66 E.F. Viglizzo et al. Agriculture, Ecosystems and Environment 83 2001 65–81
Table 1 Comparison of farming intensity in three countries that differ in resources and external-inputs use
a
Argentina USA
The Netherlands Cropland area ×1000 ha
35750 189915
924 Average yield kgha
2257 4383
6641 Annual use of fertiliser kgha
4 93
748 Annual use of pesticides kgha
0.40 1.97
10.47 Tractors number100 ha
0.58 2.46
20.58 Irrigated cropland
5 10
59 Cattle numberkm
2
18.79 10.41
130.06 Pigs numberkm
2
1.46 4.97
375.54
a
Source: WRI 1990 after various sources.
options to test hypothesis and theories when experi- mentation is not possible, the applicability of poorly
tested principles is cause of concern among ecologists Pienkowski and Watkinson, 1996.
Ecology may benefit from low external-input farm- ing to test principles and deliver practical lessons.
The pampas of Argentina represent a large scale, long term, and non-controlled experiment in low input
farming that started at the end of the 19th century and lasted until the beginning of the 1990s. Until
then, lands had maintained their pristine condition with negligible human intervention. One century of
land transformation Pizarro, 1997; Solbrig, 1997 in different ecoregions Ghersa et al., 1998 was a valu-
able source of variability that has comprised different crop, cattle, and crop-cattle production activities.
Low external-input farming refers to systems that use reduced quantities of inputs, such as fertiliser,
pesticide, irrigation, high-yielding crops, concentrate feed, machinery, etc. Matson et al., 1997, that in-
volve fossil energy in manufacturing or operation. In comparison with more intensive schemes of USA
and the Netherlands, the low input use and crop yields in Argentina before the 1990s are shown in
Table 1.
This article provides an overview of one century of land transformation under low input conditions in the
pampas, and its consequences on ecological structures like land-use and land-cover, and functions, such as
energy flow, nutrient dynamics, hydrological process, and the trade-offs between productivity, stability and
sustainability. The study focuses on large geographi- cal scales: the pampas region, and its corresponding
five ecoregions. The key expected outcomes of this investigation are to a interpret the ecological dynam-
ics of the region, and b obtain technical coefficients for application, such as land evaluation, allocation and
management.
2. Methods
2.1. Characteristics of the study area The Argentine pampas is a wide plain with more
than 52 million ha of lands suitable for cattle rearing and cropping. Similar to the Great Plains of North
America, the area has a relatively short farming his- tory. Both regions remained as native grassland until
the end of 19th century and the beginning of 20th century, and then, both were used for cattle and crop
production under dryland conditions. In both cases, the generalised application of agronomic practices
suitable for humid zones caused severe episodes of soil erosion in semiarid and subhumid areas during
the first half of the 20th century Cole et al., 1989. Examples of this ecological disruption were the ‘dust
bowl’ in USA, and a similar process in the west- ern pampas Covas, 1989; Viglizzo et al., 1991; Lal,
1994.
According to rainfall and soil quality patterns, the region was divided in five ecoregions Fig. 1. Briefly,
the arable soils of the pampas have few limitations to crop production, and the majority is suitable for
grazing. Following FAO’s guidelines for land use FAO, 1989, well-drained conditions on deep soils
that can support land use indefinitely, predominate in the so-called Rolling pampas. Organic matter, as
E.F. Viglizzo et al. Agriculture, Ecosystems and Environment 83 2001 65–81 67
Fig. 1. Location of the pampas in the Argentinean territory.
well as the nitrogen contents and the granular struc- ture of soils decrease from the eastern humid to the
western semiarid lands. Most lands are suitable for cultivation in the Central pampas, although suscep-
tibility to wind erosion imposes some limitations to crop production. Problems of salinity, drainage and
water erosion limit production in the marginal lands of the Flooding and the Mesopotamian pampas
Musto, 1979; Casas, 1998. In spite of the fact that soil deep limits crop production in the Southern pam-
pas, most lands are in general suitable for cultivation. Some marginal lands, suitable for cattle production
only, can also be found on the western sector of the region. Unsuitable lands that cannot support land use
68 E.F. Viglizzo et al. Agriculture, Ecosystems and Environment 83 2001 65–81
on a sustained basis, are very rare in the pampas. In a large part of the region, cattle and crop produc-
tion activities are combined in different proportions according to their susceptibility to environmental
constraints Viglizzo, 1986. Cattle production ranges from steer fattening to cow-calf operations on peren-
nial and annual pastures, and native grasslands Hall et al., 1992. The rainfall regime varies in space and
time, determining occasional extreme conditions of droughts and floods over wide areas Viglizzo et al.,
1997.
2.2. Data sources Different sources of information have been utilised
in this study: 1 eight general agricultural censuses of years 1881, 1914, 1937, 1947, 1960, 1969, 1973,
and 1988 that comprised the totality of farms; 2 a variety of production and yield statistics published by
the Secretary of Agriculture; 3 energy, nitrogen N, phosphorus P and potassium K concentration of in-
puts and outputs as determined by various authors and 4 published accounts of change in flora and fauna.
