Influence of biochar incorporation on TDR‐based soil water content measurements

Abstract

Summary The incorporation of biochar (BC) into agricultural soil changes the soil's physical properties, which leads to changes in the soil's hydraulic properties, such as water retention and permeability, and alters the soil moisture environment in agricultural fields. To elucidate the effects of the incorporation of BC on the soil moisture environment, measurements of the soil water in biochar‐amended agricultural fields are needed. Time domain reflectometry (TDR) is a widely used and established technique for the continuous measurement of the soil water content (SWC) in agricultural fields. However, TDR measurements are affected by the conductivity of soils. Biochar formed at higher pyrolysis temperatures is known to be very conductive. Therefore, we investigated the influence of the incorporation of BC on TDR‐based SWC measurements. We examined calcaric dark red soil and the BC produced by pyrolysis of sugarcane bagasse at 400, 600 and 800°C. The apparent relative permittivity (εa) of the BC (800°C)‐amended soil was greater than that of the non‐amended soil at a given water content, whereas the εa values of the soils amended with the BC (400°C) and BC (600°C) were the same as that of the non‐amended soil at a given water content. We concluded that when a calibration curve obtained from a non‐amended soil is used, TDR‐based measurements tend to over‐estimate the SWC containing the BC formed at higher pyrolysis temperatures because of conductive and dielectric losses. Therefore, the use of the real component ( ε r ′ ) of the soil's complex relative permittivity instead of εa is effective when making TDR‐based water content measurements of soils that contain BC formed at higher pyrolysis temperatures.

Effect of Biochar on TDR-Based Volumetric Soil Moisture Measurements in a Loamy Sand Podzolic Soil

“…On the other hand, the travel time decreased with an increasing BC rate at the dry end for BC p -amended soil. A similar observation of a decreasing travel time was previously reported when soil was incorporated with less-conductive sugarcane bagasse BC [34]. The measured VSMC values and their respective ranges at different BC incorporation rates Soil Syst.…”

“…Previous studies [34,51] reported the decrease in K b with decreasing BD, and hence increasing porosity, in low moisture soils. The waveforms at the dry end of the soils amended with BC P in our experiment can be explained by the decrease in BD [51], and thus low dielectric values resulting from a greater underestimation of the VSMC at the dry end.…”

The application of biochar on soil acidity and other physico‐chemical properties of soils in southern Ethiopia

“…) due to the nitrogen rich charred biomass inside it. Kameyama et al () concluded that was only weakly adsorbed to biochar that it could be desorbed by water infiltration and the net result may be an increase residence time for in the soil.…”

Impact of biochar addition on the physical and hydraulic properties of a clay soil

“…This is especially true when slow capillary rise procedures are used for saturating the samples. On the other hand, Kameyama et al (2014) reported that the temperature at which the biochar's pyrolysis is obtained (800 C and 400-600 C, respectively) may affect the soil water content measurements of the TDR probes which thus may or may not be overestimated. In other words, if we exclude potential overestimates of the TDR measurements (our biochar was obtained at about 500 C), the opposite cannot be excluded, since underestimates e.g., due to the air trapped in the soil, occluded or encapsulated in the form of discontinuous bubbles may always occur.…”