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Organic farm does not improve neither soil, or water quality in rural watersheds from southeastern Brazil

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Agricultura orgânica não melhora a qualidade do solo nem da água em bacias hidrográficas rurais do sudeste do Brasil


ABSTRACT

This study was conducted in a rural region where there are conventional and organic farms, the agricultural production includes more than 20 million people, and the effect on environmental quality is still poorly known in terms of indicators. Our objectives were: (1) compare soils attributes to reference areas, (2) verifying if cultivated areas under different farm systems presented differences in the soils attributes, (3) evaluate the attributes of quality water of watersheds and comparing the results with limiting values established by environmental legislation, and (4) analyze the values considering three criterion: watersheds, climatic season, and region of the landscapes. The study was conducted in two rural watersheds that have similar biophysical features and located in the Ibiúna municipality, São Paulo State, Brazil. However, one watershed encompasses farms where landowners largely use conventional agricultural systems. In the other watershed approximately 25% of the farms there are using an organic farm system. In the two watersheds soil samples were collected in sites covered with natural forest and in sites with agriculture (one watershed being organic and other being conventional). The attributes analyzed were soil bulk density (BD), concentrations of Carbon (C) and Nitrogen (N), C:N ratio, C Management Index, and the abundance of 13C and 15N in the soil organic matter. Water attributes were analyzed onsite or in laboratory after analysis of samples. Analyses included: air and water temperature, pH, dissolved oxygen, salinity, total of dissolved solids, total solids, electric conductivity, turbidity, total chloride, nitrate, total phosphorus and potassium. Regarding the soil attributes our database revealed that (1) the soils from cultivated sites of both watersheds presented significant differences from their respective forested areas, (2) Soil attributes are of equal quality in both farm systems. Concerning water attributes: (1) almost all attributes presented values better than the limiting values stipulated by Brazilian legislation; (2) the watersheds did not present significant differences of most of the attributes; (3) in the criteria climatic season data showed some significant differences. The data showed that the soils from the areas used for agricultural ends present belief that significantly worse soil quality in comparison to soils from sites still covered with natural forest. Neither the land cover nor farming system are altering the superficial water quality of the studied watershed and this appears to be related to the extensive percentage of natural remaining vegetation that still exists in both watersheds. The seasonality is an important force that drives the quality characteristics of the water. We highlight that the principles of organic agriculture should be practiced more efficiently and influences such as deforestation should be rigorously avoided.

Keywords: Land cover change, Farm systems, Soil attribute, Water attribute, Non-organi, Organic farming

RESUMO

Este estudo foi conduzido em uma região rural onde existem fazendas convencionais e orgânicas, a produção agrícola inclui mais de 20 milhões de pessoas e o efeito na qualidade ambiental ainda é pouco conhecido em termos de indicadores. Nossos objetivos foram: (1) comparar atributos do solo com áreas de referência, (2) verificar se áreas cultivadas sob diferentes sistemas agrícolas apresentaram diferenças nos atributos do solo, (3) avaliar os atributos da qualidade da água de bacias hidrográficas e comparar os resultados com valores limites estabelecidos pela legislação ambiental e (4) analisar os valores considerando três critérios: bacias hidrográficas, estação climática e região das paisagens. O estudo foi conduzido em duas bacias hidrográficas rurais que possuem características biofísicas semelhantes e localizadas no município de Ibiúna, estado de São Paulo, Brasil. No entanto, uma bacia hidrográfica abrange fazendas onde os proprietários utilizam amplamente sistemas agrícolas convencionais. Na outra bacia hidrográfica, aproximadamente 25% das fazendas utilizam um sistema de agricultura orgânica. Nas duas bacias hidrográficas, amostras de solo foram coletadas em locais cobertos por floresta natural e em locais com agricultura (uma bacia hidrográfica sendo orgânica e a outra convencional). Os atributos analisados ​​foram densidade do solo (BD), concentrações de carbono (C) e nitrogênio (N), relação C:N, índice de manejo de C e abundância de 13 C e 15 N na matéria orgânica do solo . Os atributos da água foram analisados ​​no local ou em laboratório após análise das amostras. As análises incluíram: temperatura do ar e da água, pH, oxigênio dissolvido, salinidade , total de sólidos dissolvidos, sólidos totais, condutividade elétrica, turbidez , cloreto total, nitrato, fósforo total e potássio. Em relação aos atributos do solo, nosso banco de dados revelou que (1) os solos de locais cultivados de ambas as bacias hidrográficas apresentaram diferenças significativas em relação às suas respectivas áreas florestadas, (2) os atributos do solo são de igual qualidade em ambos os sistemas agrícolas. Em relação aos atributos da água: (1) quase todos os atributos apresentaram valores melhores que os valores limites estipulados pela legislação brasileira; (2) as bacias hidrográficas não apresentaram diferenças significativas na maioria dos atributos; (3) nos critérios de dados da estação climática mostraram algumas diferenças significativas. Os dados mostraram que os solos das áreas utilizadas para fins agrícolas apresentam qualidade de solo significativamente pior em comparação com os solos de áreas ainda cobertas por floresta natural. Nem a cobertura do solo nem o sistema agrícola alteram a qualidade da água superficial da bacia hidrográfica estudada, o que parece estar relacionado à extensa porcentagem de vegetação natural remanescente que ainda existe em ambas as bacias hidrográficas. A sazonalidade é uma força importante que impulsiona as características de qualidade da água. Destacamos que os princípios da agricultura orgânica devem ser praticados de forma mais eficiente e influências como o desmatamento devem ser rigorosamente evitadas.

