Theophilo Benedicto Ottoni Filho

Estimation of field capacity and moisture retention based on regression analysis involving chemical and physical properties in Alfisols and Ultisols of the state of Rio de Janeiro

This work determines field capacity and moisture retention through correlation and regression analysis, based on physical and chemical properties in Alfisols and Ultisols in the State of Rio de Janeiro (Brazil). The field capacity was estimated “in situ” by the direct method. The other properties were obtained by laboratory methods. Studies were developed in accordance to different levels of data analysis: global or partial (local). The correlation study showed that microporosity and contents of clay, sand, organic matter and coarse sand were meaningfully correlated with field capacity and moisture retention. The results have shown that texture–organic matter–microporosity interactions are the prime factors in determining water retention of those soils. The multilinear regression equations relating clay, sand, organic matter, coarse sand and microporosity to field capacity and moisture retention variables at different tensions, fitted well to global and partial data. Similar performance was observed when the pedofunctions based on clay, sand, and organic matter contents were used, as well as the simpler pedofunctions with microporosity as the only independent variable.

Revisiting Field Capacity (FC): variation of definition of FC and its estimation from pedotransfer functions

Taking into account the nature of the hydrological processes involved in in situ measurement of Field Capacity (FC), this study proposes a variation of the definition of FC aiming not only at minimizing the inadequacies of its determination, but also at maintaining its original, practical meaning. Analysis of FC data for 22 Brazilian soils and additional FC data from the literature, all measured according to the proposed definition, which is based on a 48-h drainage time after infiltration by shallow ponding, indicates a weak dependency on the amount of infiltrated water, antecedent moisture level, soil morphology, and the level of the groundwater table, but a strong dependency on basic soil properties. The dependence on basic soil properties allowed determination of FC of the 22 soil profiles by pedotransfer functions (PTFs) using the input variables usually adopted in prediction of soil water retention. Among the input variables, soil moisture content θ (6 kPa) had the greatest impact. Indeed, a linear PTF based only on it resulted in an FC with a root mean squared residue less than 0.04 m3 m-3 for most soils individually. Such a PTF proved to be a better FC predictor than the traditional method of using moisture content at an arbitrary suction. Our FC data were compatible with an equivalent and broader USA database found in the literature, mainly for medium-texture soil samples. One reason for differences between FCs of the two data sets of fine-textured soils is due to their different drainage times. Thus, a standardized procedure for in situ determination of FC is recommended.

Estimation of field capacity from ring infiltrometer-drainage data

A Capacidade de Campo (CC) e um parâmetro largamente adotado na Ciencia do Solo aplicada. Entretanto, seu metodo de determinacao in situ pode apresentar dificuldades, geralmente por conta da necessidade de grandes suprimentos de agua nos locais dos testes. Ottoni Filho et al. (2014) propuseram uma padronizacao da determinacao de campo da CC e evidenciaram que tal CC in situ pode ser estimada por uma funcao de pedotransferencia (FPT) linear com base na umidade volumetrica do solo ao potencial matricial de -6 kPa [θ(6)] para os mesmos solos usados neste estudo. O objetivo deste trabalho foi utilizar os dados de umidade do solo abaixo de um infiltrometro de duplo anel, medidos 48 h apos o termino do teste de infiltracao, a fim de desenvolver FPTs para a CC in situ padronizada. Verificou-se que tais dados de CC de anel foram em media 0,03 m3 m- 3 maiores que os de CC in situ padronizada. A FPT linear que foi desenvolvida com os dados de CC de anel com base apenas em θ(6) foi quase tγo precisa quanto a FPT equivalente reportada por Ottoni Filho et al. (2014), que foi desenvolvida para os dados de CC padronizada. As raizes quadradas de residuo quadratico medio da CC determinada a partir de ambas as FPTs foram aproximadamente 0,02 m3 m- 3. O metodo proposto tem a vantagem de estimar a CC in situ do solo pelo uso da agua aplicada no teste de infiltracao.

A Preliminary Proposal for the Structural Classification of Soil Pore Space

This study presents a preliminary proposal of a structural classification system of soil pore space seeking to group soils with similar air availability curves. The function that relates soil air content to water suction is herein called the air availability curve. The proposed system approach is similar to that of textural classification and allows classifying soil according to types of soil structural families based on nine possible sub-areas (from A to I) represented in a classification triangle, herein called the structural triangle. Besides family types, it is also necessary to predict the family orders according to different ranges of variation for the effective soil porosity. Both family type and order are obtained by parameterization of the moisture retention curve. 467 samples were classified according to the proposed methodology, which confirmed that the structural families grouped soils with similar air availability curves. This result shows the potential usefulness of the proposed methodology for pedologic knowledge and for the development of pedotransfer functions of the soil water properties.