For many years water management in the Roswell ground-water basin (Roswell
Basin) and other declared basins in New Mexico has been the responsibility
of the State of New Mexico. One of the water management issues requiring
better quantification is the amount of deep percolation from applied
irrigation water. Two adjacent fields, planted in alfalfa, were studied
to determine deep percolation by the water-budget, volumetric-moisture,
and chloride mass-balance methods. Components of the water-budget method
were measured, in study plots called borders, for both fields during the
1996 irrigation season. The amount of irrigation water applied in the west
border was 95.8 centimeters and in the east border was 169.8 centimeters.
The total amount of precipitation that fell during the irrigation season
was 21.9 centimeters. The increase in soil-moisture storage from the
beginning to the end of the irrigation season was 3.2 centimeters in the
west border and 8.8 centimeters in the east border. Evapotranspiration,
as estimated by the Bowen ratio energy balance technique, in the west
border was 97.8 centimeters and in the east border was 101.0 centimeters.
Deep percolation determined using the water-budget method was 16.4 centimeters
in the west border and 81.6 centimeters in the east border. An average deep
percolation of 22.3 centimeters in the west border and 31.6 centimeters in
the east border was determined using the volumetric-moisture method. The
chloride mass-balance method determined the multiyear deep percolation to be
15.0 centimeters in the west border and 38.0 centimeters in the east border.
Large differences in the amount of deep percolation between the two borders
calculated by the water-budget method are due to differences in the amount
of water that was applied to each border. More water was required to flood
the east border because of the greater permeability of the soils in that
field and the smaller rate at which water could be applied.
