Effect of Biochar on the Unsaturated Hydraulic Conductivity of Two Amended Soils.

Water and solute transport in the vadose zone are highly dependent on the distribution, shape and configuration of the pores. This is especially true for soil hydraulic properties as processes such as water storage, infiltration, groundwater recharge, erosion and runoff are directly related Small pores enhance relatively the unsaturated hydraulic conductivity (), whereas large pores enhance the saturated hydraulic conductivity (). Soil amended with biochar are prompt to improve their physical and hydraulic properties, such as water retention, porosity and pore distribution. This work studies the effect of the addition of biochar on the hydraulic conductivity, at two different doses (2.5 and 5% dry wt.) added to two textured soils. The unsaturated hydraulic conductivity () was measured using a modified method of evaporation. Changes in soil moisture and matric potential () were registered with TDRs and microtensiometers at two different depths. Saturated hydraulic conductivity () was measured with a falling head permeameter. After obtaining the pairs, the Van Genuchten Mualem closed form equation was used to fit the measured data. Results show the effect of biochar on the pore size distribution and consequently on its water conducting capacity. For the sandy soil, the higher the dose of biochar the more constant and relatively higher is the hydraulic conductivity up to a pF of 3.5. At higher matric potentials, the unamended sandy loam soil showed a slightly higher with respect to the amended soils; for this type of soil, behaves relatively flat for high matric potentials, but decreases rapidly for lower matric potentials. These results underline that biochar addition enhances the transport of water under unsaturated conditions by reducing the formation of larger pores, but enhance the finer interparticle pores formation.