Towards Mapping of Soil Crust Using Multispectral Imaging

Soil crusts and surface roughness are properties which are highly dynamic in both space and time that change in response to biotic processes, meteorological conditions and farming operations. These factors, however, are difficult to quantify and are usually described using simplified expert-based classes. This hampers a clear identification of the controlling factors and their relation to soil erosion and sediment generation processes. The availability of new small portable multispectral cameras offers the potential to study soil surface dynamics at a high spatial and temporal resolution. The objective of this study was to analyse the relationship between soil crusting, represented by cumulative rainfall kinetic energy, and soil surface reflectance, as derived from vis-NIR multispectral imaging. We designed a series of rainfall-soil surface experiments to disentangle the effects of soil crusting on spectral reflectance factors from those related to surface micro-scale roughness. Partial least squared regression (PLSR) models were developed to predict both kinetic energy and roughness from multispectral images. We evaluated different roughness removal methods which were based on the transformation of reflectance through standard normal variate (SNV) and roughness thresholding using high resolution digital elevation models. Furthermore, we assigned the light scattering effect related to roughness in the multispectral spatial domain by calculating the inter-quantile range of the reflectance values in a kernel. Our experiments and workflow demonstrate that it is possible to model crust development, using rainfall kinetic energy as a proxy, from vis-NIR based multispectral imaging.

Investigating Parameter Transferability across Models and Events for a Semiarid Mediterranean Catchment

Physically based distributed hydrologic models (DHMs) simulate watershed processes by applying physical equations with a variety of simplifying assumptions and discretization approaches. These equations depend on parameters that, in most cases, can be measured and, theoretically, transferred across different types of DHMs. The aim of this study is to test the potential of parameter transferability in a real catchment for two contrasting periods among three DHMs of varying complexity. The case study chosen is a small Mediterranean catchment where the TIN-based Real-time Integrated Basin Simulator (tRIBS) model was previously calibrated and tested. The same datasets and parameters are used here to apply two other DHMs—the TOPographic Kinematic Approximation and Integration model (TOPKAPI) and CATchment HYdrology (CATHY) models. Model performance was measured against observed discharge at the basin outlet for a one-year period (1930) corresponding to average wetness conditions for the region, and for a much drier two-year period (1931–1932). The three DHMs performed comparably for the 1930 period but showed more significant differences (the CATHY model in particular for the dry period. In order to improve the performance of CATHY for this latter period, an hypothesis of soil crusting was introduced, assigning a lower saturated hydraulic conductivity to the top soil layer. It is concluded that, while the physical basis for the three models allowed transfer of parameters in a broad sense, transferability can break down when simulation conditions are greatly altered.

Soil wind erosion in ecological olive trees in the Tabernas desert (southeastern Spain): a wind tunnel experiment

Wind erosion is a key component of the soil degradation processes. The purpose of this study is to find out the influence of material loss from wind on soil properties for different soil types and changes in soil properties in olive groves when they are tilled. The study area is located in the north of the Tabernas Desert, in the province of Almería, southeastern Spain. It is one of the driest areas in Europe, with a semiarid thermo-Mediterranean type of climate. We used a new wind tunnel model over three different soil types (olive-cropped Calcisol, Cambisol and Luvisol) and studied micro-plot losses and deposits detected by an integrated laser scanner. We also studied the image processing possibilities for examining the particles attached to collector plates located at the end of the tunnel to determine their characteristics and whether they were applicable to the setup. Samples collected in the traps at the end of the tunnel were analyzed. We paid special attention to the influence of organic carbon, carbonate and clay contents because of their special impact on soil crusting and the wind-erodible fraction. A principal components analysis (PCA) was carried out to find any relations on generated dust properties and the intensity and behavior of those relationships. Component 1 separated data with high N and OC contents from samples high in fine silt, CO3= and available K content. Component 2 separated data with high coarse silt and clay contents from data with high fine sand content. Component 3 was an indicator of available P2O5 content. Analysis of variance (ANOVA) was carried out to analyze the effect of soil type and sampling height on different properties of trapped dust. Calculations based on tunnel data showed overestimation of erosion in soil types and calculation of the fraction of soil erodible by wind done by other authors for Spanish soils. As the highest loss was found in Cambisols, mainly due to the effect on soil crusting and the wind-erodible fraction aggregation of CaCO3, a Stevia rebaudiana cover crop was planted between the rows in this soil type and this favored retention of particles in vegetation.

