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).