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P.M. 1987. Rethinking Continuous
Copyright: American Institute for Biological Sciences (AIBS)
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RETHINKING CONTINUOUS CULTIVATION IN
Subhead: The "Yurimaguas Technology" may not provide the
bountiful harvest predicted by its originators
Philip M. Fearnside
Department of Ecology
National Institute for Research in
the Amazon (INPA)
Published: BioScience Vol 37, No. 3: 209-214.
The land surrounding the
potential cornucopia, which could allow South American nations to
thrive despite continued population growth and poorly-distributed
resources. A set of recommendations to increase agricultural
productivity of this region is under trial at
(Nicholaides et al. 1985). This "Yurimaguas technology" involves
continuous cultivation, with the consecutive planting of two or
more crops per year, and requires a tailored program of
fertilizer application to the acidic and nutrient-deficient
soils. My analysis of the program indicates that previous
assessments of its long-term sustainability and profitability
were overoptimistic, and its proposed effect of reducing
deforestation is questionable. Governments should not count on
the Yurimaguas technology for an agricultural bonanza in
The "Yurimaguas technology" (Nicholaides et al. 1983a,b,
Sánchez et al. 1982; see also Sánchez 1977, Sánchez and Benites
1983, Valverde and Bandy 1982) refers to planting
crops per year as continuous rotations of either upland rice/
maize/soybeans or upland rice/peanuts/soybeans (Sánchez et al.
1982). A variation, called the improved Yurimaguas technology,
has rotations of maize/peanuts/maize; peanuts/rice/soybeans; or
soybeans/rice/soybeans (Nicholaides et al. 1985). Not all of the
problems affecting the Yurimaguas technology apply to the
other agricultural systems under testing at the Yurimaguas
The Yurimaguas technology was developed by agronomists from
Institute for Agricultural Research and Promotion (INIPA) to
demonstrate continuous cultivation in the Amazonian uplands.
The system's developers (Sánchez et al. 1982, p. 825) state "The
continuous production system is economically viable over a wide
range of crop and fertilizer prices, capital levels and labor
Soil fertility maintenance
cultivation cannot survive in
successive agronomic problems introduce costs that prevent the
strategy from being competitive with production elsewhere and
with other alternatives within
depletion, for example, becomes increasingly expensive and
difficult to correct. The cost of replacing all the nutrients
removed in the harvested crops or lost through such processes as
erosion, leaching must include not only the purchase and
transport of fertilizers, but also the expense of identifying for
each field, and informing the farmer, which elements are
deficient in what amounts. The principal macronutrients
(nitrogen, phosphorus and potassium), together with lime,
account for most of the expense of purchase and transport.
Sánchez et al. (1982) state that the quantities of fertilizer
needed to supply these elements are similar to those used by
farmers in the southern
imply that agriculture could be as profitable in the Amazon as in
much higher and the prices received for the crops much lower in
southeastern United States reflect the power of soil depletion
even under economic conditions that are more favorable than those
Although correction of micronutrient depletion requires only
small amounts of fertilizer, micronutrient deficiencies add
substantially to the farmers' cost and risk. Nutrients must be
balanced to avoid detrimental synergisms. In the Yurimaguas
technology, soil samples are analyzed after each crop in order to
calculate the proper nutrient mix for fertilization.1 Separate
information is needed for each field in order to make the system
work. Sánchez et al. (1982, p. 824) state that "the timing of
the appearance of soil fertility limitations and the intensity of
their expression varied among the (three test) fields, even
though they were near each other, were on the same soil mapping
unit, and had the same vegetation before clearing."
An awesome expansion of laboratory and extension services
would be necessary if the Yurimaguas technology were widely
implemented. While these services have been provided free of
charge (i.e., as a subsidy) by NCSU for the farmers collaborating
with the Yurimaguas experiment station, either the farmers,
taxpayers or consumers in the Amazonian countries would have to
bear these expenses in an expanded system.
The capital required to assure adequate fertilizer
application is more than all but a few Amazonian farmers have.
Not only must the requisite doses be purchased and applied for
each crop, but the farmer must be capable of making the outlay a
second time should an application be lost to heavy rains.
Torrential rainstorms that can sometimes drop several hundred
millimeters of precipitation in a 24-hour period occur every few
away an application of lime and lowering yields (NCSU Soil
Science Department 1975). In 1983 a similar event eliminated
recently applied nitrogen. In both cases the experiment station
was able to obtain and reapply the chemical inputs (Weischet
When the Yurimaguas results were obtained (Sánchez et al.
