Soil quality in the urban gardens of Barcelona (Spain)

Abstract

[EN] Urban agriculture is expanding worldwide and is being promoted by the FAO as a strategic activity because of its environmental, socio-economic, and educational benefits for citizens. In Spain, it is estimated that there are more than 20,000 urban gardens. There are many variables to take into account when starting to cultivate an urban garden, among which the quality of the soil is crucial. Nevertheless, some studies have shown high levels of contamination in soils dedicated to urban horticulture. The sources of contamination can be various, such as previous unrecognized management and irrigation with poor quality water, or the addition of polluted compost and other soil improvers. Soil contamination can migrate to vegetables and fruits, thus entering the food chain.

Materials and methods In this study, we analyzed the soils from ten urban gardens in the city of Barcelona, with a special focus on possible contaminants. Based on the possibility that irrigation water is a source of pollution, this was also analyzed in all investigated gardens.

Results and discussion Some of the waters analyzed for irrigation have a high concentration of salts, and a few of them contain nitrites, which are listed as a pollutant. The dominant texture of the soils was sandy clay loam and loamy sand, the pH was generally high, between 7.87 and 8.41, clearly carbonated, with Ca generally being the dominant exchangeable cation, but without the risk of a high percentage of active carbonates that could make it difficult to grow vegetables. The content in organic matter was very variable, but in all cases it appeared to be potentially incrementable. The three tests used to check possible soil contamination from heavy metals, do not attest to significant pollution.

Conclusions The soil quality overall is suitable for growing vegetables and allowing growers to work in these areas in complete safety. Although it would be necessary to analyze also other toxic elements, not considered in this study, some of the measured ones could come from the gases of road transport or even from the port of Barcelona.