Data on land use and crop yields were analysed for all districts. Land use was expressed in terms of the
relative area of crops, pastures and natural grass- lands with respect to the total area devoted to farm-
ing activities. The analysis comprised dominant crops, such as wheat Triticum aestivum L., maize Zea mays
L., sorghum Sorghum bicolor L. Moench., linseed Linum usitatissimum L., soybean Glycine max L.
Merr., sunflower Helianthus annuus L. and peanut Arachis hypogaea L., and pastures based on annual
and perennial grasses, leguminous perennial pastures, and mixed grass-leguminous pastures. Because of the
lack of long term data, beef production was estimated from equations for each ecoregion Viglizzo, 1982
that relate stocking rate available data to meat pro- duction per hectare. Simple linear and quadratic re-
gression models were used to estimate trends in land use. Average values on land-use and statistic variabil-
ity among political departments for each ecoregion are provided in Appendix A.
The complement of different approaches and infor- mation sources was used to reinforce the explanation
of ecological processes Carpenter et al., 1998; Foster et al., 1998; Fuller et al., 1999. Interpretation
of results under the framework of basic ecologi- cal principles was useful to check the coherence
of analysis. The theory of ecological succession Clements, 1916 and its later conceptual evolution
Odum, 1969; Connell and Slatyer, 1977; Clapham, 1983 seem to be particularly suitable to this
purpose.
2.3. Land useland cover Land use involves both the purpose for which the
land is used, and the manner in which the biophysical attributes of the land are manipulated, affecting the
structure and function of ecosystems. On the other hand, land cover is the biophysical state of the land
surface, which determines the basic structure and functional characteristics of ecosystems IGBPHDP,
1995. Different patterns of land use in time and space were estimated by means of the relative oc-
cupation of lands by natural grasslands, crops, and introduced pastures in the five-study ecoregions along
the century. A land-cover factor was an estimation of the relative seasonal coverage of land with
resources natural grasslands, introduced pastures, crops during one century of farming in the five-study
ecoregions. The difference between 100 and the cover factor value allows the identification of periods of
bare soil Viglizzo et al., unpublished. Maps show- ing changes of land use in different historical periods
were elaborated with the use of kriging analysis Burgess and Webster, 1980a,b, which is a method
to estimate areas through an interpolation of geo- graphically referenced points that were not physically
sampled.
2.4. Energy model An energy model proposed by Odum 1975
based on basic input–output relationships, was utilised for the energy analysis. Different sources
Grossi-Gallegos et al., 1985; Reed et al., 1986; Stout, 1991; Conforti and Giampietro, 1997 were used to
estimate the energy values of inputs and outputs. The following energy values expressed in MJ ha
− 1
per year were used for inputs: a incoming solar energy
ranged between 55.12 and 59.13×10
6
from cloudy to sunny areas; b average energy consumption in terms
of oil equivalents was estimated at 462, 323, 12, and 639 and for tillage, agrochemical application, input
E.F. Viglizzo et al. Agriculture, Ecosystems and Environment 83 2001 65–81 69
transportation, and output transportation, respectively, and c energy consumption was 418, 20.3, and 277
as pesticides, seeds, and tractors and machinery, re- spectively. Energy values of outputs in MJ kg
− 1
were estimated at 25.53 for sunflower, soybean and peanut grains, 16.33 for wheat, maize and sorghum,
and 13.36 for bovine meat. An aggregated analysis of inputs, outputs, and
output–input relations for solar and fossil energy was computed for different points in time. Fossil
energy consumption in typical farming operations and machinery was estimated for the 1940s and the
1980s, and for the five-study ecoregions. The amount of operations was considerably higher during the
1980s. Estimations have been made for perennial pastures, summer and winter grain pastures, sum-
mer and winter grain crops, and oil–seed crops. The analysis involved estimations of oil consumption for
tillage, agrochemical applications, and input and out- put transportation, as well as the energy utilised to
manufacture herbicides, insecticides and genetically improved seeds. Based on literature data Ehrlich
et al., 1977, it was assumed that fossil energy consumption during the 1880s was approximately
equivalent to 1 of the estimations made for the 1940s.
2.5. Nutrient balance Using a simple mathematical model, the balance of
N, P and K was estimated by difference between the main sources of gain and loss Lértora et al., 1998.
The respective nutrient content in g kg
− 1
of prod- uct of wheat, maize, sorghum, linseed, soybean, sun-
flower, peanut and meat were 22.9, 16.3, 20.0, 40.8, 58.1, 40.8, 51.2 and 27.0, respectively, in terms of
N; 4.3, 3.5, 3.4, 8.0, 6.8, 7.6, 6.1 and 43.1, respec- tively, in terms of P; and 4.9, 3.7, 4.0, 9.8, 11.3,
11.6, 11.3 and 5.9, respectively, for K Lloyd et al., 1978; NRC, 1978. In the case of N, extraction from
soil by crops and cattle production was subtracted from literature-based N input estimation to the soil
by legumes in different ecoregions. The following is- sues have been taken into account: a the area de-
voted to crop production; b the area devoted to legu- minous perennial pastures; c the N lost by outputs
grain and beef that was closely related to yield and N density in products and d the N fixed by legu-
minous, and negligible amounts added by occasional fertilisation.
3. Results and discussion
