Chemical Transport from Coastal Plain Soils Under Simulated Rainfall: L Surface Runoff, Percolation, Nitrate, and Phosphate Movement

Abstract

ABSTRACT Astudy was conducted to determine amounts and rates of surface runoff, percolation, nitrate and phosphate movement from the upper root zone of three upland Coastal Plain soils. Surface soil samples of Greenville sandy clay loam. Red Bay loamy sand, and Bonifay sand were packed into rectangular stainless steel boxes equipped with surface runoff and percolate collection devices. The soils ranged in clay content from 29.3% to 3.6%, and represented a range of soil textures commonly found in the Coastal Plain. Simulated rainfall was applied to each soil at high (125 mm/hr), medium (75 mm/hr), or low (43 mm/hr) intensities. Surface runoff rates varied from none to about 100 mm/hr depending on soil texture, crusting and sealing, and rainfall intensity. Percolation was found to be the major water-loss pathway on the sandier soils at the lower rainfall intensities. Surface runoff was the major water-loss pathway at the high rainfall intensity on the Bonifay sand (69.8%), and for all three rainfall intensities on the Greenville sandy clay loam. The study showed that percolation is the major pathway for NO3-N movement from the upper root zone of the sandier Coastal Plain soils. Some PO4 moved with percolation on the two sandier soils, but not on the clayey soil. Nitrate and PO4 movement from the clayey soil was primarily in surface runoff. Comparison of NO3-N and PO4 movement predictions made by the GLEAMS model with actual observations showed that the model worked best on the sandier soils. The study indicates that care should be taken to avoid applying NO3-N and PO4 when probability for immediate intense rainfall is great.