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Abstract "Heft 26"

Freiburger Bodenkundliche Abhandlungen

Schriftenreihe des

Institut für Bodenkunde und Waldernährungslehre
der Albert-Ludwigs-Universität Freiburg i.Br.
Schriftleitung: F. Hädrich

Heft 26

Antonio F.J. Bellote

Nährelementversorgung und Wuchsleistung von gedüngten
Eucalyptus grandis-Plantagen im Cerrado von São Paulo (Brasilien)

Freiburg im Breisgau 1990

ISSN 0344-2691


Brazil has the biggest Eucalyptus plantations of the world. The timber of these plantations is nearly exclusively used for the production of paper and cellulose as well as for the generation of primary energy, the latter above all in the iron and steel industry.

The Federal State of Sao Paulo is the most important Brazilian manufacturer of paper and cellulose obtained from eucalyptus timber.

The productivity of the plantations is rather different, there are increments from 19-72 m3/ha.a. This big variety is due to the different intensities of inorganic fertilizer application.

The main objective of this study was to find out the nutritional condition of differently fertilized Eucalyptus grandis plantations. Hereby the height growth of trees was related to the foliar nutrient content as well as to the nutrient supply of the soil.
A pilot study was necessary to find out the optimal sampling method in order to characterize the nutritional condition. The element contents in leaves were examined depending on tree age, season and crown position. For this purpose 6 plots were chosen which were timbered with plantations of different age (1-6 years) on each plots, 16 dominant trees were determined which were divided into 4 groups with 4 trees each. According to the 4 seasons, samples were taken from one tree groups whereby leaves of the upper, middle and undercrown were collected.

For the main examination, 15 plots with 3-year-old plantations were chosen, situated in 4 regions of the Federal State of Sao Paulo. These plots had been fertilized with N-P-K at the time of planting.  From each plot, 20 leaves each were taken  from the middle crown of 15 dominant trees. The samples were taken during summer from December, 20, 1987 until January, 30, 1988. Besides the leaves, samples of soil in dephts of 0-10, 10-20 and 20-30 cm were taken.

By means of chemical analyses macro- and micronutriente elements (N, P, K, Ca, Mg, S, B, Fe, Mn, Zn) and Al were determined as total contents of leaves; the exchangeable cations K+, Ca+2, Mg+2, H+ and Al+3 of the soil were extracted with 0,5 n NH4Cl-solution; phosphorus with 1% citric acid and humus with In K2 Cr207-solu-tion. In addition the pH-value of soil in water and in CaCl2-solution was determinated.

The pilot study showed, that the foliar content with the nutrient elements P, K, Ca and Mg varies depending on the tree age. The nutrient content is mainly influenced, however, by seasonable differences.

In summer, the foliar nutrient contents are maximal. Calcium and magnesium makes an exception among 4-year-old trees and N and Mg among 6-year-old trees, which are supplied best during autumn. There are also differences with respect to the nutrient contents of leaves from the various crown parts. With N and Mg, depending on tree age, there are significant differences with respect to nutrient content of the upper crown part; thus, leaves from the middle crown appeared most representative. Among K such differences do not occur. For this element, the leaves of any crown part are representative. This fact is similar among P and Ca, except with 6-year-old trees (for P) and 3-year-old trees (for Ca). In these two age classes significant differences exist between the nutrient contents of the different crown parts.

According to statistical results - leaves of 3-year-old trees have maximal nutrient content in summer. During that season, the variation coefficient of the content of all elements is also at the  lowest. During summer, the contents of nutrient elements of the leaves, taken from various crown parts do not show any significant differences, so that during that season any compartment crown many serve as sample.

The results of the main study in order to determine the nutritional status of the 3-year-old tree reveal, that the supply with S, Fe, Mn and Zn is sufficient. These elements do not restrict growth of Eucalyptus grandis.

The supply of the trees with nitrogen varies between latent deficiency (among the lowest trees) and optimal values (among the highest trees). In spite of those deviations, nitrogen is not the mainly responsible for the height growth of the trees but can easily become as such. Fertilization with this element is recommended for plots with the lowest growth.

The foliar contents of phosphorus are above the value, regarded as optimal in literature. The results presented demonstrate however, that already values of more than 0,9 mg/g d.m. are enough for a sufficient supply with, phosphorus.

The majority of the plots shows a rather low content of P in soil. The growth of trees can be improved by raising the fertilization.
Potassium and Mg restrict the growth most in the studied area. Optimal contents of the tree are for Mg 2.6-3.2 mg/g d.m. and for K 7.5-8.3 mg/g d.m.. This level is reached only on a part of the study area.

As threshold values in the soil (exchangeable fraction) can be seen 1.0 / µeq/g for Mg and 0.45 / µeq/g for K.
Among Ca und B, negative correlations were noticed, which are to be interpreted as dilution effects. The content available with exchangeable  calcium  in  the  soil is  enough  to  guarantee  a sufficient supply with this element for the trees. The latosols soils show higher values than the sand soils (Areias Quartzosas) .

The Al content among leaves are in a normal range and there are no problems with this element on any fields. The soils are very rich in exchangeable Al so that trees grow better the more they take up Al. Al-toxicity was not observed.

The humus content of the soils is of great impostance, expecially for the cation-exchange capacity. Therefore there is a significant correlation with the growth of the trees.

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