Effects of residual and reapplied biosolids on forage and soil concentrations over a grazing season in North Florida. II. Microminerals*

Effects of applications of exceptional quality biosolids (sludge) to bahiagrass (Paspalum notatum) pastures in successive years, or residual effects of applications the previous year, on micromineral status of forage and soils in north Florida were studied in relation to beef cattle requirements. Thirty 0.8 ha pastures were assigned one of 9 treatments representing three sources of biosolids. Two biosolids (Baltimore and Tampa) were applied at an “agronomic rate” (X) and 2X. Four of the treatments represented residual applications of Baltimore and Tampa biosolids which had been applied to pastures as in the previous year. The control plot received NH4NO3. Forages were analyzed for copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), molybdenum (Mo), cobalt (Co) and selenium (Se), and soils were analyzed for Mehlich-l extractable Cu, Mn, and Zn. Forage Co, Cu, and Se concentrations were low and deficient in relation to beef cattle requirements for most of the grazing season. Forages receiving Tampa treatments had improved (P<0.05) Zn concentrations over the control at most sampling times, with this increase often seen in the Tampa residuals as well. Forage Mo concentrations were minute, and though some treatment effects were observed (P<0.05), there was no threat of toxic accumulations observed at any time. Forage Fe concentrations were improved over year one and Mn concentrations were high and adequate for grazing ruminants. Biosolids fertilization improved the extractable soil Zn status of some treatment groups, and extractable soil concentrations of treated pastures were generally adequate in Cu and Mn for plant growth. In relation to beef cattle requirements, the majority of forages were deficient in Co, Cu, Se, and Zn. *Florida Agricultural Experiment Station Journal Series No. R-07563.