G roundwater is the most important source of potable water in Kansas. Chemical contamination of groundwater by pesticides and other agricultural chemicals such as nitrogen fertilizers has been documented in Kansas and surrounding states (Steichen et al., 1988; Leonard, 1974; Hallberg, 1986; Sophocleous et al., 1990). Concern has developed about long-term environmental consequences of current agricultural practices on groundwater quality, especially regarding the toxicity and health implications of agrochemicals on both humans and animals. An epidemiological study of occurrence of non-Hodgkins lymphoma (NHL) in Kansas found farm herbicides used to be associated with NHL. Occurrence of NHL was associated with the number of days of exposure to herbicides per year (Hoar et al., 1986). A Kansas farmstead study (Steichen et al., 1988) indicated that of the 103 statistically representative samples collected statewide, 29 had nitrate levels above the maximum contaminant level for drinking water and eight had detectable pesticides. In Kansas, atrazine is the most commonly used herbicide and about 2.5 million kilograms of atrazine or combinations including atrazine were applied to corn in 1978 (Nilson and Johnson, 1980). Steichen et al. (1988) reported from their survey of drinking water wells in Kansas that 13 of the 108 wells sampled contained measurable levels of pesticides, and four of the wells contained atrazine. A major concern is that low concentrations of less soluble but widely used pesticides are being detected in shallow aquifers under a wide range of agricultural and climatic conditions (Isensee et al., 1988). Direct downward leaching was found to be largely responsible for atrazine residues at low levels detected in groundwater in many irrigated corn production areas. The Great Bend Prairie in south central Kansas and the Cornbelt area in northeast Kansas are two prime agricultural areas where agrochemicals have been used for decades. The Great Bend Prairie is characterized by mostly sandy soils underlain by relatively thin, widespread, clayey layers of shallow depth (generally 1-2 m deep) and a shallow water table, generally 4-9 m deep. The Cornbelt area in northeast Kansas is characterized by the Grundy silty clay loam soil that has a black silty clay loam surface usually more that 0.4 m thick and a silty clay subsoil. Field studies that report agrochemical fate and transport in Kansas have been conducted at locations with wide variability in soil and climatic conditions (Adams and Thurman, 1991; Sophocleous et al., 1990) and do not provide necessary data to document the various processes involved in chemical fate and transport to groundwater. Data obtained from these studies are also insufficient for use in chemical transport modeling. Therefore, the fate and transport of agricultural chemicals need further study under Kansas conditions. AMONOLITHIC WEIGHING L YSIMETER FOR CHARACTERIZING THE F ATE AND TRANSPORT OF AGRICULTURAL CHEMICALS IN SOILS P. K. Kalita, G. J. Kluitenberg, P. L. Barnes, A. P. Schwab, J. K. Koelliker, J. M. Steichen, R. Black, M. J. Borah, D. L. Oard ABSTRACT. Four monolithic weighing lysimeters (1.83 m × 1.83 m × 1.52 m deep) were installed at Kansas State University in 1994 with undisturbed soils from two different locations in Kansas. The soil tanks were constructed with 6.4-mm (0.25-in.) thick metal plate, instrumented with solute suction tubes, drain tubes, tensiometers, thermocouples, and neutron probe access tubes; and installed on load cells. A tipping bucket rain gauge was installed to monitor precipitation at the site. Load cells, thermocouples, and the rain gauge were connected to a datalogger and measurements were read automatically through a computer-telephone network system. Herbicides and fertilizers were applied at conventional rates for corn during 1995-1997. Weekly water samples collected from different depths of the lysimeters were analyzed for atrazine and nitrate-N concentrations. Soil moisture contents were measured using a neutron probe and tensiometers. During three years of chemical transport investigation, the system effectively characterized the fate and transport of agricultural chemicals in soils. This system will be utilized to collect several more years of chemical transport data for developing and validating predictive models of chemical leaching through soils. Keywords. Water quality, Groundwater, Pesticide, Fertilizer, Monitoring, Modeling. Article was submitted for publication in March 1998; reviewed and approved for publication by the Soil &Water Div. of ASAE in July 1998. This research was funded and supported by the Kansas Agricultural Experiment Station, Manhattan, Kansas, Contribution No. 98-474-J. The authors are Prasanta K. Kalita, ASAE Member Engineer, Assistant Professor, Philip L. Barnes, ASAE Member Engineer , Assistant Professor, James K. Koelliker, ASAE Member Engineer, Professor and Head, J. M. Steichen, ASAE Member Engineer, Professor, Richard Black, ASAE Member Engineer, Emeritus Associate Professor, Manas J. Borah, ASAE Student Member, Research Assistant, and D. L. Oard, Research Technician, Biological and Agricultural Engineering Department, Gerald J. Kluitenberg, Associate Professor of Soil Physics, and A. P. Schwab (currently at Purdue University), formerly a Professor of Soil Chemistry, Agronomy Department, Kansas State University, Manhattan, Kansas. Corresponding author: P. K. Kalita, Kansas State University, Biological and Agricultural Engineering Dept., 147 Seaton Hall, Manhattan, KS 66506-2906; tel: (785) 532-6189; fax: (785) 532- 5825; e-mail: pkalita@ksu.edu. Applied Engineering in Agriculture VOL. 14(5): 485-491 © 1998 American Society of Agricultural Engineers 0883-8542 / 98 / 1405-485 485