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
The pristine pampas can be considered a vast natu- ral grassland ecosystem that have reached a condition
of dynamic equilibrium with the surrounding environ- ment along succession processes. Following accepted
principles in ecology Margalef, 1968; Odum, 1969, a condition of dynamic equilibrium in the pampas could
be characterised as follows: a large accumulation of biomass mainly from herbaceous species and nutri-
ents in biomass and soil due to the predominance of closed natural cycles; b high diversity of functional
groups comprising different plant and animal species; c maintenance of complex trophic networks; d con-
tinuity of biological processes through out the year; e low rate of energy flow and low biomass productivity
due to the accumulation of fibrous inert material; f high stability of functional groups and g high sus-
tainability and self-regeneration capacity of the whole ecosystem. All these features have been periodically
subjected to normal fluctuations and both, forward and backward movements, in response to environmental
variability.
3.1. Structural changes 3.1.1. Land use
Significant shifts in the ecoregional pattern of land use have taken place during the analysed century.
Elaborated on national census data, sequential maps in Fig. 2 show the evolution of croplands at the be-
ginning 1880s, the middle 1940s, and the end 1980s of the period. After finishing the so-called
conquest of desert in 1879, most of the area remained for decades as a wide natural grassland with little
human intervention. Approximately one-half of the region showed 10 of the land cultivated with
annual crops in the 1880s Fig. 2a, while the rest was exclusively covered by natural grassland. The
majority of the land was utilised for cattle grazing with different levels of managerial organisation from
open fields to varying ranching schemes. Consider- ing the long-term duration of ecological succession,
a major ecological disruption was induced by man in
70 E.F. Viglizzo et al. Agriculture, Ecosystems and Environment 83 2001 65–81
Fig. 2. One century of conversion of grazing lands into croplands in the Argentinean pampas.
relatively few years. Thus, no areas completely free of annual crops were recorded during the 1930s, with
a crop occupation of lands that ranged between 20 and 60 Fig. 2b, even in the marginal and fragile
western lands. Although an extensive flooding had produced major alterations on land use especially in
the flooding pampas at the end of the 1980s, the area of annual crops ranged between 40 to more than
60, being quite evident in the most fertile lands of the rolling, the central and the southern pampas
Fig. 2c.
The conversion of natural grasslands into cultivated grasslands and croplands was not homogeneous in all
ecoregions Fig. 3. Conversion happened very early in the rolling pampas, given that more than 60 of
natural lands had been transformed in the 1910s. Only 10 of the land has no agricultural use nowadays.
On the other extreme, the flooding pampas has experi- enced the lowest conversion rate. On average, 60 of
land remained as modified natural grassland at the end of the 1980s. The other ecoregions showed different
degrees of land transformation. With the only excep- tion of the rolling pampas, where the cropland raised
steeply between the 1960s and the 1990s, the others had maintained a rather stable cropping area after a
wave of rapid increase during the 1920s. Again, with the exception of the rolling pampas, the rest of the
zones showed a persistent increase of cultivated pas- tures, contradicting the belief that croplands had ex-
panded all over the pampas since the 1950s, displacing cattle production to the semiarid, marginal lands of the
western pampas. Neither crop has expanded all over the region, nor livestock has been removed from better
lands.
3.1.2. Land cover Land use and land cover are interrelated. Because of
land transformation, natural habitats have been deeply fragmented with unknown consequences on biodiver-
sity. The land cover pattern, which refers to physical attributes of the land surface, was modified in a few
decades, especially in the rolling, the central, and the southern pampas, where annual periods of biological
recession by the shorter life cycle of crops have in- creased during the century Fig. 4. This was partic-
ularly evident when the wheat–soybean rotation was introduced into the rolling pampas. Land cover and bi-
ological disruption have been much less severe in the flooding and the Mesopotamian pampas, where a di-
versity of natural and perennial species has persisted until now.
