Dissolved Organic Matter from Organic Fertilizers and its Impact on Phosphate Leaching in Turf.

Simulated USGA greens were established as Penncross creeping bentgrass (Agrostis stoloniferous L.) sod to examine two commercial organic fertilizers (OFs) Milorganite (MO) and Nature Safe (NS) influence on dissolved organic carbon (DOC) and nutrient concentrations in turfgrass soil leachates. OFs are recommended as an alternative to synthetic fertilizer (SF) to reduce contamination from leachate. Leachates for both OFs and SF were analyzed for pH, DOC, phosphate (PO₄^3-), and nitrate (NO₃^-) concentrations. Fertilizer was applied in the field to greens in 3 applications at 50 kg N ha^-1 per application. Fertilizer treatments were applied 26 July, 6 September, and 19 October 2006. Overall, the SF treatments yielded higher DOC concentrations in turfgrass soil leachates than OFs. This was attributed to the high solubility of SFs. Concentrations of PO₄^3- were significant in plots treated with MO and positively correlated with DOC concentration in leachate from those plots. Dissolved organic matter (DOM) from the MO and NS fertilizers were examined for structural characteristics and chemical compositions. FTIR, elemental analysis and Total Organic Carbon (TOC) analysis were used to characterize the DOM extracts. The MO DOM was composed primarily of non-polar, aromatic components. By comparison, the NS DOM consisted of much lower concentrations of these component structures. Previous studies have observed that the polarity of DOM may strongly influence nutrient transport. Differences between SF and OFs applied as MO and NS were observed by the second treatment application. Our results show that NS has the potential to decrease PO₄^3- concentrations in turfgrass soil leachates but MO provided no advantage over SF in preserving water quality. Differences observed between MO and NS in PO₄^3- concentration in leachate were independent of P rate. The results suggest that DOM of OFs and their chemical properties may strongly influence PO₄^3- leaching.