Estado nutricional, níveis críticos foliares pelos métodos DRIS e CND e sazonalidade de nutrientes para a cultura do pessegueiro na região sul do Brasil

Abstract

The assessment of nutritional status is of paramount importance for the peach tree, being a key part of the success of the fertilization program of the culture throughout the cycle. Leaf analysis, based on the assumption of a positive relationship between the doses of nutrients provided, is the one that best reflects the nutritional status of a crop. However, its success depends, among other factors, on the sampling of leaves and on the interpretation of the values obtained. The present work aimed at the nutritional characterization of the peach tree in the southern region of Brazil to serve as a substrate for policies and interventions by research and extension; the application of the DRIS and CND methods to evaluate the nutritional status of the crop and development of updated reference values as a tool to improve the precision and efficiency of the fertilizer program of the producers, in addition to the validation and evaluation of the efficiency of the obtained DRIS norms; the evaluation of the seasonal fluctuation of nutrients in the leaves and leaf sampling time in order to anticipate the collection time. For nutritional characterization and application of DRIS and CND methods, samples collected in commercial peach orchards in three municipalities of Rio Grande do Sul in the 2018 and 2019 cycles were used, where 319 leaf tissue samples were analyzed for their macro and micronutrients (N, P, K, Ca, Mg, B, Fe, Mn, Cu and Zn). For the nutritional characterization of the crop, the samples were divided into two subpopulations and distributed into frequency classes and classified according to the sufficiency ranges used in the region. The DRIS and CND norms were obtained and from which the critical levels of each nutrient for the culture in the region were calculated, which were compared with the regional and international literature. The validation of the DRIS standards was based on a database of 101 leaf tissue samples analyzed for their macronutrient content. The evaluation of seasonality and leaf sampling time in peach trees was carried out from 180 tissue samples, obtained on 15 collection dates between 60 and 201 days after full flowering, with each date composed of 12 repetitions. With the nutritional characterization of the crop, it was concluded that there is no relationship between productivity and levels of foliar macro and micronutrients alone, with the need for further studies regarding the adequacy and revision of the sufficiency ranges in the studied region, mainly N and K, in addition to the observation of a nutritional imbalance in the region's orchards. The concentration of nutrients showed a significant correlation with the respective DRIS indices. The foliar concentration considered optimal by the DRIS method indicated similarity for the nutrients N, Ca, Mg, B and Cu and dissimilarity for P, K, Mn and Zn in comparison with the values adopted as a regional reference. The relationship between nutritional balance index and production showed statistical significance, as well as the relationship between DRIS indices and foliar contents of macronutrients, confirming the efficiency of DRIS norms. The CND method was efficient to obtain the optimal levels of foliar nutrients, and they are applicable for the nutritional diagnosis of peach trees. Leaf nutrient contents in peach trees showed stability in the period from 60 to 120 days after full flowering, indicating that leaf sampling for nutritional diagnosis can be anticipated.