Wednesday, November 15, 2006

Monitoring Dissolved Organic Carbon and Nutrients in Soil Solution from an Urban Landscape.

David Zuberer1, Frank Hons2, Tony Provin2, Terry J. Gentry2, and Stephen Caster2. (1) Texas A&M Univ., Soil & Crop Science Dept., 2474 TAMU, College Station, TX 77843-2474, (2) Texas A&M Univ., Soil and Crop Sciences Dept., College Station, TX 77843

To monitor the characteristics of soil solution in an urban landscape (home lawns in central Texas), monitoring wells were installed to a depth of 30 cm.  The wells consisted of slotted PVC well-screen points (3.18-cm diam.) fitted with removable domed caps.  Soil solution was sampled by inserting a rigid plastic tube, fitted on a 160-ml syringe, to the bottom of the well point and drawing off the contents of the well.  Sampling was begun on May 31, 2005 and collections were made whenever the wells contained sufficient solution generated from rainfall or sprinkler irrigation.  Samples were analyzed for dissolved organic carbon (DOC), C reactive with bicinchoninic acid (BCA) and a range of nutrients (N, P, S, Fe, Mg, etc.).  DOC ranged from 40 – 181 mg C/L (mean 80 mg/L, +/- 26 mg/L) and peaked between July and August after which it declined into the cooler months.  The BCA reactive fraction of DOC ranged from 7 to 16% of DOC (mean 11%, +/- 1.5%).  Mean nitrate-N concentration was 0.9 mg N /L (+/- 1.7).  Nitrate-N concentration peaked shortly after fertilizer applications and then quickly returned to low levels.  Soluble P ranged from 0.8 to 6 mg/L (mean 2.0 mg/L, +/- 1 mg/L).  Like nitrate, soluble P peaked after fertilizer applications but generally remained at environmentally high levels.  Sodium increased with increasing irrigation as did conductivity, a result of applying municipal irrigation water.  The data suggested that water management in these turfgrass systems may have implications for managing nutrients in runoff from lawns as P mobility increased during periods when the soil profile was saturated due to rainfall or irrigation. Significant soluble P was routinely observed in soil solution even though soil tests showed that 90% of soils adjacent to well sites would have received a soil-test recommendation to apply P.