Differences in rainfall and temperature define the use of different types of nitrogen fertilizer on managed grassland in UK, NL [Netherlands] and Eire

There are distinct differences between the Netherlands (NL) and the United Kingdom (UK) in the use of urea and calcium ammonium nitrate (Ca-AmmN) fertilizers on grassland. It has been known for some time that rainfall and temperature affect NH3 volatilization from urea and its agronomic efficiency. This study aimed (i) to examine rainfall and temperature pattern in NL and UK in relation to the observed urea efficiency, and (ii) to provide a simple decision support model for farmers to enable them to choose the most appropriate N fertilizer. A statistical analysis (residual maximum likelihood) of existing data from numerous field trials was undertaken. The agronomic efficiency of urea compared to Ca-AmmN in field trials was expressed as (i) urea relative N yield (Urel-N-y), and (ii) apparent-urea relative (N) yield (Uarel-(N)-y). In NL, (Urel-N-y) did not significantly differ from 100% on peat grassland. Mean (Urel-N-y) on sand and clay was 95%, in both cases. Mean seasonal Uarel-y and Uarel-N-y for the summed data of sand and clay soils was 92.3 and 86.4%, respectively, without significant differences between first and later cuts. There was no significant improvement of UNapp-relY in the last decades. In the first cut, mean Uarel-y was lower than in UK (100.9%) and Eire (100.2%). Differences in efficiency between countries could be described by short-term rainfall and temperature. By aggregating NL, UK and Eire data a simple regression equation was derived: Uarel-y= 89.48(+or-0.78) +[2.188(+or-0.15)xR3] -[1.091(+or-0.07)xT3], where R3 and T3 are rainfall amount and average temperature within three days after fertilizer application, respectively. The decision support model based on this equation showed that under prevailing NL weather conditions it will be profitable for the farmer to apply urea instead of calcium ammonium nitrate, for the first and second cut, only once every 5 and 7 years, respectively, because R3's exceeding 6 and 9.5 mm are required.