Above-ground biomass, nutrient content, and nutrient use efficiency of eucalypt plantations growing in different sites in Brazil.

Abstract

The annual increment in above-ground biomass, and the corresponding nutrient content of eucalypt plantations growing in nine different sites, were evaluated in order to analyse the growth and the nutrient accumulation of Eucalyptus spp. in Brazil. The sites represented a wide range of edaphic and climatic conditions, resulting in a large variation in growth increment and tree nutrient content. The highest productivities (approximately 36 t/ha-year) were observed in sites with the lowest water deficits. On average, the stem represents 89% of the above-ground biomass but it can be as low as 78% in the least productive site. The nutrient content in the stem was highest in the most productive sites, showing a close relationship with biomass production. There were two distinct patterns of stem annual nutrient accumulation. At three of the sites, the amount of nutrients in the stem decreased in the order nitrogen > calcium > potassium > magnesium > and phosphorus. However, calcium exceeded nitrogen at the other six sites. Nutrient use efficiency (NUE) for stem and above-ground biomass production was significantly different among sites. On average, the values of NUE for both stem and above-ground biomass decreased in the order phosphorus > magnesium > potassium > nitrogen > calcium. Unlike dry matter, there were appreciable differences among sites in relative nutrient allocation. Although bark constitutes only 10% of the above-ground dry matter, it contains large amounts of nutrients (73% of the calcium in the stem, 65% of the magnesium, 46% of the phosphorus, 41% of the potassium, and 24% of the nitrogen). Debarking in the field can substantially reduce nutrient exportation, which could lead to greater sustainability or less fertiliser use in eucalypt plantation forests of Brazil.