Factors of Pedogenesis - Major Soil Groups of the World - page 25

2
Factors of Pedogenesis
The factors of pedogenesis were defined in Chapter 1. They are the
features of the environment that influence the development of soils.
We shall study them further now. In theory, the subject is inexhaustible
because anything that affects the environment concerns the soil directly
or indirectly. Actually we will limit ourselves here to the essentials,
which all scientists should know in order to understand the genesis and
spatial organization of soils.
We shall follow the same plan for each factor. Firstly, we shall make
observations showing what acts on the soil. Then we shall attempt
to understand its mode of action without going into details of the
mechanisms. Lastly, we will examine the range of consequences in
regard to the types of soils and their geography.
2.1 CLIMATE
2.1.1 Observations
Dokuchaev, wanting to work objectively, demarcated the soils in Russia
with equal humus content—the isohumic soils—and published his map
in 1883. The master of pedology established that the soils richest in
humus, the black earths, the famous Chernozems (Chap. 14), extended
east-west. Dokuchaev knew how to generalize and realized that the
great groups of soils were organized by latitude, on the scale of Greater
Russia, according to the types of vegetation: soils of the tundras, of
coniferous forests, of broad-leaved forests, of steppes and of deserts.
Obviously the soils depended on the climate. Dokuchaev then thought
that the same zonality had to be found in the mountains, because the
climate there varied from the bottom to the top. He verified this roughly
by organizing expeditions in the mountain ranges (Caucasus, Altai, etc.).