Various surveys Parodi, 1930; Lewis et al., 1985; Burkart et al., 1990; Soriano et al., 1991 support the
study of evolution of plant communities in some areas of the pampas, but no definitive conclusion on changes
in biodiversity is available. According to Lewis 1997,
E.F. Viglizzo et al. Agriculture, Ecosystems and Environment 83 2001 65–81 71
Fig. 3. Land use transformation in five ecoregions of the pampas plain along one century.
only 57 and 77.3 of the species identified by Parodi 1930 in two different locations of the rolling pampas
can be found nowadays. But at the same time, approx- imately 10 new species that were not described by
Parodi in 1930 have appeared. An important percent- age of the remaining natural species are considered
and treated as weeds in the main crops Ghersa et al., 1998.
From a successional perspective, the anthropogenic disturbance that began at the end of the 19th century
pushed the pampas away from their climax condi- tion. Over one century of farming intervention, land-
scapes were altered by interacting human-induced and natural disturbance forces that led to mosaics
and patches of different successional ages. They rep- resent, in variable degree, a backward movement
of succession to younger seral stages Krebs, 1972 with major alteration of structure and function. Such
backward movement that was induced by man aim- ing at utilitarian objectives has represented, in prac-
tice, a simplification of structures and functions that resemble the younger and more productive succes-
sional stages of centuries ago. Nowadays, different degrees of human-induced successional regression
can be observed all over the region. Extreme cases of over-rejuvenation can be found in the highly sim-
plified crop rotation schemes wheat–soybean of the rolling pampas, where the energy flow and the pro-
ductivity are enhanced, the nutrient and water cycles are disturbed, the long-term accumulation of inert
material is inhibited, and the lifetime of the principal biological activities annual crops, in this case is
short and discontinuous. Since stability and sustain- ability are lost by the disruption of natural processes,
a human subsidy is needed to keep the ecosystem viable.
3.2. Change of functional properties 3.2.1. The energy flow and the nutrient dynamics
Two energy sources have been considered in this study: solar and fossil energy. Both types of energy
flow through the agro-ecosystem before converting into final products. Most of the incoming energy has
been highly degraded into heat and lost after pass- ing through plant and animal metabolic processes.
As a consequence, the net amount of energy con- centrated as final product output represents only a
negligible proportion of the total incoming energy input.
The analysis of the energy performance shows a large difference among agro-ecozones and historical
periods during the studied century Table 2. Dispar- ity of agricultural productivity between zones can be
appreciated by comparing the gross energy output. For example, in the 1980s, the rolling pampas pro-
duced 3.3, 4.6, 11.2, and 11.3 times more energy than the central, southern, flooding and Mesopotamian
pampas, respectively. Besides, comparing the be- ginning with the end of the century, productivity
increased 63.0, 31.5, 16.7, 9.2 and 8.7 times in the rolling, central, southern, flooding and Mesopotamian
pampas, respectively. These results demonstrate that zones differ greatly not only in their current potential,
72 E.F. Viglizzo et al. Agriculture, Ecosystems and Environment 83 2001 65–81
Fig. 4. Evolution of land cover along the century in five ecoregions of the pampas plain.
but also in their potential response to agricultural pressure.
In agreement with accepted ecological principles, as productivity increased in time, the efficiency of solar
energy use increased also, because more product was obtained at a constant rate of incoming solar energy.
On the other hand, the efficiency of fossil energy use has declined along the century probably because of the
law of decreasing yields: less MJ of product per MJ of invested fossil energy was obtained. In all cases,
E.F. Viglizzo et al. Agriculture, Ecosystems and Environment 83 2001 65–81 73
Table 2 Analysis of energy inputs, outputs and efficiency through incoming solar radiation and fossil energy MJ ha
− 1
per year consumption during the period 1880–1990 in the five-study ecoregions of the pampas plain
a
Ecoregions Period
Incoming solar radiation ×10
6
Fossil energy Energy output
Output–input relationship Incoming solar
radiation ×10
− 6
Fossil energy Rolling
1880s 57.7
24.5 881.8
15.3 35.99
1940s 57.7
2456.2 27614.1
479.0 11.24
1980s 57.7
6110.8 55548.0
663.0 9.09
Central 1880s
59.1 15.0
534.4 9.0
35.63 1940s
59.1 1522.1
9224.7 156.0
6.06 1980s
59.1 3190.5
16801.0 284.0
5.27 Southern
1880s 55.1
16.4 721.4
13.1 43.99
1940s 55.1
1644.3 5883.0
107.0 3.58
1980s 55.1
3027.0 12027.3
218.0 3.97
Mesopotamian 1880s
57.7 11.0
534.4 9.3
48.58 1940s
57.7 1100.4
6992.5 121.0
6.35 1980s
57.7 1576.5
4919.2 85.3
3.12 Flooding
1880s 55.1
5.1 561.1
10.2 110.02
1940s 55.1
512.5 3740.1
67.9 7.30
1980s 55.1
1141.0 4895.7
88.9 4.29
a
References: it was assumed that the consumption of fossil energy during the 1880s was equivalent to 1 of total consumption during the 1940s.
