Groundwater Use on Southern Idaho Dairies

Abstract

<abstract> <bold><sc>Abstract. </sc></bold>Dairy production has expanded in irrigated areas of the western and southwestern United States, potentially competing for limited water supplies. Groundwater withdrawal was measured for two years on six dairy farms with 660 to 6400 milk cows in southern Idaho. Groundwater withdrawal was calculated on an equivalent cow basis to account for relative differences in the numbers of milk cows, dry cows, heifers, and calves on each farm. Average groundwater withdrawal from each dairy varied from 110 to 250 L d^-1 eq. cow^-1 with an overall average of 190 L d^-1 eq. cow^-1 for the six farms. On an area basis, groundwater withdrawal varied from 180 to 880 mm y^-1 on each farm with a mean of 530 mm y^-1. Estimated annual irrigation requirements in southern Idaho are 510 mm for spring barley, 590 for corn, and 920 for alfalfa. Wastewater that was available for irrigation was only measured on three farms and varied from 21 to 150 L d^-1 eq. cow^-1, with the highest amounts from a freestall dairy. Assuming that wastewater replaced a portion of groundwater used for irrigation, the net groundwater used on these three dairies was 290 to 370 mm y^-1. Data from these six dairies indicated that groundwater withdrawal by dairy farms was similar or less than the amount of water required to meet evapotranspiration needs of irrigated crops in southern Idaho, especially if wastewater is used to offset irrigation and is not applied in addition to irrigation.