AN ABSTRACT OF THE THESIS OF BRENT C. SUNDERLAGE, for the Master of Science degree in Plant, Soil, and Agricultural Systems, presented on March 8, 2017, at Southern Illinois University Carbondale. TITLE: LATE APPLICATION NITROGEN ON CORN IN SOUTHERN ILLINOIS AND SOIL PROPERTIES AFFECTING AMMONIA VOLATILIZATION FROM UREA FERTILIZER MAJOR PROFESSOR: Dr. Rachel L. Cook In corn (Zea mays L.) production systems, typical nitrogen fertilization occurs either before planting or after crop emergence, as late as the V6 stage. Since the majority of nitrogen uptake does not occur until V10 through R1, delaying nitrogen fertilization until V10 may reduce potential for early season soil N transformations and losses, while sustaining crop yields. A two-year study, conducted across three southern Illinois locations, evaluated the effects of various late sidedress nitrogen applications and enhanced efficiency fertilizers on corn yield and residual mineral soil N. The various nitrogen treatments compared: rates from 0-224 kg N ha-1; sources of urea and 32% UAN, with and without urease inhibitors 0.09% N-(n-butyl) thiophosphoric triamide (NBPT) as Agrotain® Ultra (AT) and 0.06% NBPT + 0.02% N-(n-propyl) thiophosphoric triamide (NPPT) as Limus® (L), and polymer-coated urea (ESN®); application timings at planting, V6, V10, and VT; placement either dribble applied, broadcasted, or injected. Across sites and years, late (V10) nitrogen split applications generally resulted in corn yields greater than or equal to the same total nitrogen rate applied at planting. Most late N treatment differences varied between sites and years, but 56 kg N ha-1 as broadcasted UAN at planting with 112 kg N ha-1 as broadcasted urea, either with or without AT or L at V10 were on average highest yielding treatments among sites in both years, with 16% greater yield than 168 kg N ha-1 as broadcasted UAN at planting. Urease inhibitors did not enhance yield in most instances, likely due to sufficient incorporating rainfall shortly after application. The effects of urease inhibitors used with late-application nitrogen on corn yield and actual ammonia volatilization remained ambiguous. Residual soil mineral nitrogen concentrations between 0-30 cm after harvest in the late nitrogen treatments did not elicit water quality concerns. Furthermore, ammonia volatilization from surface applied urea is controlled by many interrelated soil properties as well as environmental conditions. However, conclusions about the influence of soil properties on ammonia volatilization differ according to geographies and are not well established across a wide range of soil types. A laboratory soil incubation experiment measured the effects of soil properties on ammonia volatilization over 7 days from surface-applied urea and the efficacy of three urease inhibitors: Agrotain® Ultra (AT) as 0.09% NBPT, Limus® (L) as 0.06% NBPT + 0.02% NPPT, and NutriSphere-N® (NS) 30% calcium salt of maleic-itaconic copolymer among 83 soil surface samples from across the United States with a wide range of soil properties. The soil properties evaluated were: total exchange capacity, 1:1 CaCl2 pH, organic matter, buffering capacity, clay content, and urease activity. In Urea (R2 = 0.69) and Urea + NS (R2 = 0.62) models, total exchange capacity, clay, and buffering capacity significantly reduced ammonia volatilization, and organic matter significantly increased ammonia volatilization, while 1:1 CaCl2 pH and urease activity were non-significant. Clay, organic matter, and buffering capacity were correlated to total exchange capacity. Total exchange capacity was the strongest predictor and best consolidated variable to predict N loss of urea. In Urea + AT (R2 = 0.54) and Urea + L (R2 = 0.67) models, ammonia volatilization was significantly reduced at lower 1:1 CaCl2 pH and total exchange capacity, and all other soil properties were non-significant. The NBPT in Urea + AT and Urea + L likely decayed more rapidly under acidic soil conditions, resulting reduced NBPT efficacy and greater N loss at lower pH. Urea + AT and Urea + L reduced volatilization significantly by 18.2 percentage points compared to Urea or Urea + NS, and there were no significant differences between Urea + AT and Urea + L (α = 0.05). On average, NutriSphere-N® did not reduce volatilization.

