A. Parshotam et al., Carbon residence times obtained from labelled ryegrass decomposition in soils under contrasting environmental conditions, SOIL BIOL B, 32(1), 2000, pp. 75-83
Thc rate of decomposition of ryegrass in New Zealand soils was studied. Six
soils from contrasting New Zealand environments were amended with C-14-lab
elled ryegrass (Lolium hybridum Hausskn), which was allowed to decompose in
micro-lysimeters under field conditions for 2 yr. Periodically, the micro-
lysimeters were destructively sampled, and the amount of C-14 remaining in
the soil and the fraction of C-14 incorporated into microbial biomass measu
red. After 2 yr of exposure, 18 to 32% of the labelled C-14 was retained by
the soils. Decomposition was initially rapid, with almost one-half of the
labelled C-14 being lost after 2 months. Thereafter, the rate of decomposit
ion was much reduced. During the initial phase of decomposition (2 months),
a larger portion of the C-14 was retained by one soil which had major wate
r deficits. The influence of environmental factors on decomposition rate wa
s assessed by assuming a three compartment model and calculating the mean a
nd variances of residence times of biomass-C-14 and residual-C-14. Analytic
al solutions are presented to the model equations. The C-14 residence times
, adjusted for soil surface area, were related to rainfall. The residence t
imes were compared with times obtained in our earlier study on soils varyin
g in clay content and mineralogy. This provides a range of C-14 residence t
imes for decomposition of ryegrass in New Zealand soils. These results may
be used to validate rate-reduction factors in soil organic matter models. (
C) 2000 Elsevier Science Ltd. All rights reserved.