Quirijn de Jong van Lier

Short note: Runoff mapping using WEPP erosion model and GIS tools

Soil erosion, associated with environmental impacts and crop productivity loss, is usually considered the most impacting of surface hydrology processes. Runoff plays a major role in the erosion process, but it is also important by itself as it directly influences several surface hydrologic processes. In this paper, a computer interface (Erosion Database Interface, EDI) is described that allows processing the surface hydrology output database of the Water Erosion Prediction Project (WEPP) erosion prediction model, resulting in a georeferenced estimation of runoff. WEPP output contains non-georeferenced daily information about estimated runoff at the lower end of each Overland Flow Element. EDI, when running with WEPP, allows extracting WEPP-calculated runoff values, transforming them into annual means and relocating them in a georeferenced database readable by Geographic Information Systems (GIS). EDI was applied to a 1990ha watershed in southeast Brazil, with vegetation of mainly sugarcane, forest, and pasture. A 100-year climate simulation was used as input to WEPP, and erosion values were calculated at about six points per hectare and interpolated to a raster format. EDI was successful in preparing the database for automatic calculation of erosion and hydrologic parameters with WEPP and to restore georeferences to mean annual accumulated runoff data that were imported in the GIS as a vector database. Of all the resulting maps, the runoff map is the one that integrates all of the input parameters required for WEPP simulation, thus reflecting not only the physical environment but also crop growth and management and tillage operations. A very small correlation between runoff and erosion shows them to behave independently. Moreover, it is concluded that on analyzing runoff related to agricultural management, georeferenced runoff studies are especially important. In this context, EDI may be a useful tool to assess the effect of tillage and crop management on runoff production.

Revisiting the S-index for soil physical quality and its use in Brazil

O indice S foi introduzido em 2004 numa publicacao de A.R. Dexter. Esse indice foi proposto como um indicador da qualidade fisica do solo. Propos-se um valor critico para delimitar solos com qualidades fisicas rica e pobre. Atualmente, o Brasil e lider mundial de citacoes do artigo de Dexter. Nessa publicacao, a teoria do indice S e matematicamente revisitada e estendida. Demonstra-se que S se correlaciona matematicamente com a densidade e a porosidade total do solo. Como indicador absoluto, o valor de S tem demonstrado ser incapaz de predizer a qualidade fisica do solo. O valor critico nao permite previsoes confiaveis sob diversas condicoes de contorno descritas na literatura. Esse fato e esperado, uma vez que o S e um parâmetro estatico, portanto implicitamente incapaz de descrever processos dinâmicos. Como indicador relativo da qualidade fisica do solo, o indice S nao possui valor adicional em relacao a densidade do solo ou a porosidade do solo. A determinacao da densidade ou porosidade do solo e muito mais simples que a determinacao de uma curva de retencao para obtencao do S, razao pela qual se desqualifica o S como um indicador interessante da qualidade fisica relativa do solo. Entre as varias equacoes disponiveis para o ajuste da curva de retencao, a de Groenevelt-Grant e preferivel para uso em combinacao com o S, uma vez que um de seus parâmetros se correlaciona linearmente com S. Tendo como finalidade a descricao de processos dinâmicos, os esforcos de pesquisa em fisica do solo deveriam se deslocar na direcao da fisica do solo mecanistica, em detrimento da busca por correlacoes empiricas como S, que, atualmente, representa muito mais do que deveria na fisica do solo no Brasil.

Erosion database interface (EDI): a computer program for georeferenced application of erosion prediction models

