End of Project Reports Project No. 4025 LAND APPLICATION OF ORGANIC MANURES AND SILAGE EFFLUENT Research Centre, Athenry, Co. Galway LAND APPLICATION OF ORGANIC MANURES AND SILAGE EFFLUENT Authors

Saturated [K s ], field saturated [K fs ] and unsaturated [K(ψ)] SUMMARY There is increasing interest in the landspreading of slurries, sludges, effluents and fertilisers, resulting from the need to recycle increasing volumes of waste from high production agriculture units, old and new sewage treatment works and industrial facilities. Wastes should be spread only on suitable unsaturated soils at normal loading rates, such as 20 to 40 m 3 /ha.yr, to avoid contamination of surface and ground waters. This experimental study at Teagasc Athenry Centre examined the leaching of NO 3-N derived from cattle and pig slurries and silage effluent-spread on the surface of free-draining unsaturated soils-down to depths of 1.5 m; these gravelly, stony loam soils less than 5.0 m in depth overlie limestone bedrocks with fissures and solution channels which are good sources of water supply (aquifers). The watertable at the study site is about 25 m below ground surface. Six experimental plots were selected and instrumented after a geophysical survey. Cattle slurry and silage effluent were applied separately to 4 of the plots at normal and heavy rates; pig slurry was applied 150 days later to the cattle slurry plots also at normal and heavy rates. A chloride tracer was sprayed on a grass and fallow plot to simulate the likely movement of a conservative anion through the soil. The grass plot sprayed with the tracer served as control for the slurry and silage effluent plots. Various field and laboratory methods were used to measure the hydraulic conductivity of the soil down to depths of 1.5 m. Soils moisture contents were measured using a neutron probe, soil suctions by tensiometers and the rainfall was recorded on-site throughout the duration of the study. Suction samplers with ceramic cups-installed at different depths-provided iii samples for chemical analyses of N0 3-N. Samples of groundwater were taken from a nearby well and analysed for N0 3-N and a number of other parameters. The soil at Site 1, representative of the vast majority of soils on the farm, was studied in detail and was used for the landspreading of the slurry manures, silage effluent and tracer. The soils at two other sites, Site 2 and Site 3, representative of most of the remaining soils were studied in outline. At Site 1 the soils in two test holes to a depth of 3 m were described. As the holes were being deepened, …