Page 20 - Soil Degradation, Conservation and Remediation

1.4 Soil Fertility, Soil Productivity, Soil Quality, and Soil Health 5

Class IV. Soils in this class have severe limitations that restrict the choice of plants
require very careful management, or both. The restrictions in use for soils in this
class are greater than those in Class III, and the choice of plants is more limited.
These soils may be used for cultivated crops, pasture, woodland, range, or wildlife
food and cover.

Class V. Soils in this class have little or no erosion hazard but have other limitations
impractical to remove that limit their use largely to pasture, range, woodland, or
wildlife food and cover. Soil limitations restrict the kinds of plants that can be
grown. They are nearly level, but some are wet, frequently overflowed, are stony,

have climatic limitations, or have some combination of these limitations.

Class VI. Soils have severe limitations that make them generally unsuited to cultiva-
tion and limit their use largely to pasture or range woodland, or wildlife food or
cover. Physical conditions of soils in this class are such that it is practical to
apply range or pasture improvements. Limitations include steep slope, severe
erosion hazard, stoniness, and shallow rooting.
Class VII. Soils have very severe limitations that make them unsuited to cultivation

and that restrict their use largely to grazing woodland, or wildlife. Limitations
include very steep slopes, erosion, shallow soil, stoniness, wet soil, salts, and
unfavorable climate.
Class VIII. Soils and landforms in this class have limitations that preclude their use

for commercial plant production and restrict their use to recreation wildlife, or
water supply or to aesthetic purposes. Limitations include erosion, stoniness, wet
soil, low moisture, salts, and severe climate.

1.4 Soil Fertility, Soil Productivity, Soil Quality,
and Soil Health

To avoid confusions, let us fi rst define and explain some terms closely related to
each other and frequently used in soil science literature. These terms are not only
important in soil use but also for its future management and environmental impact.

1.4.1 Soil Fertility

Soil fertility refers to the capacity of soils to supply plant nutrients in available forms,
in proper balance and the absence of any sort of toxicity. Plants absorb 14 nutrients
from the soil (nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron,
manganese, copper, molybdenum, zinc, boron, chlorine, and nickel). Plants need the
presence of these nutrients in ionic forms (soluble and exchangeable) for absorption.
If the soil contains inadequate amount of any one or more of these nutrients, plants
will suffer in growth and reproduction. If the soil is adequately fertile, plants may