What problems may be caused by applying biosolids at agronomic N rates?
Many soils in Virginia contain very high levels of phosphorus (P) due to long term manure application or repeated fertilization with commercial P fertilizer. High concentrations of soil phosphorus may increase P runoff into surface water, which can cause algal blooms that subsequently deplete oxygen for plant and animal life. The potential for such contamination exists where biosolids are applied on soils whose P concentrations are very high. Biosolids normally supply similar amounts of plant available nitrogen and phosphorus, but crops require one-fifth to one-half as much phosphorus as nitrogen. Applying biosolids at rates to supply the nitrogen needs of the crop can increase the potential for P contamination of surface water where soil P levels are already high. To alleviate the potential of phosphorus runoff in such cases, it may be advisable to apply the biosolids at rates to meet the P needs of the crop. This would probably require the farmer to purchase nitrogen to meet the crop
