Soil carbon and nitrogen in pasture soil reforested with eucalyptus and guachapele

Fabiano De Carvalho Balieiro,Avílio Antonio Franco,Marcos Gervasio Pereira,Bruno José Rodrigues Alves,Alexander Silva De Resende

doi:10.1590/s0100-06832008000300033

Abstract

In spite of the normally low content of organic matter found in sandy soils, it is responsible for almost the totality of cation exchange capacity (CEC), water storage and availability of plant nutrients. It is therefore important to evaluate the impact of alternative forest exploitation on the improvement of soil C and N accumulation on these soils. This study compared pure and mixed plantations of Eucalyptus grandis and Pseudosamanea guachapele, a N2-fixing leguminous tree, in relation to their effects on soil C and N stocks. The studied Planosol area had formerly been covered by Panicum maximum pasture for at least ten years without any fertilizer addition. To estimate C and N contents, the soil was sampled (at depths of 0-2.5; 2.5-5.0; 5.0-7.5; 7.5-10.0; 10.0-20.0 and 20.0-40.0 cm), in pure and mixed five-year-old tree plantations, as well as on adjacent pasture. The natural abundance 13C technique was used to estimate the contribution of the soil organic C originated from the trees in the 0-10 cm soil layer. Soil C and N stocks under mixed plantation were 23.83 and 1.74 Mg ha-1, respectively. Under guachapele, eucalyptus and pasture areas C stocks were 14.20, 17.19 and 24.24 Mg ha-1, respectively. For these same treatments, total N contents were 0.83; 0.99 and 1.71 Mg ha-1, respectively. Up to 40 % of the soil organic C in the mixed plantation was estimated to be derived from trees, while in pure eucalyptus and guachapele plantations these same estimates were only 19 and 27 %, respectively. Our results revealed the benefits of intercropped leguminous trees in eucalyptus plantations on soil C and N stocks.

Highlights

Eucalyptus forests in Brazil cover over 3 million hectares replacing, to some extent, the natural Atlantic Forest and Cerrado vegetation
Another benefit of intercropping eucalyptus with leguminous trees is a potential increase in soil organic matter (SOM)
The homogenity of soil bulk density in tree stands and pasture areas indicated no need for a correction of soil compaction in the calculation of soil C and N stocks, because no compaction had been induced, neither in the tree stand nor the pasture

Summary

Introduction

Eucalyptus forests in Brazil cover over 3 million hectares replacing, to some extent, the natural Atlantic Forest and Cerrado vegetation This land use calls for new management techniques that would lessen impacts on biodiversity and processes of soil fertility exhaustion (Novais & Barros, 1997; Paschoal, 2005; Forrester et al, 2006). Recent studies showed that intercropping eucalyptus with tree legumes was not detrimental to timber yield and resulted in increased soil N availability for eucalyptus (Binkley et al, 1992; Balieiro et al, 2002; Forrester et al, 2006) These results suggest that the implementation of such mixed forests may result in significant economical and ecological advantages due to the N input through biological nitrogen fixation (Forrester et al, 2006). The lower C/N ratio of the legume combined with eucalyptus litter results in a material with a higher turnover rate that could influence eucalyptus production (Balieiro et al, 2004; Forrester et al, 2006) and SOM contents (Resh et al, 2002; Resende et al, 2006) positively

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