Saturated hydraulic conductivity of soils in the presence of vermicast: Effects of soil texture and vermicast sizes

The present experiment was conducted to observe the effects of different size fractions of vermicast on the saturated hydraulic conductivity (Ks) of loam and sandy loam soils. To set up the experiment, loam and sandy loam soils were incorporated with vermicast of different sizes as raw, 1.0 – 2.0 mm, 0.5 – 1.0 mm, and <0.5 mm, at 0, 5 t/ha, 10 t/ha, 15 t/ha, and 20 t/ha, which resulted in five different treatments for each soil type. The Ks was determined based on the principle of Darcy’s Law by maintaining a constant water head on the top of the soil column. Results indicated that sandy loam soils had significantly higher Ks than loam soil for all the application rates (p < 0.01). Irrespective of the size, the applications of vermicast at the rates of 5 t/ha, 10 t/ha, 15 t/ha, and 20 t/ha resulted in 113.67 – 196.79%, 135.47 – 442.76%, 10.0 – 150.0%, and 29.63 – 135.47% higher Ks in sandy loam soils relative to the loam soils. There were significant differences in Ks among the vermicast sizes at all the rates of incorporation for both loam and sandy loam soil treatments (p < 0.01). As the size of vermicast decreases (<0.5 mm), the Ks also decreases relative to the control, indicating the greater retention capacity and water-holding capacity of finer vermicast fractions in the soil column. At 15 t/ha and 20 t/ha, the highest relative Ks (74.42% and 88.37%) were found in loam soils with raw vermicast.