energy efficiency was higher in zones with the greater agricultural potential. It should be noted that, in terms
of fossil energy, low input systems in the pampas are more efficient than the intensive farming Viglizzo,
1984.
Large amounts of N, P and K are required, among other nutrients, by agricultural production. Consider-
ing the increasing productivity of ecoregions during the century, it is obvious that nutrient cycles have be-
come more and more open. However, given that the outflow was higher than the inflow of nutrients under
low input conditions, negative balances were unavoid- able in the pampas Table 3.
According to ecological theory, since nutrient dy- namics an energy flow are interdependent processes,
nutrients in ecosystems are mobilised in response to the energy impulse Odum, 1975. Thus, the larger
the energy flow, the greater the recycling and removal of nutrients. In practical terms, higher productivity of
agriculture means both, higher rates of flowing energy, and larger amounts of nutrients taken up and carried
away from the system. Fossil energy reinforces nutri- ent dynamics. Spatial and temporal data of Tables 2
and 3 were incorporated into a correlation analysis to compare fossil energy consumption with extraction of
N, P, and K. Highly significant P0.01 correlation coefficients were obtained. Coefficients and best fit-
ting models were 0.96 linear, 0.79 quadratic, and 0.98 linear for N, P, and K, respectively, thus, con-
firming a parallel performance between energy and nutrient dynamics.
3.2.2. The hydrology Water cycles between the surface and the atmo-
sphere. Like in other bio-geo-chemical cycles, wa- ter enters into abiotic and biotic chemical reactions
Clapham, 1983. The hydrological cycle is driven by energy dynamics and gravity. It moves along
the food chain, and the higher the agricultural pro- ductivity, the greater the amount of water that is
channelled into the agricultural process. As long as land is transformed to increase productivity in agri-
culture, increasing proportions of water are taken up and processed by agriculture. In response to land
74 E.F. Viglizzo et al. Agriculture, Ecosystems and Environment 83 2001 65–81
Table 3 Estimation of input, output and balance of nitrogen N, phosphorus P and potassium K during the period 1880–1990 in the study
ecoregions of the pampas plain
a
Ecoregions Period
Nutrient kg ha
− 1
per year Input
Output Balance
N P
K N
P K
N P
K Rolling
1880s 2.59
– –
1.69 3.6
0.6 0.9
− 3.6
− 0.6
1940s 24.40
– –
36.35 7.30
6.40 −
11.95 −
7.30 −
6.40 1980s
75.30 –
– 81.39
13.50 19.50
− 6.09
− 13.50
− 19.50
Central 1880s
1.32 –
– 1.02
4.20 0.60
0.30 −
4.20 −
0.60 1940s
39.23 –
– 12.43
4.70 2.00
26.80 −
4.70 −
2.00 1980s
23.21 –
– 25.38
10.90 6.70
− 2.17
− 10.90
− 6.70
Southern 1880s
2.08 –
– 1.38
3.50 0.50
0.70 −
3.50 −
0.50 1940s
14.20 –
– 9.26
4.10 2.90
4.94 −
4.10 −
2.90 1980s
18.47 3.1
– 20.74
8.70 5.10
− 2.27
− 5.60
− 5.10
Mesopotamian 1880s
3.02 –
– 1.02
1.60 0.20
2.00 −
1.60 −
0.20 1940s
9.14 –
– 8.80
3.00 1.80
0.34 −
3.00 −
1.80 1980s
4.93 –
– 7.49
6.20 2.50
− 2.56
− 6.20
− 2.50
Flooding 1880s
2.88 –
– 1.08
2.00 0.30
1.80 −
2.00 −
0.30 1940s
1.16 –
– 5.49
3.60 1.70
− 4.33
− 3.60
− 1.70
1980s 11.2
– –
7.28 5.40
1.40 3.92
− 5.40
− 1.40
a
− Means that there was no input by fertilisation.
