a1 Field Drainage Experimental Unit, Trumpington, Cambridge
Poaching damage to a new grass ley was measured over a period of time using a surface profile meter. Individual profiles obtained on different drainage treatments in the ley showed little change over 3 years of measurements. Poaching could be denned visually as a depression greater than 4 cm depth on this site. Degree of poaching was adequately described by the standard deviation of the soil surface. Typically, standard deviations along a poached, undrained transect were twice those of an unpoached, drained one. In this experiment drainage with pipes alone at 12 m spacing controlled poaching as well as mole drainage at 2 m with pipes at 40 m spacing even though watertable levels were usually not lower than those of the undrained control.
(Received June 25 1985)