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Nitrogen immobilization in decomposing litter contributes to productivity decline in ageing pastures of green panic (Panicum maximum var. trichoglume)

Published online by Cambridge University Press:  27 March 2009

G. B. Robbins
Affiliation:
Queensland Department of Primary Industries, ‘Brian Pastures’ Research Station, Gayndah, Queensland 4625, Australia
J. J. Bushell
Affiliation:
Queensland Department of Primary Industries, ‘Brian Pastures’ Research Station, Gayndah, Queensland 4625, Australia
G. M. McKeon
Affiliation:
Queensland Department of Primary Industries, ‘Brian Pastures’ Research Station, Gayndah, Queensland 4625, Australia

Summary

The extent and rate of N release from nylon bags containing green panic (Panicum maximumvar.trichoglume)litter was measured for up to 319 days (long-term studies) in 1978/79 and 1979/80 in Gayndah, Australia. Dry matter (DM) decomposition rates were measured in 41 periods of 39 days and related to environmental variables and initial litter N concentrations (short-term study).

About half of litter DM decomposed during the long-term studies, while N concentration in the remaining litter increased from an initial average of 0–57 % N, to 0–95 % N. Net release of N from bags began when its concentration in the residue increased to c.0–65% N (or when the C:N ratio decreased to 75:1). Only a net 20–30 % of the initial N was released for potential plant uptake by the end of the study. The short-term study showed that DM decomposition was rapid and independent of pasture age. Decomposition rate increased with soil moisture and average daily temperature but was unaffected by initial litter N concentration. Release of N from decomposing litter was slow, despite rapid DM decomposition. It was concluded that a major cause of declining productivity in sown grass pastures is the immobilization of N in decomposing grass litter.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1989

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