Interaction of Phosphorus and Dissolved Organic Carbon in Runoff and Drainage Water.

Land application of bioresources can increase extractable soil phosphorus and dissolved organic carbon (DOC). Factors affecting release and transport of P and DOC need to be identified to minimize environmental effects from bioresources. The objective was to evaluate relationships between DOC and dissolved reactive P (DRP) in surface and subsurface water. Runoff water from a replicated field study using composted municipal biosolids (CMB) was sampled and analyzed to quantify relationships between DRP and DOC. Similarly, drainage volumes were collected from a replicated lysimeter study under greenhouse conditions to evaluate effects of Geotube® residual solids (GR). Volumes were measured and sampled and concentrations and forms of total dissolved P (TDP) and DOC were analyzed. A final study of residual solids (DS) from methane digestion evaluated management effects on drainage and runoff losses of TDP and DOC. Analysis of runoff from seven natural rain events for turfgrass established with and without CMB revealed a linear relationship (r² = 0.899) between DOC and DRP. Similarly, analysis of runoff collected from simulated rainfall on turfgrass with and without DS revealed a linear relationship (r² = 0.844) between DOC and DRP. For drainage water collected 45 d after amending soil with GR and sprigging of turfgrass, a linear relationship (r² = 0.735) was observed between DOC and TDP and 94% of TDP was dissolved un-reactive P. Yet, the coefficient of determination was reduced (r² = 0.074) for collections 90 days after planting of sprigs. A similar coefficient of determination (r² = 0.806) was observed between DOC and TDP in drainage water 34 days after planting turfgrass in soil amended with CMB. Questions remain whether chemical interactions between DOC and DRP occur and exert control over losses in surface water and in subsurface drainage.