Estado nutricional e adubação em plantios de Eucalyptus brassiana S.T. Blake X Eucalyptus grandis W. Hill ex Maiden na Amazônia Oriental.

Abstract

The mineral nutrition of plants at adequate levels is essential to maintain vigorous growth in addition to high productivity. In this sense, new monitoring standards have been established, such as, for example, the assessment of nutritional status through leaf diagnosis interpreted by the methods of Kenworthy, DRIS and CND. In addition, it is believed that the use of technologies, such as those involving machine learning, such as artificial neural networks (ANNs) that provide reliable estimates capable of assisting in decision making regarding the level of fertilization that provides sustainability to the managed planting. In this context, the Amazon region, more specifically the southeastern region of Pará, is considered a silvicultural frontier and, consequently, the researches that guide the subject in question are considered incipient. Thus, the objective of the research was to evaluate the nutritional status and fertilization levels of a clonal plantation of Eucalyptus brassiana x Eucalyptus grandis in the Eastern Amazon. For the analysis of the nutritional status, the Kenworthy, DRIS and CND methods were used. To define the maximum productive potential, 9 trees were cubed, dividing them into 3 classes of circumferences measured at 1.3 m from the ground: from 17 to 28.5 cm (Class I), from 28.6 to 40.2 cm (Class II) and 40.3 to 52 cm (Class III). In the analysis with artificial neural networks, 60% of the database were separated for training and 40% for validation. In which 20 networks were trained with three multilayer perceptron RNA configurations. To test the levels of maximum productive potential in the field, 6 plots of 125m² each were installed, systematically distributed. The treatments used were arranged through a randomized block design, consisting of six treatments and four repetitions: T1 - 0%, T2 - 50%, T3 - 75%, T4 - 100%, T5 - 125% and T6 - 150% fertilization respectively. Fertilizers were applied in two stages, one at 10 and the other at 90 days after planting the seedlings, in which the survival variables, growth of the stem diameter, crown diameter and total height were measured. It was found that the techniques used to assess nutritional status were similar. In the compartmentalization of nutrients, it was observed that only the leaf contents are not sufficient to provide differences in the biomass production of the Annual Average Increment in Volume - IMAvol. Thus, these levels are not intended to be used as nutritional standards of the studied hybrid. However, by analyzing the nutritional status with RNAs, it is possible to reliably estimate the volume of the trees by the content of nutrients allocated in the compartments of the trees and by the leaf contents. The methodologies for assessing the nutritional status of Eucalyptus sp. provided concordant results and can be used reliably under the conditions of the study. The level of fertilization that used the maximum productive potential was the one that generated the highest productivity in the field trial, thus being able to be taken as a guide for fertilization programs in the Eastern Amazon.