N-fertilizer (N-urea) utilization by sugarcane foliar-applied in the period of maximum crop growth as a complement to soil fertilization

A cana-de-açúcar é uma das principais culturas agrícolas produzidas no Brasil e tem grande importância em nível mundial não só por ser produtora de sacarose, mas especialmente, devido ao aumento na demanda por combustíveis renováveis, como o etanol, para diminuir a emissão de gases do efeito estufa. O nitrogênio é o segundo elemento mineral mais demando pela cana-de-açúcar, aplicado anualmente no solo para que se obtenha um canavial longevo e produtivo, contudo, grande parte desse permanece no solo, podendo ser perdido para o ambiente. Na adubação nitrogenada foliar, a recuperação do N-fertilizante pela planta é maior, quando comparado com a adubação feita no solo, e permite que haja sincronia entre as exigências das plantas de cana-de-açúcar e a aplicação do N-fertilizante. Nesse contexto, pode ser inferido que a adubação nitrogenada via foliar em complemento a aplicação do nutriente no solo proverá o equilíbrio entre produção de biomassa e o meio-ambiente trazendo benefícios para a sustentabilidade nos agrossistemas com cana-de-açúcar com ganhos financeiros. Para validar essa hipótese, experimentos foram conduzidos em condição controlada e em campo. Primeiramente, objetivou-se avaliar a anatomia das folhas de cana-de-açúcar para que variedades contrastantes fossem utilizadas nos experimentos visando a adubação foliar com ureia. Quatorze variedades de cana-de-açúcar foram selecionadas, sendo consideradas as mais plantadas no sudeste do Brasil, e agrupadas em função das características anatômicas foliares e relacionadas com os mecanismos de absorção foliar. Quatro variedades contrastantes quanto às variáveis anatômicas foram selecionadas e utilizadas em experimento conduzido em casa-de-vegetação para avaliar a recuperação e a redistribuição do N-fertilizante aplicado via foliar (15N-ureia) em função da concentração de nitrogênio na solução (8, 16, 24 e 36 % 15N-ureia). As variedades diferiram quanto a velocidade de absorção do 15N-ureia. Aos 5 dias após a adubação nitrogenada foliar houve um máximo de absorção do nitrogênio, alcançando até 78 % de recuperação do 15N-ureia. Até os 20 dias ocorreu a redistribuição do 15N-ureia, sendo o colmo e as folhas não expandidas os drenos de nitrogênio. Uma das variedades utilizadas no experimento em casa-de-vegetação foi selecionada e utilizada nos experimentos em campo para validar esse manejo da adubação nitrogenada. Dois experimentos em campo foram conduzidos, por três anos, para avaliar a produtividade e a qualidade do caldo da cana-de-açúcar quando realizado a adubação nitrogenada via foliar, no período de máximo crescimento da planta, em complemento a aplicação do nutriente no solo. Quinze tratamentos foram instalados sendo esses 0 + 0, 40 + 0, 60 + 0, 80 + 0, 120 + 0, 160 + 0, 0 + 12, 0 + 24, 0 + 36, 40 + 12, 40 + 24, 40 + 36, 60 + 12, 60 + 24, e 60 + 36 kg ha-1 N aplicados, respectivamente, no solo e por via foliar. No somatório dos três anos, ambas as áreas foram responsivas à adubação nitrogenada e demonstraram que é possível reduzir a dose de nitrogênio aplicada no solo sem causar prejuízos na produtividade e na qualidade do caldo da cana-de-açúcar. No 2º ano dos experimentos, 15N-ureia foi aplicado às folhas e a recuperação do N-fertilizante pela planta foi, na média, de 53 %, diferindo entre as áreas. Concluísse que o uso da adubação nitrogenada via foliar é uma importante