Food, Soil, and Pest Management - Environmental Science - page 215

Causes Consequences

Overgrazing Worsening drought

Deforestation Famine

Erosion Economic losses

Salinization

Lower living
standards

Soil compaction

Environmental
refugees

Natural climate
change

Figure 10-12 Natural capital degradation: causes and consequences of desertification.

According to a 1995 study, severe salinization has
reduced yields on about one-fifth of the world's irri-
gated cropland, and another one-third has been mod-
erately salinized. The most severe salinization occurs
in Asia, especially in China, India, and Pakistan.
Salinization affects almost one-fourth of irrigated
cropland in the United States. The proportion of dam-
aged land is much higher in some heavily irrigated
western states (Figure 10-14).
We know how to prevent and deal with soil salin-
ization, as summarized in Figure 10-15. Unfortunately,
some of these remedies are expensive.

Transpiration

Evaporation

Figure 10-14 Natural capital degradation: Because of high
evaporation, poor drainage, and severe salinization, white alka-
line salts have displaced crops that once grew on this heavily
irrigated land in Colorado.

Evaporation

Evaporation

Solutions

Soil Salinization

Prevention Cleanup

Waterlogging

Reduce irrigation Flushing soil

(expensive and
wastes water)

Less permeable
clay layer

Not growing crops
for 2-5 years

Salinization Waterlogging

1. Irrigation water contains

small amounts of
dissolved salts.

1.

Precipitation and
irrigation water
percolate downward.

Switch to salt-
tolerant crops
(such as barley,
cotton, sugarbeet)

Installing
underground
drainage systems
(expensive)

2. Evaporation and trans-

piration leave salts
behind.

2.

Water table rises.

3. Salt builds up in soil.

Figure 10-13 Natural capital degradation: Salinization and
waterlogging of soil on irrigated land without adequate
drainage can decrease crop yields.

Figure 10-15 Solutions: methods for preventing and cleaning
up soil salinization. Critical thinking: which two of these solu-
tions do you believe are the most important?