Palavras-chaves: Mudança na cobertura do solo, Sistemas agrícolas, Atributo do solo, Atributo da água, Agricultura não orgânica, Agricultura orgânica

Introduction

Integrated assessment of natural resources is of paramount importance anyplace worldwide, once human well-being depends on the quality of natural resources (UNEP (United Nations Environmental Program), 2011). It is highly important in establishing strong and coherent institutional arrangements that are needed to ensure the efficient collection, storage, analysis and summary of data and the availability of data, for instance of soil and water quality, to potential users. One of the difficulties in carry out integrated studies is due the existence of interaction and response in multiple scales within and between natural subsystems (Sykes et al., 2001). Consequently, studies integrating databases regarding soil and water have not been so common. The accomplishments of a watershed management programs are dependent on survey data and analysis in the different compartments and verification of the influence among each other.

In the Brazilian southeastern region we have the Ibiúna municipality, sited approximately 80 km west far from São Paulo Capital City. Ibiúna is an important tourist region and also encompasses important areas used for agriculture. The São Paulo’s metropolitan region encompasses the Capital City São Paulo and also 38 municipalities, and has a population of approximately 21 million people. This region is the main consumer center of most of the agricultural products produced in Ibiúna. In Ibiúna there are two adjacent watersheds that jointly constitute an interesting scenario for conducting a comparative analysis of attributes of soil and water, because on the one hand, such watersheds have similar natural characteristics among them, and the other hand, in one of the watersheds organic farming is practiced there, and in the other conventional agriculture is practiced. Hence, this scenario is suited for developing an integrative study considering responses of the soil and water quality attributes according to land cover and land use.

Soils play a key role in the definition of sustainable land management since they represent the basis of food production (Fliessbach et al., 2007). A fertile soil provides essential nutrients for crop plant growth, supports a diverse and active biotic community, exhibits a typical soil structure, and allows for undisturbed decomposition of organic materials (Mader et al., 2002). The ecosystem services provided by the soil are usually constituted by a set of chemical, physical and biological attributes and commonly indicate the quality of soil. On its turn, isotopic abundances could be a powerful tool to elucidate differences in ecosystem functioning and driving mechanisms of element cycling in the different land cover situations, like forest-covered and agricultural sites, as well as different land uses, like organic and conventional management systems (Choi et al., 2003, Klaus et al., 2013).

On the other hand, soils exert a fundamental influence on water attributes. How we handle the soil and what we deposit on it determine, in part, the level of treatment required to protect our water supplies. Agriculture is estimated to be responsible for 70% of nitrate and 30–50% of phosphorus pollution (Kay et al., 2012) and the land use is responsible for a major amount of total solids delivered to water bodies (Welch and Jacoby, 2004). This shows why an efficient soil management and planned land cover help protect water quality.

The concept of what is rural has an exceptional range of variations worldwide. In this study, we consider the concept of proposed by Brazilian Institute for Geography and Statistics (www.ibge.gov.br): a rural area is an area that is located externally to a town. In rural areas there are many kinds of land cover, leading to different forms of soil management and with different amounts and intensities of environmental impacts, including loss in quality to both soil and stream water.

Agriculture is a kind of human activity developed to produce goods of value to people. Farmers commonly use a set of approved agronomic practices in order to get the best agricultural yield from the field. Some of the activities include, but is not limited to: genetic melioration of the cultivars, soil management techniques, including several kinds of fertilization and tillage, pest control, water management, among others. Some agronomic practices are included in the concept called “conventional farm system”, as the adoption of monocultural agroecosystems, use of several types of pesticides, mineral fertilizers and other practices that admittedly are degrading both for environment and human health. However, it is well known that a large number of farms worldwide are still using this type of farming system.

Conversely, since the last decades, new agronomic practices have been developed, aiming to sustain and enhance the health of ecosystems and organisms from the smallest in the soil to human beings (Naturland, 2014, Seufert et al., 2012). Due to the capacity of producing good crop yields with minimal impacts on environmental features, many people believe that “organic farming systems” that consider different practices and crop rotations and/or use of organic fertilizers in adequate amount and quality might represent a realistic alternative to conventional farming systems (Mäder et al., 2002). However, in several situations, especially in areas where it is not usual to work with consultants, groups of farmers with a commercially interest in cash crops who work without any inputs are certified organic and able to sell for a premium price without signification changes in agricultural practice (Brul, 2012).

