Water quality as related to the concentrations of nitrate-N, chloride, orthophosphate-P, and dissolved solids in runoff from agricultural watersheds

Experiments were conducted from the Fall of 1974 until the Spring of 1977 on the Middle Tennessee Experiment Station at Spring Hill and on the Milan Field Station in West Tennessee to determine the quality of runoff and nutrient losses from agricultural watersheds. A total of 713 water samples were analyzed for NO₃-N, chloride, ortho-P and dissolved solids. The two watersheds at Spring Hill were treated annually with applications of liquid dairy manure. One watershed at Milan received single appli-cation of municipal sewage sludge and was planted to corn. The other watershed at Milan underwent extensive land grading to reduce runoff losses. Only the ortho-P levels at MTES 1 and MFS 2 were significantly different from each other for the four constituents analyzed. This was probably due to the phosphatic parent material of the soils at Spring Hill and the relatively low P fertility of the soils on MFS 2. In most cases, the nutrient levels in the runoff were not significantly higher after the various treatments were implemented. This indicates future applications of the same and possibly higher rates of waste loading might be used on certain soils. The inorganic fertilizers applied at MFS 2 apparently did not affect the water quality. An attempt was made to formulate an equation to predict nutrient concentrations in runoff from runoff rate and volume. Though significant positive correlations appeared for runoff rate with nutrient concentrations for a given watershed, similar patterns are not found for other watersheds. Individual and combined regression equations proved of little benefit as predicted concentrations often fell below 0.0 ppm.