The evaluation of the spatial and temporal variability of soil properties can be valuable to improve crop productivity and soil health. A study of soil properties was carried out in southern Portugal, in three farm fields with irrigated annual crops (layers 0–20 cm and 20–40 cm), over three years. Factor Analysis (FA) and Discriminant Analysis (DA) were used to analyze the data. With FA, the observed variables were grouped into a smaller number of latent variables related to soil attributes. Discriminant Analysis was used to classify and identify the most dominant attributes and indicators for the time and space variability of soil parameters. The FA performed for the surface layer included factors related to texture, water and nutrient retention capacity, chemical composition, and soil fertility. In the sub-surface layer, the factor structure was similar, with four factors related to texture, chemical composition, nutrient availability, and soil fertility. The most influential factors and variables in temporal discrimination (sampling dates) in both layers were those related to chemical composition, with electric conductivity as the preponderant indicator. As for the spatial differentiation (fields), the dominant factor in the surface layer was texture, and in the sub-surface layer, nutrient availability. The most important discriminant indicators of spatial variability were fine sand proportion and available potassium, respectively, for the surface and sub-surface layers. The results obtained showed potential for the multidimensional and integrated assessment of patterns of temporal and spatial variation of soil functions from agricultural practices or soil degradation processes.
Irrigation-induced or secondary salinization can occur when salts are introduced by irrigation water and accumulate within the root zone due to insufficient leaching. Mediterranean regions are especially susceptible, given the predominant climate and the expanding of irrigation areas. In this study, two indices to assess the risk of salinization (RSA) and sodification (RSO), previously applied at a regional scale, were used in a hydro-agricultural area (AHA) in Southern Portugal, in ten crop fields. Information on climate, irrigation water quality, soil characteristics, and land use was obtained from large databases and from local data. The results revealed the feasibility of using the RSA and RSO indices both on large and smaller scales, seeing as most of the area in the monitored crop fields presented the same risk classes (62% in RSA and 78% in RSO). Deviations were due to the reduction in scores for drainage and, in the case of RSO, the assigned irrigation method based on the land occupation class. Considering that different spatial scales of risk assessment are associated with different objectives and management options, a risk management framework was outlined following a multi-scale perspective for mitigation actions in salt-sensitive areas, ranging from territorial planning to the adoption of on-farm practices that can contribute to the sustainability of irrigated agriculture.
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