A necessidade da adubação nitrogenada no milho e as perdas significativas de N que podem ocorrer, tanto do solo, como pela folhagem das plantas, são fatores que elevam os custos de produção. Contudo, com a possibilidade de aplicação do N em cobertura em diferentes estádios fenológicos da cultura do milho e, como o N pode ser perdido na forma de amônia e as plantas apresentam a capacidade de absorver NH3 da atmosfera pela folhagem, torna-se interessante a quantificação dessa via de ganho de N nos agrossistemas em diferentes estádios de desenvolvimento das culturas, com a finalidade de proporcionar maior aproveitamento do nutriente pelas plantas. Nesse contexto, objetivou-se: i) avaliar a época de aplicação da ureia em cobertura no milho que proporcione maior aproveitamento do N do fertilizante e produtividade de grãos; ii) mensurar a absorção foliar de NH3 oriunda da ureia aplicada na superfície do solo em diversos estádios fenológicos do milho, e verificar a correlação entre a quantidade de NH3 absorvida e a área foliar da cultura. O estudo foi desenvolvido no bairro rural de Tanquinho, município de Piracicaba, SP, nas safras 2011/12 e 2012/13. Foram desenvolvidos dois experimentos em campo, em delineamento experimental de blocos ao acaso, com quatro repetições. O solo da área experimental é classificado como Latossolo Vermelho Distrófico, manejado em sistema convencional de preparo do solo. No primeiro experimento foi quantificado o aproveitamento do N do fertilizante pela cultura, a produção de fitomassa seca da parte aérea em diversos estádios fenológicos, bem como a produtividade de grãos, em função dos tratamentos testados, a saber: cinco épocas de aplicação de ureia (140 kg ha-1 de N) em cobertura nos estádios fenológicos V4, V6, V8, V10 e V12, e um controle sem adubação de cobertura. No segundo experimento, foi quantificada a área foliar e a absorção da amônia volatilizada da ureia aplicada em bandejas contendo o mesmo solo da área experimental, para que não fosse exposto ao sistema radicular de plantas de milho, em função de cinco tratamentos (épocas de aplicação - idem ao primeiro experimento). Os resultados foram submetidos à análise de variância (p<=0,05) e à comparação das médias pelo teste de Tukey. Não houve diferença entre os tratamentos quanto ao acúmulo de fitomassa seca da parte aérea em todos os estádios fenológicos avaliados. Do mesmo modo, não houve incremento na produtividade de grãos com a aplicação de N em cobertura em diferentes estádios fenológicos. Por outro lado, a aplicação de N em cobertura nos estádios mais precoces (V4 ou V6) proporcionou maior recuperação do N do fertilizante, chegando a valores de 53 %. Na média das duas safras, o nitrogênio volatilizado da ureia que foi absorvido pelas plantas apresentou valores de 3,4, 5,5, 6,2, 9,0 e 14,8 %, respectivamente, nos estádios V4, V6, V8, V10 e V12; aproximadamente 90 % do N absorvido pela folhagem foram acumulados nas folhas e apenas 10 % nos colmos. Houve alta correlação entre a área foliar e a porcentagem de amônia absorvida pelas folhas (r = 0,93, p<=0,05). Isto ocorreu porque a área foliar representa a superfície de contato da planta com a amônia da atmosfera, confirmando a hipótese de que a maior área foliar reflete em maior absorção foliar percentual de amônia / The need for nitrogen fertilization of corn crop and the significant losses of N that can occur both from soil and plants foliage are factors that increase production costs. However, with the possibility of sidedress application of N at different corn growth stages and considering that N can be lost as ammonia, and that plants have the capacity to uptake NH3 from the atmosphere by the foliage, it is interesting to measure this pathway of N uptake in agricultural systems in different stages of crop development, in order to provide greater N fertilizer recovery by plants. In this context, this study aimed to: i) evaluate the urea sidedress timing in corn that provides the greater N fertilizer recovery and grain yield; ii) measure the foliar uptake of NH3 volatilized from