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*

Abstract

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 macromineral crude protein (CP) and in vitro digestibility (IVOMD) status of forage and soils in north Florida were studied in relation to beef cattle nutrient requirements. Thirty 0.8 ha pastures were assigned one of 9 treatments representing two sources of biosolids. 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 (agronomic 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 treatment effects were observed for each macromineral, the results were variable among treatments at various sampling times. Little or no difference (P > 0.05) was observed between pairs of residual and reapplied treatments. Forage CP concentrations were high and met beef cattle requirements for all treatments. Forage digestibility was similar for all treatments, with a general decline in digestibility evident at season's end. Soil extractable Ca, P, and Mg concentrations for all treatments were adequate to promote plant growth, while soil K concentrations were marginal or low, depending on treatment and sampling time. In relation to grazing beef cattle requirements, forages from all treatments contained adequate Ca, P, Mg, K, CP, and IVOMD, but were 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 biosolids having no cumulative effects in most cases, although the soil P levels of some treatments did appear higher in year two. *Florida Agricultural Experiment Station Journal Series No. R-07561.