instalação. A adubação nitrogenada aumentou significativamente as variáveis relacionadas com a produtividade, sendo que a SD proporcionou a maior produção de matéria seca da parte aérea, matéria seca do grão, nitrogênio na parte aérea, nitrogênio do grão, produtividade de grãos, eficiência de absorção e uso do nitrogênio. A faixa de suficiência de nitrogênio na folha variou de 25,7 a 28,4 g kg-1. As doses máximas econômicas em 2008 e 2009 foram respectivamente de 125 e 160 kg ha-1 N / Nitrogen is the nutrient absorbed in largest quantities in maize which provides more grain yields, and its use in soil-plant system is modified by the tillage system utilized. Aiming to evaluate the effect of cropping systems and nitrogen rates on dry matter production, nitrogen in the plant, leaf nitrogen, grain yield and nitrogen efficiency in maize, field experiment was established in 2008 and 2009 in a dystrophic red-yellow Argisoil under irrigation. The split-plot experimental design were used with eight replications. The plots were established by no-tillage (NT) and conventional tillage (CT). Subplots were set in six levels of N(0, 40, 80, 120, 160 and 200 kg ha-1) as urea. In 2009, in order to assess the speed of decomposition and nitrogen release from the bean plant used as cover crop, plant residues were packaged in nylon bags, which were arranged on the ground in the plots corresponding to NT and its contents examined at intervals of 25 days until 100 days after its installation. The nitrogen fertilization increased significantly the variables related to productivity, being that no-tillage provided the highest dry matter yield on shoot, dry matter of grain, nitrogen on shoot, grain nitrogen, grain yield, nitrogen uptake efficiency and nitrogen use efficiency. The sufficiency range of leaf nitrogen ranged from 25.7 to 28.4 g kg-1. The maximum economic rates in 2008 and 2009 season were respectively 125 and 160 kg ha-1N