1 INTRODUCTION
São Paulo State Secretariat for Agriculture and Supply, through the
Coordination of Agricultural Defense (CDA), is responsible for applying
the Law on Use, Conservation and Preservation of Agricultural Soil -
State Law nº. 6.171 / 88 - (São Paulo, State, 1988) to monitor and
discipline the soil use and conservation to fight soil erosion. This
work has been carrying out for 20 years with very positive results,
mainly in inspections carried out at Watersheds. The area of the state
occupied by agriculture, which is called the agricultural area of the
state of São Paulo, is approximately 18 million hectares, with 330
thousand agricultural properties. During that period, 772,000 hectares
were already worked on 19,846 agricultural properties that were notified
and rehabilitated agroecologically. Using conservation legislation as a
tool, the ideal work unit for carrying out soil conservation study is
the watershed. The watersheds have the important function of regulating
the water balance, in addition to housing agricultural production and
promoting the storage of rainwater, which seeps into the soil and is
made available to rivers throughout the year. The degradation of the
watershed is related to the lack or deficiency of vegetal cover from
cultures that occupy the soil and has as a consequence the erosive
processes that cause the silting of the watershed water network,
interfering in the quantity and quality of the water (Rodrigues et al.,
2015). The first principle of soil conservation is soil cover, whether
vegetable or mulch. The use of conservationist practices, such as the
use of varieties that provide greater vegetal coverage of the soil,
reducing the direct impact of raindrops on the soil surface, reduces the
soil losses, water, organic matter, and nutrients because of water
erosion (Silva et al., 2005; Rodrigues et al., 2015). The inappropriate
use of agricultural soils causes the gradual loss of its productive
capacity and the contamination of water resources by sediments,
resulting from the erosion process (Lelis & Calijuri, 2010). This
occurs as a result of the inexistence, or because of the erroneous
adoption of conservationist practices in the cultivation areas of
agricultural properties, which can transform a large river into a
sprawling stream, a fact commonly verified in Brazil, mainly in pasture
areas (Menezes et al., 2009). Irrational soil management makes
production unfeasible and compromises the balance of ecosystems (Santos
et al., 2007) and soil cover, which is a form of management for a
specific crop, in a management system and specific locations, represent
a joint effect in reducing water erosion (Silva et al., 2009). The
second principle of soil conservation is to prevent the surface run-off
regime from changing from laminar to turbulent and, for that, the
construction of an agricultural terracing system is carried out, which
has the function of sectioning the length of the ramp and promoting the
infiltration of soil water. According to Pruski (2006), the more the
soil surface is protected by vegetation cover, against the rain action,
lower the propensity for erosion to occur. Studies by Minella et al.
(2007) to identify the origin of sediments at watersheds, concluded that
the areas of crops are the main sources of sediments and suggested that
programs for the implementation of conservationist soil management
practices are essential. By adopting proper management and mitigating
actions to recover the impacted areas, there will be an improvement in
water quality at the watersheds (Araújo et al., 2009). As a final
product of soil conservation, its contribution to minimizing floods
during periods of heavy rainfall and increased availability of water in
the dry period of the year is considered.
At the Rio do Peixe watershed, in June 2007 the inspection activities
began, which consists of the preliminary survey (PS) stages, the visit
to the properties (inspection), the presentation of technical
conservation projects for each property and ends with the rehabilitation
of all visited and notified properties. To carry out the work, at the
Vera Cruz section of the watershed, the conventional methodology was
used in 2007, accomplishing this stage in December 2011, where 14076 ha
were evaluated; in the Ocauçu stretch (from 2011 to 2015), 8,175 ha were
evaluated, making a total of 22,251 ha, that is, 216 ha per month, as
the study was carried out by a team of four Agronomists who worked one
week per month, for 103 months. The CDA inspection/diagnosis methodology
(conventional) was developed as from 1999, by a technical group of
Agricultural Engineers, published in 2003 and that was improved in 2017,
receiving the name of Innovative CDA Diagnostic Methodology (Vischi
Filho et al., 2017). This came out because action strategies needed to
be created to streamline all of this demand. Several options for
technological innovations were tested, including the use of model
aircraft, helicopter and drone, however, the results were only favorable
when a new method of work was developed. The pilot project of the CDA
Innovated methodology was carried out at the Rio do Peixe Watershed, in
a 53 thousand hectares stretch, located in Vera Cruz, Ocauçu and Marília
(Vischi Filho et al., 2018). In this study, with an emphasis on the
inspection of Rio do Peixe watershed, the type of intervention aimed at
transforming conventional and soil-degrading agriculture into
conservationist agriculture, implementation conservationist technical
projects that contemplated this novelty. Conservation Agriculture is an
agricultural system that promotes the maintenance of permanent soil
cover, minimal soil disturbance or no-tillage and the diversification of
plant species. It increases biodiversity and natural biological
processes above and below the soil surface, which contributes to
increasing the efficiency of water and nutrients use and to improve and
sustain agricultural production (FAO, 2019). On June 15, 2019, it turned
twelve years of activities to inspect the use and conservation of the
soil at Rio do Peixe watershed, in the stretches located in Vera Cruz,
Ocauçu and Marília. The objectives of this study were to test
innovations for diagnosis of agricultural properties, to locate erosions
and to correct them with changes in the ways of soil management, aiming
at transforming the degraded agricultural properties at Rio do Peixe
watershed into rehabilitated properties, promoting conservationist
agriculture and evaluating the results through remote sensing and water
quality indicators. This is a great study by the São Paulo State
Secretariat of Agriculture and Supply, which brings benefits to farmers
whose properties make up Rio do Peixe watershed and especially to the
entire population of this region that has benefited from the development
of this study, including in improvement of the water quality that
supplies the cities, mainly Marília (216,684 inhabitants) and Presidente
Prudente (227,072 inhabitants) that capture waters from Rio do Peixe for
public supply. It is the Secretariat of Agriculture “Caring for the
Well-Being of Society”.
