Variação temporal de propriedades físicas do solo e do crescimento de eucalipto em diferentes sistemas de preparo

Abstract

This study aimed at verifying, over time, the alterations in the physical properties of a Red-Yellow Ultisol and in the growth of Eucalyptus grandis, cultivated with the use of different methods of soil preparation. The experiment was carried out in the experimental area that belongs to the State Foundation for Agricultural Research (FEPAGRO), in Santa Maria, RS. The experimental design consisted of a randomized block design with three replications and four treatments, namely: manual tillage (CM), chisel plow (Esc), chisel plow with harrows (EG) and rotary hoe (ER). In order to ascertain the variation of the physical properties of the soil, sampling data of the soil obtained prior to the application of the treatments as well as three, twelve and seventy-two months after the treatments were used. Growth assessment was carried out at 3, 6, 9, 12, 74 and 81 months of stand age. The physical properties total porosity, macroporosity, microporosity and bulk density were obtained through samples collected in row and inter-row seeding, at depths 0.00-0.10; 0.10-0.20; 0.20-0.30; 0.30-0.40 m. Soil resistance to penetration (RP) was determined up to 0.50 m of soil depth, each 0.20 m perpendicularly distant from row seeding. Humidity at the moment of data collection of RP was determined at depths 0.00-0,10; 0.10-0.20; 0.20-0.30; 0.30-0.40 and 0.40-0.50 m. Size distribution of water-stable aggregates and of organic matter of soil were assessed at depth 0.05 m. The plant parameters evaluated were: the root distribution and growth, which is obtained by measuring the height and diameter of trees, volume, basal area and tree survival. The replacement of native grasses by planting Eucalyptus grandis, cultivated with the use of different methods of soil preparation, did not degrade the structural quality of the soil over time. The effects of Esc, still evident at twelve months after the treatments ceased to exist seventy-two months, indicating a prior soil reconsolidation. Soil preparation provided the improvement in the physical properties of the soil for the initial growth of Eucalyptus grandis, however, with the passage of time, the growth of trees became homogeneous among treatments. The effect of tillage on root systems, evaluated in depth, was more pronounced at eight months old plants.