Seven Years of Biosolids vs. Inorganic Nitrogen
Applications to Tall Fescue
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Cogger, C.G., A.I Bary, S.C. Fransen, and D.M. Sullivan
Repeated applications of municipal wastewater biosolids to a site is cost effective for biosolids managers, but may lead to undesirable accumulations of nutrients or contaminants. We evaluated the effects of repeated applications of biosolids on tall fescue (Festuca arundinacea Schreb.) production and nutrient availability in an intensive forage system during a 7-year period. We planted tall fescue on a well-drained sandy loam soil in western Washington and applied digested, heat-dried biosolids and thermophilically digested, dewatered biosolids at mean annual rates of 290, 580, and 870 kg total N ha-1 yr-1, using a randomized complete block design. The experiment also included inorganic N and zero-N controls. We measured yield and N uptake for each forage harvest, soil nitrate to a depth of 1.2 m each fall, plant tissue metals at selected harvests, DTPA extractable metals after 5 years of applications, and soil pH, available P, and organic C after 7 years. Forage yields increased with biosolids rate throughout the experiment. Apparent N recovery (ANR) for biosolids averaged over all treatments was 18% in 1993 (Year 1), 35% in 1994, and 46% in 1999. ANR for inorganic N averaged 62% from 1994-1999. Residual soil nitrate was less than 25 kg ha-1 for all treatments through 1995, but increased beginning in 1996 for the high biosolids rate. Biosolids increased organic C levels by 2 to 5 g kg-1 and Bray-1 P levels by 300 to 600 mg kg-1 in the surface soil (0 to 15 cm). Plant tissue Zn increased from 24 mg kg-1 to 66 mg kg-1 at the highest cumulative application rate. Nearly all of the DTPA extractable metals remained in the 0- to 8-cm soil depth. Repeated biosolids applications are feasible in an intensive forage system, but managers will need to adjust rates or cease applications as appropriate to avoid excess N or P levels in soil.
Cogger, C.G., A.I Bary, S.C. Fransen, and D.M. Sullivan. 2001. Seven years of biosolids vs. inorganic nitrogen applications to tall fescue. J. Environ. Qual. 30:2188-2194.