Soils of Argentina - Nature and Use
Gustavo Moscatelli - Instituto de
Suelos - INTA Castelar – Argentina,
Pazos - Facultad de Agronomía UNICEN - Azul, Argentina,
Moscatelli, G. and
Pazos, M.S. 2000. Soils of Argentina: Nature and Use. Presentación oral en:
International Symposium on Soil Science: Accomplishments and Changing Paradigm
towards the 21st Century and IUSS Extraordinary Council Meeting, 17-22 de abril,
Bangkok, Tailandia. En: I. Kheoruenromne and S. Theerawong (Eds.) 2000.
Proceedings of International Symposium on Soil Science: Accomplishments and
Changing Paradigm towards
the 21st Century, 81-92. ISBN 974-87749-4-5.
The soil resources in
Argentina have been the main support of economical development in the country.
Long lasting periods of large harvests made the country to be called "The
world barn". From other latitudes, the name of Argentina was associated
with wide plains of everlasting deep, dark soils, able to produce high grain
yields and meat of excellent quality.
These concepts are
relatively true for the Humid Pampa that occupies somewhat less than one third
of the territory, where plains are dominant, formed by modern unconsolidated
sediments, with natural grasslands and temperate climate (Hall et al., 1992).
Highly contrasting are
the remaining two thirds of the surface of Argentina, most of which are
dominated by arid climate. Irrigation has to be applied for crop production,
which is only done in the surroundings of the main rivers, or in narrow oases of
small extent in the mountainous areas.
The soil studies in
Argentina started as a need for producing food crops. Around 1850, cattle
production was sufficient for domestic needs but it was necessary to import
wheat. There were unsuccessful intents to develop farms with the natives and the
government appealed to promote the immigration. For them, it was necessary to
know the land quality and some scattered soil data started to be collected
without the production of soil maps. In 1898 the Ministry of Agriculture was
created with four Secretariats: Agriculture and Cattle, Commerce and Industries,
Lands and Colonies and Immigration. Colonisation was promoted and some soil maps
were produced on the basis of geological criteria. Between 1930 and 1940 at the
same time that big hydroelectric dams were constructed, projects for irrigation
areas were developed and the need appeared to know the soils to be irrigated
(Gómez y Scoppa, 1994). During the fifties a long drought period occurred, with
the concomitant intense wind erosion in the semiarid area and an important
decrease in the production of grain crops, which determined a strong tendency to
study the soils in order to prevent the desertification. Finally, soil
cartography started as a political need for the implementation of a tax reform.
As a consequence, in the
sixties, a very ambitious project started towards increasing the knowledge of
the soil resource. It was named "Soil Map Project of the Pampean
Region" (Plan Mapa de Suelos de la Región Pampeana), and was
carried out by the INTA (National Institute of Agricultural Technology).
The output of this project was very prolific in publications. Serves as an
example the soil map of the Pampean Region at the scale of 1:50.000 (INTA,
International aid and
the compromise of young professionals from different disciplines (geology,
agronomy, geography, soil science, and others) supported this undertaking. The
most updated concepts and technologies of that time were utilised in soil
genesis, classification and cartography works. Aerial photographs were
systematically utilised, as well as the former 7th Approximation
(Soil Survey Staff, 1960) as soil classification system and the Land Capability
Classification (Klingebiel and Montgomery, 1966) as interpretative system. The
soil and landscape studies were dedicated to the Pampean Region (Tricart, 1973;
Etchevehere, 1976), but the experience constituted a true school for the
specialists in soil classification and cartography. Later on they were the
leaders of working groups in different provinces out of the Pampean Region and
worked for national and provincial organisations, universities and research
centres. In this way, the country counted on a network of specialists utilising
a homogeneous methodology adapted to the peculiarities of each region.
Like a corollary, in the
eighties under a United Nations Project, the Soil Atlas of Argentina (SAGyP –
INTA, 1990) started to be prepared, integrating information about well studied
regions because of their high productivity together with others lacking soil
cartography because of their low agricultural vocation. The Atlas will be
updated in the near future.
soil scientists from the universities and other research centres, particularly
those working in soil genesis, carried out their postgraduate studies in well
known universities from different countries, mainly the United States, Belgium
and France. Presently, good postgraduate courses have been developed in
NATURE OF THE LAND
AND THE SOIL FORMING FACTORS
materials are present in the country. Various rocks outcrop in some natural
regions but not all of them give rise to soil formation due to climate with low
The most important soils
from the agricultural standpoint are developed on the aeolian quaternary
sediments that cover the Chaco-Pampean Plains, indicated as eco-regions Dry and
Humid Chaco, Espinal and Pampa in Fig. 1 (Secretaría de Recursos Naturales y
Desarrollo Sustentable, 1999). The material is formed by debris of weathered
rocks, and it also contains significant amounts of volcanic glass, product of
the eruption of Andean volcanoes.
