ABSTRACT Grazing 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-NH4+), nitrate (N-NO3-), 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-NO3- stocks in the surface and subsurface layers and of N-NH4+ 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-NH4+, respectively. At 70 DAPS, the behavior was inverse, and LG presented the highest N-NO3- stock and the MG and IG the lowest N-NO3- 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.

Resumo 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.

Abstract 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.