1 INTRODUCTION
Aiming to regulate the use and conservation of soil, to combat soil
erosion, 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 and
has been carrying out this work for 20 years with very positive results,
mainly in inspections carried out at Watersheds.
The area of the state occupied by agriculture has approximately 18
million hectares, with 330 thousand agricultural properties. During that
period, 772,000 hectares were already worked at 19,846 agricultural
properties that were notified and rehabilitated agroecologically (Vischi
Filho et al., 2019).
The CDA Diagnostic methodology uses conservation law as a tool and
considers the watershed as the ideal work unit for carrying out this
type of activity. The watersheds have an important function of
regulating the water balance, as well as housing agricultural production
and promoting the storage of rainwater, which seeps into the soil and
are available to rivers throughout the year (Lal, 1994; Vischi Filho et
al., 2018 and 2019).
Degradation of the watershed is related to the lack or deficiency of
vegetal cover of cultures that occupy the soil and has consequently 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 practices, such as the use of varieties
that provide bigger 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; Merten et al., 2016).
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 (Araujo, et al., 2007;
Lelis & Calijuri, 2010). The last decades have been characterized by
drastic changes in land use and occupation in the region, which for
Zalidis et al. (2002) represented one of the main driving forces for
environmental degradation, especially on soil and water. This occurs
because of the inexistence, or of the erroneous adoption of
conservationist practices in the cultivation areas of agricultural
properties, 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 and soil cover (Santos et al., 2007), 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 avoid that the surface
run-off regime goes 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 management of soil
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.
In this work on the inspection of Rio do Peixe watershed, the type of
intervention aimed at transforming conventional and soil-degrading
agriculture into conservationist agriculture, implementing
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 below and on the soil
surface, which contributes to increasing the efficiency use of water and
nutrients, to improve and sustain agricultural production (FAO, 2019).
In 2019, it turned twelve years of activities to inspect the use and
conservation of soil at Rio do Peixe watershed, in sections I, II and
III, located in Vera Cruz, Ocauçu and Marília cities. This work aimed 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.
2 MATERIALS AND METHODS
This work was carried out in the sections of Rio do Peixe Watershed,
located in Vera Cruz, Ocauçu and Marília cities, SP, Brazil, at
coordinates S22° 14’52.68 ”, W49° 44’59.97”, start and end at
coordinates S22° 18’13.28 ”, W50° 2’54.22”, Datum WGS 84 (Figure 1).
The climate of the region is humid subtropical of Cwa type, according to
Köppen-Geiger classification, having temperatures in the warmest month
above 29.7°C and the coldest month, below 10.6°C, average annual
rainfall of 1,193 mm.
Predominant soils are Red-Yellow Ultisol Abrupt, moderate horizon A,
sandy/medium texture and Litolic Entisol, eutrophic (Santos et al.,
2018). Geological formation consists of rocks from the Bauru Group,
covered by neocenozoic sediments (Bezerra et al., 2009). Predominant
relief is the smooth undulating, in the western plateau of São Paulo
and, in the depression, strongly undulating in the escarpments (Itambé)
that separate the plateau from the depression.
CDA inspection/diagnosis methodology (conventional) was developed from
1999 on, by the technical staff of Agronomist Engineers, published in
2003 and it was improved in 2017, receiving the name of Innovative CDA
Diagnostic Methodology (Vischi Filho et al., 2019). This happened
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 favourable when this new method of work was developed.
The CDA Innovative pilot project was carried out at Rio do Peixe
Watershed, on a 53 thousand hectare stretch, located in Vera Cruz,
Ocauçu and Marília cities.
Inspection and agro-environmental rehabilitation work at Rio do Peixe
Watershed started on June 15, 2007, and it has been currently happening
(from 2007 to 2020). Inspections are carried out at all properties that
compose these three sectors of Watershed. CDA Conventional methodology
was applied, which consists of preparing an action with the delimitation
of Watershed in a topographic map scale 1:50.000, elaborating a mosaic
of aerial images, which will be used in the field, “in loco” to help
in the localization strategy and, also in the visit to all Watershed
properties. Subsequently, the properties are visited using the
”checklist” (official CDA document for Soils), in which erosions and
other forms of degradation are included, in compliance with conservation
legislation (São Paulo State, 1988).
Erosions are georeferenced using a Global Positioning System (GPS)
receiver, classified, photographed (photos that will compose a
photographic report) and noted in the ”checklist” leading to the data
generated in the diagnosis that will be used to compose the processes
relevant to each agricultural property visited and based on the
information contained in the diagnosis database. The owner of the area
hires an Agronomist Engineer who will prepare a technical conservation
project for the recovery of the degraded area, respecting the projects,
the class of land use capacity (Lepsch et al., 2015), for this property.
