Soil fertility and growth of <i>Eucalyptus grandis</i> in Brazil under different residue management practices

Abstract

Silvicultural operations such as soil preparation, logging residue management and application of fertilisers can influence soil fertility, and hence nutrient uptake and tree growth. This paper reports the effect of site management practices of minimum and intensive cultivation of the soil on the growth of a stand of Eucalyptus grandis and soil fertility. The experimental site is a commercial plantation in the Itatinga district, São Paulo State, Brazil. This site was originally covered by climax vegetation known as ‘Cerrado\' (savanna) which is characterised by seasonal soil water deficits and very low soil fertility. The effects of complete harvest residue removal, residue retention and residue burning were assessed in a randomised block experiment. The highest productivities were obtained where the residues were retained or burned and the lowest where all the residues (slash, litter and bark) were removed. These results highlight the temporary but large release of nutrients due to burning and the effect of forest residues on tree growth. Temporary variations in organic C and N contents, exchangeable cation contents and pH were found only in the 0–5cm soil layer, except for the burned residue treatment where variations in the layer beneath (5–10cm) were also found. No modification of soil properties was found in the 10–20cm layer. It was found that burning resulted in the loss of 82% of biomass, 86% of N, 60% of P, 49% of K, 11% of Ca, 29% of Mg and 84% of S. Exchangeable K initially increased up to 0.8 years after harvesting and later decreased. Over a 21-month period, the largest rates of N mineralisation were found in the standing crop treatment (77kg ha<sup>–1 of N), followed by the treatment where the residues were retained with minimum disturbance of the site (58kg ha–1 of N). The removal or burning of the residues inhibited the N mineralisation with values of 45 and 28kg ha–1 of N respectively, recorded in these treatments. The different residue management treatments resulted in pronounced effects on the growth of E. grandis.

Southern Hemisphere Forestry Journal 2007, 69(2): 95–102</sup>