Soil formation - Fundamentals of the Physical Environment - page 620

Scheme of the British government unsuccessfully attempted to cultivate groundnuts
(peanuts) on tropical soil in Tanzania (then Tanganyika). It was the induration of the soil
structure which proved to be the most difficult physical factor of soil fertility to
ameliorate. The gravelly, concretionary surface erodes mechanical implements very
quickly and in the Groundnut Scheme it was found that a conventional set of discs would
last little more than a month! Lateritic soils are still very much 'problem soils', as they
occur in less developed countries which are keen to improve their agricultural
productivity; shifting cultivation is still the normal practice in many of these areas (see
Colour Plate 22 between pp. 400 and 401).
THE SOIL CATENA: THE TOPOGRAPHICAL FACTOR IN SOIL
FORMATION
We have seen earlier in this chapter (p. 401) that the Russian soil scientist Dokuchaiev in
the late nineteenth century was the first to recognize that soils are independent natural
bodies reflecting the effects of zonal and local soil-forming agents. By the end of the
century he realized, however, that some soils are not only a factor of local zonation but
could exist in several zones (gleys, alkali soils, limestone soils); these he called
transitional soils . There are also soils which do not appear to be controlled by zonal
effects, which he called abnormal soils (alluvium, aeolian deposits). Sibirtsev, a follower
of Dokuchaiev at the beginning of the twentieth century, called the three types of soils
zonal , intrazona l and azonal soils. This concept of soil zonality classifies soils which
primarily reflect climate and vegetation as normal or zonal. Those soils which reflect
some local factor such as excess water or carbonates (which relate to relief and parent
material) are intrazonal and may occur in several geographic zones. Similarly, azonal
soils cross zonal boundaries and are essentially young, unweathered parent materials.
During the twentieth century one of the major additions to the concepts of soil science
was the innovative concept of the catena , introduced by Milne in the 1930s whilst
studying the regular repetition of soils in East Africa. The term (Latin catena , 'chain')
was originally used to designate a complex mapping unit, but later soil scientists came to
recognize it as a fundamental unit in the landscape, reflecting the ways in which soils are
influenced by slope or the topographic factor of soil formation. Milne recognized two
types of catena. In the first the parent