Organic agriculture has as one of the principal principles sustaining and improvement of the soil (Naturland, 2014). However, while some analyzes regarding the effectiveness of using organic-based agronomic techniques in order to actually promote environmental ameliorations has generated highly diversified results, where some studies showing effectiveness (Winqvist et al., 2012), and others showing that the performance is not significantly different (Hokazono and Hayashi, 2012). For example, albeit there is some evidence that concentrations of Carbon (C) in the soil are greater in soils managed organically than in those from integrated or conventional farming, other studies have not found such differences (Marinari et al., 2006, Mondelaers et al., 2009, Parras-Alcántara et al., 2014). If soils from organic farms have been practiced on nutrient limited soil they do not respond as strongly as production from irrigation or conventional systems. On the other hand, better water-holding capacity and water infiltration rates have produced greater yields than conventional systems under drought conditions and excessive rainfall (Seufert et al., 2012).

Furthermore, while studies involving soil-related attributes with organic farming systems are abundant, studies relating surface water-related attributes and organic farming systems are less common, especially in Brazil (Takino and Maier, 1997). Some researchers suggest that “organic farmscapes” might reduce the amounts of nitrogen (N) and phosphorus (P) transported from the soil surface due the reduction of volume of runoff, and conversely, environmental problems most commonly found on organic farms result from mismanaging manure applications or soil incorporation of green-manure crops, or from improper storage of manure or compost (Bellows, 2002).

One of the features that is responsible, is the high variability of performance of organic farm systems is regarding the time of adoption of organic-based farm system in the rural property (Marinari et al., 2006, Assis and Romeiro, 2007). Another factor is the differentiated use of organic-based agronomic techniques and organic fertilizers among sites. Because of these inconsistent findings, advantages and disadvantages of the organic farming system vs. integrated or conventional production are hotly debated (Gattinger et al., 2012).

This study was conducted with the aim to compare soil-related and water-related features in two rural watersheds located in rural area of Ibiúna Municipality. We considering two hypotheses: (a) the land cover significantly changes the topsoil attributes and (b) the soil management systems adopted in the agricultural areas of study areas are enough to cause significant alterations in the investigated soil and water attributes.

Section snippets

Location and environmental features of the study area

The study was carried out in two watersheds fully included in the geopolitical boundaries of the Ibiúna Municipality, São Paulo State, Brazil (Fig. 1). The geographical coordinates are 23°35′50″ and 24°01′14″ of South Latitude, and 46°59′05″ and 47°23′17″ of West Longitude, with approximately 930 meters of mean altitude. From the 71,157 inhabitants of Ibiúna, 66.4% live in the rural areas (IBGE (Brazilian Institute for Geography and Statistic), 2013). The two studied watersheds are named Paiol

Soil sampling and analyzes

Intact soil cores were collected from each of 60 sampling points at the 0–20 cm depth, using a steel ring. Just to the side of where the core was collected an additional sample was taken with a Dutch auger. Samples were collected during October and December of 2009. For each land cover class, soil samples were collected in one core for each site in order to avoid influence of edge effects on the characteristics of the investigated attributes. Thirty samples were collected in each watershed. In

Soil attributes

Soils from agricultural sites from both watersheds had high similarity among them for all attributes studied, permitting us to affirm, beforehand, which independent of the farm system, that the soil characteristics from organic farms were not better than the cultivated soils from conventional farms. However, cultivated soils from both farm systems are significantly altered in relation to the respective reference forested soil areas.

First, observing the total database, we observed that all soil

Soil attributes

BD data show that soils from Ibiúna are highly prone to compaction for land cover shifting from forest to cultivation. Such information was already observed by Manfré et al. (2011a) also for pastured areas in the same studied watersheds. Textural attributes have a discrete participation in the BD, but BD did not have a significant correlation with textural attributes (sand, silt or clay). On the other hand, SOM exerts a significant influence over the changes in BD, supported by significant

Conclusions and final remarks

Our data show that the soils from Ibiúna have a modest land use capability because they are highly prone to compaction and degradation. Soil and water have characteristics not significantly different in both organic and conventional farms regions, indicating that in Ibiúna, after approximately fifteen years after conversion, organic farming system did not improve the qualities neither of soil or water of the studied watersheds, meaning be of low ecological efficiency in terms of restore the

Acknowledgements

Authors are grateful to agencies CAPES, FAPESP and FUNDUNESP for financial support and to Centro de Energia Nuclear na Agricultura (CENA—USP—Piracicaba—SP) for isotopic analyses of the soil samples. We are specially thank to Engineer MSc Ana Cecília Arroyo Santos (in memorian), for extensive work in several steps of the project and Agronomist Carlos Rombine dos Santos, from Municipal Secretary of Agriculture from Ibiúna—SP, Brazil, by providing information regarding the organic farms in Ibiúna

References (68)

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