Q. de Jong van Lier

Variabilidade dos parâmetros da equação que relaciona a condutividade hidráulica com a umidade do solo no método do perfil instantâneo

Hydraulic conductivity is one of the most important soil properties for studies dealing with infiltration, water movement within the soil profile and to plant roots and internal drainage. The availability of the function hydraulic conductivity x soil water content (K(θ)) is essential to these studies. However, little is known about the variability of the empirical parameters of this function. Aiming to contribute with information on the variability of these parameters, a study is described in which observations of hydraulic conductivity as a function of soil water content by the instantaneous profile method were made in twelve locations within an area of 1000 m2. The equation used for K(θ) was K = K0.exp[γ(θ-θ0)], in which K0 and θ0 are K and θ values, respectively, for zero time of water redistribution. The measurements of soil water content and matric potential were performed for about 50 days in nine depths between 0.2 and 1.0 m. Results show coefficients of variation of about two to three for the majority of depths for the K0 values, while values for γ showed lower variation coefficients, between 0.2 and 0.5, the higher occurring close to the surface and the lower ones at greater depths. It is concluded that soil water content data fit very well to time by a potential equation, while total water potential fits very well to depth by a second order polynomial equation. Results suggest that a relationship between K and θ, determined by the instantaneous profile method in an area of a few square meters, is not representantive for a much larger area than that where it was determined.

OXIGENAÇÃO DO SISTEMA RADICULAR: UMA ABORDAGEM FÍSICA

The understanding of the physics of root aeration may allow a more correct and dynamic estimate of the minimum air-filled porosity, providing a more complete estimate of the plant behavior in relation to soil water content and gas conductivity of the soil. The aeration process is physically described in this paper to show that the result may be useful for estimating minimum air-filled porosity as a function of the total soil porosity, depth to be aerated and oxygen consumption rate. The value 10/3 for the exponent of the Millington and Quirk equation between air-filled porosity and tortuosity factor results in the best agreement between calculated minimum air-filled porosity and values considered as normal.

An Alternative Approach for the Determination of Soil Water Mobility

Abstract A new laboratory method was proposed to establish an easily performed standard for the determination of mobile soil water close to real conditions during the inflltration and redistribution of water in a soil. It consisted of applying a water volume with a tracer ion on top of an undisturbed ring sample on a pressure plate under a known suction or pressure head. Afterwards, soil water mobility was determined by analyzing the tracer-ion concentration in the soil sample. Soil water mobility showed to be a function of the applied water volume. No relation between soil water mobility and applied pressure head could be established with data from the present experiment. A simple one- or two-parameter equation can be fltted to the experimental data to parameterize soil water mobility as a function of applied solute volume. Sandy soils showed higher mobility than loamy soils at low values of applied solute volumes, and both sandy and loamy soils showed an almost complete mobility at high applied solute volumes.

Infiltração de água e perdas de água e solo por erosão influenciadas por diferentes métodos de melhoramento da pastagem nativa gaúcha

A paralisacao do crescimento da pastagem nativa no periodo do inverno na regiao Sul do Brasil tem incentivado tecnicas de melhoramento das pastagens. Com o objetivo de estudar a infiltracao de agua no solo e as perdas de solo e agua por erosao influenciadas por metodos de melhoramento da pastagem nativa, realizou-se um estudo em area da Estacao Experimental Agronomica da UFRGS, no municipio de Eldorado do Sul (RS), em um Podzolico Vermelho-Amarelo submetido ao uso prolongado com pastagem nativa, no qual se fez a introducao de uma mistura das especies hibernais: aveia preta (Avena strigosa ), azevem (Lolium multiflorum ) e trevo vesiculoso (Trifolium vesiculosum). O delineamento experimental foi completamente casualizado e com cinco tratamentos que diferiram quanto a maneira de introducao das novas especies: testemunha (a lanco), gradagem, plantio direto, convencional e subsolagem. As parcelas tinham a dimensao de 3,5 x 11,0 m e uma declividade aproximada de 0,107 m m-1. Aplicaram-se chuvas simuladas de 64 mm h-1, durante 75 min, em tres epocas: (a) aos 55 dias do preparo do solo e semeadura, logo apos o primeiro pastejo, (b) aos 125 dias do preparo do solo e semeadura, e (c) logo apos o segundo pastejo, aos 175 dias do preparo do solo e semeadura. Entre as chuvas simuladas, realizou-se um pastejo por dois dias. A subsolagem apresentou a maior taxa constante de infiltracao e a menor taxa constante de enxurrada. As perdas de solo foram pequenas nas tres epocas avaliadas. As maiores perdas de agua ocorreram na testemunha e as menores na subsolagem, indicando ter sido este ultimo tratamento efetivo em quebrar camadas compactadas subsuperficiais.

