Sectoral Fallow Systems and the Management of Soil
Fertility: The Rationality of Indigenous Knowledge in the
High Andes of Bolivia
Author: Pestalozzi, Hansueli
Source: Mountain Research and Development, 20(1) : 64-71
Published By: International Mountain Society
URL: https://doi.org/10.1659/0276-
4741(2000)020[0064:SFSATM]2.0.CO;2
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Introduction
In the High Andes of Peru and Bolivia, at the upper
limit of agriculture, the indigenous population prac-
tices an agricultural system whereby fields are sectorally
cultivated for a few years and then lie fallow for several
years or decades. The fallow fields spontaneously cover
with vegetation and are used for cattle grazing (Zim-
merer 1991; Morlon 1992).
This traditional farming method based on potatoes
as the main crop produces comparatively high yields of
15,000 kg/ha under normal weather conditions, com-
pared with the average Bolivian yield of 5,000 kg/ha
(INE 1996). Fallow systems are widely practiced
throughout the High Andes as well as in other moun-
tainous regions (Andreae 1981; Orlove and Godoy
1986; Sarmiento et al 1993) and constitute a successful
strategy for utilizing soil with low nutrient content. How
can these comparatively high yields be explained?
There are two main reasons.
1. All authors and farmers agree that fallowing is a suc-
cessful way of restoring fertility to fields (Ruthsatz
and Fisel 1984; Mahnke 1985; Hanagarth1987).
However, only a handful of studies have been con-
ducted to determine how this regeneration takes
place (Hervé 1994; Sarmiento and Monasterio 1995;
Schaad 1995), while the comparable slash-and-burn
systems practiced in the humid tropics have been
studied in depth (Pfund et al 1997). In both sys-
tems, plant biomass plays a key role as a source of
nutrients.
2. By practicing special farming methods, farmers skill-
fully exploit ecological factors and convert them into
high yields (Schulte 1996; Saravia 1997). Specific
farming parameters such as choice of sector, fallow
age, and exclusion period for grazing, as well as ritu-
als, are collectively dictated by the land use system,
while the concrete aspects of farming such as choice
of crop, sowing date, quantity of fertilizer, etc., can
be individually selected by each farmer. Both are
rooted in a profound indigenous knowledge of the
local ecology, acquired over the centuries by careful
observation and through trial and error in working
the fields.
This article uses a case study to examine the eco-
logical principles and nutrient dynamics of a typical
fallow system. The results are compared with concrete
farming measures. How well are they adapted to eco-
logical conditions?
New influences and changing conditions such as
population increase, easier market access, and availabil-
ity of artificial fertilizers are presenting new challenges
to the farming community. How do farmers tackle these
innovations? Can they integrate them effectively into
the system? These questions are addressed at the end of
the article.
The study area
The study area lies in the eastern cordillera of the Bo-
livian Andes (66° 46′W, 17° 41′S) in the Department of
Cochabamba between 4000 and 4500 m above sea level
(Figure 1). The highest lying fields examined were at
4500 m. The climate is typical of mountainous regions
in the outer tropics, with a summer rainy season from
November to March and a winter dry season from April
to October. With barely 400 mm of annual precipita-
tion, the region is on the threshold of the semiarid cli-
mate zone (Lauer 1986), with an annual average tem-
64
Sectoral Fallow Systems and the Management of Soil
Fertility: The Rationality of Indigenous Knowledge
in the High Andes of Bolivia
Hansueli Pestalozzi
In the High Andes of
Bolivia, sectoral fallow
systems are a com-
mon form of land use.
