Fjölrit RALA - 05.12.1999, Page 53

OsvaldoA. Fernández et al.
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moderately affected by wind erosion in plowed areas at the eastem part of this Prov-
ince, while 185x10"' ha have suffered severe damage (Covas and Glave 1988).
Vegetation cover and size of soil aggregates are the two most important factors that
affect soil losses through wind erosion (Michelena and Imrtia 1995). Land manage-
ment must contemplate the utilization of short agricultural periods (not more than 4
years), use of perennial pastures, and application of conservation tillage systems to
maintain surface residues. More studies are needed to consider other land management
types and conservation practices in areas with the highest wind erosion rates. One of
such practices has been cultivation of relatively small and selected areas (50-200 ha)
with weeping lovegrass (Eragrostis curvula), a drought tolerant species, which gives a
permanent pasture during many years after successful implantation. Nutritional value
of weeping lovegrass is ffom medium to poor; however, it does provide a maintenance
diet for animals during the summer when the productivity of the poorly managed
rangeland vegetation is at a minimum. A comprehensive work on the biology and
utilization of weeping lovegrass for the semi-arid region of the country has been ed-
ited by Femández et al. (1989b).
Western Chacho
The region known as the Gran Chaco is a huge low elevation outwash plain of about
65 million ha build up of sediments derived from the eastem Andes. It comprises the
north of Argentina, west of Paraguay and the southeast of Bolivia, broadly coinciding
with the Chaquena Province described by Cabrera and Willink (1980). Rainfall in-
creases uniformly from west to east with increasing distance from the Andes. In Fig-
ure 1, only the west portion of the Argentine Gran Chaco is indicated. This region is
referred to as the Westem Chaco and represents the driest part of the Gran Chaco
while the most humid east portion of this extensive sedimentary basin is covered by
forests, savannas, marshes and subtropical wet forests. The limits for this region cor-
respond to those established by Morello (1968) for the Chaco Lenoso and broadly
overlap with those of the Parque Chaqueno Occidental described by Ragonese and
Castiglione (1970) or the Distrito Chaqueno Occidental by Cabrera (1970).
The climate of Westem Chaco is characterized by its humid and hot summers (Oc-
tober to April) and mild, dry winters (May to September). Absolute maximum tem-
peratures can reach over 48°C, while absolute minimum temperatures can go to -8°C.
There is a general impoverishment in species richness and replacement of taxa with a
subsequent general structural impoverishment associated with the rainfall decreases
from the Chaco forest and woodlands to the east (800 mm yr_l) to the Monte scmb
and desert to the west (320 mm yr-1) (Cabido et al. 1993).
The predominant soils of this territory are coarse textured, of a high base status,
without an argillic horizon, but they have a epipedon darkened by organic matter. Fre-
quently there are also alluvial soils on the floodplains of the rivers. The soil moisture
regime was determined as aridic and hyperthermic or thermic for the north and south
portions, respectively.
The Westem Chaco vegetation consists of a medium and low forest of mesophytic
and xerophytic trees with a dense understory of shrubs of Cactaceae and Bromelia-
ceae. There may be a prairie rich of grasses of good forage value among the woody
vegetation represented by Leptochloa virgata, Paspalum inaequivalve, P. unispica-