Rainfall climate limitation to slurry spreading in Ireland

Animal production systems in Ireland are generally based on rotational grass grazing, grass forage conservation, winter housing and indoor winter feeding because of the humid, temperate climate. These systems give rise to the need for slurry storage and land spreading. Slurry spreading in winter can cause pollution due to excessive runoff when soils have a water content above field capacity. A method of determining the rainfall climate limitation to safe slurry spreading is presented for Ireland. The method examines rain gauge records using a filter of set duration, magnitude and shape. If a sequence of days all have less rainfall than the defined filter then a safe spreading day is allotted. Using this approach it is possible to estimate the probability of safe spreading periods arising on an annual basis. Several filter types were tested using 10 rain gauge locations to find the most suitable filter characteristics. A somewhat conservative, off-set V-shaped filter of 8 days duration was then used to evaluate 151 rain gauge records throughout Ireland and produce a map of the probability of safe spreading periods having occurred within the rainfall climate record. Such a map, once combined with other regional scale soil and environmental information could be used for developing national strategies for planning of, and data acquisition for, site-specific, regulated, safe slurry spreading.