Euzebio Medrado da Silva

Valores de tensão na determinação da curva de retenção de água de solos do Cerrado

A curva de retencao de agua do solo e essencial para o estudo das relacoes solo-agua. A escolha do numero e da combinacao de pontos a serem levantados para o seu tracado normalmente e feita de forma arbitraria. O objetivo deste trabalho foi definir o menor numero e a melhor combinacao de pontos de tensao que resultem na descricao da curva de retencao de agua de solos do Cerrado. Utilizaram-se cinco curvas de retencao de diferentes solos como referencia, cada uma com 15 pontos medidos pelo metodo da centrifuga e ajustada ao modelo de Genuchten. A partir desses 15 pontos, 385 curvas foram geradas para cada solo, com seis, sete, oito e nove pontos, a fim de serem comparadas com a curva de referencia. A analise da distribuicao estatistica da soma de quadrados dos erros padronizados, entre as curvas geradas e as respectivas curvas de referencia, permitiu definir um modelo de probabilidade que serviu como instrumento para a escolha das melhores combinacoes de pontos de tensao. A combinacao definida pelos oito valores de tensao de 1, 3, 6, 10, 35, 84, 611 e 1.515 kPa e a recomendada para o levantamento das curvas de retencao de agua de solos do Cerrado.

Comparação de modelos matemáticos para o traçado de curvas granulométricas

A distribuicao granulometrica de particulas solidas e essencial para as areas de material de construcao, mecânica dos solos, fisica dos solos, hidrossedimentologia, entre outras. As tecnicas utilizadas na avaliacao da distribuicao granulometrica de amostras resultam em valores pontuais, dependendo de posterior interpolacao para o tracado da curva granulometrica e a obtencao de diâmetros caracteristicos especificos. A transformacao de valores pontuais em funcoes continuas pode ser realizada por meio de modelos matematicos. Entretanto, ha poucos estudos com a finalidade de determinar o melhor modelo para o ajuste de curvas granulometricas. O objetivo deste trabalho foi testar e comparar 14 diferentes modelos passiveis de utilizacao no tracado da curva granulometrica de particulas solidas com base em quatro pontos medidos. O parâmetro de comparacao entre os modelos foi a soma de quadrado dos erros entre os valores medidos e calculados. Os modelos mais recomendados no tracado da curva granulometrica, a partir de quatro pontos, sao os de Skaggs et al. 3P, Lima & Silva 3P, Weibull 3P e Morgan et al. 3P, todos com tres parâmetros de ajuste.

Proposição de um modelo matemático para a avaliação do desempenho de sistemas de irrigação

Mathematical models have been proposed to represent the applied irrigation water distribution profile, which is fundamental to evaluate the performance of irrigation systems. Even though there have been advances, so far, there is not a universally accepted model as the most adequate to fit water distribution profiles from irrigation systems. The objectives of this work were to propose a model for evaluating the performance of irrigation systems, and to develop an irrigation adjusting factor for calculating the gross water depth that takes into account both water application uniformity and efficiency measures. The fitting parameters of the proposed model were determined by using the routine Solver from the spreadsheet Excel and the water application uniformity and efficiency measures were calculated from mathematical expressions derived for this model. According to data from the evaluation of a center pivot irrigation system, the proposed model is adequate for analyzing irrigation performance and for obtaining the devised irrigation adjusting factor, by gathering the required system performance indicators. It also simplifies the analysis procedures and allows a direct calculation of the water depth demand for irrigation.

Qualidade física do solo sob sistemas de integração lavoura-pecuária

The objective of this work was to evaluate the physical quality of soil in integrated crop-livestock systems (ICL) in comparison to continuous pasture and native Cerrado. During two years (2005 and 2006), soil samples from a clayed Rhodic Ferralsol were collected from two layers (0-20 and 70-80 cm), in six areas under different crop rotation and ICL. Continuous pasture and native Cerrado were used as reference. The following physical and hydraulic properties were evaluated: bulk density, water saturation, total porosity, macroporosity, effective microporosity, effective saturation, lab and field-saturated hydraulic conductivity, and soil-water retention curve. All the cultivated systems caused impact on the physical and hydraulic properties of the 0-20 cm layer. The continuous pasture provided the best soil physical quality. In the comparison between years, only the soil under conventional tillage had its bulk density increased and its soil porosity decreased. The pasture in the rotation system with ICL, even after four years, does not restore soil physical quality in comparison to continuous pasture.

