| Journal Article |
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| Article Title | Estimating dinitrogen fixation of hedgerow vegetation using the Nitrogen-15 natural abundance method | | Author | Jagdish K Ladha, M B Peoples, Dennis P Garrity, V T Capuno and P J Dart | | Year | 1993 | | Journal Title | Soil Science Society of America Journal | | Institution | Soil Science Society of America | | Volume | 57 | | Issue | 3 | | Pages | 732-737 | | Call Number | JA0052-04 | | Keywords | Halley cropping, Nitrogen fixation, Maize, Rice, Upland areas, Pruning, Isotopes, Nitrogen-cycle, Acid soils, Estimation, Hedges, Cropping systems, Agroforestry |
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| Abstract: |
| Leguminous trees play a major role in alley farming and hedgerows 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 (delta15N) method could be applied successfully to an alley cropping system to estimate N2 fixation by Gliricidia sepium. The study also assessed the suitability of the non-nodulating legume Cassia spectabilis as a suitable reference for investigations with N2-fixing trees. The hedgerow species (and also Napier grass, Pennisetum purpureum) were planted in double rows, 3 m long with 5-m wide alleys, on an acid upland site in the Philippines in 1988. An upland rice (Oryza sativa)/maize (Zea mays) crop sequence was established in the alleys, and hedgerow pruning was initiated, in 1989. The delta15N of the total N of prunings from each species was determined from 6 samplings taken between January 1990 (17 months after establishment) and July 1991. The delta15N of the total N of samples from C. spectabilis ranged from 4.47 to 7.28o/oo with an average and standard error of 6.16 ± 0.41o/oo. These values were similar to those of extractable N of soil from different soil depths, which ranged from 4.66 to 7.33o/oo (although it was not significantly different between depths), suggesting that C. spectabilis is a suitable non-fixing reference species. The delta15N of the total N of samples from G. sepium ranged from 0.67 to 4.1o/oo with an average and standard error of 2.87 ± 0.44o/oo.The changes in delta15N of total N of prunings were similar in both tree species; therefore, the observed variation was considered not to have interfered with estimation of the proportion of plant N derived from N2 fixation (%Ndfa). On 4 of the 6 sampling times, G. sepium had an Ndfa close to 50%, whereas at two other sampling dates the Ndfa dropped to 30 and 35%. This study also provides the first quantitative data demonstrating that C. spectabilis is a non-N2-fixing legume. Ndfa estimates are also given for the maize crop and for Napier grass; these were similar to those from C. spectabilis in August 1990, but values for C. spectabilis and maize were greater in January 1990. |
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