This empirical yield model is based on a multiple regression of
experimental yields from 14 experiments across 10 different sites in
the UK, with SAWC ranging from 300 mm within the
rooting depth and observed local weather records [6]. A yield map
had been generated using long-term weather data (1950e2000)
[15] at a 1 km by 1 km grid scale across the UK and SAWC was
estimated using the method described earlier [10]. In short, soil
hydrological site properties combined water retention properties
(derived from soil physical properties) [16] with depth to groundwater
and water from underlying porous rock (i.e. hydrology of soil
type (HoST) classes [17]). For the on-farm yield evaluation all
relevant soil data were downscaled from NATMAP1000 to a
100 100 m2 grid by combining the soil survey data and NATMAP
vector maps [18] and selecting the respective soil properties and
yield potential of the dominant soil series and association.