Agriculture Reference
In-Depth Information
Figure
9.5.
Textural triangle showing the textural name for soils with various amounts of sand,
silt, and clay.
clay. The term loam, found in the lower middle of the textural triangle, is a little differ-
ent. This term indicates that all three soil fractions—sand, silt, and clay—contribute
equally to the characteristics of this texture soil. The textural names of soils are encoun-
tered frequently in all agricultural work and food production.
Some soils contain a large amount of gravel, rocks, or stones. In these cases the
textural name will be prefixed with the appropriate designator, for example, stony
silt loam. Gravel, rocks, and stones can be important in crop production particularly
in carrying out cultivation and because such soils often have limited water and nutrient
holding or supplying capacities. Stones and rocks can be removed from a field to make
soil and water retaining structures (Fig. 9.6); however, it is usually impossible to
remove all larger rocks from a field.
A second characteristic of soil important in food production is its profile. That is, what
horizons it has and their characteristics; see Figures 9.1, 9.2, and 9.3. For instance, a soil
that is deep and sandy, with some clay in its lower horizons, will be good for crops
because it will provide deep rooting and provide water so that the crop can withstand
drought. Such soils will be good for root crops, allowing for easy development of
tubers. A soil with a lower layer that is high is clay might be good as a rice paddy since
the clay will slow or in some cases prevent the downward movement of water. Again
one can determine the characteristics of each horizon by the feel method mentioned above.
Another important aspect is any change in the soil profile with depth. Any change
in texture or compaction will tend to impede the movement of roots and water down
through the soil profile. This can be highly detrimental to rooting of plants and can
prevent them from developing a rooting system that will fully explore the soil. This
in turn will limit the ability of the plants to take full advantage of the nutrients and
water contained therein.
