Spatial Variation of Soil Suction and Radiant Energy Around a Tree Vicinity in an Urban Green Infrastructure

Many studies had been conducted to analyse soil moisture/suction distribution in a vegetated soil in context of slopes (geotechnical engineering) or agricultural field (bio-technology). However, such studies are rare in context of urban landscape. Soil suction distribution is essential as it can influence hydraulic conductivity of soil and any subsequent water balance of green infrastructure in an urban landscape. Urban landscape involves complex interaction of vegetation species (tree) with other species, which can influence radiant energy distribution (require for photosynthesis) and hence, soil moisture/suction distribution in green infrastructure. The objective of this study is to investigate soil suction distribution in a green infrastructure in an urban landscape. Mix species cover (presence of grass cover in vicinity of tree) is selected as a green infrastructure site for monitoring. One month field monitoring programme has been designed to monitor the soil (soil suction, moisture), vegetation parameters (tree height, grass leaf area) and environmental parameters (radiant energy distribution; rainfall, humidity and temperature) under drying-wetting cycles. Soil parameters at different distances from tree stem was monitored to understand influence of it. It was found from the field test that suction magnitude is highest near the tree stem and also at shallower depths. Further, the rate of change of suction is also higher near the tree stem and at shallower depth. For drying, this may be because of presence of large number of roots and higher radiant energy interception, which causes higher transpiration induced suction. For wetting, this may be due to higher preferential flow caused by large number of roots near the tree at shallower depths.