Soil wind erosion in ecological olive trees in the Tabernas desert (S.E. Spain): a wind tunnel experiment

Wind erosion is a key component of the soil degradation processes. The purposes of this study were to find out the influence of material loss from wind on soil properties for different soil types and the changes in soil properties in olive groves when they are tilled. We used a wind tunnel over three different soil types (Calcisol, Cambisol and Luvisol) and concentrated on micro-plot losses and deposits detected by a laser scanner integrated in the tunnel. We also studied the image processing possibilities for examining the particles attached to collector plates located at the end of the tunnel to determine their characteristics, and whether they were applicable to the setup. We paid special attention to the influence of organic carbon, carbonate and clay contents because of their special impact on soil crusting and the wind-erodible fraction. A Principal Components Analysis (PCA) was done to estimate any relationships on generated dust properties and the intensity and behavior of those relationships. Then analysis of variance (ANOVAs) were done to analyze the effect of soil type and sampling height on different properties of capted dust. Calculations based on tunnel data showed overestimation of erosion in tilled Cambisol compared to the other tilled soil typologies and calculation of the fraction of soil erodible by wind done by other authors for Spanish soils.

Soil crusting and surface runoff in agricultural land in Galicia (NW Spain)

This study discusses the soil surface conditions under which crusting and runoff are generated. A field survey was conducted in three agricultural districts in the province of A Coruña (Galicia, Spain), where the soils, developed over basic schists in a temperate-humid climate, are prone to crusting. A total of 168 freshly tilled surfaces and the cumulative natural rainfall since the last tillage operation were studied. The agricultural situations corresponded to primary and secondary tillage, crop seedbeds and pasture seedbeds. Stages of soil crusting were recorded by visual assessment, based on the estimation of the extent of structural, transitional and sedimentary crusting. The runoff was estimated by measuring the maximum distance reached by soil particles carried by the runoff and then deposited on the soil surface where there were no incisions on soil. Surface crusting was observed in all agricultural situations. The amount of accumulated rainfall required to form a fully sedimentary crust was variable, depending largely on the initial soil surface roughness. On average, 50, 150 and 350 mm of accumulated rainfall were required for soil surfaces with a low, medium and high roughness, respectively. The combination of three soil surface conditions (crusting stage, roughness and vegetation cover) was primarily responsible for the start of runoff formation.

Integrating Irrigation, Tillage, and Herbicides for Weed Control in Dry Bean

Field trials were conducted from 2010 through 2012 to evaluate the integration of three factors: overhead irrigation after planting great northern dry bean; three methods of seedbed preparation: no-tillage, one or two diskings; and eight weed control treatments on dry bean development and weed control. The previous crop each year was corn. Overhead irrigation with 13 mm of water immediately after herbicide application and planting in early June did not improve or reduce herbicide efficacy but where herbicides were not utilized, irrigation increased weed emergence. Soil crusting increased in 2 of 3 yr when soil was disked at a 20-cm depth before planting. Crop injury from herbicides applied PRE increased when soil crusting occurred. No tillage before planting reduced crop injury from herbicides in 2010 and 2011 and weed density in 2012. Dry bean injury was minimal from herbicides applied PRE except for flumioxazin, which reduced crop density in 2011 and 2012. Imazamox plus bentazon applied POST caused early-season dry bean injury in 2 of 3 yr and resulted in a reduction in crop seed yield compared to dimethenamid-P or halosulfuron applied PRE. As producers move away from intensive tillage before planting to reduced tillage or no-tillage production systems, the results of this experiment show that dimethenamid-P, halosulfuron, pendimethalin, andS-metolachlor can be utilized PRE to provide acceptable weed control and crop selectivity. Although flumioxazin applied PRE reduced plant density, Great Northern dry bean yields were not affected by the loss of plant stand.