Effect of tillage and crop rotations on pore size distribution and soil hydraulic conductivity in sandy clay loam soil of the Indian Himalayas

Tillage management can affect crop growth by altering the pore size distribution, pore geometry and hydraulic properties of soil. In the present communication, the effect of different tillage management viz., conventional tillage (CT), minimum tillage (MT) and zero-tillage (ZT) and different crop rotations viz. [(soybean-wheat (S-W), soybean-lentil (S-L) and soybean-pea (S-P)] on pore size distribution and soil hydraulic conductivities [saturated hydraulic conductivity (K-sat) and unsaturated hydraulic conductivity {k(h)}] of a sandy clay loam soil was studied after 4 years prior to the experiment. Soil cores were collected after 4 year of the experiment at an interval of 75 mm up to 300 mm soil depth for measuring soil bulk density, soil water retention constant (b), pore size distribution, K-sat and k(h). Nine pressure levels (from 2 to 1500 kPa) were used to calculate pore size distribution and k(h). It was observed that b values at all the studied soil depths were higher under ZT than those observed under CT irrespective of the crop rotations. The values of soil bulk density observed under ZT were higher in 0-75 mm soil depth in all the crop rotations. But, among the crop rotations, soils under S-P and S-L rotations showed relatively lower bulk density values than S-W rotation. Average values of the volume fraction of total porosity with pores <7.5 mu m in diameter (effective pores for retaining plant available water) were 0.557, 0.636 and 0.628 m(3) m(-3) under CT, MT and ZT; and 0.592, 0.610 and 0.626 m(3) m(-3) under S-W, S-L and S-P, respectively. In contrast, the average values of the volume fraction of total porosity with pores >150 mu m in diameter (pores draining freely with gravity) were 0.124, 0.096 and 0.095 m(3) m(-3) under CT, MT and ZT; and 0.110, 0.104 and 0.101 m(3) m(-3) under S-W, S-L and S-P, respectively. Saturated hydraulic conductivity values in all the studied soil depths were significantly greater under ZT than those under CT (range from 300 to 344 mm day(-1)). The observed k(h) values at 0-75 mm soil depth under ZT were significantly higher than those computed under CT at all the suction levels, except at -10, -100 and -400 kPa suction. Among the crop rotations, S-P rotation recorded significantly higher k(h) values than those under S-W and S-L rotations up to -40 kPa suction. The interaction effects of tillage and crop rotations affecting the k(h) values were found significant at all the soil water suctions. Both S-L and S-P rotations resulted in better soil water retention and transmission properties under ZT. (C) 2005 Elsevier B.V. All rights reserved.