ferramenta para adequar o manejo da adubação nitrogenada na cana-de-açúcar visando obter um canavial longevo, produtivo e em equilíbrio com o meio-ambiente.Sugarcane is one of the main agricultural crops produced in Brazil and is important worldwide not only because it produces sucrose, but especially because of the increased demand for renewable fuels, e.g., ethanol, to reduce the greenhouse gases emission. Nitrogen is the second most demanded mineral essential element by sugarcane, applied annually to the soil to obtain a long-lived and productive sugarcane field, however, much of it remains in the soil and can be lost to the environment. In foliar nitrogen fertilization, the N-fertilizer recovery by the plant is greater, when compared to soil nitrogen fertilization, and allows for synchrony between the sugarcane plant requirements and the N-fertilizer application. In this context, it can be inferred that foliar nitrogen fertilization in addition to the soil nutrient application will provide a balance between biomass production and the environment, bringing benefits to sustainability in sugarcane agrosystems with financial gains. To validate this hypothesis, experiments were conducted under controlled conditions and in the field. Firstly, the objective was to evaluate the sugarcane leaves anatomy so that contrasting varieties could be used in experiments aiming at foliar fertilization with urea. Fourteen sugarcane varieties were selected, the most planted in southeastern Brazil, and grouped according to leaf anatomical characteristics and related to leaf absorption pathways. Four contrasting varieties in terms of anatomical variables were selected and used in an experiment carried out in greenhouse conditions to evaluate the N-fertilizer recovery and redistribution applied to the leaves (15N-urea) as a function of the nitrogen concentration in the solution (8, 16, 24 and 36 % 15N-urea). Sugarcane varieties differed in the absorption rate of 15N-urea. At 5 days after foliar nitrogen fertilization there was, a maximum of nitrogen absorption, reaching up to 78 % of 15N-urea recovery. Up to 20 days there was a 15N-urea redistribution; stalk and not- expanded leaves were the nitrogen sinks. One of the sugarcane varieties used in the greenhouse experiment was selected and used in the field experiments to validate this nitrogen fertilization management. Two field experiments were carried out, for three years, to evaluate the sugarcane biomass production and juice quality when foliar nitrogen fertilization was carried out in the maximum plant growth period as a complement to soil nitrogen fertilization. Fifteen treatments were installed, i.e., 0 + 0, 40 + 0, 60 + 0, 80 + 0, 120 + 0, 160 + 0, 0 + 12, 0 + 24, 0 + 36, 40 + 12, 40 + 24, 40 + 36, 60 + 12, 60 + 24, and 60 + 36 kg ha-1 N applied, respectively, to soil and to the leaves. In the sum of the three years, both sites were responsive to nitrogen fertilization and demonstrated that it is possible to reduce the soil nitrogen fertilization rate without causing damage to sugarcane biomass production and juice quality. In the 2nd year of the experiments, 15N-urea was applied to the leaves and the N-fertilizer recovery by the plant was, on average, 53 %, differing between sites. It is concluded that the use of foliar nitrogen fertilization is an important tool for the adjustment of nitrogen fertilizer management in sugarcane in order to obtain a long-lived, productive, and environment-friendly sugarcane field

