Infiltration rate assessment of some major soils.

Abstract

Landspreading of fertilisers and wastes require an evaluation of the risk of overland flow in order to minimise risks of polluting rivers and lakes. Infiltration capacity measurements offer a practical means of indexing runoff risk. The objectives of this study were to assess the spatial and temporal variability of infiltration capacity and to assess the capacity of some major Irish soils. Infiltration capacity was measured using double ring infiltrometers at freely drained (8) imperfectly drained (1) and poorly drained (1) sites. The first series was performed for one day in summer. Eight years later a second series was conducted for two days in winter and summer at the same sites. On average six replicates were required in summer and fourteen in winter to estimate the mean with 50 percent precision. Capacities were reasonably stable between years but there was a significant difference between seasons. Capacities in summer were about 3.5 times the winter values. Except on the poorly drained soil the infiltration capacity exceeded or equalled the five year return rainfall rate indicating a very small risk of overland flow in summer. In winter the capacity at three sites, including freely drained sites, were less than 2.5 mm hr-1 indicating a significant general risk in winter.