Jorge Dafonte

Ephemeral gully erosion in northwestern Spain

This study aimed to describe types of ephemeral gullies and to determine their origin, evolution and importance as sediment sources in A Coruna province (northwest Spain). Ephemeral gullies and/or rills have been measured in a representative sample of medium-textured soils, most prone to crusting, developed over basic schist. This sample consisted of 11 small sites, ranging from 0.63 to 7.34 ha. A case study of concentrated (rill+gully) erosion in a 0.47-ha catchment with coarse-textured soils developed over granite was also reported. The mean slope of the sites studied ranged from 6.1% to 16.8%. Main periods when soil surface was poorly covered were late spring (maize seedbeds) and late autumn–early winter (grassland and winter cereal seedbeds). Case studies where fields were left bare in winter were also investigated. Soil incision and channel formation were observed even with relatively low rainfall intensities when the soil surface was sealed, but also after a single short intense rainfall event on recently tilled surfaces. Concentrated erosion took place mainly on seedbeds and newly tilled soils in late spring and by autumn or early winter, but gullies also appeared in other seasons when the soil surface was left bare. In most of the cases studied, ephemeral gully erosion caused significant soil losses, ranging between 2 and 5 m3/ha for a single season to locally, over 25 m3/ha. Gully development was significantly affected by agricultural operations, such as lineal elements often acting as initial axes of concentrated erosion. Main gullies tended to reappear at the same position.

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

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.

Using Multivariate Geostatistics to Assess Patterns of Spatial Dependence of Apparent Soil Electrical Conductivity and Selected Soil Properties

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.

Distribuição espacial da condutividade elétrica do solo medida por indução eletromagnética e da produtividade de cana-de-açúcar

The current agriculture requires the use of new technologies that allow the identification of soil and plant patterns, and the determination of their spatial variability. This work determined the spatial relationship between the sugar cane yield and soil apparent electrical conductivity (ECa) measured by electromagnetic induction (EMI) and soil texture. The experimental area is located in Goiana (Pernambuco State, Brazil) (07°34’25”S, 34°55’39”W). The experimental area was 6.5 ha. Sugar cane yield and soil apparent electrical conductivity (ECa) were measured at 90 sampling points randomly distributed in the study area. Maps of soil electrical conductivity (ECa-V and ECa-H) were similar to that of sugar cane yield. The linear correlation showed values of 0.74 (yield x ECa-H) and 0.85 (yield x ECa-V). The electrical conductivity measured by electromagnetic induction has been shown to be an important tool for predicting the yield of sugar cane. The textural properties (clay, silt and sand) showed high spatial variability.

Spatial soil sampling design using apparent soil electrical conductivity measurements

Soil sampling is an important stage of digital soil mapping. The objective of this study was to characterize the spatial design of soil sampling using soil apparent electrical conductivity (ECa) and its optimized spatial sampling. For the characterization, it was used the Spatial Simulated Annealing (SSA) technique, incorporated on the software SANOS 0.1, and the method of response surface sampling design on the software ESAP 2.35. The ECa was measured at 1,887 points in an area of 6 ha located in the northwestern region of Spain. The EM38-DD equipment (Geonics Limited 2005) was used at 2 depths: vertical dipole (1.5 m effective measurement depth) and horizontal dipole (0.75 m effective measurement depth). Semivariogram showed trend for ECa in vertical dipole (ECa-V) and ECa in horizontal dipole (ECa-H). Software SANOS 0.1 and ESAP 2.35 were used to obtain the 40-point sampling scheme, using the 2 schemes (SANOS and ESAP). ECa-V estimation values at the 1,887 points were calculated with residual ordinary kriging. The sampling scheme obtained from ESAP was better than with SANOS.

A Geostatistical Analysis of Rubber Tree Growth Characteristics and Soil Physical Attributes

The cultivation of rubber trees [Hevea brasiliensis (Willd. ex Adr. To Juss.) Muell. Arg.] plays an important role in Brazilian forestry production. However, the relationship between tree production and soil physical attributes is poorly understood. Geostatistical tools such as spatial variability modeling assist the study of the relationships between plant and soil attributes. The objective of this paper is to determine the spatial variability of rubber tree growth characteristics and its relationship to soil–water physical properties (soil mechanical resistance to penetration and field saturated hydraulic conductivity of soil). The experiment was located at Campinas, State of Sao Paulo, Brazil, at a experimental station of the Instituto Agronomico, in a 10 ha area with rubber trees planted in 1992. Samples were taken at 232 points in a 20 ×20 m grid. Average diameter at 1.30 m height and tree height were calculated from average measurements of four trees. The soil physical attributes studied were soil resistance to penetration at 0.40 m depth and field saturated soil conductivity at two depths (0–0.10 m and 0.10–0.20 m). All tree and soil parameters showed moderate to weak spatial dependence among samples. The linear correlation between the attributes of rubber trees and soil was weak. The cross-semivariograms used to evaluate cross-spatial correlations revealed that most of the studied properties did not follow a similar cross-spatial pattern. Spatial variability maps show that areas with higher field saturated hydraulic conductivity of soil have lower soil mechanical resistance to penetration. The field saturated hydraulic conductivity of soil in the 0–10 cm layer showed strong linear and spatial correlation with the diameter of rubber trees, as confirmed by the spatial variability maps of both attributes.

Comparing effects of tillage treatments performed with animal traction on soil physical properties and soil electrical resistivity: preliminary experimental results

Abstract Soil Compaction results from compressive forces applied to compressible soil by machinery wheels, combined with tillage operations. Draft animal‐pulled equipment may also cause soil compaction, but a huge gap exists on experimental data to adequately assess their impacts and, actually, animal traction is an option seen with increasing potential to contribute to sustainable agriculture, especially in mountain areas. This study was conducted to assess the impacts on soil compaction of tillage operations with motor tractor and draft animals. In a farm plot (Vale de Frades, NE Portugal) treatments were applied in sub‐plots (30 m × 3 m), consisting in a two way tillage with tractor (T), a pair of cows (C) and a pair of donkeys (D). Undisturbed soil samples (120) were taken before and after operations for bulk density (BD) and saturated hydraulic conductivity (Ks). The relative changes in BD observed after tillage in the 0-0.05 m soil depth increased after operations in all treatments. The increase was higher in the tractor sub-plot (15%) than in those where animal traction was used (8%). Before operation Ks class was rapid and fast in all samples, and after operation this value was reduced to 33% in T, whereas it reached 83% in C. Electrical Resistivity Tomography (ERT) was useful as a tool to identify the alterations caused by tillage operations on soil physical status. These preliminary results confirm the potential of animal traction as an option for mountain agri‐environments, yet it requires much wider research to soundly ground its assets.

Using Soil Apparent Electrical Conductivity to Optimize Sampling of Soil Penetration Resistance and to Improve the Estimations of Spatial Patterns of Soil Compaction

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.

Water Erosion from Agricultural Land Under Atlantic Climate

Montserrat Valcarcel1, Antonio Paz Gonzalez2, Jorge Dafonte1, Jose Manuel Miras-Avalos2, Jorge Paz-Ferreiro3, Ildegardis Bertol4 and Eva Vidal Vazquez2 1Escuela Politecnica Superior de Lugo. University of Santiago de Compostela (USC) 2Facultad de Ciencias. University of Corunna (UDC) 3Centro de Investigaciones Agrarias de Mabegondo (CIAM). Corunna 4CAV. Universidade do Estado de Santa Catarina (UNESC). Lages, SC 1,2,3Spain 4Brazil