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3.3 Results and discussion

agronomic and water balance compartments. The simulations of the soil water
profiles or soil water drainage and of the conservative transfer of solute using
bromide are then compared with the observations. Finally, the model is assessed
on pesticide transfer and fate.

3.3.1 Agronomic and hydrologic results
The contrasting climate of the three sites led to large differences in the water
balance (Table 3.5) : the ratio of infiltration to precipitation is ranges from 58%
at Vredepeel to 24% at Thiverval-Grignon. Estimated evaporation is lower at the
northern site, Vredepeel, and is in the lower range of the values estimated by ten
pesticide fate models 71 (349mm over a 474-day period compared to a range of 362
to 549mm ).
71

unit Vredepeel Kerlavic Thiverval-Grignon
year 1990/1991 2002/2003 2003/2004 1993 1994
Prec. mm/year 697.0 1101,4 1046,2 522,5 562,5
Infil. mm/year 402.0 542.0 545,3 123,8 135,8
Evap mm/year 324,9 492,7 495,3 416,3 492.0
BareSoilE mm/year 221,1 407,6 384,5 208,2 245,4
Trans. mm/year 103,8 85,1 110,8 208,1 246,6
!S mm/year -30,3 68,6 4,9 -17,3 -65,0
Infil/Precip % 57,7 49,2 52,1 23,8 24,1
Transp/Evap % 32,0 17,3 22,4 50,0 50,1
Yield T/ha 8.3 7.5 10.0 12.0 13.0
LAImax m!/m! 3.0 2.1 2.4 5.0 4.7
Max Root depth m 0.9 0.6 0.7 1.2 1.2

Table 3.5 – Annual water budget and main crop variables simulated by the model
at the three sites, Prec. : precipitation ; Infil. : infiltration ; Evap. :
evaporation ; Trans. : transpiration ; ∆S soil moisture variation, In-
fil/Precip : ratio of the infiltration to precipitation, Transp/Evap :ra-
tio of transpiration to evaporation, LAI max : maximum leaf area index

The different crops have a strong impact on the partition of the evaporation :
The highest transpiration is simulated for the maize at Thiverval-Grignon (50%
of the total evaporation) and the lowest for the wheat at Kerlavic (20%), which
is consistent with the LAI values. As the observed crop yields and LAI were not
provided, the simulated values can only be compared to the literature. The yields

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