This study presents a combined application of an EM38DD for assessing soil apparent electrical conductivity (ECa) and a dual-sensor vertical penetrometer Veris-3000 for measuring soil electrical conductivity (ECveris) and soil resistance to penetration (PR). The measurements were made at a 6 ha field cropped with forage maize under no-tillage after sowing and located in Northwestern Spain. The objective was to use data from ECa for improving the estimation of soil PR. First, data of ECa were used to determine the optimized sampling scheme of the soil PR in 40 points. Then, correlation analysis showed a significant negative relationship between soil PR and ECa, ranging from −0.36 to −0.70 for the studied soil layers. The spatial dependence of soil PR was best described by spherical models in most soil layers. However, below 0.50 m the spatial pattern of soil PR showed pure nugget effect, which could be due to the limited number of PR data used in these layers as the values of this parameter often were above the range measured by our equipment (5.5 MPa). The use of ECa as secondary variable slightly improved the estimation of PR by universal cokriging, when compared with kriging.
O objetivo deste trabalho foi avaliar a distribuição espacial da rugosidade do solo em microparcelas compostas por diferentes solos de Galícia (Espanha) após aplicação de distintas chuvas simuladas. Os agregados do solo, de 3-5 cm, foram coletados nos municípios de Lugo e Taboada. Em laboratório as parcelas experimentais foram construídas utilizando-se base metálica móvel de 0,86 m x 0,86 m (0,73 m 2). A rugosidade do solo (dm) foi determinada com rugosímetro laser, antes e depois da aplicação de quantidades crescentes de chuva simulada (50 mm h-1 e 75 mm h-1) durante uma hora. O índice de rugosidade aleatória (RR) cresceu com o aumento do volume de chuva simulada no solo franco (Taboada). Todos os tratamentos estudados apresentaram alta razão de dependência espacial entre amostras (RD) em função do grande número de leituras fornecidas pelo rugosímetro laser, que favorece uma minimização da variabilidade ao acaso. Palavras-chave: geoestatística, manejo do solo, erosão hídrica, agregação do solo Spatial distribution of soil roughness in experimental microplots under different intensities of simulated rainfall ABSTRACT The objective of this study was to evaluate the spatial distribution of soil roughness in microplots composed of different soils in Galicia (Spain) after application of different simulated rainfall. Clusters of 3-5 cm soil were collected in the municipalities of Lugo and Taboada. In the laboratory experimental plots were built using metallic mobile 0.86 m x 0.86 m (0.73 m 2). The roughness of the soil (dm) was determined with laser reliefmeter before and after application of different amounts of rain (50 mm h-1 and 75 mm h-1) for an hour. The index of random roughness (RR) increased with increasing the volume of simulated rain in loam soil (Taboada). All treatments studied showed a high rate of spatial dependence between samples (RD), depending on the number of readings provided by laser reliefmeter, which favors a minimization of random variability.
The spatial variability of soil properties can be assessed through concepts of scale invariance, fractals and multifractals. The aim of this study was to characterize the scaling patterns and structural heterogeneity properties of general soil chemical properties along a short (i.e. 52 m large) transect. Field measurements were carried out at the experimental farm of CIAM located in Mabegondo, A Coruña, Spain. The studied transect was marked following land slope, and 66 soil samples were collected at the 0-20 cm depth every 0.8 m. The soil properties analyzed were: pH (H2O ), organic carbon content, exchangeable Ca, Mg and K, exchangeable acidity (H + Al), exchangeable bases (SB), cation exchange capacity (CEC), percent base saturation (V) and extractable P. The soil properties studied showed various degrees of multifractality. The spatial distribution of pH was characterized by quasi-monofractal behaviour; CEC, (H+Al) and OM, presented a relatively low degree of multifractality, and the other soil properties studied showed stronger degrees of multifractality, being the highest one for Olsen extractable P. In general, the scaling features of the properties studied implied a multifractal nature, where the low and high density regions scaled differently.
The apparent soil electrical conductivity (ECa) was continuously recorded in three successive dates using electromagnetic induction in horizontal (ECa-H) and vertical (ECa-V) dipole modes at a 6 ha plot located in Northwestern Spain. One of the ECa data sets was used to devise an optimized sampling scheme consisting of 40 points. Soil was sampled at the 0.0–0.3 m depth, in these 40 points, and analyzed for sand, silt, and clay content; gravimetric water content; and electrical conductivity of saturated soil paste. Coefficients of correlation between ECa and gravimetric soil water content (0.685 for ECa-V and 0.649 for ECa-H) were higher than those between ECa and clay content (ranging from 0.197 to 0.495, when different ECa recording dates were taken into account). Ordinary and universal kriging have been used to assess the patterns of spatial variability of the ECa data sets recorded at successive dates and the analyzed soil properties. Ordinary and universal cokriging methods have improved the estimation of gravimetric soil water content using the data of ECa as secondary variable with respect to the use of ordinary kriging.
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