| Journal Article |
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| Article Title | Testing the safety-net role of hedgerow tree roots by 15N placement at different soil depths | | Author | Edwin C Rowe, Kurniatun Hairiah, Ken E. Giller, Meine van Noordwijk and Georg Cadisch | | Year | 1999 | | Journal Title | Agroforestry Systems | | Institution | Kluwer Academic Publishers | | Volume | 43 | | Issue | 1-3 | | Pages | 81-93 | | Call Number | JA0134-04 | | Keywords | Alley cropping, Agroforestry systems, Ammonium Sulfate, Hedges, Nutrients cycling, Root systems, Nutrient uptake, Nitrogen cycle |
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| Abstract: |
| Trees which root below crops may have a beneficial role in simultaneous agroforestry systems by intercepting and recycling nutrients which leach below the crop rooting zone. They may also compete less strongly for nutrients than trees which root mainly within the same zone as crops. To test these hypotheses highly enriched 15N-labelled ammonium sulfate was placed at 3 depths (5, 35, 55 cm) in the soil between 4-yr-old alternating hedgerows of the shallow-rooting (and nitrogen fixing) Gliricidia sepium and the deep rooting (and non-nodulating) Peltophorum dasyrrhachis [P. dasyrachis], spaced at 4 m apart with 0.5 m between trees, in a farmer's field in North Lampung, Sumatra. The labelled N was applied in May 1995, after sowing 7 rows of groundnuts at 0.5x0.25 m spacing in the alleys between trees in April. A year after the isotope application most of the residual 15N in the soil remained close to the injection points due to the joint application with a carbon source which promoted 15N immobilization. Temporal 15N uptake patterns (2-weekly leaf sub-sampling) as well as total 15N recovery measurements suggested that Peltophorum obtained more N from the subsoil than Gliricidia. Despite this Gliricidia appeared to compete weakly with the crop for N as it recovered little 15N from any depth but obtained an estimated 44-58% of its N from atmospheric N2-fixation. Gliricidia took up an estimated 21 kg N ha-1 and Peltophorum an estimated 42 kg N ha-1 from beneath the main crop rooting zone. The results demonstrate that direct placement of 15N can be used to identify N sourcing by trees and crops in simultaneous agroforestry systems, although the heterogeneity of tree root distributions needs to be taken into account when designing experiments |
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