Hydraulic properties of soil are the basis for understanding the flow and transport through the vadose zone. It has been demonstrated that different soil amendments can alter the soil properties affecting soil hydrology. The aim of this study was to determine the effect of soil amendments on hydraulic conductivity (K) of a loamy sand podzolic soil under both unsaturated (Kunsat) and near-saturated (near Ksat) conditions in an agricultural setting. A field experiment was conducted with two common soil amendments: Dairy manure (DM) in 2016 and 2017 and biochar (BC) once only in 2016. DM and BC were incorporated up to a depth of 0.15–0.20 m at a rate of 30,000 L ha−1 and 20 Mg ha−1, respectively. A randomized complete block experimental design was used and the plots planted with silage corn (Zea mays L.) without irrigation. The treatments were: Control without amendment (0N), inorganic N fertilizer (IN), two types of DM (IN+DM1 and IN+DM2), and two treatments with BC (IN+BC and IN+DM1+BC). Infiltration data were collected using a mini disk infiltrometer under three tension levels in which −0.04 and −0.02 m was ascribed as unsaturated (at the wet end) and −0.001 m as near-saturated condition. Based on the measured infiltration rates, Kunsat and near Ksat hydraulic conductivities were calculated. There were no significant effects of DM and BC on bulk density and near Ksat. Treatments IN+DM1, IN+DM2, and IN+DM1+BC significantly reduced the Kunsat compared to the control. Since these soil amendments can influence soil hydrology such as reduced infiltration and increased surface runoff, carefully monitored application of soil amendments is recommended.
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.
Growing social, as well as development activities in the premises of Sabaragamuwa University of Sri Lanka (SUSL) and its surroundings, have reformed the natural landscape of the area. Consequently, water demand is increasing. Therefore, an understanding of the subsurface geology and their potential as beneficial aquifers help to overcome the impending water demand because surface water scares in the area. In view of assessing the groundwater potential of the area, an initial study was conducted using topographic and satellite maps followed by a geo-electrical resistivity survey, consisting of vertical electrical sounding (VES) and electrical profiling. Results revealed three subsurface layers in most places. The resistivity of the topsoil layer is ranging between about 50 to 2800 Ωm and the average thickness between 1 m to 15 m. The second layer is characterized by resistivity between about 16 to 9760 Ωm. The resistivity of the third layer ranges from about 2 to 5600 Ωm, and extending to a depth of more than 100 m. Most of the curves were identified as K type. The rest of the curves were H, Q, and A types. Out of 18 VES points, nine locations were identified as possible locations for groundwater abstraction. Groundwater could be located at a depth of between 25 to 60 m. Resistivity data indicate that the regolith mostly forms the aquifers in the area along with some weathered rock aquifers at depth. Most of the points close to or at valleys were found to be deep aquifers. Considering all the geological, structural, and morphological features, nine locations were identified as most convincing and could be recommended for test drilling.
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