Tuesday, November 14, 2006 - 10:15 AM

Comparing SSURGO Data to Intensive Soil Surveys in High P Soils.

David Weindorf, Box T-0050, Tarleton State Univ., Tarleton State University, Stephenville, TX 76402, Reshmi Sarkar, Indian Inst of Tech, 104 Shreepally, Asansol, West Bengal, 713304, India, and Anil Kumar Somenahally, Box T-0050, Tarleton State Univ, Stephenville, TX 76402.

Erath County, located in north central Texas, contained 117 dairy CAFO’s in 2005 with waste application fields distributed over various landscapes. Historically, continued application of dairy manure and effluent has resulted in the build up of soil phosphorus (P). Intensive soil surveys of physical and chemical properties have identified important spatial variability of these soils, thereby enabling the development and application of best management practices (BMP’s). A dairy was selected on the Leon watershed in Erath County for this study which has been a CAFO operation with waste application fields for many years. The 128 ha dairy contained 16 different soil mapping units. For sampling, the entire dairy was divided into a hypothetical grid of 0.1 ha squares; each with a geo-referenced coordinate in the center. ArcGIS 9.1 was used for mapping and geo-referencing the points. Surface soil samples (0-15 cm) were collected from every sample point and four samples were then composited into one sample representing 0.4 ha-1. A Garmin GPS unit with 1 m accuracy was used for locating the geo-referenced coordinates. Soil physical and chemical properties which would affect P dynamics in the soils were measured on all samples. Lab quantified parameters included soil test P, total carbon/nitrogen, CaCO3 equivalent, clay percentage, soil reaction and electrical conductivity. SSURGO soil data mapping units did not correspond well in most cases with data determined in the lab. Higher variations were observed in clay percentage and CaCO3 equivalent values. In some cases, these differences affected soil classification to the order level. The results of this study underscore the importance of field verification of soil properties before making management decisions such as the development of BMP’s.