AGS 701 (Basics of Agricultural
Systems)
Assignment
No. 8
1. One of the most obvious potential limitations to
the growth of the world population is the global reservoir of soil, since it is
essential to the production of food. There is a finite amount of arable
(farmable) land on Earth, and given a typical productivity level, each person
needs something like 0.5 hectares (one hectare is 104 m2
or 2.4 acres) to have a diverse, healthy diet, assuming average yields from the
land. Unfortunately, there is only about 0.27 hectares per person at the
present population level. This will drop off to about 0.13 hectares per person
when the population doubles in the next 40 to 50 years, as it is projected to
do. At present, about 20% of the population (1 billion people) is malnourished
because of food shortages and inadequate distribution of food. This
malnourishment is the cause of over 13 million deaths each year (35,000 per
day) and the vast majority are children.
a)
Identify
the reservoirs, flows, converters and connectors of the model in Figure 1.
b)
Identify
and draw feedback loops in this model and discuss.
c)
Draw
graphical functions between the following converters:
- (death_percent)
and (life_expect)
- (life_expect)
and (food_per_capita)
- (potential_land_yield)
and (soil/INIT(soil)
- (intensity_mlt)
and (food_shortage_pc)
d)
Describe
the entire model in words.
2. In Figure 2, the N
cycle is expressed as a simple system dynamics model.
a)
Identify the reservoirs, flows, converters and connectors of the model.
b) Describe the model in words.
c)
Draw a graph showing the relationship between the variables that is
represented as the only one graphical converter in this
figure.
Due: September 16,
2004.
Figure
1 Population, soil and food systems model Figure 2. A dynamic model of N cycle