Effects of residual and reapplied biosolids on forage and soil concentrations over a grazing season in north Florida. I. Macrominerals, crude protein, and in vitro digestibility

Effects of applications of exceptional quality biosolids (sludge) to bahiag rass (Paspalum notatum) pastures in successive years, or residual effects o f applications the previous year, on macromineral crude protein (CP) and in vitro digestibility (IVOMD) status of forage and soils in north Florida we re studied in relation to beef cattle nutrient requirements. Thirty 0.8 ha pastures were assigned one of 9 treatments representing two sources of bios olids. Biosolids (Baltimore and Tampa) were applied at an "agronomic rate" (X) and 2X. Four of the treatments represented residual applications of the Baltimore and Tampa biosolids which had been applied to pastures as in the previous year. The control plot received NH4NO3. Forages were analyzed for calcium (Ca), phosphorus (P), magnesium (Mg), potassium (K), sodium (Na), crude protein (CP), and in vitro organic matter digestibility (IVOMD), and soils were analyzed for Mehlichl extractable Ca, P, Mg, and K. Single (agro nomic or twice this) applications, or reapplication of different biosolids slightly improved Ca, P, and K status of some forages. Both Tampa reapplied treatments resulted in forage Ca higher than the control. Although treatme nt effects were observed for each macromineral. the results were variable a mong treatments at various sampling times. Little or no difference (P > 0.0 5) was observed between pairs of residual and reapplied treatments. Forage CP concentrations were high and met beef cattle requirements for all treatm ents. Forage digestibility was similar for all treatments, with a general d ecline in digestibility evident at season's end. Soil extractable Ca, P, an d Mg concentrations for all treatments were adequate to promote plant growt h, while soil K concentrations were marginal or low, depending on treatment and sampling time. In relation to grazing beef cattle requirements, forage s from all treatments contained adequate Ca, P, Mg, K, CP, and IVOMD, but w ere deficient in Na. Many biosolids treated pastures contained excess S, (> 0.40%) and were greater (P > 0.05) than controls. In general. results were similar to those observed in the previous year, with reapplication of bioso lids having no cumulative effects in most cases, although the soil P levels of some treatments did appear higher in year two.