Soil water retention curve (SWRC) becomes important because it guides when and how much to irrigate, optimizing the use of water; can be obtained in the field or laboratory, being commonly determined in the laboratory with porous plate apparatus, and the determination is compromised by issues such as time and labor. In this context, inverse modeling emerges, which allows to obtain a variable going from the effect to the cause, using Hydrus-1D. Hence, this study aims to obtain van Genuchten equation parameters through inverse modeling with Hydrus-1D and make the respective comparisons and inferences. Matric potential data were obtained over time in an instantaneous profile-type experiment. Six sets of three tensiometers each were installed surrounding the center of the experimental plot, at depths of 0.20, 0.35 and 0.50 m. Target depth was 0.35 m, where the roots of most crops are concentrated, and the other tensiometers were used to obtain the potential gradient. Matric potential data were used to feed Hydrus-1D and obtain the van Genuchten equation parameters. Laboratory curves were obtained using porous plate apparatus, with four replicates. It was concluded that, in general, the Hydrus-1D model estimates van Genuchten equation parameters and, consequently, the SWCC of an Argissolo more consistently with field conditions than those obtained in the laboratory; and, provided it is fed with field data, the Hydrus-1D simulates well the behavior of matric potential and moisture over time, reducing the time and labor in the procedures to obtain van Genuchten equation parameters in the laboratory.

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Resumo: O conhecimento da variabilidade espacial dos parâmetros da equação de van Genuchten é importante para a interpretação de determinados indicadores de qualidade física do solo, uma vez que alguns índices derivam da curva característica da água no solo. Partindo da hipótese de que mesmo em área considerada homogênea há variabilidade espacial distinta para os parâmetros dessa equação, objetivou-se com o presente trabalho avaliar a variabilidade espacial dos parâmetros θs, θr, α, m e n em Latossolo VermelhoAmarelo. Para esse estudo, estabeleceram-se 60 pontos de amostragem, distanciados 5 m entre si, em uma grade de 10 x 6 pontos (50 x 30 m). Foram coletadas amostras de solo com estrutura preservada em anéis de aço com dimensões de 0,05 m de altura e diâmetro, em cinco repetições na profundidade de 0,80 m, totalizando 300 amostras. Foram avaliados os atributos granulometria, densidade das partículas, densidade do solo e curva característica de água no solo. A curva foi construída considerando as tensões 1, 2, 3, 4, 5, 6, 7, 8, 9 e 10 kPa (no funil de Haines) e 30, 50, 70 e 100 kPa (no extrator de placa porosa de Richards). Os dados foram ajustados ao modelo de van Genuchten (1980) com o programa Table Curve 2D, versão trial 5.01, inclusive para a extrapolação da umidade residual. Os parâmetros da equação de van Genuchten foram analisados quanto à variabilidade espacial com uso da técnica da diferença relativa. Concluiu-se que apesar da uniformidade na textura e na densidade do solo, os parâmetros da equação de van Genuchten variam espacialmente de modo que não há um ponto amostral único que represente o valor médio de θs, θr, α, m e n.Palavras-chave: Curva característica de água no solo. Amostragem de solo. Agricultura de precisão. Abstract:The knowledge of the spatial variability of the van Genuchten equation parameters is important for the interpretation of certain indicators of soil physical quality, since some indices derived from the soil water retention curve. Assuming that even in considered homogeneous area there is different spatial variability of parameters of this equation, aimed evaluate the spatial variability of parameters θs, θr, α, m and n in a Latossolo Vermelho-Amarelo. For this study were established 60 sampling points with distance apart of five meters, in a grid of 10 x 6 points (50 x 30 m). Soil samples were collected with preserved structure, in steel rings with dimensions of 0.05 m high and 0.05 m in diameter, with five replicates collected at a depth of 0.80 m, totaling 300 samples. Was evaluated the attributes grain size, particle density, soil bulk density and soil water retention curve. The soil water retention curve was constructed considering the points 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 kPa (in the Haines funnel) and 30, 50, 70 and 100 kPa (in the Richards extractor). The data were adjusted to the van Genuchten model (1980) with the program Table Curve 2D, trial version 5.01, including for extrapolation of residual moisture. The parameters of the van Genuchten equation were analy...

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