3rd UF Water Institute Symposium Abstract

Submitter's Name Biswanath Dari
Session Name Posters - Understanding Natural, Anthropogenic and Legacy Sources of Nutrients
Category Understanding natural, anthropogenic and legacy sources of nutrients
Poster Number 60
Author(s) Biswanath Dari,  Graduate Assistant (Ph.D student) (Presenting Author)
  Vimala D. Nair,  Research Professor
  Donald A.  Graetz, Professor Emeritus
  Rao S.  Mylavarapu, Professor
  Soil Phosphorus Dynamics in a Dairy Farm during a Seven-year Period
  Continuous application of dairy manure leads to increased phosphorus (P) accumulation in the soil resulting in P loss via surface and subsurface drainage. This study evaluated changes in P storage and release from soil profiles at three locations in a dairy farm – holding, pasture and sprayfield – located on an Ultisol in the Suwannee River Basin, Florida. Soil sampling (to 5m) was conducted in 2000 and 2007 at 0.5m depth intervals with four replicates at each location. Mehlich 1-P and metals were analyzed for all soils; soluble reactive P (SRP) was determined for the 2007 soils. The soil P storage capacity (SPSC) was calculated: SPSC = (0.1 – Soil PSR)* [(Fe/56) + (Al/27)] * 31 * 1.3 (mg kg-1) where PSR, the P saturation ratio, is the molar ratio of P to (Fe+Al) in the Mehlich 1 extract. In 2000, SPSC (kg ha-1) was negative to 0.5 m depth for the holding (-2290) and pasture (-40), but positive for the sprayfield (80). The trend in SPSC was similar, though lower, in 2007 for the holding (-5900), pasture (-1840) and sprayfield (-120) locations. SPSC values to 5m-depth decreased from 2000 to 2007 for all locations. Negative SPSC indicate that soils are a P source; SRP values ranged from almost zero at the sprayfield to 4.7 mg kg-1 at the holding area for the 0.5m-depth in 2007. Depth to the clay layer was variable, from 1.0m at the sprayfield to ~2.0m at the dairy pasture. Since SPSC was lower at the lower depths in 2007 compared to 2000, it appears that P has moved below the clay layer. Thus, there has been substantial reduction in SPSC, particularly in the upper 0 to 0.5m depth, and increase in P release during the seven-year period suggesting increased degradation in water quality leaving the farm.