urea applied on the surface at different corn growth stages, and to evaluate the correlation between the amount of NH3 absorbed and corn leaf area. The study was performed in Piracicaba, State of São Paulo, during the growth seasons of 2011/12 and 2012/13. Two field experiments were performed in experimental design of randomized blocks with four replications. The soil of experimental area is classified as Rhodic Haplustox, cultivated under conventional tillage system. In the first experiment, N fertilizer recovery by crop, dry matter yield in different growth stages and grain yield were evaluated as a function of five urea sidedress timing (140 kg ha-1 N), represented by growth stages V4, V6, V8, V10 and V12, and a control without N application. In the second, leaf area was measured and the absorption of volatilized ammonia from urea applied in trays containing the same soil of the experimental area, to avoid that N was exposed to the corn roots, according to five treatments (application times - same as the first experiment). The data were submitted to analysis of variance (p<=0.05) and comparison of means by Tukey test. There was no difference among treatments for dry matter accumulation of shoots in all growth stages. Similarly, there was no increase in grain yield with the N application at different growth stages. However, the N application in the early stages (V4 or V6) provided greater N fertilizer recovery, reaching values of 53 %. In average, the nitrogen volatilized recovered by plants presented values of 3.4, 5.5, 6.2, 9.0 and 14.8 %, respectively, in V4, V6, V8, V10 and V12; approximately 90 % of N absorbed by foliage were retained in the leaves and only 10 % in the stalks. There was a high correlation between leaf area and the percentage of ammonia absorbed by the leaves (r = 0.93, p<=0.05). This occurred because the leaf area is the contact surface of the plant with atmospheric ammonia, confirming the hypothesis that the greater leaf area reflects in greater percentage of leaf ammonia absorption

A necessidade da adubação nitrogenada no milho e as perdas significativas de N que podem ocorrer, tanto do solo, como pela folhagem das plantas, são fatores que elevam os custos de produção. Contudo, com a possibilidade de aplicação do N em cobertura em diferentes estádios fenológicos da cultura do milho e, como o N pode ser perdido na forma de amônia e as plantas apresentam a capacidade de absorver NH3 da atmosfera pela folhagem, torna-se interessante a quantificação dessa via de ganho de N nos agrossistemas em diferentes estádios de desenvolvimento das culturas, com a finalidade de proporcionar maior aproveitamento do nutriente pelas plantas. Nesse contexto, objetivou-se: i) avaliar a época de aplicação da ureia em cobertura no milho que proporcione maior aproveitamento do N do fertilizante e produtividade de grãos; ii) mensurar a absorção foliar de NH3 oriunda da ureia aplicada na superfície do solo em diversos estádios fenológicos do milho, e verificar a correlação entre a quantidade de NH3 absorvida e a área foliar da cultura. O estudo foi desenvolvido no bairro rural de Tanquinho, município de Piracicaba, SP, nas safras 2011/12 e 2012/13. Foram desenvolvidos dois experimentos em campo, em delineamento experimental de blocos ao acaso, com quatro repetições. O solo da área experimental é classificado como Latossolo Vermelho Distrófico, manejado em sistema convencional de preparo do solo. No primeiro experimento foi quantificado o aproveitamento do N do fertilizante pela cultura, a produção de fitomassa seca da parte aérea em diversos estádios fenológicos, bem como a produtividade de grãos, em função dos tratamentos testados, a saber: cinco épocas de aplicação de ureia (140 kg ha-1 de N) em cobertura nos estádios fenológicos V4, V6, V8, V10 e V12, e um controle sem adubação de cobertura. No segundo experimento, foi quantificada a área foliar e a absorção da amônia volatilizada da ureia aplicada em bandejas contendo o mesmo solo da área experimental, para que não fosse exposto ao sistema radicular de plantas