1982; see also Nicholaides et al. 1985), the eight-year-old
experimental plots required--in addition to nitrogen, phosphorus
and potassium--replacement of five other nutrients:
copper, zinc, boron and molybdenum. Three years later, two more
nutrients were deficient: sulfur and manganese.2 The research
group complains about the difficulty of obtaining adequate purity
in the soil samples and sufficient precision in the laboratory
analyses: with micronutrients, a difference of only a few parts
per million can have a large impact on crop yields. The
difficulty of obtaining such precision would be much greater for
farmers handicapped by geographical isolation, little education,
and a tenuous link to laboratory facilities through a chain of
often poorly trained and poorly motivated extension personnel.
The Yurimaguas authors admit: "In the complete treatment,
fertilizers and lime were added according to recommendations
based on soil analysis. During the second or third year,
however, yields began to decline rapidly. Soil analysis
identified two possible factors ... lime and ... magnesium."
(Sánchez et al. 1982, p. 824). If yields can suffer from
misassessment of nutrient needs in an experimental plot closely
monitored by a highly-qualified team of research agronomists,
such declines would be much more frequent in the fields of
Amazonian farmers--particularly the "shifting cultivators"
identified as the system's intended beneficiaries.
Erosion also impedes widespread use of the Yurimaguas
technology. The Yurimaguas experiment station is almost totally
flat, but signs of erosion are apparent at Yurimaguas wherever
slight slopes occur. Only a small portion of
a scale of a few tens of meters. Sá ánchez et al. (1982) indicate
that 50% of the Amazon region is well drained and has slopes less
than 8%, the maximum slope the group suggests for the system.
The survey on which the information is based (Cochrane and
Sá ánchez 1982) used the side-looking airborne radar (SLAR) imagery
of the RADAM Project (
Departamento Nacional de Produçăo Mineral, Projeto RADAMBRASIL
1973-1982) mapped at a scale of 1:1,000,000. When specific
localities are examined that are within the less-than-eight-percent slope areas, much of the land is found to have steeper
slopes. In a 23,600 ha area on
shown by Cochrane and Sánchez (1982) as all having less than 8%
slope, a map of 1180 20-ha quadrats based on measurements at 225
locations showed 49.3% of the land to have slopes at least 10%,
and some to have slopes as high as 89% (Fearnside 1984, 1986).
According to Sánchez et al. (1982, p. 822), "Only about six
percent of the Amazon has soils with no major limitations to
agriculture. Nevertheless they represent a total of 32 million
hectares. They are classified mainly as Alfisols, Mollisols,
Vertisols, and well-drained alluvial soils, and where they occur
permanent agriculture has a good chance of
and Vertisols, which are among the more fertile soils, normally
occur on more steeply sloping terrain than do the less fertile
soil types (Falesi 1972, Fearnside 1984). In selecting sites for
continuous cultivation in the Amazonian uplands, a tradeoff will
be faced between soil fertility and suitable topography. In
by ignoring long-term restrictions from unfavorable topography in
order to exploit higher-fertility soils. The choice of sloping
Alfisols for siting the sugarcane production area of the
plantations at Jari (Fearnside and Rankin 1985) illustrate this
tendency. The same temptation will apply to the Yurimaguas
Crop pests and weeds
The number and severity of pest and disease organisms
generally increase formidably as the cultivated area expands.3
Using pesticides to counter such problems is expensive. In
addition, insects typically develop resistance to pesticides,
leading to escalating dosages and costs.4 Heavy insecticide
dosages are already being applied at Yurimaguas. Tropical
agriculture generally is plagued by higher insect populations
than is agriculture in temperate locations because no winter ever
reduces insect populations (Janzen 1970, 1973).
Weed populations are already a major problem. Some weeds,
such as the grass Rottboelia exaltada in upland rice fields, have
not been controlled with herbicide spraying.5 Intensive hand
labor is used to control this weed at Yurimaguas--otherwise it
takes over the rice fields and seriously reduces yields.
Herbicides, like the other agricultural chemicals required by the
system, must be available at critical times. The herbicide
preferred at Yurimaguas for rice weeds (other than Rottboelia) is
metolachlor (tradename, Dual) which had been unavailable
While the experiment station has an adequate stockpile of this
and other chemicals, irregular market availabilities of inputs
would be a serious impediment for Amazonian farmers.
The preliminary results at Yurimaguas are poor indicators of
the system's performance under more representative circumstances.
In addition to subsidizing extension and soil analyses, NCSU and
the Peruvian government underwrite the true costs in a number of
indirect ways. Fifty percent of the cost of transportation for
fertilizer is provided by the Peruvian government, lowering the
between the experiment station and the Peruvian Air Force
provides free transportation for many lighter items and
needed when roads are impassable during the rainiest months.
