| Urbanization is the mainstream of today’s social development, particularly in developing countries such as China. Matching with the urbanization development, urban greening also gets rapid development. However, in order to meet the demand of urban rapid greening, a large number of machines are used in greening construction, which leads to compact seriously. Man-caused trampling is also serious because of large density of urban population. Compaction leads to the deterioration of soil physical properties of urban green space. In addition, because of the shortage of urban soil resources, the source of urban soil is complex. The level of soil is confusion and topsoil is often removed or buried by underlying soil. Soil is often mixed with rigid soil or raw soil as well as a large number of gravels and construction wastes.All above action can lead to soil structure confusions and poor physical properties. The degradation of urban soil physical properties is the major reason that causes the deterioration of urban soil quality. Soil quality does not only become one of the main reasons to limite the development of urban greening, but also restrict the development of soil ecological function and the improving of urban ecological environmental quality.Therefore, the Shanghai Chenshan Botanical Garden is taken as an example to investigate the soil physical properties of the typical green spaces in details. The characteristics of soil physical properties, the correlation relationship among the physical properties, the physical properties of different vegetation types and different compaction disturbance soils and the influence factors of soil water characteristic were all researched. Aimed at the main problems of soil physical properties of urban green spaces, the greenery waste, desulfurization gypsum, peat, organic fertilizer and sand were choosed in different ratio to improve soil physical properties. The main conclusions obtained were summarized as follows:(1) The soil physical properties of Shanghai Chenshan Botanical Garden in each zone were generally poor, with average soil bulk density of1.42g/cm3,73.08%sample more than1.35g/cm3and13.46%to1.60g/cm3. Soil total porosity was only46.51%, and non-capillary porosity was3.85%which was much lower than the standard of planting soil for greening of5%. Soil texture was stick, and the silt and the clay content was higher which is59.54%and36.18%respectively. Soil saturated water capacity and field capacity was lower at336.25g/kg and305.05g/kg respectively. Saturated hydraulic conductivity was lower, that the average was only3.52mm/h, and98.08%sample belong to very badness (<10mm/h).(2) Soil physical properties were difference in different vegetation types which the bush land was significant better than other types of soils. Soil bulk density of the bare land was the largest (1.64g/cm3), followed by the grassland (1.51g/cm), and the bush land was the smallest (1.26g/cm3). Total porosity of the bush land was51.83%which was the largest than the others, and the bare land was the smallest. Saturated water capacity and field capacity of the bush land was425.47g/kg and379.92g/kg respectively, which was also the largest and the bare land was the smallest. Saturated hydraulic conductivity of the bush land was the maximum (13.43mm/h), followed by the tree land (3.07mm/h), and the bare land was the minimum (0.09mm/h). There were also significantly differences in different compaction disturbance soils, and the mechanical compaction was the most influence on soil physical properties, followed by the man-caused trampling, while the noninterference soil was significant better than compacted soil.(3) Based on the correlation analysis of soil physical properties of urban green spaces, the results showed:there was highly significant negative correlation between soil bulk density and mass water content (r=-0.537, P<0.01), and it was also highly significant negative correlation with saturated water capacity (r=-0.967, P<0.01), field capacity (r=-0.966, P<0.01), NCP/CP (r=-0.568, P<0.01), total porosity (r=-0.948, P<0.01) and saturated hydraulic conductivity (r=-0.475, P<0.01). Due to the highly negative/positive significantly or significantly between soil bulk density and the other key physical indexes, bulk density can be as an important indicator to evaluate urban soil physical properties.(4) Soil water characteristic curves of urban green spaces can be fitted by Garden model (θ=AS-B), and the fitting effects were well because the equations all reached the goodness of fit. The soil water characteristic curves were differences in different soils, such as vegetation types and different compaction disturbance soils. Field capacity, wilting water content and available water can be concluded by soil water characteristic curves. The results showed that available water of the bush land was significant greater than other types of soil (P<0.01). Soil moisture characteristics were also significant in different compaction disturbance soils. Field capacity, wilting water content and available water were extremely significant differences between the noninterference soil, mechanical compaction soil and man-caused trampling soil (P<0.01), while the differences were insignificant between the mechanical compaction and man-caused trampling soils.(5) Greenery waste, desulfurization gypsum, peat, organic fertilizer and sand were used for ratio tests, and the results showed that the soil physical and chemical properties of different ratio soils were improved significantly compared with control group. The ratio3which contained80%soil,30%greenery waste,8%organic fertilizer and0.5kg/m3desulfurization gypsum got the best soil physical and chemical properties, and the properties were effective and lasting. Therefore, the ratio3can be used to improve the urban green space soils which had the meaning of economic and environmental protection. |
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