Vergara - 1976 - Physiological and morphological adaptability of ri

506 CLIMATE ANT) RICF.
Thus again, the simulation of the phasic development pattern provides the
template upon which the whole system is constructed. In this case, however,
we need more than the prediction of major phasic events such as floral initiation
or anthcsis. We need to predict rates of initiation of leaf initials. root axes,
branching stems or tillers, and floral organs. Again we have strong evidence
that these processes are highly deterministic and largely driven by heatsum
(degree-days above the appropriate temperature base for the nominated
cultittar). Although this determines the rate of appearance of organs. their
ultimate survival and growth depend on the supply’ of carbon and nitrogen
during their development.
As yet, the model does not consider major nutrient elements other than
nitrogen. which is seen as having a key’ role in the paflitioning of photosynthate
within the crop system. Allocation of carbon and nitrogen to different organs
is conceptualized as a feedback mechanism which seeks to maintain carbon:
nitrogen ratios Within defined limits. Experimentation with this model has
provided some useful insight into the key role played by addition of fertilizer
nitrogen in high-yielding crop systems.
Although we have concentrated effort. in this ease, on a more detailed understanding
of growth and development processes and their interaction. our basic
objective continues to be the development of an operational model which can
be used for prediction of crop performance at any location under any set of
conditions. With NICKOX we are still some distance from this goal, but progress
with the simpler semi-empirical model CROPEVAI. is encouraging.
ACKNOWLEDGEMENTS
The crop system models and programs described in this paper have evolved
through fruitful collaboration between a number of individuals in the Land
Evaluation Unit of the CSIRO Division of Land Use Research. Dr. K. D.
Cocks and Mr. D. G. Morris and lately Dr. J. F. Angus have played a major
role in the development of NICKOX. Dr. R. J. K. Myers was responsible for
development of a soil nitrogen subsystem model which has been incorporated
into NTCKOX. Mr. D. G. Morris has been responsible for the major part of
the programming associated with all modelling activilyfl Last but not least. Mr.
J. J. Basinski has made much of this work possible through his active support
and encouragement.