Transportation to and from the Yurimaguas area is also subsidized
through government price supports. Fertilizers available in
commercial outlets in the town of
essentially the same prices as those in
phosphates, potassium and nitrogen fertilizers come to Yurimaguas
from the coast. Lime, fortunately, is available from limestone
outcrops along the
River is an affluent. The government buys products such as rice
at the same fixed prices whether in Amazonian locations or in the
irrigated rice areas along the northern part of
coast with paved highways to the major consumer markets. Thus,
in effect, the costs of transporting Yurimaguas rice to market
are being paid by urban consumers, taxpayers and
international creditors. The cost of providing these subsidies
to the increased number of farmers if the Yurimaguas technology
became widespread in
financially pressed governments of the Amazonian countries.
The collaborating farmers at Yurimaguas have received many
free inputs from the experiment station, including seeds,
fertilizers, lime, pesticides, and herbicides. In addition, the
roughly 25% of the participating farmers who live along a road
near the experiment station have received an important subsidy in
the form of the station's agricultural machinery. The farmers
pay rent for the machinery use, but rental equipment
more expensive elsewhere. The farmers would need to assume the
debt service costs for the capital necessary to buy tractors and
other equipment used only during a small portion of the
agricultural year. Farmers would also have to maintain the
equipment--an extremely expensive enterprise in the Amazon. Not
only does machinery deteroriate more quickly than in temperate
zones, but parts and the services of skilled mechanics are much
less readily obtainable.
Those collaborating farmers in locations too isolated to
have access to tractors have been subsidized more directly.
Digging and turning the soil using hand tools is a particularly
onerous task as the soil becomes progressively more compacted
under continuous cultivation. The amount of labor required
became prohibitive in the absence of tractors, and NCSU paid
outside laborers to go to the more remote properties and turn the
soil for the collaborating farmers. The Yurimaguas technology is
unlikely to spread if the work of turning the soil by hand is too
heavy for the collaborating farmers to do themselves and too
expensive for the agricultural production to justify their paying
others to do.
Subsidies are only one reason that the interpretation the
Yurimaguas authors give to their results is probably
overoptimistic. The farmers participating in the Yurimaguas
trials are not typical of the rural Amazonian population.
Nicholaides et al. (1984) leave no doubt that these model
farmers, described as "respected community leaders" (Nicholaides
et al. 1985), are some of the best in the Yurimaguas area.
Certainly the farmers who have volunteered to collaborate with
the experiment station are a select set who have more money,
initiative, and contact with urban society than the "shifting
cultivators" indicated by Sánchez et al. (1982) as the target
population for the Yurimaguas technology.
The agricultural extension portion of the program is also
atypical of Amazonian conditions. It has trained a team of local
extension agents, who have not yet been entrusted with the task
of serving as intermediaries between the station and the
collaborating farmers. Even such fundamental concepts as the
difference between linear and square measures are not easily
grasped by the local extension agents. The head of the
experiment station's extension sector has therefore retained
personal responsibility for communicating with the collaborating
farmers. Only the small number of farmers allows such a highly
qualified person to advise them directly.
The results presented in 1982 were overoptimistic because
the collaborating farmer program had been underway onlt three
years (Sánchez et al. 1982), and only two years of production
data were available. Even with traditional methods, yields in
tropical farmers' fields are usually reasonably high in
two years after clearing, only thereafter declining rapidly (Nye
collaborating farmers are therefore a poor indicator of long©term
sustainability. Heavy fertilization, of course, allowed much
higher yields and more crops per year than would otherwise have
been possible in the first two years. The claim that "the first
eight farmers averaged 3 tons of rice per hectare, 4.5 tons of
corn, 2.6 tons of soybeans and 1.8 tons of peanuts--similar
yields to those obtained at the station" (Sánchez et al. 1982, p.
825) does not demonstrate that high yields will be maintained in
the collaborating farmer plots over the nine-year period the
experiment station plots had run at that time, much less over the
The most telling evidence that the "technology validation in
farmer fields" (Sánchez et al. 1982) was premature in claiming
commercial success is the later history of the program. In 1982
the Yurimaguas researchers were able to state that "the tests
have expanded, and farmers are attracted by the prospects of
increasing their yields" (Sánchez et al. 1982, p. 825). The
picture has changed markedly in the years since. In 1985,
according to researchers at the experiment station, no farmers in
the Yurimaguas area were employing the Yurimaguas technology of
high-input continuous cultivation on a commercial basis. Even
the farmers in the special program, with inputs given or
subsidized by NCSU, had switched to lower-input options
introduced under the program. The Yurimaguas researchers'
calculation that the system would be highly profitable using
input and product prices prevailing in Yurimaguas (i.e., without
direct subsidies, but still including the indirect ones through
price supports, free extension, etc.) is contradicted by this
lack of response on the part of the area's farmers.
