Me. Probert et al., MODELING WATER, NITROGEN, AND CROP YIELD FOR A LONG-TERM FALLOW MANAGEMENT EXPERIMENT, Australian journal of experimental agriculture, 35(7), 1995, pp. 941-950
Two models that differ markedly in how they represent the crop-soil sy
stem have been used to simulate soil processes and crop production in
the long-term experiment at Hermitage Research Station, Warwick, Queen
sland. The experiment was designed to examine the effects of tillage,
stubble management, and nitrogen (N) fertiliser on the productivity of
a winter cereal-summer fallow cropping system. It commenced in 1968 a
nd the treatments have been maintained until the present. CENTURY oper
ates on a monthly time step, considers all soil N transformations to o
ccur in a single soil layer, and has a very simple crop growth routine
that does not deal with crop phenology. APSIM provides a framework wh
ereby a model of a cropping system is configured from component module
s, which operate on a daily time step. For simulating the Hermitage ex
periment, modules to represent the dynamics of soil-water, N, surface
residues, and growth of a wheat crop were used. The water and N module
s deal with a multilayered soil, whilst the wheat module develops leaf
area, intercepts light, and accumulates and partitions dry matter in
response to weather, soil-water, and N. Both models were specified to
simulate the whole experimental period (1969-92) as a continuous run.
The ability of these models to simulate grain yields, soil-water and d
rainage, nitrate-N, and soil organic matter were examined. Both models
predict, in agreement with the observed data, that for this continuou
s cereal cropping system there has been a decline in soil organic matt
er for all the treatments and a reduction through time in the capacity
of the soil to mineralise and accumulate nitrate during the fallows.
CENTURY performed better than APSIM in predicting the relative yields
of the N treatments but was less satisfactory than APSIM for absolute
grain yield, soil-water, and drainage. Yield predictions with APSIM we
re sensitive to carry-over errors in the water balance from one season
to the next, so that in some seasons large errors occurred in the pre
dicted relative yields. Both models reproduced the observations well e
nough to indicate their suitability for providing useful insights into
the behaviour of cropping systems where the focus is on depletion of
soil fertility.