Characterization of Technosols for Urban Agriculture

Soil characterization is essential for planning activities in urban areas in order to detect potential risks and understand the possible impacts derived from those activities. Nine soils located in Alicante (southeast of Spain) developed over construction debris were studied. Soil characteristics including mineralogy, elemental composition and metal availability were analyzed in two consecutive years, 2019 and 2020. These soils were similar to forest soils in the same area, with no evidence of asbestos clays or excess harmful elements. However, the use of DTPA extraction revealed high levels of Mn and Zn in some soils. Organic carbon and metals extracted with DTPA differed in 2019 and 2020, but no relationship between metal-DTPA and organic carbon content was observed. In general, organic matter content was higher in 2019, and elements extracted with DTPA were lower. The above-average rainfall in 2019 could have led to the washing away of dissolved materials and fine soil particles, decreasing elemental availability on the one hand, while promoting the development of natural vegetation, increasing soil organic matter, and immobilizing elements in living organisms on the other hand. The fact that the metal mobility varies depending on weather and soil characteristics is important when planning. Despite the demonstrated advantages of increasing urban green areas from an environmental and social point of view, we should not forget the materials on which urban soils are developed. Therefore, it is essential to establish annual plans for monitoring variations in the availability of heavy metals. This is of the most relevance when the plants are for human consumption. It is therefore also necessary to control the vegetables that grow on these soils and, in the event of possible problems, use the soil for gardening.