DRILLING METHOD FOR COLLECTION OF UNDISTURBED SOIL MONOLITHS

In studies of water and solute movement in soils, use of undisturbed monoliths is usually preferred. A drilling technique to collect such monoliths (0.295 m i.d.; 1.0, 0.5, or 0.3 m in length) with minimal soil disturbance was developed. The drill consists of a steel cylinder with four mounted cutting teeth at the bottom, into which a plastic casing is inserted. The drill-cylinder rotates around the casing and carves out a soil core that is gently pushed into the casing using only a minimum of hydraulic pressure. The technique has been used in a wide variety of research applications within soil science, including the measurement of hydraulic properties, soil evaporation, and soil aeration studies. Here, one application is described in which the monoliths were used as field lysimeters planted with either barley (Hordeum vulgare L.) or meadow fescue (Festuca pratensis Hudson). During a 6-mo period, the grass lysimeters had a much lower total drainage (106 compared with 213 mm for barley) and also lower mean NO3 concentrations in the drainage water (< 0.1 compared with 9.3 mg N L-1). The uniformity of response among the replicates and large differences between the two treatments was taken as indirect evidence that sidewall flows were of little significance when using this technique.