Nitrogen cycling in leucaena (Leucaena leucocephala) alley cropping in semi-arid tropics |
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| Authors: | Z H Xu R J K Myers P G Saffigna A L Chapman |
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| Institution: | (1) Division of Environmental Sciences, Griffith University, 4111, Queensland, Australia;(2) Present address: Northfield Research Laboratories, GPO Box 1671, 5001 Adelaide, South Australia, Australia;(3) Division of Tropical Crops and Pastures, CSIRO, 4067, Queensland, Australia;(4) Present address: IBSRAM, Bangkhen, PO Box 9-109, 10900 Bangkok, Thailand;(5) Tropical Ecosystems Research Centre, CSIRO, 0820 Darwin, NT, Australia |
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| Abstract: | In an alley cropping system, prunings from the hedgerow legume are expected to supply nitrogen (N) to the associated cereal. However, this may not be sufficient to achieve maximum crop yield. Three field experiments with alley-cropped maize were conducted in a semi-arid environment in northern Australia to determine: (1) the effect of N fertilizer on maize growth in the presence of fresh leucaena prunings; (2) the effect of incorporation of leucaena and maize residues on maize yield and the fate of plant residue15N in the alley cropping system; and (3) the15N recovery by maize from15N-labelled leucaena, maize residues and ammonium sulphate fertilizer.Leucaena residues increased maize crop yield and N uptake although they did not entirely satisfy the N requirement of the alley crop. Additional N fertilizer further increased the maize yield and N uptake in the presence of leucaena residues. Placement of leucaena residues had little effect on the availability of N to maize plants over a 2 month period. The incorporation of leucaena residues in the soil did not increase the recovery of leucaena15N by maize compared with placement of the residues on the soil surface. After 2 months, similar proportions of the residue15N were recovered by maize from mulched leucaena (6.3%), incorporated leucaena (6.1%) and incorporated maize (7.6%). By the end of one cropping season (3 months after application) about 9% of the added15N was taken up by maize from either15N-labelled leucaena as mulch or15N-labelled maize residues applied together with unlabelled fresh leucaena prunings as mulch. The recovery of the added15N was much higher (42.7%) from the15N-labelled ammonium sulphate fertilizer at 40 kg N ha-1 in the presence of unlabelled leucaena prunings. Most of the added15N recovered in the 200 cm soil profile was distributed in the top 25 cm soil with little leached below that. About 27–41% of the leucaena15N was apparently lost, largely through denitrification from the soil and plant system, in one cropping season. This compared with 35% of the fertilizer15N lost when the N fertilizer was applied in the presence of prunings. ei]H Lambers |
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| Keywords: | decomposition fertilizer N leucaena residues maize residues N loss N uptake 15N recovery residue incorporation residue N |
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