114 D.D. Poudel et al. Agriculture, Ecosystems and Environment 79 2000 113–127
instilled amongst farmer cooperators of the magnitude of soil loss, strengthen the argument for farmer participatory research. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Soil erosion; Cropping sequences; Contour hedgerows; EPIC model; Steepland; Farmer participatory research
1. Introduction
Commercial vegetable production on steeplands of Southeast Asian countries has expanded considerably
over the past decades, due to increasing demand for fresh vegetables in the lowland Asian cities Pres-
bitero et al., 1995; Midmore and Poudel, 1996; Cox- head, 1997. Population growth and bans and import
restrictions imposed by governments on selected veg- etables in some Southeast Asian countries are largely
responsible for increased domestic supply and demand for fresh vegetables, leading to the expansion of veg-
etable crop production in ecologically fragile areas Coxhead, 1997. Productivity decline induced by soil
erosion is one of the major problems constraining the sustainability of agricultural crop production in the
steeplands of Southeast Asia Hashim et al., 1995; Presbitero et al., 1995; Midmore and Poudel, 1996.
Without doubt, expansion of steepland vegetable pro- duction in Southeast Asian highlands has, besides re-
sulting in increased soil erosion, also led to significant externalities such as sedimentation of waterways and
reservoirs, nutrient losses in runoff water, and decline in down-stream water quality Midmore et al., 1996,
1997.
In attempts to stem and manage soil erosion on steeplands, researchers have evaluated a number of
erosion control technologies, such as alley cropping, contouring, strip cropping, and grass barriers Tacio,
1993; Comia et al., 1994; Paningbatan et al., 1995; Presbitero et al., 1995; Sombatpanit et al., 1995. Alley
cropping, which is a special form of an agroforestry system in which food crops are grown in alleys formed
by hedgerows of trees or shrubs Kang et al., 1986, has been effective in minimizing soil erosion on steep-
lands Tacio, 1993; Comia et al., 1994; Paningbatan, 1994. Considerable interest on the part of various
research and extension agencies, especially in South- east Asia, exists in the planting of leguminous con-
tour hedgerow trees on sloping lands as barriers for soil erosion and for the production of green manure
for field crops. However, there is no strong evidence of farmers’ adoption of these technologies Fujisaka,
1989; Garrity, 1993; Comia et al., 1994; Poudel et al., 1998.
The practice of growing crops in sequence in the same field, which is also known as sequential crop-
ping, is considered as one of the major tools of soil conservation Troeh et al., 1991; Amir, 1996. Se-
quential cropping provides a crop cover during most of the year. The crop cover during rainfall events re-
duces kinetic energy of the raindrops and increases the infiltration rate, which minimizes runoff and soil
loss. Presbitero et al. 1995 reported as much as 25 times more soil loss from bare plots than from
plots with multiple cropping of corn and peanut Arachis hypogaea with Leucaena leucocephala con-
tour hedgerows. Hashim et al. 1995 reported about 11 times more soil loss from a bare plot compared
to a plot planted with cocoa Theobroma cacao in Malaysia. Several factors have been reported as major
determinants of soil loss and runoff, especially with annual cropping systems. These include the number
of days required for the development of a full canopy cover, planting distances, time of planting, fertility
level, and soil management practices Hudson, 1957; Aina et al., 1976; Lal, 1977; Paningbatan, 1994; Mid-
more et al., 1996. Steepland vegetable production systems in the highlands of Southeast Asia are char-
acterized by their broad range of cropping patterns, such as sole cropping e.g. potato Solanum tuberosum
L.-fallow, monoculture e.g. cabbage-cabbage, and sequential cropping e.g. tomato-corn-cabbage Tau-
tho and Kumori, 1991; Jansen et al., 1995; Poudel, 1995; Midmore et al., 1996. Because of the multiplic-
ity of possible cropping sequences, field experiments to evaluate their effects on soil loss and runoff water
may be constrained by time and resources.
Erosion models can be used to evaluate the long-term effects of a large number of management
strategies, including cropping sequences, on soil ero- sion in a relatively short time and at low cost National
D.D. Poudel et al. Agriculture, Ecosystems and Environment 79 2000 113–127 115
Soil Erosion-Soil Productivity Research Planning Committee, 1981. While the well-tested empirical
Universal Soil Loss Equation USLE can be modi- fied to cope with steepland situations in the tropics
Lo, 1994, process-based models are generally pre- ferred Paningbatan, 1994; Hashim et al., 1995. The
Erosion-Productivity Impact Calculator EPIC model Williams et al., 1984 is a comprehensive field-scale
model that operates on a daily time step King et al., 1996. It is process-based and has been tested exten-
sively in a number of local, regional, and national studies in continental USA and Hawaii Steiner et al.,
1987; Williams, 1991; Phillips et al., 1993; Richard- son and King, 1995; King et al., 1996; Cavero et al.,
1998. EPIC has the capability to simulate complex crop rotations for decades and centuries; it is designed
to help the decision makers to evaluate alternative cropping systems, and predict their socio-economic
and environmental sustainability Cabelguenne et al., 1990; Jones et al., 1991.
Farmer participatory research FPR has been proposed as an approach in developing appropriate
agricultural systems that are indisputably acceptable to farmers yet contribute to the improvement and mainte-
nance of agricultural sustainability and environmental quality Fujisaka, 1989; NRC, 1991; Edwards et al.,
1993; Cox et al., 1996; Rhoades, 1997. Rhoades and Booth 1982 developed the Farmer-Back-to-Farmer
model which was a forerunner to the participatory ap- proach. This model begins and ends with farmer, and it
involves four activities: 1 farmer-scientist diagnosis 2 interdisciplinary team research 3 on-farm testing
and adaptation, and 4 farmer evaluationadaptation. Thus, the farmer is considered as an ‘expert’ member
of the interdisciplinary team and is integrally engaged in problem identification, definition, and solution
design.
In the upper slopes of the Manupali watershed in northern Mindanao in the Philippines, soil erosion on
commercial vegetable farms was reportedly largely responsible for a declining crop productivity. As part
of a larger project on Sustainable Agriculture and Natural Resources Management SANREM-CRSP
NRC, 1991, farmer participatory research on soil erosion management was started in 1994. The ob-
jectives of this research were: 1 to measure soil erosion losses on farmers’ fields using Farmer Partic-
ipatory Research approach, 2 to assess the effects of cropping sequence on soil erosion in steepland veg-
etable systems, and 3 to provide recommendations for choice of cropping sequences to farmers, credit
agencies and agricultural technicians for enhanced production system sustainability.
2. Methods
