Author:
Thompson R. B.,Fillery I. R. P.
Abstract
Nitrogen (N) mineralisation from mature subterranean clover
(Trifolium subterraneum L.) shoots and roots and from
sheep urine and faeces, and N uptake by wheat from the shoots, urine, and
faeces, were determined with 15 N in a field study in the Western Australian
wheatbelt. Treatments were applied to the soil surface of confined micro-plots
in autumn and incorporated into soil immediately before wheat was sown in
winter. Mature subterranean clover shoots containing 18 kg N/ha were
applied to the soil surface, and root material containing 17 kg N/ha was
mixed into soil. 15N-labelled urine and faeces were
obtained from housed sheep fed 15N-labelled wheat straw
and grain. Urine was applied at the rates of 151 and 301 kg N/ha, and
faeces was added at the rate of 47 kg N/ha. There was a loss of 14%
of shoot 15N in the 2 months this residue was on the
soil surface, although very little mineralisation occurred. On the assumption
that wind-blow caused the initial loss of 15N,
28% of shoot N mineralised in 6 months following incorporation of shoot
residues into soil, and crop recovery was 11% of the
15N applied. N mineralisation from the mature roots was
26% in 6 months. NH3 volatilisation from urine,
estimated by difference, was 25% for high urine (0·517
mL/cm2) and 33% for low urine (0·258
mL/cm2) application rates, the loss occurring in
the first 2 weeks. Wheat uptake was 23% of the high urine
15N and 22% of the low urine
15N. Leaching losses from unplanted micro-plots were
approximately 25-30% of urine 15N. In contrast,
leaching losses from planted micro-plots were estimated to be approximately
10% of urine 15N. Approximately 30% of
faecal N was mineralised and recovery of faeces N by wheat was 1% of
applied 15N. The relative contributions of these
components to N turnover in the ley pasture wheat rotation are discussed. It
is concluded that assessments of the potential turnover of N in pastures to
cropping phases need to consider the low rates of N mineralisation of
above-ground herbage, the potential for supply of N from the total root
system, the effect of grazing on NH3volatilisation, and
consequent loss of N fixed by legumes.
Subject
General Agricultural and Biological Sciences
Cited by
21 articles.
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