The multidisciplinary approach of soil erosion research often requires erosion to be treated as spatial georeferenced information. This condition is essential so as to be compatible with information analyzed via Geographic Information Systems (GIS). The original versions of important soil erosion prediction models such as the Universal Soil Loss Equation (USLE) and Water Erosion Prediction Project (WEPP) do not operate on a georeferenced basis. The Erosion Database Interface (EDI) is a computer program for georeferenced application of USLE and WEPP. EDI uses, as input, a text format database with points defined by coordinates (x, y and z) representing hillslopes, each point associated to soil type and land use. Such input data can be provided by different methods. Exclusive field work with ordinary topographic equipment and GIS procedures are examples of methods that can be used for this purpose. Flexibility in the methods adopted for providing input data is an important prerequisite for erosion prediction in tropical and developing regions, where soil erosion is a major concern and the availability of digital data is usually restricted. Hillslopes for EDI were defined as straight line segments beginning at the upper slope and ending down at runoff output. This restricts EDI as a complete erosion-prediction method for areas where runoff deflecting features predominate or where channel or gully erosion is to be considered. As output, EDI provides georeferenced soil erosion values in another text format database. This database can be used directly for statistical or geostatistical analysis or imported into a GIS for further processing. A practical example representative of a sugarcane-growing area located at the southeastern part of Brazil is used to illustrate EDIs performance. In this example, soil erosion maps were produced from GIS data using EDI as interface for erosion calculations for WEPP and USLE.

A split-pot experiment with sorghum to test a root water uptake partitioning model

Correct modeling of root water uptake partitioning over depth is an important issue in hydrological and crop growth models. Recently a physically based model to describe root water uptake was developed at single root scale and upscaled to the root system scale considering a homogeneous distribution of roots per soil layer. Root water uptake partitioning is calculated over soil layers or compartments as a function of respective soil hydraulic conditions, specifically the soil matric flux potential, root characteristics and a root system efficiency factor to compensate for within-layer root system heterogeneities. The performance of this model was tested in an experiment performed in two-compartment split-pot lysimeters with sorghum plants. The compartments were submitted to different irrigation cycles resulting in contrasting water contents over time. The root system efficiency factor was determined to be about 0.05. Release of water from roots to soil was predicted and observed on several occasions during the experiment; however, model predictions suggested root water release to occur more often and at a higher rate than observed. This may be due to not considering internal root system resistances, thus overestimating the ease with which roots can act as conductors of water. Excluding these erroneous predictions from the dataset, statistical indices show model performance to be of good quality.

General procedure to initialize the cyclic soil water balance by the Thornthwaite and Mather method

The original Thornthwaite and Mather method, proposed in 1955 to calculate a climatic monthly cyclic soil water balance, is frequently used as an iterative procedure due to its low input requirements and coherent estimates of water balance components. Using long term data sets to establish a characteristic water balance of a location, the initial soil water storage is generally assumed to be at field capacity at the end of the last month of the wet season, unless the climate is (semi-) arid when the soil water storage is lower than the soil water holding capacity. To close the water balance, several iterations might be necessary, which can be troublesome in many situations. For (semi-) arid climates with one dry season, Mendonca derived in 1958 an equation to quantify the soil water storage monthly at the end of the last month of the wet season, which avoids iteration procedures and closes the balance in one calculation. The cyclic daily water balance application is needed to obtain more accurate water balance output estimates. In this note, an equation to express the water storage for the case of the occurrence of more than one dry season per year is presented as a generalization of Mendoncas equation, also avoiding iteration procedures.

Pedotransfer functions to estimate water retention parameters of soils in northeastern Brazil

Foram desenvolvidas funcoes de pedotransferencia (PTFs) para estimar os parâmetros (α, n, θr and θs) do modelo de van Genuchten (1980), utilizados para descrever curvas de retencao de agua no solo. Os dados usados foram provenientes de diversas fontes, principalmente de estudos realizados na Regiao Nordeste pelas universidades, pela Embrapa e Codevasf, totalizando 786 curvas de retencao, que foram divididas em dois conjuntos de dados: 85 %, para desenvolvimento das PTFs, e 15 %, para teste e validacao, considerados como dados independentes. Alem do desenvolvimento das PTFs de carater geral para todos os solos conjuntamente, desenvolveram-se PTFs especificas para as classes Argissolos, Latossolos, Neossolos e Planossolos, utilizando tecnicas de regressao multipla, com o uso do procedimento stepwise (forward e backward), para selecionar os melhores preditores. Dois tipos de PTFs foram desenvolvidos: o primeiro inclui todos os preditores, densidade do solo, teores de areia, silte, argila e de materia orgânica, e o segundo, apenas com os teores de areia, silte e argila. A avaliacao da adequacao das PTFs foi com base no coeficiente de correlacao (R) e indice de Willmott (d). Para avaliar as PTFs, para o teor de agua em potenciais matriciais especificos, utilizou-se a raiz do erro medio quadrado (RMSE). A predicao da curva de retencao por PTF e relativamente fraca, exceto para o teor de agua residual. A inclusao do teor de materia orgânica como preditor da PTF melhora a predicao do parâmetro a de van Genuchten. Nao houve melhora de desempenho das PTFs especificas por classe de solo, em comparacao com uma PTF geral. Exceto no caso do teor de agua do solo saturado, estimado pela distribuicao granulometrica, modelos para a predicao do teor de agua em potenciais matriciais especificos sao bons. Predicoes do teor de agua em potenciais matriciais mais negativos do que -0,6 m, usando uma PTF contendo a distribuicao granulometrica, sao somente um pouco inferiores aquelas obtidas por PTFs, que incluem densidade do solo e teor de materia orgânica.

