Introducing Acacia mangium trees in Eucalyptus grandis plantations: consequences for soil organic matter stocks and nitrogen mineralization
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Background and aims
Eucalyptus plantations cover 20 million hectares on highly weathered soils. Large amounts of nitrogen (N) exported during harvesting lead to concerns about their sustainability. Our goal was to assess the potential of introducing A. mangium trees in highly productive Eucalyptus plantations to enhance soil organic matter stocks and N availability.
A randomized block design was set up in a Brazilian Ferralsol soil to assess the effects of mono-specific Eucalyptus grandis (100E) and Acacia mangium (100A) stands and mixed plantations (50A:50E) on soil organic matter stocks and net N mineralization.
A 6-year rotation of mono-specific A. mangium plantations led to carbon (C) and N stocks in the forest floor that were 44% lower and 86% higher than in pure E. grandis stands, respectively. Carbon and N stocks were not significantly different between the three treatments in the 0–15 cm soil layer. Field incubations conducted every 4 weeks for the two last years of the rotation estimated net soil N mineralization in 100A and 100E at 124 and 64 kg ha−1 yr−1, respectively. Nitrogen inputs to soil with litterfall were of the same order as net N mineralization.
Acacia mangium trees largely increased the turnover rate of N in the topsoil. Introducing A. mangium trees might improve mineral N availability in soils where commercial Eucalyptus plantations have been managed for a long time.
KeywordsCarbon Brazil N2 fixation Eucalypt Acacia Plantation Forest Soil Fertility Ecological intensification
Financial support was provided by ANR (Agence Nationale de la Recherche) SYSTERRA programme ANR-2010-STRA-004 (Intens&fix), ATP Neucapalm (CIRAD) and the USP/COFECUB project (No. 22193PA). We thank EMBRAPA Agrobiologia for providing selected Rhizobium strains and the entire staff of the Itatinga experimental station for field measurements. We are particularly grateful to Rildo Moreira e Moreira (ESALQ) and Eder Araujo da Silva (FLORAGRO) for their contribution to this study, as well as Peter Biggins (CIRAD) for the revision of the English.
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