This sediment is known
as Pampean loess because of its similarities with loess materials and deposits
in other parts of the world (Frenguelli, 1955; Teruggi, 1957). From the
mineralogical standpoint, the loess is rich in weatherable minerals with
conspicuous amounts of calcium, potassium, phosphorus and microelements and
amorphous materials of volcanic origin (Scoppa, 1974). In Figure 2 (Pazos and
Moscatelli, 1998) an example is shown of the average mineralogical composition
of soils developed on Pampean loess, a rich source of plant nutrients. The
physical characteristics of the Pampean loess favour the formation of well
structured, deep, dark surface horizons, adequate for root development
The dominant climates in
Argentina are arid and semiarid (Burgos and Vidal, 1951). For this reason, soils
of wide areas are strongly marked by a parent material with little
transformation. It is only in the NE, the Paranaense Forest in Fig. 1, that the
contrast is strong between the soil and the underlying rock that has been deeply
weathered in situ under an aggressive climate.
Figure 1 –
Eco-Regions of Argentina (Modified from Secretaría de Recursos
Naturales y Desarrollo Sustentable. 1999).
The important mountain
ranges have hillsides with colluvial deposits where different types of soils are
developed and the soil profile development is associated with the local climate
In the wide humid and
subhumid plains of the Pampean Region, Pampa in Fig. 1, little differences in
topography give rise to very different soils on the same parent material due to
runoff and the accumulation of rainwater in the low positions of the landscape
(Pazos, 1981; Pazos and Fittipaldi, 1994).
|Figure 2 - Average
mineralogical composition of the sand fraction of six soil profiles from
Central Buenos Aires Province. R = rutile; Z = zircon; T = tourmaline; A
= anatase. (From: Pazos and Moscatelli, 1998).
The natural vegetation
and partially the soil fauna have been deeply modified in the areas long
utilised for crop production and cattle grazing. It is only where the
autochthonous flora and fauna are conserved that their influence as soil forming
factor can be verified. This is still more evident when the forest is cleared to
change the land use to agriculture, as in the NE of the country, and the
physical and chemical soil characteristics are quickly deteriorated (SAGyP,
Since 1970 Argentina
adopted the 7th Approximation (Soil Survey Staff, 1960) as the soil
classification system for the soil surveys, and later on the Soil Taxonomy (Soil
Survey Staff, 1975) and all the subsequent updates until the Second Edition
(Soil Survey Staff, 1999). Every soil scientist in the country is acquainted
with the system that is taught in most universities both at graduate and
Due to the N-S
dimensions of the country and its climatic diversity, all the twelve orders are
represented in Argentina. In Figure 3 the dominant soil orders in Argentina
(Moscatelli and Puentes, 1998) are shown, according to the Soil Taxonomy (Soil
Survey Staff, 1999). Following is a brief description of nature and distribution
of each of the orders.
Geographically the Alfisols are closely associated with Mollisols. They are
widely represented in the Chaco-Pampean plains and belong to the Alfisols mostly
due to a surface horizon that is too thin or too low in organic matter or too
light coloured for a mollic epipedon. They usually occupy flat or concave areas
between higher parts of the landscape. Very frequently they have natric horizon
and/or aquic soil moisture regime (Moscatelli, 1991). The Alfisols are utilised
for cattle grazing, as natural grasslands or for water and sodium tolerant
pastures. There are also Alfisols with lower base saturation than the Mollisols,
which are restricted to the NE of the country where they occur in association
with Oxisols and Ultisols.
|Figure 3 – Dominant
soil orders in Argentina according to the Soil Taxonomy (Moscatelli and
The Andisols are distributed in narrow belts along the Andes in the S of the
country, mostly under temperate to cold climate. Thick deposits of volcanic ash
overlie glacial deposits or outcropping igneous rocks. They constitute a soil
cover on which native tree species have thrived. The natives called the ash
deposits as "manna from the sky" meaning that God distributed
productive soils covering the inert rock. Important contributions to the
knowledge of Andisols and its mineralogy have been obtained through the research
of both ORSTOM and Argentinian universities from the S of the country.
