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where Pi and Oi are the predicted and observed values, respectively, and n is the number of observations.

4.5.2 SWAP Calibration. The Results

Table 5 summarizes the calibration results; comparing the experimentally-obtained temperature sums at FCS and maturity, as well as the LAI and Ky values at several development stages with the corresponding values of the original SWAP calibration for Northern Europe.

Average FCS, i.e. maximum foliar development, corresponds to 71 days after germination in the irrigation managements that provide all the sugarbeet water requirements (Velicia, 1998). Therefore, development stage (DVS) reaches one at that date. The temperature sum at this development stage is 1141 °C, which is much higher than the 365 °C

originally considered in SWAP. Indeed, average temperatures in Southern Europe after May are higher than the temperatures usually recorded in the Netherlands and other sites of Northern Europe, where SWAP has been previously calibrated. However, temperature sums from germination to FCS similar to those shown in Table 5 for Mediterranean conditions have been found in France (Durr and Mary, 1998) and the UK (Werker and Jaggard, 1997). Furthermore, the difference between the temperature sums at FCS and maturity is lower under Mediterranean conditions than in Northern Europe, which indicates a faster growing rate during summer. Estrada (2001) pointed out the influence of direct sun radiation on sugarbeet growing while cropped under Mediterranean conditions with unlimited water supply. Such direct radiation influence could determine that the temperature sums needed for sugarbeet maturation under Mediterranean conditions is lower than that required in Northern Europe.

Table 5: Average temperature sums, Leaf Area Index, Root Lengths and Root Length Densities; as well as Kc and Ky coefficients as function of development stages (DVS) under Mediterranean conditions and those values originally considered in the SWAP calibration provided for Northern Europe (after Utset et al., 2007b).

Table 5: Average temperature sums, Leaf Area Index, Root Lengths and Root Length Densities; as well as Kc and Ky coefficients as function of development stages (DVS) under Mediterranean conditions and those values originally considered in the SWAP calibration provided for Northern Europe (after Utset et al., 2007b).

Function

Locally-obtained

| SWAP original

Temperature

Anthesis

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