Water Retention and Transmission Characteristics of Subtropical Soils of Varying Parent Materials in Parts of Bihar and West Bengal

Representative surface soil samples and undisturbed soil cores from nine locations representing varying parent materials and altitude spreading over the subtropical area in parts of Bihar and West Bengal were studied for water retention, saturated hydraulic conductivity (K_s), unsaturated conductivity (K_(θ)) and diffusivity (D_(θ)), Water retention of top 0.30 m soil layer at 0.03 MPa was maximum (34.8%, w/w) in soil developed on meta-amphibolite (MAmp) followed by soils formed on granite (Gr: 27.0%, w/w), basic Deccan trap (BDt: 24.7%, w/w), basic/calc-silicates (BCS: 19.9%, w/w), alluvium (AL: 17.1%, w/w), calc-schist with ferruginous nodules (CSFN: 13.1%, w/w), phyllite (PH: 12.6%, w/w), granitic gneiss (GGn: 9.6%, w/w) and alternating sandstone and shale (ASS: 7.5%, w/w) parent materials. Available water capacity (AWC) was higher in soils developed on BDt, MAmp, Gr, BCS and AL parent materials as compared to others. Soils formed on ASS, GGn and CSFN released more than 65 per cent of available water within 0.1 MPa tension. These soils along with soil on PH exhibited higher K_s as compared to others. About 75 per cent variation of K_s of these soils could be described by linear equation involving two variables i.e., bulk density and ‘sand + gravel’. The highest and lowest K_(θ) and D_(θ) were associated with soils on Gr and ASS, respectively, showing intermediate values for others. These results clearly indicated that sprinkler and/or drip irrigation would be most suitable in soils developed on ASS, GGn, GSFN and PH for efficient use of water and minimizing the water and nutrient losses through percolation, while the soils derived from BDt, MAmp, Gr and BCS parent materials may be taken under surface irrigation.