Vergara - 1976 - Physiological and morphological adaptability of ri

502 CLIMATE AND RICE
subsystems can be studied independently (and usually are) and modelled
separately before incorporation into the total working system.
Despite intensive research on separate system components and processes
(and perhaps because of it), our understanding of crop production systems as a
functioning whole is very limited. 1f we are to mobilize existing knowledge and
organize research strategies such that the most important gaps in that knowledge
are filled quickly: we need to devote at least as much energy to whole-system
research as is presently given to single-discipline and process-oriented research.
MODELLING CROP PRODUCTION SYSTEMS
As yet, very few comprehensive models of crop production systems have been
developed. Stapletons (1968) model of a cotton production system is an early
example, but such models really‘ remain a challenge for the future. Despite this
lack. there exist a great many partial models of important sy-‘stem components
and processes such as photosynthesis (e.g. Monsi and Saeki, 1953; de Wit, 1965;
Duncan et a1. 1967) and the water-balance (eg. Holmes and Robertson. 195‘);
Slatyer, 1960". Shaw, 1964; Baier and Robertson. 1966; Fitzpatrick and Nix‘.
1969). Many such partial models have proved useful in generating new insights
and in prediction. because single environmental factors (eg. light, temperature.
water) commonly dominate crop performance at a given location.
Because the water-regime tends to dominate crop performance in Australian
agriculture. great emphasis has been placed on the development of water-balance
models for agroclimatie analysis. These generalized water-balance models (e.g.
Slatyer. 1960) are primarily concerned with simulation of soil-vl-"ater regime in
specified crop or pasture systems and normally operate over daily or weekly
intervals. 1n many crop systems it is necessary to simulate soil-water regime
through complete cropping sequences or rotations, as the preceding crop,
pasture or bare fallow influences the carry-over of soil-water to the succeeding
crop. Such a model was. developed for alternating fallowerop systems in central
Queensland. in the eastern agroecological region (Fitzpatrick and Nix. 1969).
The output from this fallout-crop model was used to calculate various measures
of crop water-stress at different phases of development and these were
correlated with grain yields of grain-stirghum (summer-crop) and wheat (wintercrop).
One of these indices accounted for 60-83% of yield variation at the experimental
site and between 60 and 70% of wheat yield variation at five centers
in the Queensland wheat belt (Nix and Fitzpatrick. 1969). Using long-term
records of weekly' mean rainfall, fallout-crop sequences have been simulated
and yield predictions made for other locations in the region which have not yet
been developed for agriculture.
The relatively" simple fallow-crop water balance functions have been developed
further and now form the core of a model (CROPEVAL) which is designed for
rapid evaluation (if any postulated crop sjvstem. in any environment. at continental
seale. The computer program CROPEVAL requires as input, weekly mean