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

Abstract

Considering the increased interests in biochar (BC) as a soil amendment and a growing media substrate in agriculture, we evaluated the effect of BC incorporation on TDR (time-domain reflectometer)-based volumetric soil moisture content (VSMC) estimations in a loamy sand podzolic soil. Two commercial BC types (powdered-BC P , and granular-BC G ) were mixed in different rates (w/w) with a podzolic soil. The dielectric constants measured using a TDR cable tester (MOHR CT 100) were converted to VSMC. Three commonly used models: (i) Topp's equation, M-1; (ii) mixing model, M-2; and (iii) the forest soil model, M-3, were used. The accuracy of the estimated VSMC using these three models was statistically compared with measured VSMC. BC P at lower rates produced very similar results to the actual VSMC with M-1 and M-2 but deviated with increasing rates. The M-3 showed a non-linear relationship with measured VSMC. In BC G treatments, all models overestimated the VSMC. BC G rates higher than 15% (w/w) resulted in highly attenuated TDR waveforms and the signal was completely dissipated when rates higher than 50% (w/w) were used (typical application for field soils is less than 5% w/w). These results showed that predictions of the soil moisture content based on the soil dielectric constant might not be feasible for tested podzolic soils amended at high BC rates.

Investigating the Influence of Biochar Amendment on the Physicochemical Properties of Podzolic Soil

“…Then BD of the samples (dry sample mass/volume of sample) was calculated. The BD of all the treatment combinations were calculated following Equation (4) [52].…”

“…This is important to note considering the boreal ecosystem is facing an increase in agricultural production and covers approximately 11% of the terrestrial land surface on Earth [48]. In 2019, Wanniarachchi et al [52] reported that biochar application influences some properties of podzolic soil (e.g., water repellency-WR). However, biochar stability in agricultural practices and the mechanism of alteration of physicochemical properties in acidic soils has not been investigated [30].…”

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“…Synthesizing the moisture data on graphs of each mulch at different depths, it is very clear that the mixture retains more moisture than the rest of the mulch and that the ideal retention depth is 15 cm. According to Dinushika et al (2019) and Adams (1996), in arid or semi-arid zones, mulching would increase water retention in the soil from 0-40 cm depth. However, Stagnari et al (2014) state that in a Mediterranean environment, mulching in general and straw in particular would increase the water retention in the soil from 5-15cm depth.…”

Ground-Penetrating Radar and Electromagnetic Induction: Challenges and Opportunities in Agriculture

“…Topp's equation is the most widely applied and accepted empirical equation in GPR applications since it is simple, relatively accurate, and valid for fully and partially saturated conditions [43]. However, in peat or organic-rich and heavy clay soils, the applicability of this relationship has limitations [44][45][46].…”