Environmental Engineering Reference
In-Depth Information
Salinization
The buildup of salts in soil is an increasing problem in areas where there is heavy crop irrigation, as in the Cen-
tral Valley of California. In this lab, students germinate seeds in increasing concentrations of salt to determine
the point at which the seeds cease sprouting. Any seeds can be used, but fast-germinating seeds such as Mung
beans are commonly used because you can see results in about five days. Salt concentrations begin at 0 percent
(as the control) and are increased up to about 4 percent, usually in 0.5 percent increments. The data can be
graphed to show results.
Soil Analysis Labs
During this series of labs, students conduct both chemical and physical tests on soil samples. The results help
determine the suitability of the soil to grow crops. The lab directs students to construct an assortment of build-
ings, bury septic systems, and conduct additional activities.
Chemical properties:
•
pH:
measures the concentration of H
+
and OH
-
ions. The pH scale ranges from 1 to 14, with 7 being
neutral. Values below 7 are acidic, and values above 7 are basic. Some soil types require additives to
help neutralize the soil. In low-pH soils, some nutrients will not be available to be used by plants.
•
Nitrogen:
Common plant nutrient; major component of most commercial fertilizers.
•
Phosphorus:
Common plant nutrient; major component of most commercial fertilizers.
•
Potassium:
Common plant nutrient; major component of most commercial fertilizers. Also called potash.
Physical properties:
•
Color:
Moist soils are darker than dry soils and commonly contain many nutrients from decaying organic
material. Other soil colors may indicate the presence of iron and/or other minerals.
•
Friability:
This is the ability of the soil to crumble into smaller pieces with little pressure. This is import-
ant for the roots of plants to grow. The greater the friability, the easier it is for plant roots to grow.
•
Percent humus:
This test determines the soluble organic component of the soil. The higher the percent,
the better the water-holding capacity.
•
Permeability:
This is the measure of how much fluid can flow through soil. This can be determined by
investigating pore size and the connection between soil particles.
•
Ribbon test:
Roll a sample of moist soil beneath your fingers; the longer the roll of soil, the greater the
percentage of clay.
•
Soil type (particle size distribution):
Determines the percentage of clay, silt, and sand by placing a mix-
ture of soil in a cylinder, allowing the soil sample to settle, and then determining the percentage of each.
Sand, being heaviest, settles first; then silt; and finally clay. The percentages of each are then used to de-
termine the soil type, according to the soil texture triangle shown in Figure C-5.
•
Water-holding capacity:
How much water is held by the soil. Sand has the least, while clay has the
greatest.
