HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Ladha, J. K. Articles by Dart, P. J. Search for Related Content PubMed Articles by Ladha, J. K. Articles by Dart, P. J. Agricola Articles by Ladha, J. K. Articles by Dart, P. J.

Estimating Dinitrogen Fixation of Hedgerow Vegetation Using the Nitrogen-15 Natural Abundance Method

International Rice Research Institute, P.O. Box 933, 1099 Manila, Philippines

M. B. Peoples

CSIRO, Division of Plant Industry, GPO Box 1600, Canberra, ACT, 2601, Australia

V. T. Capuno

Philippine National Institute of Biotechnology, Univ. of Philippines at Los Baños, Philippines

P. J. Dart

Dep. of Agriculture, Univ. of Queensland, Qld 4072, Australia

*Corresponding author.

ABSTRACT

Leguminous trees play a major role in alley farming or hedgerow by providing or recycling N and organic matter to annual crops. Little is known, however, about their capacity to fix N₂ under field conditions because of methodological difficulties. This study evaluated whether the ¹⁵N natural abundance (¹⁵N) method could be applied successfully to an alley-cropping system to estimate N₂ fixation by Gliricidia sepium (Jacq.) Walp. The study also assessed the suitability of the non-nodulating legume Cassia spectabilis (L.) DC [syn. Senna spectabilis (DC.) Irwin and Barneby] as a suitable reference for investigations with N₂-fixing trees. The hedgerow species were planted in double rows, 3 m long with 5-m-wide alleyways, at an acid upland site in the Philippines. The ¹⁵N of total N of Cassia and Gliricidia prunings was determined from six samplings between January 1990 (17 mo after establishment) and July 1991. The ¹⁵N of the total N of samples from nonfixing Cassia ranged from 4.47 to 7.28 with an average and standard error of 6.16 ± 0.41. These values were similar to those of extractable N of soil from different soil depths, ranging from 4.66 to 7.33%, suggesting that Cassia is a suitable nonfixing reference species. The changes in ¹⁵N of total N of prunings were similar in both tree species; therefore, the observed variation was considered not to have interferred with estimation of N₂ fixation (%Ndfa). At four of the six sampling times, Gliricidia had an Ndfa close to 50%, whereas at other two sampling dates the Ndfa dropped to 30 and 35%. This study also provides the first quantitative data demonstrating that Cassia is a non-N₂-fixing legume.

This study is part of a collaborative program between IRRI and the Australian Centre for International Agricultural Research (ACIAR) under the project no. 8800 and 8731. The work was supported in part by the Australian International Development Assistance Bureau (AIDAB).

Received for publication April 15, 1992.