Nitrogen fertilizer in sugarcane due to sunn hemp, straw removal and nitrogen rates

O Brasil é o país que possui o maior potencial de crescimento na produção de etanol, podendo esse aumento ser através do incremento na produtividade da cana-de-açúcar ou a partir do uso dos resíduos vegetais, etanol de segunda geração. A recuperação do nitrogênio proveniente do fertilizante pela planta (RNP-fertilizante) é baixa, sendo questionado a importância desse no sistema de colheita sem queima associado à rotação de cultura. Dessa maneira, muito se questiona sobre a possibilidade de redução da dose de N-fertilizante e de remoção da palha do campo no atual sistema de manejo da cana-de-açúcar. Experimentos de campo foram desenvolvidos com os seguintes objetivos: avaliar a RNP-fertilizante, a dinâmica desse nutriente e a resposta da segunda soqueira de cana-de-açúcar à doses de N-fertilizante; e avaliar a RNP-fertilizante, a imobilização do N no solo (RNS) e na palha (RNPa) e os parâmetros produtivos da cana-de-açúcar ao longo do ciclo, na mesma dose de nitrato de amônio, com remoção parcial ou total ou manutenção total da palha em área com e sem plantio de Crotalaria spectabilis sob sistema de plantio direto. O plantio da crotalária na renovação do canavial apresentou pequena influência na segunda soqueira da cana-de-açúcar em sistema de plantio direto. Nos parâmetros produtivos e tecnológicos não houve alteração na produção de açúcar e de colmos, aumentou-se a RNP-fertilizante quando associada à remoção total da palha, não houve interferência na imobilização do N-fertilizante na palha e diminuiu-se a imobilização desse no solo ao final do ciclo. As quantidades de palha deixada sobre o solo também não modificaram os atributos tecnológicos, contudo a presença desse resíduo vegetal favoreceu a produtividade de colmos. A RNP-fertilizante no início da rebrota da cana foi beneficiada pela presença da palha em ambas as áreas a qual não se manteve até a colheita devido à condição climática e aos benefícios do plantio direto. Os resultados indicaram que pode-se reduzir a dose de nitrogênio a fim de aumentar a RNP-fertilizante, não havendo influência da rotação de cultura, e que a palha proporciona diversos benefícios à cultura, como aumento da RNP-fertilizante no início do ciclo na segunda soqueira da cana-de-açúcar, tornando a remoção desse resíduo vegetal inviável.Brazil is the country that has the greatest increase potential in ethanol production, which may be achieved through a rise in the sugarcane yield or from the use of the plant residue\'s waste to produce second generation ethanol. The recovery of the nitrogen from the fertilizer by the plant (NPR-fertilizer) is low when questioning the importance of this in the new sugarcane system (green cane trash blanket) associated with crop rotation. In this case, there are a lot of questions about the possibility of reducing the fertilizer-N rate and about the straw removal from the field in the current management system of sugarcane. Field experiments have been developed with the following aims: to evaluate the NPR-fertilizer, the nitrogen dynamic and the response of the second sugarcane ratoon to the fertilizer-N rates; as well as to evaluate the NPR-fertilizer, the fertilizer-N immobilization in soil (NSR) and straw (NStR), and the productive parameters of sugarcane over the cycle in the same ammonium nitrate rate with partial or total removal or total maintenance of straw in the area with and without planting Crotalaria spectabilis under a no-till system. The planting of sunn hemp in the sugarcane\'s renewal presented little influence in the second sugarcane ratoon under the no-tillage system. In the productive and technological parameters there was no change in sugar and stalk production, NPR-fertilizer increased when associated with total removal of straw, there was no interference in the N-fertilizer immobilization in straw and it decreased the fertilizer-N immobilization in soil at the end of the cycle. The quantities of the straw left on the soil also did not change the technological attributes, however the maintenance of plant residue favored stalk yield. The NPR-fertilizer in the beginning of the sugarcane regrowth was benefited by the straw presence in both areas which did not remain until the harvest due to weather conditions and to the no-till system benefits. The results indicated that the fertilizer-N rate can be reduced in order to increase the NPR-fertilizer without influence of the crop rotation in this parameter and that the straw provides several benefits to the crop such as an increase of NPR-fertilizer in the beginning regrowth of the second sugarcane ratoon, making the straw removal infeasible

Leaf Scorching following Foliar Fertilization of Wheat with Urea or Urea–Ammonium Nitrate Is Caused by Ammonium Toxicity

