Land application of sugar beet by-products: Effects on runoff and percolating water quality
Water quality concerns, including greater potential for nutrient transport to surface waters resulting in eutrophication and nutrient leaching to ground water, exist when agricultural or food processing industry wastes and by-products are land applied. Plot- and field-scale studies were conducted to evaluate the effects of sugar beet by-products on NO3–N and P losses and biochemical oxygen demand (BOD) in runoff and NO3–N concentrations in percolating waters. In the runoff plot study, treatments in the first year included two rates (224 and 448 Mg ha–1 fresh weight) of pulp and spoiled beets and a nonfertilized control. In the second year, no by-products were applied on the treated plots, the control treatment was fertilized with N fertilizer, and an additional treatment was added as a nonfertilized control in buffer areas. Wheat (Triticum aestivum L.) was grown in the year of by-product application and sugar beet (Beta vulgaris L.) in the following year. In the percolation field study, the treatments were the control, pulp (224 Mg ha–1), and spoiled beets (224 Mg ha–1). Results from the runoff plot showed that both by-products caused immobilization of soil inorganic N and thus reduced NO3–N losses in runoff and soil waters during the first growing season. There was some risk of NO3–N exceeding the drinking water limit of 10 mg L–1, especially between the period of wheat harvest and soil freezing in fall when pulp was applied at 448 Mg ha–1. The field-scale study showed that by-product application at 224 Mg ha–1 did not result in increased ground water NO3–N concentrations. Application of spoiled beets at both rates caused significantly higher BODs in runoff in the first year of application. The concentrations of total and soluble reactive P (SRP) were also higher from both rates of spoiled beet application and from the higher application rate of pulp during the 2-yr study period. These high BODs and total P and SRP concentrations in runoff waters from land application of sugar beet by-product suggest that application rates should not be higher than 224 Mg ha–1. Best management practices that prevent runoff from entering surface waters directly from these fields are warranted.