Aridisols are widely distributed in Argentina covering 60% of the country,
mostly in Patagonia, Cuyo (Centre E) and NW. They amount to 160 million hectares
with different percentages in 17 out of the total 23 provinces. The severe
conditions that determine the occurrence of Aridisols bring about
socio-economical problems and difficulties to settle sustainable towns or
villages in many areas of the country with very low population density in very
wide regions. These circumstances determine population exodus with negative
rates of population growth, subsistence economies with low or no insertion in
the markets resulting in very low investment and technology incorporation (José
Ferrer, personal communication, 2000). Moreover, the poor environmental offer is
worsened by the subsistence difficulties of the population who frequently
perform unsuitable tillage or irrigation, or overgrazing, searching for short
term results. These procedures undoubtedly cause the quick deterioration of
these labile lands. An important action to prevent desertification is and has
been carried out from different government institutions. Most of the land
involved in these projects and studies consist of Aridisols and there exists a
healthy consciousness with respect to the need of knowing these soils in detail.
are widely distributed in the arid and semiarid areas, occupying large
parts of Patagonia and the NW of the country. This order is particularly
important because most of the soils under irrigation along the main rivers are
Entisols. They are also common along the extensive coasts, utilised in this case
for tree plantations and horticultural crops.
(Not shown in the map) The Gelisols have been described in Antarctica where
there are Argentinian military bases, particularly in the studies carried out at
the Marambio Island after the introduction of the order in 1998. The
classification at the suborder level is not yet completed but it is already
clear that the introduction of this order was very helpful and contributed to
solve previous uncertainties in the classification of soils of Antarctica.
Histosols are poorly represented in Argentina. They are mostly localised at high
elevation and/or latitude as in Tierra del Fuego, Malvinas islands, Antarctica
and some areas in the Andes. In the N they occur in low areas with permanent
wetness close to lagoons and salt accumulations. In the southern part of the
country they constitute peat deposits. Histosols are utilised for cattle grazing
but the southern peat deposits are utilised only during very favourable periods.
Inceptisols occur in a wide range of environments in Argentina, from the
southernmost provinces as Tierra del Fuego and Malvinas Islands to the north in
Jujuy and Formosa. In consequence, very different soil profiles classify as
Inceptisols. They have been described in half of the provinces. Due to their
diversity a common land use cannot be established for the order. In general they
do not constitute good agricultural soils.
They occupy important areas in the Chaco-Pampean plains and constitute the
dominant soils among those with the best aptitude for agriculture. Mollisols
have been mapped in every province from the subtropical area in the NE to the
island of Tierra del Fuego in the S. Mollisols have been mentioned as occurring
in Antarctica, being still under discussion if such soils actually belong to the
The Pampean Region, both
humid and semiarid, is characterized respectively by Udolls and Ustolls with
minor occurrence of Aquolls in flat areas utilized for cattle production. The
Mollisols have been the object of many studies and postgraduate theses mostly
referred to its genesis. This wide research subject is based on the undoubtedly
polygenetic character of the soils. There are layers of materials with similar
lithology and origin that have been deposited during alternating episodes of dry
and moist climate. The intent to show such discontinuities in the soil name has
introduced some confusion in the local classification of Mollisols, an issue
that still has not been solved with a general agreement among the soil
scientists. Another feature of the Pampean soils is the presence of a CaCO3
enriched horizon that sometimes qualifies as petrocalcic horizon, and occupies
wide areas under humid climate. To solve this peculiarity some local
modifications were introduced to the Soil Taxonomy, which are not yet fully
satisfactory. Neither are adequate the recent changes in the second edition of
the Soil Taxonomy.
(Not shown in the map) The Oxisols are little represented in Argentina,
mostly in Misiones province, in the NE of the country, indicated as Paranaense
Forest in Fig. 1. It is practically the only area of the country where soils
have developed through intense weathering of the parent rock, mostly basalt.
Oxisols occur on old stable surfaces. In their virgin state they are under
natural forest and preserved from degradation. Oxisols are utilised for yerba
mate, tea, tung tree and tobacco and wide areas are found where land has been
abandoned because of the quick loss of fertility after few years of crop
production. Satellite images clearly show that deforestation in the neighbouring
countries, Brazil and Paraguay, is quite more intense than on the Argentinian
(Not shown in the map) They occupy small areas, restricted to high latitudes, as
those described in Tierra del Fuego and the Andean area of Santa Cruz province.
