Ciclagem de nutrientes por árvores em sistemas agroflorestais na Mata Atlântica

Abstract

Agroforestry systems are effective in improving and conserving soil quality. The trees in these systems absorb nutrients from deep soil layers and continually contribute to the soil top layer with litterfall, generating impacts above and below‐ ground. Our objective was to study the characteristics involved in the nutrient cycling by three species used in agroforestry systems, seeking to contribute to better design and management of the systems. The species selected for the study were ipê‐preto (Zeyheria tuberculosa), açoita‐cavalo (Luehea grandiflora), mulungu (Erythrina verna), fedegoso (Senna macranthera), ingá (Inga subnuda), papagaio (Aegiphila sellowiana) and avocado (Persea americana). The increase in tree biomass, the contribution of literfall and the contents of nutrients in the aerial tree parts were measured from November 2005 to October 2006. The decomposition rate and release of nutrients of the residues, the contents of chemical and biochemical components of these materials were evaluated. Increases of biomass (kg year‐1 of dry matter per tree, DM) were larger for mulungu (135,4), fedegoso (120,4), açoita‐ cavalo (99,0), avocado (81,7) and ingá (39,3). The contributions (kg ha‐1 year‐1 of DM) of litter fall were larger for fedegoso (6.086,9), inga (4.331,2), açoita‐cavalo (2.397,7) and avocado (2.004,5). The reallocation of nutrients in the green material before the fall of senescent material was larger for N (papagaio and mulungu), P (avocado and fedegoso) and K (papagaio, fedegoso and avocado), reaching values up to 73% for the reallocation of P in avocado. Fedegoso, ingá, açoita‐cavalo along with abacate produced litterfall with the largest nutrient content. In general, leaves contained the largest amount of nutrients and there was no difference among seasons when the material of all species was pooled. However, the nutrient contents of each species varied among seasons and plant parts. The decomposition rate, measured using the production of C‐CO2, was larger for fedegoso, mulungu, ipê‐preto and papagaio than for the other species. Lignin/N and lignin + polifenol/N was correlated to the decomposition rate of the materials of the different species. Among the Leguminosae species, mulungu and fedegoso had the highest decomposition rate (measured with litter bags) and inga the lowest. The largest amount of nitrogen fixation was found for mulungu (22,6%) and ingá (20,6%). Potassium was released quicker and magnesium and calcium slower than other nutrients. The characteristics of the litterfall and their decomposition dynamics were different for the different species. Understanding of these characteristics and processes can contribute to a better design of family agroecological systems that combine productivity and soil and biodiversity conservation. When used in a diversified manner, tree species can contribute to a balanced and constant nutrient cycling. Therefore, diversification of agroforestry systems allows better use of the native trees of the Atlantic Rainforest.