Low-ammonia-emission application methods can increase the opportunity for application of cattle slurry to grassland in spring in Ireland.

Application of slurry in spring to grassland in north-west Europe increases the efficiency of nitrogen recovery compared with the application in summer. In Ireland, however, more than 0·50 of slurry is applied in the summer. The splash-plate method of application, most commonly used in Ireland, can make application in spring difficult because of the risk of contamination of grass with slurry, affecting subsequent silage quality and grazing preferences. This study evaluated the potential of low-emission spreading methods to increase the opportunity for spring application of slurry using an agro-meteorological modelling approach. Weather data from two weather stations were combined with data on grass growth from two nearby sites. Using three soil-drainage classes (well, moderate and poor), each with a typical regime of grassland management, a database of soil moisture deficits, drainage, patterns of grazing and cover of grass herbage was developed for three hypothetical management systems, one for each soil drainage class, at each site. Simulations of four slurry application methods [splash-plate (SP), band-spreader (BS), trailing-shoe (TS) and shallow-injection (SI)], subject to a series of constraints, were compared over an 8-year period (1998–2005) in order to determine the number of days during the period from 1 January to approximately 10 May of each year, when it was considered that grassland was suitable for application of slurry. These constraints were: (i) restrictions on spreading imposed by current legislation in Ireland; (ii) the period before occurrence of drainage or overland flow; (iii) soil trafficability; (iv) the time-lag before a subsequent grazing or harvest event; and (v) herbage mass of the pasture. On well and moderately drained soils, the model predicted that the highest number of days available for slurry spreading was found for the TS method followed by the BS, SI and SP methods. There was no difference between application methods in the number of available days on poorly drained soils. [ABSTRACT FROM AUTHOR]