Effect of preceding rainfall on sediment, nutrients, and bacteria in runoff from biosolids and mineral fertilizer applied to a hayfield in a mountainous region

Biosolids and mineral fertilizers (MF) can provide nutrient recycling and nutrients for hay production, but excessive or inappropriate applications can also contribute to water quality degradation when sediment, nutrients, and bacteria are included in surface runoff. Rainfall simulation studies were completed in a hayfield typical of the Ozark mountain region to compare sediment and nutrient content, and bacteria concentration in surface runoff from plots receiving biosolids or MF with or without pre-irrigation that simulated small (no runoff) rainfall events. No differences among treatments were detected for total suspended solids. According to an LSD test, fecal coliform colony-forming unit (CFU) levels in runoff in all biosolids treatments and the pre-irrigated MF treatment were similar to the unamended control; however, pre-planned orthogonal contrasts indicated more CFUs were included in runoff from pre-irrigated plots. Pre-irrigating treatments decreased certain forms of nitrogen and phosphorus losses found in surface runoff when compared to treatments that did not receive irrigation before a runoff event. Total Kjeldahl nitrogen, dissolved total Kjeldahl nitrogen, ammoniacal-nitrogen, dissolved ammoniacal-nitrogen, total phosphorus (TP), and dissolved phosphorus (DP) losses from the MF treatment that received a runoff producing rainfall immediately after application were greater than any other treatment (P≤0.05). Similarly, an orthogonal contrast of all MF treatments (with and without pre-irrigation) against the low rate of biosolids treatments (with and without pre-irrigation) revealed that MF had greater runoff losses of TP (P≤0.0001) and DP (P≤0.0002). Results suggest that MF applications have the potential to deliver higher nutrient pollutant loads through surface runoff than biosolids applications when a runoff producing rainfall event occurs soon after amendments are applied. This results in increased risk of nutrient loading to surface waters in states or areas where buffer areas are not required to protect them from MF runoff. In addition, nutrient losses in runoff may decrease when application is made such that small rainfall events occur prior to a runoff producing event.