Effect of gravel mole drainage on soil physical properties and pasture production of a gleyed recent soil, West Coast, South Island, New Zealand

Abstract

The effect of gravel mole drainage on soil characteristics, root distribution, and pasture production under dairying in high rainfall areas (mean annual rainfall of 4000 mm) was investigated over 3 years on an imperfectly drained Harihari silt loam (gleyed recent soil) on the West Coast, South Island. A limited amount of soil disturbance occurred during gravel mole drainage, with relatively rapid soil consolidation occurring after installation. Water content was significantly lower at 225-675 mm depth in the moled than non-moled soil throughout the trial because of more rapid movement of water in the moled subsoil. Topsoil (0-225 mm) water content was less affected by drainage because of the similar slow water infiltration rates at the soil surface of both treatments. Drainage increased root length at 100-200 mm depth and in the vicinity of the gravel mole drains. Pasture production from October to May was greater with gravel mole drainage than the surface drained non-mole treatment in the second year of the trial (1988/89), when rainfall was exceptionally high in the spring. This was attributed to the greater root length and improved aeration of the drained soil. Drainage did not significantly increase pasture production in the first and third years of the trial when rainfall was lower. The overall pasture production response to gravel mole drainage was not economic for West Coast dairying. © 1991 Taylor & Francis Group, LLC.