Limits to the technology
Large-scale expansion of the Yurimaguas technology is likely
to encounter limits. One is the inherent difference in
production efficiency between upland and irrigated rice.
Irrigated rice plantations in Peru's coastal lowlands, for
example, apparently can produce this cereal more cheaply than can
upland farming in the Amazon. Another constraint to high-input
agriculture is the availability of phosphate rock. Amazonia has
virtually no phosphate rock (de Lima 1976, Fenster and León
central state of Minas Gerais, and
coast state of
phosphates are located in
phosphate deposits are finite, and use has been increasing
exponentially since the end of World War II (Smith et al. 1972,
United States, Council of Environmental Quality and Department of
State 1980). As phosphate supplies dwindle in Amazonian
countries and in the world, the price of this input can
expected to increase dramatically, shifting the economic balance
even further away from high-input systems like the Yurimaguas
The Yurimaguas technology was presented as a practical means
of combatting deforestation. The systems developers imply that
Amazonia's high deforestation rates are caused by shifting
cultivators clearing land in order to grow food for their
subsistence needs: "We believe that the continuous cropping
technology can have a positive ecological impact where it is
practiced appropriately, because for every hectare that is
cleared and put into such production, many hectares of forest may
be spared from the shifting cultivator's ax in his search to grow
the same amount of food. People do not cut tropical rainforests
because they like to, but because they need food or fiber"
(Sánchez et al. 1982, p. 827; see also Nicholaides et al. 1985).
This view of the deforestation problem is incorrect.
Especially in Brazil, large ranching operations account for most
deforestation (Fearnside 1983). Even in parts of Amazonia where
small farmers are of greater relative importance, the farmers do
not fit the mold of traditional subsistence farmers who limit the
areas they cultivate once the production satisfies the
nutritional needs of themselves and their families, plus
to protect against shortfalls in lean years. Brazilian colonists
in government settlement programs, for example, have a virtually
insatiable demand for goods: the areas cleared and planted are
limited not by humble ambitions but rather by the amount of labor
and capital available to the farmers for expanding their
agricultural activities (Fearnside 1980). Increasing yields
would have little negative effect on clearing rates. Profits
from the intensive farming would probably be invested in rapid
deforestation for extensive land uses such as cattle pasture.
This scenario has often been the response of beneficiaries
of another cropping system promoted as an antidote to
have ready cash from a good cacao harvest frequently invest these
profits in cattle--an understandable strategy to insure against
low cacao prices or increased losses of cacao to fungal diseases.
Similarly, should farmers find the Yurimaguas technology
profitable, the earnings might well be invested in deforestation
for cattle pasture.
This is not to imply that farmers should be kept poor to
avoid deforestation. In considering the pros and cons of the
Yurimaguas technology, however, impact on deforestation is likely
to be a con rather than a pro. A correct understanding of the
deforestation process is essential both to formulating
policies to slow clearing and to developing sustainable land
The illusion that new technologies are about to transform
Amazonia into an agricultural breadbasket is inherently alluring
to government planners, who have in the past often promoted the
region as an
of every description. The El Dorado myth diminishes planners'
incentive to find solutions to such problems as the underlying
causes of the rapid spread of cattle pasture in
and the land tenure concentration and population growth in the
non-Amazonian areas from which a rising flood of migrants is
The Yurimaguas technology points to a persistent dilemma in
the search for ways to improve Amazonian agricultural systems.
Research and extension efforts to improve agricultural technology
are vitally important for the future of the area. At the same
time, their development must not be presented in a way that feeds
false hopes of an agricultural bonanza in
freeing national policymakers from facing the politically riskier
issues of population growth and resource concentration.
1.) Soil analyses and fertilizer dosage adjustments after every
crop in the "technology validation in farmer fields" described by
Sánchez et al. (1982) strongly suggest that this frequency of
sampling is integral to commercial application of the Yurimaguas
technology. Elsewhere in the Peruvian Amazon a commercial system
with only one sample per year for every five to ten hectares is
reported to be successful so far (J.H. Villachica, personal
communication, 1985, INIPA,
rate is a logical cost-reducing step, but would probably result
in lower yields than those reported for the Yurimaguas
2.) D.E. Bandy,
personal communication, 1985, NCSU/INIPA,
3.) This pattern accords with the theoretial expectations of
MacArthur and Wilson (1967); for an example with sugarcane, see
Strong et al. (1977).
4.) For an example from coastal Peru see Barducci (1972).
5.) J. Mt. Pleasant, personal communication, 1985, NCSU/INIPA,
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