1. INTRODUCTION
In the context of agriculture, land degradation leads to decreasing of
production capacity, through the reduction of soil quality with negative
impacts on soil physical, chemical and biological attributes. The main
agent of soil degradation worldwide is water erosion, which is a natural
process in the formation of landscapes but is intensified by anthropic
actions such as agriculture. Soil erosion in croplands and rangelands is
mainly caused by the soil usage and land management with inadequate
agricultural practices; in turn, the water erosion is the main factor
responsible for expansion of degraded lands in the world. Water erosion
compromises the attainment of high levels of crop production and the
intensification of agricultural, as well as the environmental quality of
ecosystems, due to water contamination and the reduction of water
availability for many usages ( Andrade & Chaves, 2012; FAO,
2019) .
Besides compromising the potential of agricultural production and the
resilience of different ecosystems, with the loss of land and aquatic
biodiversity, soil erosion increases rural exodus due to land
degradation, causes silting and contamination of water resources,
increases occurrence of floods, decreases the capacity of hydroelectric
plants to generate power and increases costs for water treatment. Thus,
water erosion was considered one of the most extreme environmental
problems of the humanity (Feng et al., 2010). According to Eswaran et
al. (2001), soil erosion and desertification are responsible for a
decline of productivity of 50% in some croplands and pastures of the
world, as a consequence the global annual soil loss is of 75 billion
tons, with a cost of about 400 billion US dollars per year. FAO (2015)
documents estimate that 33% of the world’s lands are degraded. Soil
erosion by water also has large economic impacts; thus, agricultural
production systems that can provide soil and water conservation are
crucial in achieving the sustainable use of these natural resources.
In Brazil, the absence of information
on the spatial distribution and type of soil resources, at compatible
scales with the agriculture demand, has led to expansion of crops and
pasture in areas with low productive capacity or where careful soil
management is required. Detailed mapping of soil distribution and better
interpretation of soil properties are important to achieve a sustainable
agriculture and to reduce soil erosion, as land usage and
crop/pasture/forest production are intensified. The first step to
control water erosion in a regional scale is planning the land use with
respect to its agricultural suitability (Ramalho Filho & Beek, 1995)
and, at the farm level, it is essential that lands are used according to
their capability and following the recommended conservation practices
(Lepsch et al., 2015). Evaluations based on existing soil information
indicate that over 5.5 million km2 or 65% of the
Brazilian territory have aptitude for annual or perennial crops
(Manzatto et al., 2002). On the other hand, degraded lands occupy about
22% of the territory with varying levels of degradation (Bai et al.,
2008); thus, programs for recovering these lands and to increase
adoption of soil conservation practices and technologies are essential
for a sustainable agriculture (Oliveira et al., 2019).
The 1970’s models of agriculture in Brazil, based on intensive tillage,
monocropping and high inputs of fertilizers and products for controlling
pests and diseases, were not efficient to control loss by water erosion.
In the 1990´s it was already recognized that, for an effective soil
erosion mitigation, it was necessary the integration of cultivation
practices with biological technologies and management of crop residues.
The initial No-till concept with the direct planting of seeds over the
previous crop residues was not enough to control water erosion,
especially in the tropical soils. This led to evolution of a land
management system in which no-tillage, crop rotation (pluri-annual
rotation of annual crops with no repetition of crops in subsequent
years), permanent soil cover and controlled traffic are associated.
These are the technological bases of the Zero Tillage / Conservation
Agriculture (ZT/CA) management system and they are universal, although
technical solutions depend on local soil, climate, relief and
socio-economic conditions (Landers, 1999; Landers et al., 2013). The
application of these principles may reverse the historically
accelerating soil erosion and the degradation of soil organic matter and
soil structure (Landers et al., 2013).
The potential soil loss by water erosion for the entire Brazilian
territory was estimated at the end of the 1990s as being of 822.6
million tons per year, with 751.6 million tons in the areas with annual
and perennial crops and 71.1 million tons in the rangelands (Hernani et
al., 2002a). In 2010, these authors estimated that such annual soil
losses due had the annual cost of about 6 billion US dollars. This value
included losses due to removal of plant nutrients and soil amendments,
in addition to other losses generated inside and outside the farm.
To control erosion in the highly weathered Brazilian soils, the
evaluation of land capability is essential, which requires detailed
surveys of soils, landscape and climate conditions. These demands
culminated with the setup of a recent national governmental program for
soil survey and interpretation for land usage, the PronaSolos (Polidoro
et al., 2016). The PronaSolos program plans, in the next three decades,
to overcome the lack of adequate data and to provide the necessary
information about soil and water resources. By mapping the soils in
detailed scales in the regions prioritized by PronaSolos, it will be
possible to carry out appropriated land use planning and mitigating land
degradation processes. The division of the rural areas into land
management zones will enable the efficient use of the soil, with all the
inputs required for crop production, for achieving a sustainable
agriculture for large and small farmers. In this way, it will be
possible to recommend the most appropriate models for different
landscapes and climates, in different regions of Brazil subsidizing the
elaboration and implementation of a national soil and water conservation
plan.
The PronaSolos will join in national programs toward the adoption of
recovering practices and technologies for converting degraded lands into
productive crop- and pasturelands, such as, the Plan of Mitigation and
Adaption to Climate Changes for the Consolidation of an Economy of Low
Carbon Emission in the Agriculture (ABC Plan) (Gurgel & Laurenzana,
2016). In addition to the goals of reducing water erosion and increase
soil carbon stock, other objectives of these government programs are to
control desertification, water and soil contamination, surface and
subsurface compaction, surface impermeabilization and to reduce emission
of greenhouse gases and risks of disasters.
A recent FAO (2019) document strengthens the principles of Conservation
Agriculture (CA) as following: minimum soil disturbance in the planting
row and confined to the planting operation; permanent soil cover with
crop residues (straw) and live plants; and crop rotation, intercropping
and root diversity. Based on this principles, which were already
implemented into the conservation practices adopted by a large number of
Brazilian farmers, the objective of this paper is to report the impacts
of Brazil´s conservation agriculture initiatives towards the control of
soil erosion and the economic effect of adoption of plans, policies,
practices and technologies closely linked with the land use
intensification, having Zero Tillage / Conservation Agriculture (ZT/CA)
and integrated Crop-Livestock-Forest under Conservation Agriculture
(iCLF-CA) management systems as the centre policies.