Impact of biochar and dairy manure on the hydraulic properties and their measurements in boreal agricultural podzols

Wanniarachchi, Wanniarachchige Dinushika Kumari (2018) Impact of biochar and dairy manure on the hydraulic properties and their measurements in boreal agricultural podzols. Masters thesis, Memorial University of Newfoundland.

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Abstract

Soil hydraulic properties such as hydraulic conductivity and volumetric soil moisture content are the basis for understanding flow and transport processes in the vadose zone. In addition, hydraulic properties of surface soils influence the partition of input water (by precipitation / irrigation) into runoff and soil water storage and are altered with the use of soil amendments in agricultural soils. Therefore, the present study has two different parts i.e. first section looking into hydraulic conductivity and second section into volumetric moisture content measurements. The first study was focused on field unsaturated (Kunsat) and near saturated (near Ksat) hydraulic conductivity of agricultural soil with an emphasis on amending the soil with dairy manure (DM) and biochar (BC). The study was conducted at both field and the laboratory scales using mini disk infiltrometer (a tension infiltrometer). The second study evaluated the effect of BC incorporation on TDR (Time Domain Reflectrometry) based soil moisture measurements. TDR is a well-established method for measuring volumetric soil moisture content (VSMC) at point scales using soil’s dielectric properties. To calculate VSMC from dielectric constant obtained from a TDR cable tester (MOHR CT 100), Topp’s equation–M1, mixing model–M2 and the forest soil model–M3 were used. The three models were compared with a standard (M0) VSMC calculated using gravimetric moisture and soil bulk density. According to the results, there was no significant effect of DM and BC on near Ksat. BC was observed to have no considerable influence, while IN+DM 1, IN+DM 2 and IN+DM 1+BC had significantly lower Kunsat under 2 cm suction (p=0.009, 0.002 and 0.031, respectively) compared to the control. The results from regression analysis showed the M1 and M2 reported significantly lower VSMC values, while M3 reported higher values than M0 for both powdered and granular BC treatments (p<0.001). However, for powdered BC treatment, the relationships between M1, M3 with M0 were not significant (p=0.228, 0.052), while it was significant for M2 with M0 (p=0.028). For granular BC treatments, the M2, M3 with M0 regressions have shown significant similarity (p=0.009 & 0.032); this was not true for the M1 to M0 comparison (p=0.571). These results show that the effects of types and rates of BC on VSMC prediction models based on soil dielectric constant need to be further studied under both laboratory and field conditions. Since these soil amendments can influence soil hydrology such as reduced infiltration and increased surface runoff, carefully monitored agronomic practices are recommended.

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