Their occurrence in such areas is due to the lower height of the mountain range
with orientation W-E that allows the influence of moist W winds from the Pacific
Ocean. The natural vegetation on Spodosols is a coniferous forest.
They are well represented in the provinces of Corrientes and Misiones, in the NE
of the country. They cover a wider area than the Oxisols on younger developed
landscapes. The considerations about natural vegetation, crops and land use are
similar to those of the Oxisols.
They are found under different moisture conditions: humid, semiarid and
arid. Vertisols are characteristic of the eastern half of Entre Ríos province
in the NE of the Pampean Region, the coastal area of Buenos Aires province at
Samborombón and they have also been described in some river valleys in
Patagonia. Its genesis is attributed to materials coming from Brazil through its
very wide runoff network. Vertisols in Argentina are mostly utilised for cattle
because of their restrictions for tillage. To a minor extent, they are also
utilised for crops as wheat, soybean, sunflower and flax. Vertisols are
particularly suitable and utilised for paddy rice. Many Vertisols occur in
rolling landscapes which contribute to water erosion. Entre Ríos is the best
developed province in legislation on soil conservation which has been widely
accepted due to the combined characteristics of low soil permeability and strong
slopes. From the classification standpoint, there have been difficulties to
classify the Vertisols from Entre Ríos with the Soil Taxonomy, reason for which
some local modifications are still in use.
As it has been described
in the previous paragraphs, some peculiarities of the Argentinian soils,
particularly those of the Pampean Region, gave rise to propose some amendments
to the Soil Taxonomy. Some proposals have already been accepted and they can be
found in the second edition that specifies some taxa as developed for use in
Argentina (cf. Natrudolls and Calciudolls) while other proposals are still under
Besides the wide
acceptance of the Soil Taxonomy in Argentina, some experiences have been made
applying the Legend of the Soil Map of the World (FAO- Unesco, 1974) and
presently the WRB (ISSS-ISRIC-FAO, 1998). The WRB appears as an interesting
option and particularly helpful in those cases where the Soil Taxonomy is not
yet fully developed.
In Figure 4 the soils of
the Humid Pampa are shown, classified according to the WRB (ISSS-ISRIC-FAO,
|Figure 4 – Soils of
the Pampean Region according to the WRB (Modified from Moscatelli and
In the middle of the
seventies due to increasing food demands and better agricultural prices,
stronger pressure started to be applied on agricultural lands and even on the
marginal ones. The latter were utilized carelessly of the sustainability
principles, which in fact were developed afterwards, thus generating
"conflict areas" with regard to their actual capability and
traditional land use.
An increase in
production was achieved through the application of technology with inputs as
fertilizers, biocides and heavy machinery, for example.
The message from
agronomists and scientists was always to harmonize a profitable production with
the preservation of the resources but the short-term interest was difficult to
overcome with a slow but relentless soil deterioration as a consequence. In some
way, the seemingly everlasting richness of the natural resources in the Humid
Pampa together with the utilization of new genetic varieties, fertilization and
irrigation masked for a rather long period the decrease of soil productive
Soil deterioration in
Data reported by FECIC
(1988) on 219 million surveyed hectares, corresponding to 17 provinces out of 23
(78% of the country surface) indicate that about 21.400.000 ha are affected by
water erosion to a moderate and severe degree. An estimation made by INTA
(Musto, 1979) reports an increase of 4.400.000 ha eroded to a severe degree.
At present it is
accepted that a total of 60.000.000 ha are affected by wind or water erosion at
different degrees. Wind erosion is mainly expressed in arid and semiarid regions
as Patagonia and the Semiarid Pampean Region, while water erosion affects
particularly the humid areas as the Humid Pampean Region and Mesopotamia (NE of
INTA made an evaluation
of land degradation for the period 1985 up to present and considering 5.000.000
ha at the core area for grain production (Michelena, et al., 1989) with the
conclusions shown in Figure 5.
|Figure 5 – Loss of
SOM, P, N and structure in percentage under rotation agriculture-cattle
and continuous agriculture.
The level in non-cultivated soils should be considered 0%.
