Mapping of soil micronutrients in an european atlantic agricultural landscape using ordinary kriging and indicator approach

Abstract

Nutrient maps based on intensive soil sampling are useful to develop site-specific management practices. Geostatistical methods have been widely used to determine the spatial correlation and the range of spatial dependence at different sampling scales. If spatial dependence is detected, the modelled semivariograms can then be used to map the interested variable by kriging, an interpolation method that produces unbiased estimates with minimal estimation variance. The objectives of this paper were to examine and to map the spatial distribution of the micronutrients Cu, Zn, Fe and Mn on an agricultural area in Galicia, Spain, under European Atlantic climatic conditions. The ordinary kriging was first used to determine the values for the non-sampled locations, then the indicator approach was used to transform the micronutrient content values into binary values having the mean values of each nutrient as the threshold content. All four elements analyzed showed spatial dependence using the indicator semivariograms. The strength of spatial dependence was assessed using the values of nugget effect and range from the semivariogram, the fitted range values decreased in the order Mn >Fe >Zn >Cu. The spatial dependence of the combination of two or more of the studied micronutrients was also examined using indicator semivariograms. In opposition to spatial analysis of individual microelements, indicator semivariograms obtained for the binary coding of the variables showed a great nugget effect value or a low proportion of sill. The maps for each nutrient obtained using indicator kriging showed some similarity in the spatial distribution, suggesting the delimitation of uniform management areas.Key words: soil management; geostatistics; spatial variability; soil chemistry. RESUMO MAPEAMENTO DE MICRONUTRIENTES DO SOLO DE UMA PAISAGEM AGRÍCOLA EUROPÉIAATLÂNTICA UTILIZANDO KRIGAGEM ORDINÁRIA E INDICATRIZ Mapas de nutrientes do solo com base em uma amostragem intensiva são úteis para desenvolver práticas específicas de manejo. Os métodos geoestatísticos cada vez mais têm sido utilizados para determinar a correlação espacial e o alcance da dependência espacial de amostragens em diferentes escalas. Uma vez detectada a variabilidade espacial, o semivariograma experimental é modelado e usado para mapear as variáveis investigadas por meio da krigagem, um método de interpolação sem tendência e com variância mínima. O objetivo deste trabalho foi avaliar e mapear a distribuição espacial dos micronutrientes Cu, Zn, Mn e Fe em uma área agrícola, na Galícia, Espanha, sob condições climáticas do Atlântico Europeu. A krigagem ordinária foi aplicada inicialmente para se determinar os valores para os locais não amostrados. Posteriormente, a krigagem indicatriz foi utilizada para transformar o conteúdo de micronutrientes em valores binários, tendo os valores médios de cada nutriente como referência. Nos quatro micronutrientes estudados havia dependência espacial, expressa por meio dos parâmetros do semivariograma. A razão de dependência es...

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