Soil thermal diffusivity estimated from data of soil temperature and single soil component properties

A difusividade termica do solo sob condicoes de campo pode ser estimada a partir de dados da sua temperatura, mas pode tambem ser estimada por meio das propriedades individuais dos seus componentes junto com a sua organizacao espacial. A difusividade termica foi determinada com base em dados de temperatura do solo registrados de meia em meia hora num Nitossolo Vermelho, empregando-se tres procedimentos de calculo (o da razao das amplitudes, da defasagem e do proposto por Seemann), bem como a partir das propriedades individuais dos seus componentes, fazendo-se comparacao entre procedimentos e metodos. Para a determinacao da difusividade para periodos de onda curtos (um dia), o procedimento da defasagem apresentou-se mais confiavel do que o da razao de amplitudes ou o do Seemann, especialmente para a determinacao em camadas mais profundas, onde as variacoes termicas sao pequenas, pois apresentou valores coerentes para a difusividade termica. O metodo que utiliza propriedades individuais dos componentes do solo, com os valores da condutividade termica para arenito e caulinita, resultou em estimativas da difusividade termica da mesma ordem de grandeza. Ao longo da faixa de teores de agua observada, de 0,26-0,34 m3 m-3, o valor medio da difusividade termica foi de 0,034 m2 d-1 na camada superficial (0,05-0,15 m) e de 0,027 m2 d-1, na camada subsuperficial (0,15-0,30 m).

Pedotransfer Functions for Brazilian Soils

The growing need for PTFs frequently leads to the use of inadequate PTFs and databases, especially when dealing with data from different regions or climates, such as in tropical and temperate climate zones. Most PTFs have been developed for soils from temperate climates, which tend to be very different from tropical soils. In fact, PTFs are not suitable for extrapolation: they should not be applied to soils that are outside the range or region where the PTFs ware developed. In this chapter the current status of PTF development in Brazil is reviewed, and suggestions for research aiming future improvements are made.

Determinação das propriedades hidráulicas do solo utilizando tensiômetros de polímeros em experimentos de evaporação

O tensiometro de polimeros e um equipamento recentemente desenvolvido que permite medir o potencial matricial da agua no solo desde a saturacao ate condicoes mais secas do que o ponto de murcha permanente. Nesta nota descreve-se a utilizacao de tensiometros de polimeros em experimentos de evaporacao de cilindros com solo deformado, para determinar as propriedades hidraulicas do material. Nos experimentos foi utilizada terra da camada superficial de um Nitossolo Vermelho. O uso de tensiometros de polimeros em experimentos de evaporacao com colunas de solo permitiu a determinacao das relacoes entre condutividade hidraulica, teor de agua e potencial matricial na faixa de potenciais matriciais entre -1 e -150 m.

Dimensionamento de terraços de infiltração pelo método do balanço volumétrico

Soil conservation practices allow soil and water loss control in agricultural areas, aiming the maximization of profit without provoking reduction of yield potential. There is need to use technical procedures to design soil conservation structures. Therefore, the aim of the present work was the development of a computational model, in Visual Basic 6.0 language, for design of contour terrace. The model was applied for three municipalities of Sao Paulo State (Aracatuba, Piracicaba and Natividade da Serra). From the results obtained, it may be concluded that the width of a parabolic section contour terrace channel for these localities, with a return period of 5 years, was 3.30, 3.34 and 3.80 m, respectively, with 0,5 m of depth.