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For parameterization of the model, proportions of sand, silt and clay in the Halstow soil of the North Wyke site were obtained from Harrod & Hogan (2008), who used results from soil surveys of North Wyke. From these values field capacity and available water capacity were determined using the Saxton hydraulic properties calculator (Saxton & Rawls 2009) developed from statistical correlations between soil texture, soil water potential and hydraulic conductivity (Saxton et al. 1986). Although Halstow is normally better drained, all fields of the NWFP vary to some extent with compaction, and in this case the available water capacity for the Hallsworth series soil was lower than the Halstow soil (Table 1).

Table 1

Key parameters for model input from field surveys

 Longlands South Wyke Moor
HalstowHallsworth
Soil 
Volumetric field capacity as % (or as mm/dm) 36% (36 mm/dm) 36%* (36 mm/dm) 
Vol. permanent wilting point as % (or as mm/dm) 16% (16 mm/dm) 19% (19 mm/dm) 
Runoff curve number at field capacity 99 99 
Runoff curve no. at permanent wilting point 74 76 
Crop 
**Crop growth coefficient for ryegrass, Kc  
Initial/late season (75 < day of year > 200) 0.25 0.25 
Mid-season (day of year between 75 and 200) 1.05 1.05 
 Longlands South Wyke Moor
HalstowHallsworth
Soil 
Volumetric field capacity as % (or as mm/dm) 36% (36 mm/dm) 36%* (36 mm/dm) 
Vol. permanent wilting point as % (or as mm/dm) 16% (16 mm/dm) 19% (19 mm/dm) 
Runoff curve number at field capacity 99 99 
Runoff curve no. at permanent wilting point 74 76 
Crop 
**Crop growth coefficient for ryegrass, Kc  
Initial/late season (75 < day of year > 200) 0.25 0.25 
Mid-season (day of year between 75 and 200) 1.05 1.05 

*Field capacity is taken from common high moisture values of sensor during winter.

**Following FAO guidelines, Kc × reference ET = crop ET (Allen et al. 2004), where ET is evapotranspiration.

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