|M.Sc Student||Hagage Moran|
|Subject||The Effect of Biochar on the Hydraulic Properties of Soil|
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Uri Shavit|
|Professor Alex Furman|
|Full Thesis text|
Pyrolysis of organic waste is being used in creating renewable energy and can be an alternative way for compostation. A co-product of controlled pyrolysis is a carbon rich material, Biochar that can be used as a soil amendment. The biochar amendment has been proven to improve crop yields and nutrients availability, decreasing gas emissions and increasing solute absorption. Another effect of the biochar addition has an influence on the soil hydraulic properties resulting from its surface area. Researchers discovered that biochar addition led to increase in the water content as well as a minor effect on the hydraulic conductivity of the soil. However, knowledge of the hydraulic properties of soil with biochar is limited, and so is the record on the effect of biochar addition to different soils on the retention or hydraulic conductivity.
We hypothesized that addition of biochar to soils improves their water holding capacity and changes their retention and hydraulic conductivity. Therefore, the major objective of this research was to quantify the effect of biochar (created from Gefet and pyrolysed at 450°C) when incorporated with various soils on the hydraulic properties. Various experiments were necessary in order to achieve this goal. Firstly, we mixed five different levels of biochar (0%, 0.1%, 0.25%, 1% and 2% by weight of dry soil) with four different types of soils: sand, red loam, loess, and clay. Then, a preliminary pot experiment was conducted to evaluate the evaporation rate of the soils previously selected. Next, we characterized the retention curve and the hydraulic conductivity function of various soil and biochar mixtures using the HYPROP device, based upon the evaporation method, which fits the hydraulic parameters to empiric model (The van Genuchten Mualem model (vGM)). Last, the mini disk tension infiltrometer method used to evaluate the hydraulic conductivity function, both in the lab and in field settings.
Our conclusion was that biochar addition has an effect on the hydraulic properties, as seen by the changes in the vGM parameters for some of the soils. For coarse soils, more water retained within the soil with biochar addition, particularly in tensions lower than 1.5 pF. For fine soils, the retention decreased with biochar addition in tensions higher than 2.5 pF and increased in lower tensions. The effect on fine soils needs more research since the results had a significant variance. The hydraulic conductivity shows some changes for all soils, decreased for coarse soils and increase for fine soils. Our assumption was that some other physical variables such as aggregation could also affect the hydraulic properties examined. A complete estimate of the effects of biochar on the particle size distribution has not been determined, and can possibly help establishing a more thorough understanding about the biochar effects on soil hydraulic properties. _____________________________________________________________________________