Exportação de nutrientes em tangerinas produzidas em sistema orgânico no subtrópico brasilero

The knowledge on the amount of nutrients exported by citrus fruit is an adequate tool to estimate nutrient demand reposition and this information about mandarin is very scarce. In this context, the objective of this study was to determine the nutrient content and exportation by mandarin fruits harvest, in an orchard managed under organic production system. An experiment was carried out in an organic orchard of adult mandarin trees (23 years), located in Rio Grande do Sul State (Brazil). The total content of macronutrients and micronutrients was determined in the mandarin fruits and the exportation was estimated by average yields in two seasons (2013/2014 and 2014/2015). The average exportation of macronutrient was 3.3, 2.3, 1.3, 0.4 and 0.3 kg t-1 for N, K, Ca, P and Mg, respectively; and of micronutrients was 6.3, 4.6, 1.5, 0.7 and 0.5 g t-1 for Fe, B, Zn, Mn and Cu, respectively. The N exportation in mandarin fruits does not comply with the current information used for citrus fertilizer recommendations, where the K is the nutrient most exported. Regarding micronutrients, besides the exported amounts vary among the literature, the magnitude order follows the same observed in our study. We propose these new standards for reposition of macronutrients and micronutrients in established mandarin orchards under organic management, contributing to a more accurate fertilizer recommendation.O conhecimento sobre a quantidade de nutrientes exportados por frutas cítricas é uma ferramenta adequada para estimar a reposição de nutrientes, e estas informações para tangerinas são escassas. Nesse contexto, o objetivo deste estudo foi determinar o teor e a exportação de nutrientes pela colheita de frutos de tangerineiras, em um pomar manejado sob sistema orgânico de produção. Um experimento foi realizado em um pomar orgânico de tangerineiras adultas (23 anos), localizado no Rio Grande do Sul, Brasil. O teor total de macronutrientes e de micronutrientes foi determinado nos frutos de tangerina, e a exportação foi estimada pela produtividade média de duas safras (2013/2014 e 2014/2015). A exportação média de macronutrientes foi de 3,3; 2,3; 1,3; 0,4 e 0,3 kg t -1 para N, K, Ca, P e Mg, respectivamente; e de micronutrientes foi de 6,3; 4,6; 1,5; 0,7 e 0,5 g t-1 para Fe, B, Zn, Mn e Cu, respectivamente. A exportação de N pelas tangerinas não condiz com as informações atuais utilizadas para recomendações de adubação em citros, sendo o K o elemento mais exportado. Em relação aos micronutrientes, além de as quantidades exportadas variarem entre a literatura, a ordem de magnitude segue a mesma observada em nosso estudo. Propomos esses novos padrões para reposição de macronutrientes e de micronutrientes em pomares estabelecidos de tangerina sob manejo orgânico, contribuindo para uma recomendação de adubação mais precisa

Nitrogen fertilization in the winter cover crop in soybean production systems : influence of grazing and potassium and phophorus replacement time

