Materials and Methods


Column Preparation

 Undisturbed soil columns were taken from one of the unfertilized

control plots used in the field trials. Polyvinyl chloride (PVC) pipes

80 cm in length and of 9.6 cm internal diameter were put in a soil corer

constructed of a steel pipe fitted at one end with a hardened steel

cutting edge and having a heavy, threaded steel cap at the other. The

unit was hammered 75 to 80 cm into the soil and removed with a hydraulic

jack (Foale and Upchurch, 1982). The columns were sealed, crated, and

transported to the laboratory for analysis.

 The bottoms of the columns were cut so that each column contained

 a 70-cm depth of soil. The columns were then fitted with 1-bar bubble-

 pressure porous alundum plates 95 mm in diameter and 10 mm thick. The

 plates had been previously washed with 50 pore volumes of 0.1 M HC1 and

 rinsed with 100 pore volumes of deionized water (Neary and Tomassini,

 1985). Similarly washed 1-bar bubble-pressure ceramic tensiometer cups

 and 1-bar bubble-pressure alundum solution extraction cups (28.6 mm long

 by 6.35 mm outer diameter) were inserted at depths of 5, 15, 25, 35, 45,

 55, and 65 cm from the top of the soil columns. The tensiometer cups

 were connected by means of water-saturated tubing to mercury reservoirs

 for monitoring soil-water potential. The solution-extraction cups were

 connected by means of tubing to a collection vial in a pressure chamber

 (Harris and Hansen, 1975). The bottom end plates were connected to a

 constant suction of 50 cm H20 (Fig. 6-1).