Nutrient Losses from Dairy Farms

Mass nutrient balances indicate more than two-thirds of the N, P and K imported on many Northeast dairy farms each year as purchased feed and fertilizer are not exported off of the farm in saleable products (Bacon et al., 1990; Klausner, 1993; Tylutki and Fox, 1997; Klausner et al., 1998; Valk et al., 2000; Cerosaletti et al., 2003).

In another study on a NY dairy farm, 67 - 75% of the mass balance N (i.e. the surplus between inputs and products sold) was projected to escape into the off-farm environment (Hutson et al., 1998). About 10% of this excess N was predicted to leach into the groundwater. A water monitoring program on this farm indicated the concentration of N and P averaged 14.4 mg/L nitrate N and 0.4 mg/L of total P from early spring through fall (Hutson et al., 1998). These levels exceeded the federal water quality standard for groundwater (10 mg/L N and 0.10 mg/L). This data indicates nutrients can reach ground and surface water from the dairy farm through both surface runoff and leaching.

On another NY dairy farm, where all concentrate feeds had been imported to increase milk production by 44% over a 15 year period, nitrate concentration in neighboring well water increased 54% and soil test P increased from 3 to 14 mg/kg (Wang et al., 1999). These increased losses were attributed to high mass balances of N and P and it was recognized that losses could be significantly reduced if fewer nutrients were imported onto the farm in the first place (Wang et al., 1999). Thus, the NRCS 590 Nutrient Management Standard, alone, does not address the full risk to water quality as the result of high mass balances of N and P on dairy farms.