Figure 16.—Somewhat poorly drained Salmo soil
The four major processes that change parent material into soil are additions, losses, translocations, and transformations.
Additions
The most obvious addition is the accumulation of organic matter. As soon as plants begin to grow in fresh parent material, organic matter begins to accumulate. Organic matter gives a black or dark brown color to the surface layer. Even young soils may have a dark surface layer. Most additions of organic matter to the surface increase the cation-exchange capacity and the supply and availability of plant nutrients.
Losses
Most losses occur through leaching. Water moving through the soil dissolves certain minerals and transports them into deeper layers. Some materials, especially sodium salts, gypsum, and calcium carbonate, are relatively soluble.
Translocations
Salmo soil which has strata of alluvial material with textures of fine sandy loam and silt loam (0 to 18 inches) and has an accumulation of soluble salts at a depth of 4 inches. These soils exhibit translocation--the movement of soil material from one place to another. In areas of low rainfall, leaching often is incomplete. Water starts moving down through the soil, dissolving soluble minerals as it goes. There is not enough water, however, to move the minerals all the way through the soil. When the water stops moving and then evaporates, salts are left behind. Soil layers with accumulations of calcium carbonate or other salts form in this way. If this cycle occurs enough times, a calcareous hardpan can form.
Upward translocation and lateral movement occur in some soils. Low-lying soils can have a high water table, even if they are in dry areas. Evaporation at the surface causes water to move upward and salts (where present) are dissolved on the way and may be deposited on the surface as the water evaporates.
Transformations
Transformations are changes that take place in the soil. Micro-organisms that live in the soil feed on fresh organic matter and change it into humus. Chemical weathering changes the parent material. Some minerals are destroyed completely. Others are changed into new minerals. Many of the clay-sized particles in soil are actually new minerals that form during soil development.
USDA-NRCS publication "From the Surface Down", An Introduction to Soil Surveys for Agronomic Use, Second Edition, 2010.
Figure 16.—Somewhat poorly drained Salmo soil
The four major processes that change parent material into soil are additions, losses, translocations, and transformations.
Additions
The most obvious addition is the accumulation of organic matter. As soon as plants begin to grow in fresh parent material, organic matter begins to accumulate. Organic matter gives a black or dark brown color to the surface layer. Even young soils may have a dark surface layer. Most additions of organic matter to the surface increase the cation-exchange capacity and the supply and availability of plant nutrients.
Losses
Most losses occur through leaching. Water moving through the soil dissolves certain minerals and transports them into deeper layers. Some materials, especially sodium salts, gypsum, and calcium carbonate, are relatively soluble.
Translocations
Salmo soil which has strata of alluvial material with textures of fine sandy loam and silt loam (0 to 18 inches) and has an accumulation of soluble salts at a depth of 4 inches. These soils exhibit translocation--the movement of soil material from one place to another. In areas of low rainfall, leaching often is incomplete. Water starts moving down through the soil, dissolving soluble minerals as it goes. There is not enough water, however, to move the minerals all the way through the soil. When the water stops moving and then evaporates, salts are left behind. Soil layers with accumulations of calcium carbonate or other salts form in this way. If this cycle occurs enough times, a calcareous hardpan can form.
Upward translocation and lateral movement occur in some soils. Low-lying soils can have a high water table, even if they are in dry areas. Evaporation at the surface causes water to move upward and salts (where present) are dissolved on the way and may be deposited on the surface as the water evaporates.
Transformations
Transformations are changes that take place in the soil. Micro-organisms that live in the soil feed on fresh organic matter and change it into humus. Chemical weathering changes the parent material. Some minerals are destroyed completely. Others are changed into new minerals. Many of the clay-sized particles in soil are actually new minerals that form during soil development.
USDA-NRCS publication "From the Surface Down", An Introduction to Soil Surveys for Agronomic Use, Second Edition, 2010.