Uncertainty of Hydraulic Conductivity under Field Conditions and at Fixed Pressure Heads and Water Contents

Unsaturated hydraulic conductivity ( K ) can be expressed as a function of soil water content (θ) or pressure head ( h ). Methods to determine K often give highly variable results, thus making it difficult to report values for K in a reliable manner. Due to the sensitivity of pore conductivity to pore radius, it can be expected that K expressed as a function of h shows less variability than expressed as a function of θ. To test this hypothesis, K was determined at several values of θ and h using the instantaneous profile method at 48 locations in the surface and a subsurface layer of a Typic Hapludox in Brazil. Results were analyzed considering the field values of K at the time of observation ( K t), at fixed values of θ ( K θ), and at fixed values of h ( Kh ). Results show that the coefficient of variation of K θ is higher than that of Kh , especially in the surface layer, which suggests that, if one has the choice, it would be preferable to estimate soil water movement using measured h values, and using K ( h ), instead of measuring θ and using K (θ). We also show that the variability in K t increases as the soil gets drier, while Kθ and Kh show more variability for wetter soil.

Método convencional e "bootstrap" para estimar o número de observações na determinação dos parâmetros da função K(Θ)

Natural variability of soils makes it difficult to obtain values that adequately represent the soil properties within a certain area. The establishment of a minimum number of observations necessary to represent a soil property (with an acceptable error) is fundamental for the reliability of experimental results. In the present paper, the conventional t-test method has been compared with the bootstrap method, in order to estimate the number of observations needed to calculate the parameters that characterize the relation between hydraulic conductivity and soil water content, determined by the instantaneous profile method. A drainage experiment was realized in a red-yellow Oxisol (Hapludox) in Piracicaba, State of Sao Paulo, Brazil, on an experimental plot with 45 observation points in a straight line with a distance of one meter between points. Soil moisture was measured by TDR and the matric potential by tensiometers during three weeks of water redistribution. After data-processing, the parameters of the K(e) function presented a non-normal distribution and outliers had to be eliminated in order to normalize the data set for the t-test application. Therefore, the conventional method should only be used if the elimination of outliers is supposedly reasonable. Both analysis methods indicated the need of a high number of repetitions, reaffirming that hydraulic conductivity functions based on few repetitions should not be extrapolated to larger areas.

Determinação da lâmina média de irrigação em pivô central

With the purpose of improving the accuracy of the average irrigation depth calculation, an expression is presented assuming linear variation of the depth between two following collectors, for the determination of the average depth of center pivot irrigation systems. It is concluded that the proposed expression should be used for the determination of the mean weighed depth for being conceptually more correct, although, in practice the values calculated by the proposed methodology are very close to those obtained with the traditional calculation method.

Evaluating pedotransfer functions of the Splintex model: PTFs of the Splintex model

A . M . H u f D o s R e i s a, R . A . A r m i n d o b , M . F . D u r ã e s a & Q . D e J o n g V a n L i e r c aSoils and Agricultural Engineering Department, Federal University of Paraná (UFPR), Rua dos Funcionários 1540, CEP 80035-050, Curitiba (PR), Brazil, bDepartment of Physics (DFI), Federal University of Lavras (UFLA), Mailbox 3037, CEP 37200-000, Lavras (MG), Brazil, and cCenter for Nuclear Energy in Agriculture (CENA), University of São Paulo (USP), Av. Centenário 303, CEP 13416-000, Piracicaba (SP), Brazil