Modelo matemático para estimativa da temperatura média diária do ar no Estado de Goiás

The objective of this work was to develop a mathematical model to predict the daily average of air temperature in Goias, Brazil. The model was developed through a linear combination of altitude, latitude, longitude, and the incomplete trigonometric Fourier series using the first three harmonic coefficients. The parameters of the model were adjusted with data from 21 weather stations, using multiple linear regression. The resulting correlation coefficient of the model was 0.91, and the Willmotts index of agreement was close to 1. The model was tested with data from three additional weather stations at different altitudes: high (1,100 m), medium (554 m), and low (431 m). The performance of the model was reasonable for both high and low altitude stations, and very good for the medium altitude station.

Seleção de modelos para o traçado de curvas granulométricas de sedimentos em suspensão em rios

The knowledge about particle-size distribution of suspended sediments in river is fundamental for some hydro-sedimentological studies. In general, the techniques used to determine the particle-size distribution of a sample results in pointwise values, demanding a subsequent interpolation to fit the complete particle-size distribution curve and to obtain specific characteristic diameters values. The transformation of discrete points into continuous functions can be made by mathematical models. However, few studies have been developed with the purpose of determining the best model for fitting particle-size distribution curves. The objective of this paper was to select models for fitting particle-size distribution curves of suspended sediments in river water. Using the particle-size distribution, results from 30 samples of suspended sediments of river with 8 to 10 measured points, with 14 different models were tested. The parameter used to compare the models was the sum of the square errors between the measured and calculated values obtained in the adjustment of each model. The results showed that the Haverkamp & Parlange (1986) and Skaggs et al. (2001) models, both with three fitting parameters, are the best for adjusting particle-size distribution curves of river suspended sediment samples.

Indicators of Soil Physical Quality: From Simplicity to Complexity

In working with soil physics, getting new answers to the same questions is a challenge. As soil physicists, we are always hoping to find new ways of understanding such a complex soil science area. In this chapter, we will discuss some of the ways to assess soil physical quality for crop growth, using ascending complexity classification, from the simplest to the more complex soil physical indicators for crop growth.

Spatio-temporal modelling of the duration of the cotton cycle in the State Of Goiás, Brazil

The objective of this work was to develop and validate a mathematical model to estimate the duration of cotton (Gossypium hirsutum L. r. latifolium hutch) cycle in the State of Goias, Brazil, by applying the method of growing degree-days (GD), and considering, simultaneously, its time-space variation. The model was developed as a linear combination of elevation, latitude, longitude, and Fourier series of time variation. The model parameters were adjusted by using multiple-linear regression to the observed GD accumulated with air temperature in the range of 15°C to 40°C. The minimum and maximum temperature records used to calculate the GD were obtained from 21 meteorological stations, considering data varying from 8 to 20 years of observation. The coefficient of determination, resulting from the comparison between the estimated and calculated GD along the year was 0.84. Model validation was done by comparing estimated and measured crop cycle in the period from cotton germination to the stage when 90 percent of bolls were opened in commercial crop fields. Comparative results showed that the model performed very well, as indicated by the Pearson correlation coefficient of 0.90 and Willmott agreement index of 0.94, resulting in a performance index of 0.85.

Proposal and selection of a polynomial function for evaluating irrigation systems.

The use of mathematical models facilitates the calculation of the uniformity and efficiency parameters of irrigation systems and, thus, its utilization should be encouraged. This work had as its objectives the proposal of the use of a polynomial function for evaluating irrigation systems and to develop the mathematical relationships for calculating the main indicators for measuring irrigation performance, utilizing this function. In order to define the model to be proposed and to verify its suitability, comparisons were carried out among polynomial functions of various degrees against the Silvas potential model, utilizing data from 91 cases of irrigation system evaluations. The selection of the most adequate polynomial model was made by comparing adjusted curves to the cumulative frequency distribution of the sum of square errors that were obtained after adjusting the models to each set of measured water application data. The results showed that the fifth degree polynomial function is recommended to describe the applied water distribution from irrigation systems and it can be used to derive mathematical expressions for calculating the corresponding performance measures.