Geoscience Reference
In-Depth Information
a crop. The equation is helpful to determine quickly the weight
of the crop where no observation was made.
explana tory
models
This model consists of quantitative description of the mechanisms
and processes that causes the behaviour of the system. To create
this model, a system is analysed and its processes and mecha-
nisms are quantified separately. The model is built by integrating
these descriptions for the entire system. It contains descriptions
of distinct processes such as leaf area expansion, tiller produc-
tion and so on. Crop growth is a consequence of these processes.
Simula tion
models
Computer models, in general, are a mathematical represen-
tation of a real-world system. One of the main goals of crop
simulation models is to estimate agricultural production as a
function of weather and soil conditions as well as crop man-
agement. These models use one or more sets of differential
equations and calculate both rate and state variables over time,
normally from planting until harvest maturity or final harvest.
The Earth's land resources are finite, whereas the number
of people that the land must support continues to grow rapidly.
This creates a major problem for agriculture. The production/
productivity must be increased to meet the rapidly grow-
ing demands, while the natural resources must be protected.
New agricultural research is needed to supply information to
farmers, policy makers and other decision makers on how to
accomplish sustainable agriculture over the wide variations in
climate around the world. In this direction, explanation and
prediction of growth of managed and natural ecosystems in
response to climate and soil-related factors are of increasing
importance as the objectives of science (Dhaliwal et al., 1997).
Quantitative prediction of complex systems, however, depends
on integrating information through levels of organisation, and
the principal approach for that is through the construction of
statistical and simulation models. In simulation of systems, use
and balance of carbon, beginning with the input of carbon from
canopy assimilation, forms the essential core of most simula-
tions that deal with the growth of vegetation. Systems are webs
or cycles of interacting components. Change in one component
of a system produces changes in other components because of
the interactions. For example, a change in weather to warm and
humid may lead to a more rapid development of a plant disease,
a loss in the yield of a crop and consequent financial adversity
for individual farmers and also for the people of a region. Most
natural systems are complex. Many do not have boundaries.
The bio-system is composed of a complex interaction among
