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.