Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2013
Publication Date: 11/1/2013
Citation: Vadas, P.A., Powell, J.M. 2013. Monitoring nutrient loss in runoff from dairy cattle lots. Agriculture, Ecosystems and Environment. 181:127-133. Interpretive Summary: Nitrogen and phosphorus loss in runoff from areas on dairy farms, including cropland, pastures, barnyards, and outdoor cattle lots, can pollute local water bodies. There is little information on how nutrients are lost from cattle lots compared to other areas on dairy farms. We monitored nutrient runoff from dairy cattle lots and corn silage cropland, and we tested the ability of the Annual Phosphorus Loss Estimator (APLE) model to predict runoff phosphorus from cattle lots. Nutrient loss increased with the number of cows in lots because of greater nutrient application in dung and less vegetative cover. Nutrient loss in well-vegetated lots with few cows was less than from corn silage cropland, but from poorly vegetated lots with many cows, nutrient loss was much greater compared to corn silage cropland. Overall, cattle lots can be significant sources of nutrients in runoff but may constitute only about 5-10% of total nutrient loss from a dairy farm because they may represent only 15% of total farm area. Because APLE reliably predicted phosphorus loss from cattle lots, it is a valuable tool for deciding whether to target cropland or cattle lots for phosphorus loss remediation.
Technical Abstract: Nitrogen (N) and phosphorus (P) loss from agriculture persists as a water quality issue. For dairy, nutrients can be lost from cropland, pastures, barnyards, and outdoor cattle lots. We monitored nutrient runoff for 3.5 years from plots representing cattle lots and corn silage cropland, and tested the Annual P Loss Estimator (APLE) model to predict runoff P from cattle lots. About 5-10% of annual precipitation became runoff for vegetated cattle plots, while 10-15% became runoff for corn silage and unvegetated cattle plots. Sediment loss was low for cattle plots, with loss proportional to stocking density, and was greatest for corn silage plots. Runoff NO3-N was consistent over time, with ~80% of samples less than 5 mg L-1. Runoff NH4-N and organic N were also consistent through time, but high concentrations occurred soon after manure application. Sediment P loss was related to sediment loss, while dissolved P loss was more influenced by manure. Soil P and runoff dissolved P increased in cattle plots over time in proportion to stocking density. There were no similar P increases in corn silage plots. High dissolved P concentrations occurred soon after manure application, but decreased again as a function of cumulative precipitation. Cattle lots can be significant sources of P in runoff, but may constitute only about 5% of total annual P loss from a dairy farm where they represent 15% of total farm area. Because APLE reliably predicted P loss from cattle lots, it is valuable for prioritizing P loss remediation from cropland or cattle lots.