Agronomic impacts of new regulations governing land application of Class B biosolids in Florida

Although land application of biosolids is an attractive option for beneficial reuse, it represents a complex challenge for government and private organizations. This 3-year field study evaluated the agronomic impacts of reduced biosolids rates imposed by new regulations in Florida on bahiagrass (Paspalum notatum Flugge) herbage accumulation and nutritive value. Treatments consisted of a factorial combination of two phosphorus (P) sources (triple superphosphate and biosolids) applied at 0 (control), 20 (low), 40 (intermediate), and 60 kg total P ha-1 (high). Triple superphosphate plots received the same nitrogen (N) load (from ammonium nitrate) as the corresponding biosolids treatments. Bahiagrass herbage accumulation increased with increasing P and associated N rates. Bahiagrass annual herbage accumulation ranged from 2120 kg ha-1 in 2022 to 6970 kg ha-1 in 2020 and was 33%-80% less than previously published data. This was likely due to the reduced biosolids rates that did not supply sufficient N and P to sustain adequate forage production. Lesser herbage accumulation will likely lead to greater application of inorganic fertilizers, which generally have greater environmental footprint than biosolids. Biosolids generally resulted in either similar or greater bahiagrass crude protein, in vitro digestible organic matter, and tissue mineral concentrations than inorganic fertilizer. Similarly, no differences in bahiagrass N and P recovery between biosolids and inorganic fertilizer were observed. This study, along with a significant body of literature, demonstrated that biosolids have considerable fertilizer value and can be an effective alternative to commercial inorganic fertilizer while also providing environmental and economic benefits. Biosolids application at P-based rates decreases forage production and nutritive value.Reduced biosolids rates imposed by new regulations in Florida will have negative agronomic impacts.Biosolids are an effective alternative source of N and P to replace inorganic fertilizer.