COLLECTION AND MONITORING OF ONE-METER CUBIC SOIL MONOLITHS FOR LEACHING STUDIES

This report presents methodology for excavating one-meter cubic undist urbed soil monoliths for detailed laboratory investigations of solute transport through the soil profile. Eight soil monoliths were collecte d in 1992 from three field areas that had been under consistent tillag e systems since 1978. The soil was predominantly a Kenyon silt loam (T ypic Hapludoll) with the water table maintained by subsurface drainage . Each monolith was instrumented with time-domain reflectometer (TDR) waveguides, and mini-tensiometers to monitor changes in soil water con tent and soil matric potential on three sides. A rainfall simulator wa s constructed to apply water at a rainfall intensity of 33 mm-h(-1) to a 0.8 m x 0.8 m surface area of the monolith. A conservative tracer ( KBr) was applied to the soil surface and leachate samples were collect ed from 36 locations at the bottom of each monolith using fiberglass w ick extractors attached to 810 mm(2) areas in a 6 x 6 grid arrangement . Water application, soil water content and leachate were monitored to determine how surface tillage affected preferential flow. Results sug gest that the soil monolith collection and transportation procedures m aintained the integrity of the soil profile. Anion tracers provided an inexpensive means of simulating different nitrogen application method s. Grid cell samplers using fiberglass wicks allowed analysis of the s patial variation in leaching losses Leachate samples provided informat ion about the potential impact of nitrogen application method on leach ing losses. When coupled with time domain reflectometry and mini-tensi ometers, electronic data lagging equipment can be used to monitor chan ges in soil volumetric water content and matric potential.