IN-SITU CHARACTERIZATION OF HYDROLOGIC PROPERTIES OF SPARTA SAND - RELATION TO SOLUTE MOVEMENT

Hydrologic characteristics of soils are of general significance for ma ny land use activities because of their relationship to water and solu te flow. Water plays important roles in soil genesis, agricultural pro ductivity, and transport of potential contaminants to groundwater. San dy soils in portions of the Lower Wisconsin River Valley (LWRV), domin ated by Sparta sand (uncoated, mesic Typic Quart-zipsamments), have be en under intense scrutiny recently because of extensive atrazine loro- (4-ethylamino)-6-(isopropylamino)-s-triazine) contamination of groundw ater. However, groundwater beneath broadly similar sandy soils elsewhe re in Wisconsin, with similar land-use (crop) management and productio n potentials, does not show such contamination. The purpose of this st udy was to determine particular hydrological properties of Sparta sand of the LWRV for use in modeling solute flux, and whether these proper ties might be distinct from those of a dominant soil of another major intensively farmed agricultural area in Wisconsin. In situ measurement s of hydraulic conductivity and pore water pressure of the Sparta sand were made with an automated time-domain reflectometry system and pres sure transducer-equipped tensiometers, respectively. Hydraulic conduct ivity of unsaturated Sparta sand was significantly different (P<0.01) between monitored depths in the profile. The differences observed in h ydraulic conductivity were correlated with morphologically and physica lly described soil profile features. Hydraulic conductivity values for Sparta sand ranged from approximately 1 X 10(-4) to 2 X 10(-8) m s(-1 ) . This is about one order of magnitude greater than values reported for Plainfield sand (mixed, mesic Typic Udipsamments), a similar sandy soil, at comparable water content and profile depth. Water redistribu tion data for Sparta sand were fitted to a non-linear model of the for m theta(v(avg))=0.261(t+2.3)(-0.1475), where theta(v(avg))is the mean profile water content (m(3) m(-3) and t is time (minutes).