de milho, em função de cinco tratamentos (épocas de aplicação - idem ao primeiro experimento). Os resultados foram submetidos à análise de variância (p<=0,05) e à comparação das médias pelo teste de Tukey. Não houve diferença entre os tratamentos quanto ao acúmulo de fitomassa seca da parte aérea em todos os estádios fenológicos avaliados. Do mesmo modo, não houve incremento na produtividade de grãos com a aplicação de N em cobertura em diferentes estádios fenológicos. Por outro lado, a aplicação de N em cobertura nos estádios mais precoces (V4 ou V6) proporcionou maior recuperação do N do fertilizante, chegando a valores de 53 %. Na média das duas safras, o nitrogênio volatilizado da ureia que foi absorvido pelas plantas apresentou valores de 3,4, 5,5, 6,2, 9,0 e 14,8 %, respectivamente, nos estádios V4, V6, V8, V10 e V12; aproximadamente 90 % do N absorvido pela folhagem foram acumulados nas folhas e apenas 10 % nos colmos. Houve alta correlação entre a área foliar e a porcentagem de amônia absorvida pelas folhas (r = 0,93, p<=0,05). Isto ocorreu porque a área foliar representa a superfície de contato da planta com a amônia da atmosfera, confirmando a hipótese de que a maior área foliar reflete em maior absorção foliar percentual de amônia / The need for nitrogen fertilization of corn crop and the significant losses of N that can occur both from soil and plants foliage are factors that increase production costs. However, with the possibility of sidedress application of N at different corn growth stages and considering that N can be lost as ammonia, and that plants have the capacity to uptake NH3 from the atmosphere by the foliage, it is interesting to measure this pathway of N uptake in agricultural systems in different stages of crop development, in order to provide greater N fertilizer recovery by plants. In this context, this study aimed to: i) evaluate the urea sidedress timing in corn that provides the greater N fertilizer recovery and grain yield; ii) measure the foliar uptake of NH3 volatilized from urea applied on the surface at different corn growth stages, and to evaluate the correlation between the amount of NH3 absorbed and corn leaf area. The study was performed in Piracicaba, State of São Paulo, during the growth seasons of 2011/12 and 2012/13. Two field experiments were performed in experimental design of randomized blocks with four replications. The soil of experimental area is classified as Rhodic Haplustox, cultivated under conventional tillage system. In the first experiment, N fertilizer recovery by crop, dry matter yield in different growth stages and grain yield were evaluated as a function of five urea sidedress timing (140 kg ha-1 N), represented by growth stages V4, V6, V8, V10 and V12, and a control without N application. In the second, leaf area was measured and the absorption of volatilized ammonia from urea applied in trays containing the same soil of the experimental area, to avoid that N was exposed to the corn roots, according to five treatments (application times - same as the first experiment). The data were submitted to analysis of variance (p<=0.05) and comparison of means by Tukey test. There was no difference among treatments for dry matter accumulation of shoots in all growth stages. Similarly, there was no increase in grain yield with the N application at different growth stages. However, the N application in the early stages (V4 or V6) provided greater N fertilizer recovery, reaching values of 53 %. In average, the nitrogen volatilized recovered by plants presented values of 3.4, 5.5, 6.2, 9.0 and 14.8 %, respectively, in V4, V6, V8, V10 and V12; approximately 90 % of N absorbed by foliage were retained in the leaves and only 10 % in the stalks. There was a high correlation between leaf area and the percentage of ammonia absorbed by the leaves (r = 0.93, p<=0.05). This occurred because the leaf area is the contact surface of the plant with atmospheric ammonia, confirming the hypothesis that the greater leaf area reflects in greater percentage of leaf ammonia absorption