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A variety of analytical methods can be used to measure soil carbon and organic matter content and their results are not equivalent. The objective of this project is to develop and evaluate pedotransfer functions (PTFs) to convert results between analytical methods for southern Brazil. Four analytical methods will be considered: carbon content by dry combustion (TOC) and wet digestion (OC), and organic matter content by wet digestion (OM) and loss on ignition (TOM). PTFs will include include multiple environmental predictor variables. Regression model coefficients will be estimated using weighted least squares to account for the non-constant error variance. The prediction ability of the PTFs will be assessed using leave-one-out cross-validation. The calibrated PTFs will be made available online via a R Shiny app.

The assessment of soil quality is based on indicators and indices derived from soil properties. However, intrinsic soil properties may interfere with other soil properties that vary under different land uses and are used to calculate the indices. The aim of this study was to assess the extent to which intrinsic soil properties (clay and iron oxide contents) explain variable soil properties (sum of bases, potential acidity, organic carbon, total porosity, and bulk density) under different land uses (native forest, no-tillage and conventional agriculture) on small family farms in Southern Brazil. The results showed that the five properties evaluated can be included in soil quality assessments and are not influenced by the clay and iron oxide contents. It was concluded that for little weathered 1:1 and 2:1 phyllosilicate rich-soils, if the difference between the maximum and the minimum clay content under the different land uses is less than about 200 g kg-1 and the iron oxide content less than about 15 g kg-1, the physico-chemical soil properties in the surface layer are determined mostly by the land use. A avaliação da qualidade do solo depende do uso de indicadores e índices construídos com as propriedades dele. Entretanto, essas propriedades podem variar entre tipos de uso do solo, bem como interferir nas propriedades do solo usadas para construir os índices. Objetivou-se com este estudo determinar a capacidade de propriedades intrínsecas do solo (teor de argila e óxido de ferro) para explicar as propriedades variáveis (soma de bases, acidez potencial, carbono orgânico, porosidade e densidade) em diferentes usos do solo (floresta nativa, plantio direto e agricultura convencional) em pequenas propriedades familiares no sul do Brasil. Os resultados evidenciaram que as cinco propriedades do solo estudadas podem ser incluídas em avaliações de qualidade e não são influenciadas pelo teor de argila e óxido de ferro. Sugeriu-se que, para solos pouco intemperizados, ricos em filossilicatos do tipo 1:1 e 2:1, se o teor de argila estiver em um intervalo de aproximadamente 200 g kg-1 e o de óxido de ferro for menor que aproximadamente 15 g kg-1, o uso do solo é o maior fator para controlar as propriedades físico-químicas da camada superficial do solo.