Fields in the study
area (Japo, Depart-
ment of Cochabamba)
are cultivated for 3
years with potatoes
as the first crop and
then lie fallow for 9
years. Despite the low nutrient content of the soil and
the high elevation of the area (between 4000 and 4500
m above sea level), farmers achieve relatively high
yields. This is explained by traditional knowledge about
soil fertility management. The study focuses on nutrient
dynamics over a 12-year cycle. A participatory research
approach was applied to obtain information about
indigenous knowledge. Soil nutrient content, phy-
tomass, and yields were measured in 72 fields together
with the farmers. Subterranean phytomass was identi-
fied as the key factor in nutrient storage during the fal-
low period. A multiple linear regression model shows
three main factors that determine potato yields on culti-
vated fields. Farmers know about the nutrient dynamics
of the fields; hence, cultivation measures show an
impressive rationality. New elements such as mineral
fertilizer have been incorporated in the system in a sus-
tainable way. Participatory research intensifies these
processes, stimulating farmers to reflect about their
own land use system.
Keywords: fallow systems; soil fertility; High Andes;
Bolivia; agro-ecological assessments; phytomass mea-
surement; indigenous soil management.
Peer reviewed: August 1999. Accepted: August 1999.
Mountain Research and Development Vol 20 No 1 Feb 2000: 64–71
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perature of 6.6°C, as recorded by the climate measuring
station in the community of Japo, for the period 1994–
1997 (Pestalozzi 1999). The approximately 100 days of
frost are normally limited to the dry season, although,
depending on incline and altitude, acute night frosts
can occur at ground level during the vegetation period
with resultant damage to potato crops (Saravia 1997).
Fields are laid out primarily on Eutric Cambisols.
The sand-lime texture, slightly acidic pH value, and a
medium humus content of these soils favor the cultiva-
tion of potatoes, while the soil nutrient contents of P
and K are low to very low (Table 1).
The vegetation is dominated by bunchgrasses inter-
spersed with cushion plants and a large variety of
hemicryptophytic herbs and grasses, all of which form
an excellent root system (Pestalozzi and Torrez 1998).
Population and land use
The region is inhabited by an Aymara-speaking indige-
nous population. Population density is low, at 14 inhabi-
65
Research
Conductivity
b
n = 37 pH
CaCl2
a
(mS/cm) C
c
(%) N
tot
d
(%) P
e
(mg/kg) K
int
f
(mval/100 g)
Mean 4.77 47.9 2.24 0.20 6.13 0.39
SD 60.20 623.0 60.90 60.07 63.23 60.21
Rating Slightly Medium Medium Low to Low
acidic humus very low
TABLE 1 Soil parameters of
fields laid fallow for over 8
years.
a
0.01 M CaCl
2
, soil : water = 1:2.
b
Soil : water = 1:2.
c
Humid oxidation (by Walkley–Black).
d
Kjeldahl.
e
Extraction with NaHCO
3
at pH 8.2 (by Olsen).
f
Extraction with 0.5 M NH
4
Ac at pH 7
FIGURE 1 The study area lies
in the eastern cordiller of the
Bolivian Andes at altitudes
between 4000 and 4500 m
above sea level. (Photo by
author)
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Mountain Research and Development Vol 20 No 1 Feb 2000
tants/km
2
. The most important economic base is agri-
culture, with a high level of self-sufficiency. The organi-
zational forms show pre-Columbian traits. For instance,
land ownership and the sectoral fallow system are col-
lectively regulated.
The sectoral fallow system currently practiced is
illustrated in Figure 2. The region is divided into differ-
ent sectors (Aynokas). Every sector contains hundreds of
fields separated by natural vegetation, but only the fields
in three (usually adjacent) sectors are cultivated simulta-
neously. The fields in the other sectors are laid fallow.
Every year, the cultivated zone moves on a sector. In
addition to the main system, various subsystems (sub-
aynokas) have arisen in recent years, which operate
according to the same principle but substantially reduce
the distance farmers need to travel (see map, Figure 2).
The fields in the new sector are tilled toward the
end of the rainy season (Figure 3). The first crop, pota-
66
Hansueli Pestalozzi
FIGURE 2 Map of the studied sectoral fallow system showing the
boundaries of the sectors (Aynokas and Subaynokas) of the last cycle
lasting 12 years. Every year a new sector is replowed and sowed with
potato seed (indicated with date). Three adjacent sectors are farmed
simultaneously, while the remaining sectors are laid fallow and used for
grazing. The dots represent the studied fields.
