Physical properties of the urban soils of Santiago de Compostela (Spain)

Purpose

Poor physical conditions are a typical feature of urban soils that reduce their functionality regarding plant production or the water cycle. However, the increasing importance of urbanization makes it necessary to carry out additional research on physical properties of urban soils.

Methods

In this work, we have studied 64 urban soils in Santiago de Compostela (Spain), over different parent materials and under several land uses. We assessed their physical properties in the field and laboratory, with measures of bulk density and porosity, water holding capacity, aggregate stability and water-dispersible clay, permeability and resistance to penetration. The erosion risk was assessed by estimation of the k factor in the RUSLE.

Results

The results show that the soils present heterogeneous physical properties, as common in urban soils. As a result of high organic matter and Fe contents, the soils present low bulk densities and high aggregate stability. Compaction issues are widespread but dependent on land use: in general soils under urban agriculture use present higher permeability and lower compaction levels than urban grasslands and forests. High infiltration values observed despite compaction are likely due to the abundance of coarse fragments and preferential flow.

Conclusion

Overall, urban soils have potentially low erosion risk as shown by the K factor values, but sound management is essential to keep actual erosion rates down, because relief, climatic factors as well as human behavior are susceptible of increasing erosion risk at some points.