Effects of pasture-applied biosolids on forage and soil concentrations over a grazing season in North Florida. II. Microminerals

The experiment rationale was to determine forage micromineral concentration s as effected by biosolids fertilization. We determined the effects of two exceptional quality biosolids on bahiagrass trace mineral concentrations as related to beef cattle requirements. Twenty-five 0.8-ha pastures were divi ded into five blocks. Two biosolids were applied as normal and double agron omic rates. The control received NH4NO3. Forages were analyzed for total co pper (Cu), iron (Fe), manganese (Mn), zinc (Zn), molybdenum (Mo), cobalt (C o), and selenium (Se), and soils were analyzed for Mehlich I extractable Cu , Mn, and Zn. Some significant increases (P<0.05) in forage Co, Cu, Fe, Zn, and Se were observed at various sampling times, but the increases were gen erally small and biologically insignificant Although forage Mo samples from pastures with the Tampa biosolids applied were consistently higher than th e control (P<0.05), at no time did they approach levels considered toxic. S imilar results were seen in forage Mn concentrations, with treatment Baltim ore-2X elevating (P<0.05) Mn concentrations as well. Deficiencies of Co, Cu , Zn, and Se are common in this Florida region and slight elevations due to biosolids treatment could be beneficial. Biosolids applied at the highest rates improved soil Cu and Zn concentrations above control soils and soil M n was increased over the control at both sampling times for Baltimore-2X. I n relation to beef cattle requirements, the majority of forages were defici ent in Co, Cu, Se, and Zn. In summary, biosolids fertilization slightly imp roved the micromineral status of forage and soil, without creating toxicity .