Foliar fertilization is a potential tool to increase the use-efficiency of nitrogen (N) fertilizers. However, whilst leaf scorching has frequently been reported, the underlying physiological processes are not clear. In the present work, we investigate the intensity of leaf scorching as affected by the balance between ammonium assimilation and accumulation. Leaves were sprayed with urea–ammonium nitrate (UAN) solution without surfactant or applied liquid droplets of urea in different N concentrations with surfactant. UAN solutions without surfactant containing >10% N caused leaf scorching already after 24 h and the severity increased with the N concentration. The same pattern was observed 3 days after the application of urea solutions containing >4% N together with surfactant. The scorching was accompanied by a massive increase in foliar and apoplastic ammonium (NH4+) concentration. Moreover, the activity of glutamine synthetase (GS), most pronouncedly that of the chloroplastic isoform (GS2), decreased a few hours after the application of high N-concentrations. Along with this, the concentration of glutamate—the substrate for GS—decreased. We conclude that leaf scorching is promoted by NH4+ accumulation due to a limitation in N assimilation capacity

Root extracts of Bracchiaria humidicola andSaccharum spontaneum to increase N use by sugarcane

Retaining the mineral N in the form of NH4+ in the soil for a lengthy period is desirable for reducing losses. Furthermore, there is evidence that sugarcane prefers NH4+-N in place of NO3−-N. This study aimed firstly, to evaluate the potential of root extracts of Bracchiaria humidicola andSaccharum spontaneum, in contrast with the DCD (Dicyandiamide) inhibitor, to increase absorption of N by plants fertilized with ammonium sulfate, and secondly, to quantify the emission of N2O fluxes with the use of this inhibitor. The experiment was developed in a glasshouse in an entirely randomized design where four treatments were applied: AS) ammonium sulfate (control); AS+DCD) ammonium sulfate associated with dicyandiamide; AS+BCH) ammonium sulfate associated with root extracts ofBrachiaria humidicola; and AS+SCS) ammonium sulfate associated with root extracts of Saccharum spontaneum. Differences were observed in biomass production in plants 45 and 60 days after fertilization (DAF) and 15 and 60 days in biomass accumulation of roots. The application of AS associated with DCD synthetic inhibitor kept NO3−-N values low throughout the evaluation period, while in other treatments the concentration increased right up to the second evaluation 15 DAF. Sugarcane plants did not benefit from the increased presence of ammoniacal N promoted by DCD. The use of DCD reduced the average flux of N2O during the evaluation period compared to plants receiving AS treatments only, which was not observed when root extracts of B. humidicola and S. spontaneum were used

Legume nitrogen credits for sugarcane production: implications for soil N availability and ratoon yield

One of the steps needed to achieve sustainable bioenergy is to reduce our reliance on synthetic nitrogen (N). Despite the fact that legume cover crops have the potential to increase soil quality and sugarcane (Saccharum spp.) yield, much information is still needed to determine amount of N available from cover crops to sequential ratoon cycles. This study was designed to assess the impacts of sunn hemp (Crotalaria spectabilis) cover crop on soil N dynamics and sugarcane ratoon response to N fertilization during two harvest seasons across three contrasting soil and climatic conditions in southern Brazil. The treatments consisted of cover crop and fallow established prior to sugarcane replanting; in addition to three N-fertilizer rates 60, 120 and 180kgNha(-1) and a 0-N control applied during the first and second ratoons. Although there was increased sugarcane yield (8-13Mgha(-1) in first ratoon and 10-16Mgha(-1) in second ratoon) in plots planted with cover crop, it was not possible to detect significant increases in soil inorganic N, microbial biomass C and Illinois Soil N Test content under cover crop compared with fallow. Cover crop with sunn hemp increased the accumulated two-year yields by 14-25Mgha(-1) at all sites and NUE (Mg stalks kg(-1)N) across all N rates at two sites. Our findings support the conclusion that cover crop did not change the N requirement of succeeding ratoon crops but increases the yield, thereby improving NUE in sugarcane systems1133307322CNPQ - Conselho Nacional de Desenvolvimento Científico e TecnológicoFAPESP – Fundação de Amparo à Pesquisa Do Estado De São Paulo308007/2016-62014/05591-