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toes, is sown at the beginning of the next rainy season.
Forty different varieties of potato from five botanical
species are grown in the region (Saravia 1997). In the
second farming year, barley, oats, or Quinua are sown,
and in the third year, just barley is grown. The fields
then lie fallow for 9 years. They spontaneously cover
with vegetation and are used for cattle grazing (Figure
4). Fertilizer in the form of sheep dung or artificial fer-
tilizers is spread only on the potatoes.
No cattle must be grazed in the cultivated sectors
while the crops are growing, not even in the zones of nat-
ural vegetation between the fields. Two young men from
the village (Jilakatas) monitor adherence to these rules.
The system described above offers the following
advantages:
• Reduced workload: Instead of having to tend all the
animals, only the (neighboring) fields need to be
monitored (Zimmerer 1991).
• Pest control: The fallow time significantly reduces
the incidence of soil-borne pests such as nematodes
(Esprella et al 1994).
• Regeneration of grazing land and natural apothe-
cary: The normally heavily grazed, natural vegetation
between the fields can evolve and regenerate during
the space of three vegetation periods in the absence
of grazing pressure. These are also the zones where
the residents gather medicinal herbs and other plant
products (Genin et al 1994).
• Regeneration of soil fertility: Fertility is regenerated
during the collectively observed fallow period
(Sarmiento 1995).
It is worth explaining this last point in greater
detail. According to our working hypothesis, mineraliz-
ing nutrients in the soil are absorbed during the fallow
period by spontaneously growing vegetation and are
stored as plant biomass until the fields are tilled. After
the soil is tilled, the phytomass breaks down and pro-
vides the necessary nutrients for the cultivated plants.
This hypothesis accords with the observations of the
farmers. One of them explained the regeneration of
fertility in the following way: “This straw and these
roots, fertilizer is then!”
Methodology
The studies were conducted in 1996 and 1997 in close
collaboration with the farming community of Japo and
with the workers in the fields. The information on farm-
ing methods and indigenous knowledge was acquired
through participatory field research methods such as
semistructured interviews, field inspections, joint evalu-
ation of aerial photographs, workshops, participation in
social events, etc.
Seventy-two fields belonging to three farming fam-
ilies were analyzed for the agroecological studies. The
fields cover all stages of use and are situated in varying
microclimates. From an ecological standpoint, a ran-
dom selection may be assumed. During the dry season
in 1996 and 1997, a total of 116 soil samples were tak-
en. Cultivated fields and young fallow fields were test-
ed in both years. In addition, 22 samples were taken in
the natural vegetation adjacent to the fields. One
mixed sample per field was taken, consisting of eight
cylindrical probes of 0–20 cm (2-inch diameter). The
sample was then dried and sieved, and the fine soil was
analyzed using standard chemical methods of soil
analysis (Table 1). To obtain a rough phytomass mea-
surement, the residual (>1.6 mm) was washed in water
and the floating phytomass was collected, washed,
dried, and weighed.
Detailed phytomass readings were taken on five
ecologically comparable fields with different fallow
ages: The above-ground phytomass was gathered on
four randomly laid out square plots (1 m by 1 m), and
the below-ground phytomass was then gathered using
four cylindrical probes in each square and was then
processed as described above.
To analyze the nutrient dynamics, seven fields
were periodically examined between tilling of the fal-
67
Research
FIGURE 3 A farmer tilling his
field toward the end of the
rainy season. (Photo by author)
FIGURE 4 Crop sequence in the studied sectoral fallow system:
(1) Solanum tuberosum spp andigenum, Solanum ajanhuiri, Solanum steno-
tonum; (2) Solanum curtilobum, Solanum juzepczukii; (3) Hordeum vulgare;
(4) Avena sativa; (5) Chenopodium quinoa; (6) Chenopodium palladicaule.
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