Abstract
An extensive irrigation system is being developed in Greater Thal Canal area to meet food demand of growing population. In
Greater Thal Canal area soils are predominately coarse which results in higher deep percolation losses than those occurring in
other cultivated land. Surface irrigation methods are normally used. Infiltration may be described by the Kostiakov Equation.
Soil amendments such as bentonite could be used to reduce the water infiltration rate. The objectives of the study were to
control the infiltration in the coarse soil by using bentonite admixture and improve water distribution uniformity. For this
SIRMOD model was used which showed that water traveled only 19 m along the field with no amendment because all the
water percolated deep before reaching at the field end. When 1% bentonite was mixed with soil, water did not reach at field
end but traversed 32 m for 2.54 cm mix depth, 38 m for 7.62 cm mix depth, 39 m for 5.04 cm mix depth and 37 m for 30 cm
mix depth. When 2% bentonite was mixed with soil, water reached the tail end of field with distribution uniformity of 80%
for 2.54 cm mix depth, 84.5% for 5.04 cm mix depth, 90.9% for 7.62 cm mix depth and 84.9% for 30 cm mix depth. The best
combination observed in lab. and field tests was 2% bentonite in any depth (2.54 cm - 30 cm). Hence the amendment of
sandy soils with bentonite is one of the good options to lower infiltration rate and increase water use efficiency.
