Site preparation, initial growth and soil erosion in Eucalyptus grandis plantations on steep terrain

Abstract

In Brazil, and especially in the Paraiba Valley region, Southeastern Brazil, Eucalyptus plantations are expanding to high declivity areas formerly occupied by degraded pastures, due to the limited agricultural value of these topographies and their forestry aptitude. The objective of this study was to evaluate the effect of different methods of soil preparation and water loss by erosion, and on the initial development of clonal plantations of Eucalyptus grandis in areas of high slope. The experiment was installed in a 3 x 2 factorial design, with three intensities of soil preparation (manual pitting, mechanical pitting and downhill subsoiling) and two systems of residue management (with and without harvest residues), with 4 blocks, in a fine, kaolinitic, thermic type Kanhapludults soil, with an average inclination of 20.3%. Soil loss and growth of the forest were measured during one year, between March 2004 and February 2005. In two treatments, namely manual pitting and maintenance of the residues (MAY) and subsoiling without residues (SUN); erosion was measured directly through the method of the standard-plots, installed in all the replications, with a dimension of 14 x 24 meters. An additional standard plot without soil preparation, residues and cultivation was also installed as a control plot. Erosion measured was grouped and analyzed for three periods (0 to 2, 3 to 7, and 8 to 12 months). In the other treatments, erosion was estimated using models (per period and joint) from multiple linear regression between the erosion observed in the treatments MAY and SUN and independent variables originated from local attributes of each plot and from the pins method. The initial growth of Eucalyptus was determined by estimating soil cover and aboveground biomass at 3, 6, 9 and 12 months. In the standard-plots, there was more erosion in the treatment SUN than in MAY, with mean values of 12.96 and 2.40 Mg ha(-1) year(-1), respectively. For both treatments erosion decreased with the growth of the forest. As for the residue, its maintenance in the area slightly reduced the growth of E. grandis. Pondering the gains of initial growth and the expected erosion losses; maintenance of the residues on site and mechanical pitting can be identified as the best soil preparation option for such areas.