Agroforestry for Soil Conservation - World Agroforestry Centre

22 Agroforestry for Control of Soil Erosion
Trends in research and policy
The traditional approach
The earlier or traditional approach, as practised by soil-conservation or
land-husbandry departments, is set out in standard texts and handbooks.
Most textbooks were directed at US conditions, but that of Hudson (1981)
is a clear summary, with a focus on the tropics, which has stood the test
of time. Handbooks are texts directed at the design of soil-conservation
measures in the field. Examples are FAO (1965), CTFT (Centre technique
forestiere tropicale) (1979), Leblond and Guerlin (1983), Weber and Hoskins
(1983a) and Hudson (1987), together with many national handbooks,
for example those for Kenya (Wenner, 1981) and India (Singh et al. 1981b).
The following is a summary of features of the traditional approach.
Whilst it may be selective, to point out the contrast with recent trends
discussed below, it is not intended as a parody! Features are:
1. Most attention was given to erosion of croplands, much less to that of
grazing lands.
2. Attention was focused on rates of soil loss, as tonnes per hectare/tons
per acre; as a consequence:
a. research was directed mainly at measuring rates of soil loss;
b. conservation measures were directed at reducing the rate of soil
loss; in the USA, the aim was to design conservation measures which
supposedly brought the rate below a specified level, called 'tolerable
erosion', although not many countries followed this practice of setting
a target figure.
c. attempts to assess the consequences of erosion for productivity, and
hence economic analysis, were directed at the effects of reduction
in soil depth.
3. The requirements of arable cropping with respect to soil cover were
taken as fixed and unalterable; hence conservation works were directed
at reducing runoff or breaking the force of downhill flow. This will be
referred to as the barrier approach to conservation.
4. Land-capability classification was widely employed as a basis for land-use
planning. The approach originated in the USA (Klingebiel and
Montgomery, 1961) and was adapted for many tropical countries, for
example in Africa, first by Zimbabwe (Conex, 1960) and subsequently
Malawi (Shaxson et al., 1977) and Zambia (Zambia, Department of
Agriculture, 1977). In this approach only land below a certain angle
(depending on rainfall and soil type) is classified as suitable for arable
use, primarily on grounds of erosion hazard. All steeper land should be
used for grazing, forestry or recreation and conservation.
5. Extension was conducted on the basis that soil conservation should come
first, as a necessary prerequisite for other agricultural improvements.