Results and Discussion

1. Heavy Metal Accumulation in Wheat Forage and Grain in a Continuous Biosolid ExperimentK.J. Wynn, N.T. Basta, W.E. Thomason, E.V. Lukina, G.V. Johnson, K.W. Freeman, R.L. Westerman, and W.R. RaunDepartment of Plant and Soil Sciences, Oklahoma State University, Stillwater, OK 74078 Results and Discussion Results and Discussion Results and Discussion • Summary • High concentrations of molybdenum can cause molybdenosis in cattle • If the Cu/Mo ratio (in consumed forage) falls below 2 molybdenosis will occur. • Winter wheat forage sampled in December • Biosolids applied at 0-538 kg N/ha • Forage analyzed for Cu and Mo • Cu/Mo ratios were lower where biosolids were applied • Critical levels of 5 mg kg-1 Mo and 100 mg kg-1 Cu were not exceeded in forage • After 7 years, 2 times the N rate was required for sewage sludge to achieve the same yield as ammonium nitrate • Biosolid application decreased forage Cu/Mo ratios compared to 34-0-0, but did not fall below critical level of 2 • Unwashed wheat forage contained more Cu and Mo but Cu/Mo ratio for BS was the same for washed & unwashed forage. Forage Collection Hand-clipped at Feekes 4 from 1m2 in each plot Samples split; washed & unwashed. Forage Processing: Samples dried and ground to pass 150 uM (100 mesh) Chemical Analyses: Wet digestion (HNO3/HClO4) ICP analysis, TJA IRIS ICP, 202.0 nm Practical quantitation limit 10 ppb Mo (0.2 ppm forage) Soil Type: Norge Loam (fine mixed, thermic Udertic Paleustoll) Mo mg kg-1 Mo mg kg--1 N Rate kg ha -1 N Rate kg ha -1 Cu/Mo Materials and Methods Experimental Design: RCB, 3 Reps Treatments: 14 N Sources: Biosolid, Ammonium Nitrate N Rates: 0, 45, 90, 180, 270, 538 kg N ha-1 yr-1 Non-factorial treatments: Lime applied at high N rate (both sources) Planting: October 15, 1998 Forage Sampling: Clipped at ground level (1m2) at Feekes growth stage 4 Winter Wheat Variety: Tonkawa N Rate kg ha -1 Biosolids Applied (538 kg N ha-1) Soil Copper • When applying 538 kg N ha-1 as biosolids, critical levels of 5 mg kg-1 Mo and 100 mg kg-1 Cu were not exceeded in wheat forage • After 7 years, 2 times the N rate was required for sewage sludge to achieve the same yield as ammonium nitrate • Biosolid application decreased forage Cu/Mo ratios compared to 34-0-0, but did not fall below critical level of 2 • References • O’Connor, G.A., and L.R. McDowell. 1999. Understanding fate, transport, bioavailability, and cycling of metals in land-applied biosolids. Water Environment Federation. • National Research Council (NRC). 1996. Nutrient requirement of domestic animals. 7th Ed. National Academy of Sci., National Research Council, Wash. D.C. Year 1993 1994 1995 1996 1997 Avg. U.S. median Mo (ppm) 50.2 9.3 25.7 16.7 16.4 17.0 9.0 Cu (ppm) 928 756 684 454 507 600 741 Mo (kg ha-1) 0.47 0.17 0.26 0.15 0.15 0.18 --- Cu mg kg-1 Cu mg kg-1 N Rate kg ha -1 N Rate kg ha -1