Environmental Management: Principles and practice

Universal Soil Loss Equation
The Universal Soil Loss Equation (USLE) is a predictive tool which uses data on a
wide range of parameters to estimate and predict average annual soil loss. It was
developed in the 1930s by the US Soil Conservation Service and was improved in
1954 and again in 1978 by the US Department of Agriculture. It is widely used by
planners and consultants to check on existing and likely future soil loss and to
select appropriate agricultural practices and crops to sustain production. Developed
in midwestern USA, it has been modified to make it suitable for other environments,
so there are numerous revised versions (Hudson, 1981:258). The USLE should be
used with caution: problems arise when data are imprecise or unavailable and it is
best applied in situations where water rather than wind erosion occurs (although
there are modified versions intended to cope with wind erosion). A typical form of
the USLE is:
A = (0.224) RKLSCP
where:
A
=
soil loss;
R
=
rainfall erosivity factor (degree to which rainfall can erode soil);
K
=
soil erodability factor (soil vulnerability to erosion);

---

CHAPTER SIX
110
L
=
slope length factor;
S
=
slope gradient factor;
C
=
cropping management factor (what is grown and how);
P
=
erosion control practice factor.
Agroecosystem assessment
The agroecosystem zones concept was promoted by the FAO (1978) to provide a
framework for considering a range of parameters over a limited planning term with
the aim of promoting sustainable development. An agroecosystem is an ecological
system modified by humans to produce food or commodities, which generally means
a reduction in diversity of wildlife. Agroecosystem assessment (or analysis) evolved
in Thailand and attempts rapid multidisciplinary diagnosis that includes ecological
and socioeconomic concepts and parameters (Conway and Barbier, 1990:162–193).
It considers not only the farming system but also household characteristics, regional,
national, even global factors likely to affect the local community. The area under
consideration is zoned—often making use of a land use survey or land capability
assessment. Agroecosystem assessment needs to be approached with some caution
because it can lead to over-simple interpretation.
Farming systems research (FSR) is an open-ended, iterative, multidisciplinary,
holistic, continuous, farmer-centred, dynamic process applied to agricultural research
and development (it considers biophysical, social and economic factors and seeks to
integrate their study) (Shaner et al., 1982; Brush, 1986:221). There is no single method
but all approaches share five basic steps (Maxwell, 1986):
1
Classification—the identification of homogeneous groups (‘target groups’) of
farmers.
2
Diagnosis—identification of limiting factors, opportunities, threats, etc., for
the target group.
3
Generation of recommendations—which may require field experiments, pilot
studies and/or research station work.
4
Implementation—usually working with an agricultural extension service.
5
Evaluation—which may lead to revision of what is being done.
FSR is a systems approach applied to on-farm research, and is promoted as a
way of increasing farmer participation in development, and of generating improved
and appropriate approaches and technology. FSR includes study of factors which
may be beyond control of the farming community—world trade issues, global
warming, etc. Unless some ‘off-the-shelf’ input is available, FSR usually takes time—
often two years, sometimes from five to 15 or more years.

---

ENVIRONMENTAL IMPACT, HAZARD AND RISK MANAGEMENT
111