Phosphorus fractions in monoespecific and mixed stands of Eucaliptus grandis and Acacia mangiun.

Abstract

To understand the basic phenomena of phosphorus dynamics in soil is very important for decision making about the need for the addition and definition of doses and modes of application of phosphate fertilizers. The forms and degree of lability of phosphorus vary with the characteristics and soil properties. In young soils, calcium phosphates are the main suppliers of phosphorus to living organisms. On the other hand, in highly weathered soils, the biocycling of organic phosphates is of great importance in maintaining the bioavailability, although not sufficient to obtain the maximum economic productivity of crops. Plantations mixed with N2-fixing legumes appear as an option for sustainable management of the ecosystem. This is one of the designs of ecological intensification. However, one needs a thorough understanding of the ecological interactions between different species, and this study targets that related to facilitation. Acacia mangium (N2-fixing) could benefit/facilitate Eucalyptus grandis, due to the possibility of increased absorption of phosphorus from the soil by mycorrhiza present in A. mangium, thus generating a litter more rich in phosphorus. With the decomposition of litter and its subsequent mineralization, this phosphorus would be more easily absorbed by E. grandis. Thus, one must step up research focusing on, among others: (a) fractions of phosphorus in the soil and crop productivity, (b) the fractions of phosphorus in plant tissues, (c) discern the effect of mycorrhiza in most uptake phosphorus by crops.