The conservation project is analyzed by the CDA Staff, who approves it
or not, sending it for corrections if necessary (physical project, on
paper) and if it is approved, it goes to the implantation stage, by the
farmer, correcting and remedying soil damage and erosion at that
location. The CDA Staff, in this work, is composed of four Agronomist
Engineers who work for a week, monthly. They visited each property two
to five times during the implementation of the project, the first time
during the diagnosis, monitoring the execution of the technical project,
and on the property release after the works. After the project was
implemented, the soil was preserved and the property became more
profitable, increasing productivity. This methodology was applied to two
sections of this Watershed, defined as, section I, located in Vera Cruz,
SP, Brazil, with an area of 14,076 ha (period of work from 2007 to
2011) and section II, located in Ocauçu, SP, Brazil, with an area of
9,027 ha (from 2011 to 2015).
In this CDA activity, as well as in other works distributed throughout
the territory of the State of São Paulo, having difficulty of traversing
the 330 thousand agricultural properties in the state. A strategy needed
to be developed and a new methodology for inspection was adopted, it was
the Innovated CDA Methodology, which was applied in Watershed section
III, in Marília with an area of 27,775 ha (from 2017 to 2018).
The methodology consists of making the diagnosis in the office using the
databases of Rural Environmental Registry (CAR, 2017), opening and
saving the georeferenced “shapefile” with the property limit. To learn
about the owner and property information, we used data from the Animal
and Plant Defence Management System (GEDAVE, 2017). The CAR and GEDAVE
information are specialized in Google Earth® Pro, (current aerial
images), promoting an interface of this information with databases,
performing diagnosis and inspection by remote sensing. Within the
property perimeter, whose shapefile was imported into Google Earth®, the
diagnosis begins visualizing the erosions, insertion of a georeferenced
GPS point on this erosion, drawing a polygon of this erosion contour,
classifying the erosion according to soil conservation legislation (São
Paulo State, 1988). Also, elaborating an Excel® spreadsheet containing
the following information: the number of georeferenced GPS points, the
type of erosion, description of it (Table 2), and erosion area (ha).
This work is carried out throughout the property’s perimeter.
After the diagnosis by remote sensing is completed, a colour aerial
image is saved in JPEG format and spreadsheet in Excel®, and they are
made available to the CDA Staff who will visit the property and go
straight to the erosion site, as it is geo-referenced, not needing to be
looking for erosion. It is checked whether the erosion of that point
exists or not and if it exists, whether it is according to what was
described for that point in the Excel® spreadsheet. If the erosions are
according to the data in the spreadsheet, the information is maintained
and if they are divergent, this information is corrected on the
spreadsheet. After visiting all points on the spreadsheet, obtaining
photos of the erosions, we have real data on the soil situation of the
agricultural property. The data is placed in documents that will be
handed in to the notified owner. After this stage, the procedures are
identical to the conventional CDA methodology: the owner of the area
hires an Agronomist Engineer who will prepare a technical conservation
project to recover the degraded area.
To validate the new methodology, some indicators were used to evaluate
the results obtained with the implementation of soil conservation.
Through the vegetation cover improvement, resulting from changes in soil
and water management practices that were proven by comparing the state
of the art (before evaluation/work - T1) with the results obtained
(after the implementation of technical projects - T2). Using Google
Earth® Pro images, through the historic 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, due to
the action of soil erosion, were evaluated by the water quality
indicators evaluated by the Turbidity analysed by the Standard Methods
for the Examination of Water and Wastewater - 2130 B method (SMWW a).
Suspended Solids were analysed according to the 2540 D method (SMWW b).
The Phosphorus were analysed according to the United States
Environmental Protection Agency, EPA 6010D method (USEPA). Organic
Carbon were analysed according to 5310 C method (SMWW c), which was
measured from periodic analyses of Rio do Peixe water.
The samples were obtained from the watercourse, at a station located
downstream from the areas where the watershed has the highest
concentrations of cultivated areas, and they are collected by São Paulo
Environmental Company (CETESB, 2020), once a month, in February,
October, and December. According to method 1060 and 9060 of Standard
Methods for the Examination of Water and Wastewater (SMWW d), at the
collection point code 00SP21438PEIX02100 / UGRHI 21 (coordinates:
S22°18’13.62” - W50°2’53.62”).
These indicators were chosen because turbidity shows the sediment input
in the water body due to erosion and the transport of these particles to
it. The months were defined, as there is a higher probability of
erosion, according to rainfall data, considered 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) has used as a comparison.
The data were obtained in two periods, considered as treatments, being:
T1 - data referring to the period called BEFORE the working diagnosis
and erosion control, considering the information from 2000 to 2007 and
T2 - data referring to the period named AFTER the working diagnosis and
erosion control, considering the information from 2008 to 2018. The
improvement in water quality was assessed by determining the indicators
that were tabulated and compared through graphics prepared for each
indicator for the T1 and T2 treatments (Figure 3).