Statistical evaluation of drainage treatments in simple field trials with special reference to former opencast coal mining land

Abstract

SUMMARYDrainage trials frequently lack any statistical evaluation of treatment differences, often because of practical difficulties in setting up randomized field experiments. Also, where detailed moisture measurements are carried out the usefulness of such data is small in relation to the workload involved. Procedures are described here which seek to rectify, in part, the above limitations.Routine drain and surface condition data were analysed. Parallel regression analysis was used to compare drainage response patterns based on linear relationships between rainfall and peak drain flow. A point scoring system allowed treatment effects on surface conditions to be evaluated by x2analysis.Artificial drainage seeks to simulate naturally free-draining conditions. In line with this objective, soil moisture contents in the field, on a ‘Field Capacity Day’ (Stewart & Adams, 1968), were related to those at a standard (– 10 KPa) moisture tension typical of free-draining reference sites. Effectiveness of drainage performance was indicated by proximity of field and reference tension moisture contents.Worked examples of each of the above procedures are provided. The procedures were found to be both sensitive and complementary. The value of the overall approach and its application under more normal agricultural conditions are discussed.