Land Applicaiton of Organic Manures and Silage Effluent

Abstract

In recent times there is increasing interest in the hydraulic properties of free-draining unsaturated soils and on the fate of slurries, sludges, effluents and fertilisers applied to these soils. This is especially so where relatively thin soils overlie bedrocks such as limestones with fissures and solution channels (karstic aquifers). Irish soils are commonly gravelly and stony and present special problems in determining their hydraulic properties. In this project, various field and laboratory methods were employed to measure the hydraulic conductivity of unsaturated gravelly and stony soils overlying karstic limestone with a watertable 25 m below ground surface at the Teagasc Centre at Athenry. In parallel with these measurements, cattle and pig slurries and silage effluents were applied at normal and very heavy rates in summer and in winter to a series of experimental plots. A chloride tracer was also used. Rainfall and soil moisture contents and hydraulic potentials of the soil of the various plots were measured. Samples of soil water were collected in suction tubes and analysed for nitrate nitrogen (NO3-N). In addition, samples of groundwater were taken from a nearby well and analysed for NO3-N and a number of other parameters. Finally, a finite difference computer model was used to predict contaminant transport to the groundwater.