transformation, a positive correlation between en- ergy flow, nutrient dynamics and water process can
be expected. However, cause-effect relations arise a key question that still remains unanswered: does land
use influence the hydrological process, or inversely, does the hydrological process drive changes in land
use?
Various authors have studied the hydrological pro- cess in the pampas since the beginning of agriculture
Hoffmann, 1988; Forte Lay and Falasca, 1991; Car- ballo and Hartmann, 1996; López Gay et al., 1996;
Viglizzo et al., 1997. Although there is variability between ecoregions, regression analysis has shown
a decline of precipitation all over the pampas un- til the 1950s, and then an inversion of trends dur-
ing the second-half of the century. During the study century, periods of improved hydrological conditions
seem to have favoured the conversion of grazing lands into croplands, and vice versa. Viglizzo et al. 1997
have found significant P0.05 and highly signifi- cant P0.01 correlations between rainfall variabil-
ity and percentage of cropland for the humid and subhumid districts of the pampas, respectively, and
a non-significant one P0.05 for the semiarid dis- tricts. They considered that changes in the rainfall
regime have principally explained the variability of land use in the better areas, but the lower quality
and water-retention capacity of soils could explain the loss of correlation in the western, semiarid districts.
The interaction between rainfall and technology was the main factor explaining land use change in these
districts.
Other authors seem to have an alternative view of hydrology as a causal factor of land use change.
Henderson-Sellers et al. 1993, McGuffie et al. 1995 and Zhang et al. 1996 have considered that
the replacement of forest by pastures was the principal cause of warming and drying in tropical areas. Cou-
pling a land surface process model to an atmosphere general circulation model, Bonan 1997 reached the
conclusion that climate in USA has changed in re- sponse to historical replacement of natural vegetation
grasslands and woodlands by croplands. Some areas have cooled, other have warmed, and a moistening of
E.F. Viglizzo et al. Agriculture, Ecosystems and Environment 83 2001 65–81 75
the near-surface atmosphere has happened over much of the USA territory in spring and summer. According
to this author, the climate shift could be explained by a reduction of a the surface roughness, b the leaf
and stem area index, c the stomatal resistance and d the increasing of the surface albedo. Bonan 1997
has summarised this view by saying that ‘rain follows the plow’. What was cause, and what was effect in
the relationship between land use and hydrology in the pampas? Is there perhaps a mutual reinforcing
action?
The analysis of altered functions is a valuable way to learn from ecosystems study. In agreement with
ecological theory, the results of this study confirm that the basic functions of energy flow, nutrient dynamics
and the hydrological process should not be considered in isolation because they are strongly interrelated. Pio-
neer studies by Lotka during the 1920s Krebs, 1972 have demonstrated that resources in natural systems
are mobilised in proportion to the flow of energy. Al- though the hydrological process is mobilised by the
global dynamics of energy and gravity, nutrients as well as water are ‘pumped’ by the local flow of energy.
When energy flow is enhanced by energy subsidy pesticide, tillage, irrigation, etc. or land transfor-
mation conversion of native grasslands into pas- tures or crops, nutrients and water are mobilised
at higher rates, determining open cycles that lead to less conservative ecosystems. A noticeable eco-
logical regression due to land conversion and use of machinery, pesticides and high yielding varieties
without fertiliser application, took place in the pam- pas during one century of farming. More crops and
higher yields have increased the extraction of nutri- ents, determining negative mineral balances in areas
well-suited to crop production. The models utilised in this study would confirm this, demonstrating that
actual farming systems are not sustainable in the long term. The lack of fertilisation has avoided the
problem of contamination, but at the cost of nutrient depletion.
