Soil Characteristics and Management in an Urban Park in Hong Kong

/ The limited acreage of Hong Kong's urban parks receives a huge number of visitors, imposing a heavy strain on the soil base. Most parks show widespread trampling-induced soil degradation, such as bare patches and compaction. These symptoms erode the quality of amenity vegetation and recreational experience. Soil in the most popular park was studied through detailed field and laboratory analysis of six pits denoting different levels of user impacts. Soil profiles show unnatural stratification and poor structure of decomposed granite fill materials used in reclaiming the land from the sea. Marked compaction in surface layers is induced by foot-traffic pressure, with aggregate breakdown and formation of platy structure. Compaction in subsoil layers is inherited from construction damage that persists 40 years after park opening. The predominantly coarse texture has been packed to high bulk densities exceeding the 1.75 Mg/m3 threshold. With diminished porosity, transmission of air and water, storage of plant-available moisture, and root growth suffer. Chemically, the samples have an unnatural alkaline pH; inadequate organic matter, nitrogen, phosphorus, exchangeable cations; and limited cation exchange capacity. The results can help park-soil management, including the need to evaluate soil in planned park sites, salvage high-grade soil parcels, prevent construction damage, ameliorate structure by mechanical operations and suitable amendments, and replace site soil of very poor quality. Edaphic problems can be forestalled or solved by treating soil as an integral component of park planning and management based on scientific principles and methods.KEY WORDS: Urban soil; Urban park; Trampling impact; Soil compaction; Soil management; Hong Kong