2 MATERIALS AND METHODS
This work was carried out in the stretch of the Rio do Peixe watershed
(Rio do Peixe watershed), located in Vera Cruz, Ocauçu and Marília, SP,
Brazil, under coordinates S22°14’52.68”, W49°44’59.97”, start and end
under coordinates S22°18’13.28”, W50°2’54.22”, Datum WGS 84 (Figure 1).
The climate of the region is the humid subtropical of the Cwa type,
according to the Köppen classification, with temperatures in the warmest
month above 29.7°C and in the coldest month, below 10.6°C, with rainfall
annual average of 1,193 mm. The predominant soils are Red-Yellow
Ultisol, Abrupt, moderate horizon A, sandy/medium texture and Litolic
Entisol, eutrophic (Santos et al., 2018). The geological formation
consists of rocks from the Bauru Group, covered by neocenozoic sediments
(Bezerra et al., 2009). The predominant relief is smooth-undulating, in
the western plateau of São Paulo and, in the region of the depression,
it is strongly undulating in the escarpments (Itambé) that separate the
plateau from the depression.
Inspection and agro-environmental rehabilitation work at Rio do Peixe
watershed started on June 15, 2007, and is ongoing until today, in 2020,
with inspections carried out on all properties that are part of these
stretches of the watershed, where properties whit erosion were observed
and also soil degrading processes, seen during diagnosis, which were
classified according to the legislation in force in the State of São
Paulo (São Paulo, State, 1988). After the detection of erosions, from
the report generated during the visits, the owners of the farms were
notified to readjust the properties based on technical conservation
projects, specific to each one of them. The CDA Staff, composed of four
Agricultural Engineers, during a week, monthly, visited each property
two to five times during the implementation of the project, the first
time during the diagnosis, in monitoring the execution of the technical
project and in releasing the property after the implementation of
conservationist practices. The other remaining properties that complied
with the land use and conservation legislation, received a document
informing them of this compliance. The data collected during the
diagnosis were inserted into a specific database and worked according to
the methodology described by Vischi Filho et al. (2016). The evaluation
of the results obtained with soil conservation, through the improvement
of vegetation cover and resulting from changes in soil and water
management practices were proven by comparing the state of the art
(before assessment/study - T1) to the results obtained (after the
implementation of technical projects - T2), using Google Earth® Pro
images, using the historical images tool (years: 2002, 2006, 2012, 2013,
2017 and 2018) to evaluate the post-agro-environmental rehabilitation of
properties (Figure 2). The measurement of soil losses and sediment input
to the river were evaluated by water quality indicators evaluated by
Turbidity, Suspended Solids, Phosphorus and Organic Carbon, which were
measured through periodic water analysis of Rio do Peixe. As for the
water quality indicators, the data collected was separated into two
periods, considered as treatments, being: T1 - data referring to the
period called BEFORE the study was carried out, considering the
information from the years 2000 to 2007 and T2 - data referring to the
period termed AFTER the study was carried out, considering the
information from 2008 to 2018. The improvement in water quality was
assessed by determining the indicators that were tabulated and compared
using graphics prepared for each indicator for treatments T1 and T2
(Figure 3). These indicators were chosen because turbidity shows the
sediment input in the waterbody as a result of erosion and the transport
of these particles to the watercourse. The months were chosen as they
have a higher probability of erosion, according to rainfall data,
considering as the highest rainfall averages, the months of February,
October and December, which were the months that sampled and analysed
the water. To subsidize the turbidity and suspended solids assessments
in water, the information of Setzer (1985) was used as a comparison. The
samples to evaluate these measures are obtained in the watercourse, in
the posts located downstream from the places where the watershed has the
largest cultivated areas, which are located upstream. To apply the law
for the use and conservation of agricultural soil, a diagnosis is made
that consists of delimiting the watershed and visiting all the component
properties of that watershed. This procedure is called a preliminary
survey (PS) and has a high cost to be performed, in addition to being
very time-consuming. The diagnosis is carried out with the aid of aerial
images from Google Earth® Pro, planialtimetric charts of scale 1: 50.000
and surveys ”in loco” by Staff of Agronomic Engineers from CDA. After
the inspections, the owner who is not complying with the legislation
(São Paulo, State, 1988), is notified and presents a conservation
project to recover that degraded area, respecting the class of land use
capacity (Lepsch et al., 2015). After the project was implemented, with
the area recovered and erosions controlled, it started to adopt
conservationist practices that transform soil management into a
conservationist. The present study deals with the inspection at a
watershed, specifically Rio do Peixe watershed, stretches of Vera Cruz,
Ocauçu and Marília, which correspond to 53 thousand hectares. Having the
difficulty of traversing the 330,000 agricultural properties in the
state of São Paulo, a new methodology for inspection was adopted, which
was the Innovated CDA Methodology (Vischi Filho et al., 2017). The
methodology consists in the use of the databases of the Rural
Environmental Registry (CAR), the Animal and Vegetable Defense
Management System (GEDAVE) and Aerial Images of Google Earth® Pro,
current, promoting an interface of this information with databases,
performing diagnosis and inspection by remote sensing. After this step,
the data obtained with the study carried out on Google Earth® Pro and
Excel®, are checked in the field “in loco” and the inspection and
consequent agri-environmental rehabilitation are finalized (Vischi Filho
et al., 2018).