Conditions vary in different ecoregions. In the rolling pampas, where annual crops have been the
greatest component of land use, the flow of energy and the loss of nutrients are several times greater
than in the mixed systems of the central and south- ern pampas, and in the Mesopotamian and flooding
pampas, where cattle raising is the principal activ- ity. In ecological terms, livestock systems resemble
the conditions of mature, close-to-climax natural ecosystems, more than the mixed and the cropping
systems. Various authors Odum, 1969; Vitousek and Reiners, 1975; Woodmansee, 1978; Margalef,
1980 have argued that as long as the ecosystem progresses toward mature stages, they become more
conservative in terms of energy transfer and nutrient mobilisation. The results in the present study would
confirmed this.
3.2.3. Productivity, stability, sustainability Productivity, stability and sustainability are, at
the same time, relevant emergent properties of agro-ecosystems, and an expression of performance
in ecology and agriculture. Generally speaking, pro- ductivity is, in natural ecosystems, the biological
process that determines a change of weight of plants and animals over a year Clapham, 1983, while
stability is the variation in number of plant and an- imal communities around a dynamic equilibrium
point after a normal disturbance Margalef, 1968. According to Chapin et al. 1998, sustainability is
the maintenance of characteristic diversity of major functional groups, productivity, soil fertility, and rates
of bio-geo-chemical cycling over disturbance events. Conway 1987 adapted these concepts to agricultural
ecosystems. Conway 1987 defined productivity not as a process, but the output of valued product edible
or saleable products, energy, money, etc. per unit of resource input e.g., hectare of land on an annual
basis, stability as the small inter-annual oscillation of productivity in response to small, normal variations
of the surrounding environment, and sustainability as the lasting, long term maintenance of productiv-
ity when subject to major disturbing forces that are infrequent and unpredictable.
Viglizzo and Roberto 1998 found that trade-offs between productivity, stability and sustainability are
common in low input farming. Working on actual farm data from the pampas, Viglizzo and Roberto
1998 demonstrated that productivity and stability on the one hand, and productivity and sustainability
on the other, are inversely related both in biological and economic terms. Under low input conditions,
productivity increases and stability decreases in farm systems where primary processes herbage and grain
tend to predominate over the secondary processes
76 E.F. Viglizzo et al. Agriculture, Ecosystems and Environment 83 2001 65–81
meat and milk, and vice versa. However, this in- verse relationship is not so evident in areas where the
environmental conditions rainfall and soil quality improve; e.g., towards the eastern pampas Viglizzo,
1986. Productivity and sustainability were also in- versely related in the long term Viglizzo et al.,
1995. Nitrogen in soil was the factor selected to demonstrate this, which was related to the so-called
storage function. Its size in agro-ecosystems depends on the capacity of leguminous pastures to incorpo-
rate atmospheric N. Other attributes of soils could have been selected for quantifying the storage func-
tion, such as organic matter and structural stability of soils. According to this scheme, the larger the
size of the storage function, the greater the long term sustainability of a system Viglizzo and Roberto,
1998.
The historical conversion of grazing areas into croplands in the pampas, has provided a strong em-
pirical evidence of trade-offs between productivity, stability and sustainability under real farming condi-
tions. Productivity has increased all over the region at the expense of stability and sustainability, and
this effect was particularly noticeable in the semi- arid western lands where climate conditions are more
variable Viglizzo, 1986; Viglizzo et al., 1991. This behaviour was consistent with principles of eco-
logical succession: the successive transformation of natural grasslands into pasturelands and croplands
represents for ecologists Odum, 1969 a backward movement to younger, more productive, less stable
and less sustainable stages in the ecological succes- sion. Man displaced the system away from mature,
less productive, stable and self-sustainable stages in dynamic equilibrium, towards younger and more pro-
ductive ones that can render a higher and short-term economic income. Although man can be considered
itself an ecological factor, its impact should be anal- ysed in isolation because of human-based utilitarian
purposes.
4. Lessons and applications
