68Hydraulic conductivity of a vegetated soil (i.e., mixed grass cover) is an important parameter 69 governing the hydrological performance of green infrastructure (GI). This paper focuses on 70 GI with mixed grass cover in the presence of trees. Due to shading effects (interception of 71 radiant energy) of tree canopy, mixed grass cover in the vicinity of trees may not receive 72 direct photosynthetically active radiation (PAR). This can hinder the growth rates resulting in 73 the low grass cover (i.e., in density). The hydraulic conductivity and the performance of GI 74 can be further affected. Several field studies were conducted to investigate hydraulic 75 conductivity in different types of vegetated covers. However, any variation in growth and 76 hydraulic conductivity of mixed grass cover in the vicinity of trees was rarely investigated. 77The objective of this study is to quantify spatial and temporal variation of vegetation growth 78 and hydraulic conductivity in a mixed grass cover in the vicinity of a tree. Field monitoring 79 of a mixed grass cover in the vicinity of a tree in a GI was conducted for about six months. 80Hydraulic conductivity tests were carried out using mini disk infiltrometer (MDI) at 149 81 locations in a selected site once every month. Vegetation density was quantified using image 82 analysis and the images were captured by a DJI Phantom drone. The growth of mixed grass 83 cover around tree vicinity (within 5 m radial distance) was found to be more uniform during 84 months characterized by high rainfall depth. Spatial heterogeneity in both vegetation density 85 and hydraulic conductivity is found to be more significant during a dry period than wet 86 period. Variation of hydraulic conductivity with respect to the change in vegetation density is 87 found to be significant in a wet period than dry period. It is also found that hydraulic 88 conductivity is higher at the portions where shredded leaves are present. The obtained 89 dynamic spatio-temporal relationship of soil, vegetation and atmospheric parameters can 90 support the design of green infrastructures and contribute to a better understanding of the 91 maintenance practices. 92 4
The relationship of shoot parameters, which play a major role in transpiration, with the cracking of soil has rarely been investigated. Such relation helps to analyse water use efficiency accurately. This study investigated the effect of vegetation (cowpea) age on crack formation and explored any correlation between age and cracking. The age of vegetation was expressed in the form of shoot parameters (shoot length (SL) and leaf area index (LAI)). Crack formation was expressed in the form of crack intensity factor (CIF). Ten experimental test pots were used to observe crack formation on vegetated and bare soil in a greenhouse. Image analysis in the experimental pots revealed that under drying-wetting cycles, the CIF of vegetated soil increased compared with that of bare soil. There was an evident increase in CIF with SL growth, up to a threshold length (400 mm), where lateral branch growth starts forming. There was no observable increase in CIF, with further SL growth (with negligible lateral branch formation). CIF increased with LAI up to a certain threshold value (0•56), after which the CIF was relatively the same. Two correlations have been identified for shoot parameters (SL, LAI) with the CIF for the selected species.
Limited studies have investigated the effect of vegetation growth and evapotranspiration (Etr) on desiccation parameter – crack intensity factor (CIF) considering a single species. Moreover, the role of inherent shoot parameters [stomatal conductance (SC) and photosynthetic yield (Y-II)] is generally ignored, leaving gaps in the authors’ understanding of its effects on CIF. This letter monitors and quantifies the effects of plant parameters [SC, Y-II, Etr and vegetation density (VD)] on soil suction and consequent CIF for a native mixed grass species. The vegetation undergoes eight drying cycles in compacted soil under natural environmental conditions and controlled irrigation scheduling. It is seen that the grass species helped reducing the maximum CIF of bare soil by 20%. A VD growth of 40% restricts further increase in CIF. The measured Etr of the vegetation is found to be very low in the study and potentially not induce additional transpiration-induced suction that can generate excessive cracks in crop species. Furthermore, the measured SC in the current vegetation species with respect to reported SC of crop species provides evidence that SC regulates a species’ ability to transpire and induce suction. The Y-II values did not give a conclusive idea of its role in soil crack propagation.
Eichhornia crassipes also known as water hyacinth (WH) is listed among world's most invasive weed species. In tropical regions, green infrastructures have to undergo multiple drought cycles, which induces desiccation cracks and also lead to water-stressed condition of plants. The use of organic materials is advocated in green infrastructure for increasing water retention and ground-covering ability of vegetation. The main objective of this paper is to explore the influence of inclusion of waste WH fibres on hydraulic characteristics (water retention and cracking) of vegetated soils. Three soil series including bare (without vegetation) soil (BS), soil + grass (SG) and soil + grass + WH-fibre (SGWH) were tested for 73 days. The grass parameters stomatal conductance (SC), evapotranspiration (Etr), grass density (GD), shoot length (SL) and soil parameters (i.e. suction (ψ), volumetric moisture content (θ), crack intensity factor (CIF), evaporation (Er)) were monitored for all series. SGWH decreases the CIF potential of soil by 55·5 and 25% for BS and SG respectively. The inclusion of WH fibres increases the GD and SL as compared with SG. Furthermore, WH-fibre inclusion increased the soils’ water-retention capacity throughout the suction range due to its hydrophilic nature. The higher hemicellulose content and porous surface morphology of WH fibre, naturally improves soil's ability to retain water which is conducive to vegetation even under drought conditions.
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