Chemistry of Soil Solution and Runoff from Turfgrass Irrigated with Sodic Water.

Select turfgrass areas have been monitored for dissolved organic carbon (DOC) and plant nutrients since the spring of 2005.  Slotted monitoring wells were installed to a depth of 30 cm to allow for the in situ capture of free soil water.  Runoff collection was conducted through direct sampling at the street curb.  Irrigation water typically contained between 250 and 300 mg Na L^-1 and was applied on an as-needed basis to shallow sandy loam soils with massive clay subsoil horizons.  The DOC concentrations ranged from 12-326 mg C L^-1 and were directly related to turfgrass growth.  Reactive C was assessed with bicinchoninic acid (BCA) ranged from 1-23% of DOC with a mean of 11.5%, suggesting a significant fraction of mobile organic carbon is resistant to mineralization.  Nitrate-N concentrations peaked shortly after fertilizer applications, but remained less than 1 mg N L^-1 outside of these applications.  Similarly, NH₄-N concentrations were often undetectable.  Total soluble phosphorus (P) levels ranged from 0.6-12 mg L^-1 in spite of moderate soil test P levels suggesting reducing conditions within the soil are resulting in release of iron-bound P.  The majority of this soluble P has been determined to be inorganic.  Solution sodium and electrical conductivity were directly related to irrigation practice.  The DOC fraction may present a significant down- stream impact on water quality.  A more detailed assessment of the fate of DOC and associated organic nitrogen components will be presented.