ABSTRACT Brazilian semi-arid tropical is responsible for the production and export of fine table grapes, but the demand for phosphate fertilizers and other agricultural inputs increases the cost of production and threatens local water bodies by leaching of phosphorus (P). The objectives of this study were to quantify the organic and inorganic fractions of P and to determine chemical and microbiological attributes related to its mineralization in soils cultivated with vines in São Francisco Valley. It was hypothesized that P fractions and microbial activity would increase in areas fertilized with phosphate. Soil samples from vines were collected in cultivated areas and in fallow systems. P fractionation, macro-elements analysis, microbial biomass phosphorus (Pmic), and phosphatase enzyme activity were determined and correlated with each other and with the total proportion of synthesized glomalin. In both treatments, the inorganic P fractions exceeded the organic ones, and the total phosphorus available in those soils was associated with the most recalcitrant fractions, reducing risks of leaching of this element and contamination of water bodies. Pmic was higher in the winery areas due to the presence of phosphate fertilizers and organic matter, hence the activity of alkaline phosphatase enzymes and the production of total glomalin increased respectively in three and four evaluated areas, indicating that P-mineralized bacteria and arbuscular mycorrhizal fungi have been positively affected by the current agricultural system.

O crescimento industrial e o populacional têm aumentado os teores de metais pesados nos solos e impactado a qualidade desse recurso. Nesse contexto, as agências de proteção ambiental vêm despendendo esforços para o estabelecimento de índices que possam identificar áreas suspeitas de contaminação. Valores de Referência de Qualidade para Solos (VRQs) refletem a concentração natural de determinada substância no solo, sem interferência antrópica. O trabalho objetivou estabelecer os VRQs para os metais Ag, Ba, Cd, Co, Cr, Cu, Ni, Pb, Sb, V e Zn exigidos pelo Conama, para composição da legislação direcionada ao monitoramento desses elementos nos solos do Estado do Rio Grande do Norte. Foram coletadas 416 amostras de solo em áreas de mata nativa ou com mínima influência antrópica. A abertura das amostras foi efetuada pelo método EPA-3051A, sendo os metais determinados por espectrometria de emissão ótica (ICP-OES) e absorção atômica (AA). Os resultados do trabalho comprovaram que estudos regionalizados são essenciais para definição de VRQs. Os VRQs calculados para o Rio Grande do Norte foram mais restritivos que os de outros estados do país. A análise fatorial de confirmação dos dados foi útil para obtenção de VRQs mais confiáveis e demonstrou que para o Estado esses valores podem ser estabelecidos com apenas duas repetições por local de coleta. Nesse sentido, é primordial um planejamento prévio, de distribuição dos locais de amostragem, de maneira que os diversos compartimentos geomorfológicos, pedológicos e geológicos do Estado sejam representados.

Industrial development and population growth have increased heavy metal concentrations in soils and impacted soil quality. In this scenario, environmental protection agencies have been concerned with establishing heavy metal quality reference values (QRV) that may identify contaminated sites. The study was carried out to provide soil reference values for the metals Ag, Ba, Cd, Co, Cr, Cu, Ni, Pb, Sb, V, and Zn in soils of the State of Rio Grande do Norte according to Brazilian legislation. The study analyzed 416 soil samples taken from native forest or areas with minimal human interference. These samples were digested by the USEPA 3051A method, and the metals were measured by Inductively Coupled Plasma - Optic Emission Spectrometry (ICP-OES) or flame atomic absorption (FAA). The results showed that regional geochemical surveys are essential in establishing QRVs for heavy metals. For example, the QRV for the soils of Rio Grande do Norte were more restrictive than the QRVs adopted for other Brazilian states. Confirmation factorial analysis of the data was useful for obtaining more reliable QRVs and showed that for the state these values could be obtained from two replicates only per collection location. Thus, advance planning is essential in distribution of sampling locations so that the diverse geomorphological, pedological, and geological compartments of the state are represented.