Effects of pasture applied biosolids on performance and mineral status of grazing beef heifers

Angus x Hereford heifers (n = 50) were randomly assigned to bahiagrass past ures treated with biosolids varying in mineral content and evaluated for mi neral status, with special attention to Cu. Biosolids and NH4NO3 were all a pplied at the rate of either 179 kg N/ha (X). or twice this (2X). Fertilize r was applied to .81-ha pastures for the following treatments: 1) Baltimore biosolids (1X = 179 kg N/ha); 2) Baltimore biosolids (2X = 358 kg N/ha); 3 ) Tampa biosolids (1X = 179 kg N/ha); 4) Tampa biosolids (2X = 358 kg N/ha) ; or 5) control NH4NO3 (LX: = 179 kg N/ha) applied at two times. Pastures w ere divided into five blocks with each treatment represented once in each b lock. Copper loads varied from 8.8 to 42.2 kg/ha, and Mo loads varied from .27 to 1.11 kg/ha. Heifers (two per pasture) grazed their assigned pastures exclusively for 176 d. Liver biopsies were taken from all animals at d 1, 99, and 176, and blood samples on d 1, 50, 99, 135, and 176. Liver and plas ma were analyzed for selected mineral contents, and blood was analyzed for hemoglobin and hematocrit. Experimental animals were generally low in miner al status when assigned to pastures and deficient in Se and P. By d 50, pla sma Ca, Mg, Se, P, and Zn were adequate for all treatments. Plasma Cu decli ned (P < .03) for all treatments from d 50 to 176. Plasma Cu reflected depl eted liver Cu storage, with the two Tampa and highest Baltimore treatment m eans lower in plasma Cu than the control at 176 d. Liver Fe concentrations were adequate for all treatments, and Mo concentrations (< 2.18 mg/kg) did not approach levels indicative of toxicity. Liver Cu declined (P < .05) wit h time for all treatments. By d 99, animals receiving the two Baltimore tre atments and the lowest Tampa application rate had lower (P < .05) liver Cu than the control, and all treatments were lower at 176 d. The decline of an imal Cu status (liver and plasma) reflects the low Cu status of bahiagrass and the possibility of high forage S (.30 to .47%) interfering with Cu meta bolism. Forage Mo was low but was slightly higher in biosolids-treated past ures. High levels of biosolids applications to bahiagrass pastures were not detrimental to mineral status except Cu, which had a tendency to decline i n plasma and for all biosolids treatments declined in liver.