Other marks of soil
degradation include 1.280.000 ha with partial to total loss of the surface
horizon and an increase in soil acidity that depends on the intensity of soil
use. The pH decreases in 0.4 in areas under agriculture-cattle rotation and 0.9
under continuous agriculture with respect to the non-cultivated lands.
The misbalance of
organic matter is a cause for physical and chemical land degradation,
particularly under traditional continuous agriculture and wheat-soybean double
cropping. In these cases, the incorporation of organic matter through straw is
reduced to a minimum due to both burning and cattle grazing. Surface sealing and
crusting and the development of plow pans are frequent phenomena associated with
The relationship between
degree of water erosion and yields of the main crops, (wheat, maize and soybean)
was evaluated. A moderate degree reduces grain yields in 12% for wheat, 17% for
soybean and 30% for maize, while a severe degree changes the effect to 24, 34
and 61% respectively. When transforming these rates into economical loss, 230 to
300 million dollars are lost due to decrease in yields of the three main crops
because of water erosion (irurtia, 1995).
The economical loss due
to water erosion in the entire Pampean Region amounts to 700-800 million
dollars. At national level it can reach 1000-1200 million dollars due to water
erosion and 3000-4000 million dollars taking into account all land degradation
processes as well as the damages to infrastructure.
The main causes for land
degradation in the Pampean Region are the "agriculturization" process
or intensification of agriculture, the introduction of the double annual
cropping wheat-soybean; the change from the rotation cattle-agriculture to
continuous agriculture, and an inadequate land use with excessive and/or
untimely tilling sometimes along the slopes.
To prevent and control
the degradation processes, many alternative practices of land reclamation and
land and water conservation are applied. An effective system to prevent erosion
and maintain soil structure that has been widely incorporated in the Pampean
Region is the no-tillage or direct planting, which presently covers 5.000.000 ha
in the country. In relative terms, places Argentina as the country with the
higher extension of this practice. It is worth to mention the permanent work of
AAPRESID, the Argentinian Association of Farmers utilizing No-tillage, which is
a private undertaking that has contributed to the diffusion of the system.
AAPRESID has joint research projects with research and technological centers,
universities, and extension and experimentation organisms in order to evaluate
the advantages and drawbacks of the system in the different ecological regions.
CHALLENGES FOR THE XXI
The dynamic reality
faces Argentina to new challenges that the soil studies must also accept.
Priority has to be given necessarily to those research issues with economical
importance or consequences, to satisfy people needs and to strengthen the
country competitive capacity in the market to place agricultural products. In
this sense, the environmental certification of processes and products appears as
an obliged condition in order to facilitate placing the products. In fact, the
international norms ISO 14001 constitute a way of environmental protection
The already mentioned
processes of intensification of agriculture, widening the frontiers and the
industrialization of the agricultural products brought soil, water and air
contamination to the rural area. Foreign experience and knowledge about the high
impact of such processes on human health and biodiversity shows that Argentina
must adequately prevent this danger, but the matter has been underestimated for
those making the political decisions.
A system should be
implemented for monitoring and recording the land transformations as a
consequence of changes in land use as well as the climatic variations of the
last thirty years. It is also essential to obtain sound data of the impact and
consequences of supplementary irrigation, a practice that has invaded the
Pampean Region during the last five years and may introduce both soil erosion
and salinization and depletion of the groundwater reserves.
The urban soil studies
deserve particular attention. Urban soil studies about different types of
degradation are incipient in Argentina. Moreover, it is necessary to make the
inhabitants of large cities to accept their dependence on what is happening in
the rural area. Normally they see the countryside as far away, with its own
problems without realizing that in the countries with strong agricultural base
their interdependence is particularly close.
The creation of the
Mercosur has unified an area of almost 13 million square kilometers, area in
which people and goods can freely transit. Since the opening of the frontiers a
change is occurring in demand and pressure on land use facing the need to
improve competitiveness. Agrochemical utilization is increasing together with
the use of heavy machinery and irrigation will be performed regardless of water
quality, always in the search of the short-term profit. The increase in
industrial development will produce more waste and contaminants. The
incorporation of present forestlands to crop and cattle production is
unavoidable (Moscatelli, 1995) with the already known deterioration of soil
physical and chemical properties. The processes are more evident and quickly
occurring at the borderline. The transport and communication network is changed
and increased, the cities are under an expansion process and public works are
developed. All of them grow at the expense of the surface formerly occupied by
soils, introducing surface sealing as asphalt and concrete.
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