Agriculture Reference
In-Depth Information
soil types elsewhere will improve the transfer of knowledge and may, thus, in prin-
ciple, contribute to higher soil security. The case studies show that researchers are
increasingly investigating conditions on real-life farms in close interaction with
farmers and are on the lookout for “lighthouse” examples where inventive farmers
have achieved successes on a particular soil type, sometimes to be identified as dis-
tinct phenoforms. This clearly happened in the two Dutch case studies.
The soil type, formed by a unique set of interacting soil-forming factors, is rep-
resented by mapping units on soil maps, and such units have traditionally been used
as “carriers” of information for land evaluation purposes, extrapolating experiences
obtained (Bouma et al. 2012). Bouma et al. (1998) and Bouma (2002) illustrated
in this context the significantly different behavior of seven soil types from China,
Zambia, Nigeria, Colombia, and Indonesia in terms of their Yw values (the water
limited yield). If, however, soil mapping units that are, according to the legend of the
soil map, supposed to contain certain soil types are quite heterogenous or ill defined,
the procedure is questionable and, indeed, many questions have been raised about
this procedure. Recent attempts to use sensors to directly obtain soil data (such as
the organic matter content, the cation exchange capacity, and pH of surface hori-
zons) (e.g., Kweon 2012) without using soil maps is potentially valuable but cannot
explain dynamic physical, chemical, and biological soil behavior the way a well-
characterized soil type can, be it in an often qualitative manner. Extrapolation of
soil behavior from one well-characterized location to a new location on the basis of
CEC, organic matter content, and pH of surface horizons is, of course, impossible.
Such sensing data would therefore be most useful when coupled with the type of soil
being observed.
Also, when only data obtained at the soil surface are available, important subsur-
face properties that are essential for soil behavior remain unknown. Soil chemical
analyses used in the African case studies, reviewed in this chapter, were made in
samples from 0 to 20 cm depth. However, plant roots always go much deeper. Also,
many soils have subsurface horizons that strongly affect soil behavior: Lixisols have,
for example, a clayey subsoil in contrast to Arenosols. The clay layer often ponds
water, causing anaerobic conditions that strongly impair root development and crop
growth. This is not observed when only a sample of surface soil is taken for chemical
analyses. Soil type data therefore provide a valuable context for separate chemical,
physical, and biological measurements.
2.5.3 o
ther
f
actorS
d
etermining
S
oil
S
ecurity
Aside from a set of socioeconomic, institutional, and ethical challenges for small-
holder agriculture as mentioned in Section 2.1, IFAD (2012) distinguishes three
important soil-related issues: use of fertilizers, conservation agriculture, and irriga-
tion. The restricted size of this chapter only allowed discussion of the soil fertility
issue. However, recent reviews of conservation agriculture (e.g., Vlek et al. 2008
and the Desire project,
www.desire-project.eu)
show that problems are severe but
that efforts in many countries to combat soil degradation and erosion are succesful,
particularly when approached comprehensively in large-scale watersheds, requiring
cooperation among farmers and effective institutional arrangements. Dealing with
