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Nutrient cycling under mixed-species tree systems in southeast Asia

Nutrient cycling under mixed-species tree systems in southeast Asia Eucalyptus and Acacia are two tree genera that are commonly used in industrial plantations and as components of agroforestry systems in southeast Asia. These fast-growing trees are mostly grown in monocultures. However, questions are now being raised about the long-term sustainability of their growth as well as their effects on site quality. Losses of N and P from the site through biomass harvest and during site preparation constitute a major nutrient drain. As an alternative to monocultures, mixed-species cultures which include at least one N2-fixing tree species can improve plant productivity and soil N dynamics. Among the various aspects of N dynamics in such stands, export of N during biomass harvest and inputs by the N 2 -fixing component are the most important. Reported estimates of the amount of N fixed by acacia and other N 2 -fixing trees are highly variable, depending on inherited plant characteristics, tree age, site factors (e.g., drought), soil fertility (e.g., available P, metal toxicities) and unreliable methods of measuring N 2 -fixation. Of the available techniques for assessing N 2 -fixation by trees, the total N difference method (TND) is the simplest. The contribution of roots to assessments of N 2 -fixation is recognized but rarely measured. For short-rotation mixed-species plantations, the amount and time of N transfer from N 2 -fixing trees to non-N 2 -fixing trees are important issues to consider when attempting to develop productive nutrient management strategies. Based on limited information from trials in southeast Asia, it appears that acacia fixes substantial amounts of N during the first few years of establishment and a significant amount of that N is transferred to adjacent eucalypts, thereby improving the growth and nutrition of the eucalypts. The presumed transfer of N from acacias to eucalypts during the early stages of plantation development probably results from belowground turnover of roots and nodules because aboveground litter decomposition is slight at this stage, and contributes little to the overall N dynamics. The available information on P cycling in mixed-species stands, during the early stages of stand growth, provides inconclusive evidence as to whether the availability of soil P increases, despite indications of higher levels of phosphatase activity in the fine roots of nitrogen-fixing trees. This would imply that additional inputs of P as fertilizer are required to remove any P deficiency in mixed-species stands. Long-term observations are required for better understanding of the nutritional and growth benefits of including N 2 -fixing trees in mixed-species stands. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Agroforestry Systems Springer Journals

Nutrient cycling under mixed-species tree systems in southeast Asia

Agroforestry Systems , Volume 38 (1) – Jul 1, 1997

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References (89)

Publisher
Springer Journals
Copyright
Copyright © 1997 by Kluwer Academic Publishers
Subject
Life Sciences; Agriculture; Forestry
ISSN
0167-4366
eISSN
1572-9680
DOI
10.1023/A:1005952410569
Publisher site
See Article on Publisher Site

Abstract

Eucalyptus and Acacia are two tree genera that are commonly used in industrial plantations and as components of agroforestry systems in southeast Asia. These fast-growing trees are mostly grown in monocultures. However, questions are now being raised about the long-term sustainability of their growth as well as their effects on site quality. Losses of N and P from the site through biomass harvest and during site preparation constitute a major nutrient drain. As an alternative to monocultures, mixed-species cultures which include at least one N2-fixing tree species can improve plant productivity and soil N dynamics. Among the various aspects of N dynamics in such stands, export of N during biomass harvest and inputs by the N 2 -fixing component are the most important. Reported estimates of the amount of N fixed by acacia and other N 2 -fixing trees are highly variable, depending on inherited plant characteristics, tree age, site factors (e.g., drought), soil fertility (e.g., available P, metal toxicities) and unreliable methods of measuring N 2 -fixation. Of the available techniques for assessing N 2 -fixation by trees, the total N difference method (TND) is the simplest. The contribution of roots to assessments of N 2 -fixation is recognized but rarely measured. For short-rotation mixed-species plantations, the amount and time of N transfer from N 2 -fixing trees to non-N 2 -fixing trees are important issues to consider when attempting to develop productive nutrient management strategies. Based on limited information from trials in southeast Asia, it appears that acacia fixes substantial amounts of N during the first few years of establishment and a significant amount of that N is transferred to adjacent eucalypts, thereby improving the growth and nutrition of the eucalypts. The presumed transfer of N from acacias to eucalypts during the early stages of plantation development probably results from belowground turnover of roots and nodules because aboveground litter decomposition is slight at this stage, and contributes little to the overall N dynamics. The available information on P cycling in mixed-species stands, during the early stages of stand growth, provides inconclusive evidence as to whether the availability of soil P increases, despite indications of higher levels of phosphatase activity in the fine roots of nitrogen-fixing trees. This would imply that additional inputs of P as fertilizer are required to remove any P deficiency in mixed-species stands. Long-term observations are required for better understanding of the nutritional and growth benefits of including N 2 -fixing trees in mixed-species stands.

Journal

Agroforestry SystemsSpringer Journals

Published: Jul 1, 1997

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