O sistema azevém-soja é um dos mais utilizados no subtrópico brasileiro. Muitas vezes, a adubação nitrogenada nesse sistema é negligenciada, pois a planta de soja nutre-se através da fixação biológica de nitrogênio (FBN) e o azevém não é rentabilizado. Contudo, quando a soja expressa o máximo potencial produtivo no ambiente, há maior exportação de N nos grãos do que fixado pela FBN, podendo haver uma depleção dos estoques de N no solo. Uma forma de rentabilizar a adubação nitrogenada do cultivo hibernal é a produção animal em sistema integrado de produção agropecuária. Outra prática que resulta no aumento da produção de massa seca (MS) do azevém, é a adubação de sistema, que neste caso seria a reposição no azevém do P e do K exportado pela soja. O pastejo e adubação de sistemas são ferramentas que associadas à adubação nitrogenada do azevém podem mitigar o balanço negativo de N na soja. Desta forma, o objetivo deste trabalho foi avaliar ao longo das diferentes fases do sistema produtivo azevém-soja o impacto de diferentes doses de N em sistemas pastejados por ovinos ou não e diferentes épocas de reposição de P e K exportados pela soja. O experimento foi realizado em um Plintossolo Argilúvico, no sistema azevém-soja há 3 anos. O delineamento experimental foi de blocos casualizados com três repetições, onde a parcela principal foi composta pelo bifatorial pastejo e época de reposição de P e K e as subparcelas foram as doses de N. No inverno de 2019, foram instaladas subparcelas com doses de N (0, 50, 100, 200 kg N ha-1 ). O aumento da dose de N elevou a produção e o estoque de N na MS e no resíduo do azevém, proporcionando maiores teores de N mineral no solo e a contribuição do N derivado do solo na nutrição nitrogenada da soja, diminuindo o balanço negativo de N da soja. Em ambiente pastejado, houve maior estoque de N mineral no solo ao longo de todas as fases do sistema, além de produzir 14% mais grãos de soja. A adubação de sistemas aumentou a produção de MS do azevém em doses de N inferiores a 200 kg N ha-1 e aumentou em 11% a produtividade da soja. Conclui-se que a adubação nitrogenada no azevém impacta no curto prazo todas as fases do sistema azevém-soja, nos parâmetros de solo e planta, obtendo diferentes respostas de acordo com o manejo da pastagem e da época de reposição de P e K. E ambiente pastejado necessita mais entrada de N no sistema, pois produziu mais soja e teve menor colaboração da FBN na nutrição nitrogenada da soja, em função de maior estoque de N mineral no solo.The ryegrass-soybean system is one of the most used in the Brazilian sub- tropics. Often, nitrogen fertilization in this system is neglected, as the soybean plant is nourished through biological nitrogen fixation (FBN) and ryegrass is not profitable. However, when soybean expresses the maximum productive potential in the environment, there is a greater export of N in the grains than fixed by the FBN, and there may be a depletion of the N stocks in the soil. One way to make the nitrogen fertilization of winter farming profitable is animal production in an integrated agricultural production system. Another practice that results in increased production of ryegrass dry matter (DM), is the system fertilization, which in this case would be the replacement of ryegrass P and K exported by soybeans. Grazing and fertilization of systems are tools that associated with nitrogen fertilization of ryegrass can mitigate the negative balance of N in soybean. Thus, the objective of this work was to evaluate, during the different phases of the ryegrass-soybean production system, the impact of different doses of N in systems grazed by sheep or not and different times of replacement of P and K exported by soybeans. The experiment was carried out in an Argilúvico Plintossolo, in the ryegrass-soybean system for 3 years. The experimental design was a randomized block with three replications, where the main plot was composed by the bifactorial grazing and P and K replacement time and the subplots were the doses of N. In the winter of 2019, subplots were installed with doses of N ( 0, 50, 100, 200 kg N ha-1). The increase in the dose of N increased the production and stock of N in DM and ryegrass residue, providing higher levels of mineral N in the soil and the contribution of N derived from the soil in the nitrogenous nutrition of soybeans, reducing the negative balance of N of soybean. In a grazed environment, there was a greater stock of mineral N in the soil throughout all phases of the system, in addition to producing 14% more soybeans. The fertilization of systems increased the production of DM of ryegrass at doses of N below 200 kg N ha-1 and increased soybean productivity by 11%. It is concluded that nitrogen fertilization on ryegrass impacts in the short term all phases of the ryegrass-soybean system, on soil and plant parameters, obtaining different responses according to pasture management and P and K replacement season. grazed environment needs more N input in the system, as it produced more soy and had less collaboration from FBN in the nitrogen nutrition of soy, due to the greater stock of mineral N in the soil

Liming and grazing intensities effects on soil mineral nitrogen throughout the pasture cycle in a subtropical integrated crop-livestock system

Texto completoGrazing intensity is a preponderant factor for the success of integrated crop-livestock systems (ICLS). Management of grazing intensity impacts soil organic matter (SOM) dynamics, soil reacidification process, and amount and quality of residues added to the ICLS. Consequently, the soil mineral nitrogen (N) forms may present different behavior throughout the pasture cycle, because they are directed linked to SOM and soil acidity dynamics. This study aimed to evaluate the impact of grazing intensities and liming in the temporal variation of acidity and mineral N forms in soil surface (0.00-0.20 m) and subsurface (0.20-0.40 m), throughout the pasture cycle of an ICLS under an Oxisol in the Brazilian subtropics. The study was performed 11 years after the beginning of the field experiment, characterized by the cattle grazing in a winter pasture of oat + ryegrass during the winter and soybean cropping during the summer. The experimental design is randomized block with three replicates, where the grazing intensities are in the plots and liming is the subplots. The grazing intensities were defined as grazing sward height management, being 0.10, 0.20-0.30, and 0.40 m defined as intensive (IG), moderate (MG) and light grazing (LG), respectively. We evaluated the soil ammonium (N-NH 4+ ), nitrate (N-NO 3- ), mineral N and pH at 45, 70, 156 and 192 days after pasture sowing (DAPS). Our results showed that grazing intensities only affected the soil pH at the end of pasture cycle, with MG presenting higher pH than IG and LG, regardless of liming. A decrease of soil N mineral stocks was observed throughout the pasture cycle in all managements, due to the decrease of soil N-NO 3- stocks in the surface and subsurface layers and of N-NH 4+ only in the surface layer. The influence of grazing intensities was only observed for N mineral forms in limed areas before the beginning of grazing. At 45 DAPS, MG and LG presented the highest and the lowest N-NH 4+ , respectively. At 70 DAPS, the behavior was inverse, and LG presented the highest N-NO 3- stock and the MG and IG the lowest N-NO 3- stocks. With such results, it is possible to conclude that there is an influence of grazing intensity and liming in the temporal variation of soil pH and mineral N forms in ICLS and this may be utilized for improvements in N fertilizer management, mainly before the starting of winter grazing