An equilibrium tension lysimeter for measuring drainage through soil

An equilibrium tension lysimeter (ETL) was designed to maintain equilibrium between lysimeter suction and soil matric potential. Equilibrium tension lysimeter replicates were installed in a natural prairie, and N-fertilized no-tillage and chisel-plow agroecosystems to measure drainage through undisturbed soil. The ETLs were used to monitor drainage continuously at 1.4 m below the soil surface through a 0.2-mu m pore diameter stainless steel porous plate (0.19 m(2)). Heat dissipation sensors were used to record variations in matric potential inside and outside the ETL's sampling area. Suction was maintained, on lysimeters according to the matric potential experienced by the surrounding bulb soil (Cumulative lysimeter drainage was 199, 563, and 793 mm for the prairie, fertilized no-tillage, and fertilized chisel-plow agroecosystems for 132 wk between 25 June 1995 and 3 Jan. 1998. Drainage accounted for 11, 31, and 44% of precipitation inputs for the prairie, fertilized no-tillage, and fertilized chisel plow systems. Variability between lysimeter replicates was smallest for the prairie, where the coefficient of variation (CV) was 8.2%, and largest for the N-fertilized no-tillage agroecosystem (CV = 36.6%).