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days between the two stages themselves can be very big. For example, the arithmetical
difference between BBCH 21 (beginning of the tillering) and 22 (2 tiller detectable on the
plants) is only = 1 but sometimes BBCH 21 is recorded on the fields in autumn and
simulated by the model in spring. This can mean a difference of up to 5 months. Again the
model should also be validated with a subjective method. For SIMONTO a scoring model
approach is used (Roßberg
, et al.
, 2005). The difference in days between the simulation and
the observation is classified with a subjective flaw dot table:
model more than 7 days too early or more than 7 days too late: flaw dot 7;
model too early or too late (4 to 7 days): flaw dot 3;
model too early or too late (1 to 3 days): flaw dot 1;
no difference between simulation and observation: flaw dot 0;
The sum of the flaw dots could be classified in a flaw dot coefficient with values varying
from 0 (perfect model) to 7 (simulation extremely early or extremely late). Concerning the
results in Tab. 12 the flaw dot coefficient is comprised in a range from 1.27 to 3.10. Values
are classified when the simulation results arrive with a delay or an advance of up to 3 days.
Values above 3 indicate a higher difference of days between simulation and reality.
Since most of the flaw dot coefficients are lower than 3 we can conclude that the model
accurately simulates the reality with a gap of acceptable days. In this case, the subjective
validation is essential because the statistical validation could lead to misleading results.
case with
flaw dot
coefficient
BBCH
n
flaw dot
flaw dot 7 flaw dot 3 flaw dot 1 flaw dot 0
BBCH 23 22 4 2 0 18 28 1.27
BBCH 32 1490 252 228 320 636 2930 1.97
BBCH 39 1070 140 203 188 514 1852 1.73
BBCH 61 703 216 212 60 224 2181 3.10
BBCH 65 732 184 0 142 194 2066 2.82
Table 12. SIMONTO: Validation. Error point, sum of the flaw and flaw dot coefficient for
some BBCH growth stages in winter cereals (seasons 2003-2008).
Another type 4 model validated in 2010 (Tschöpe & Racca, 2010) was SIMONTO-lupin, a
model which simulates the crop stages of the lupin (
Lupinus angustifolius
).
For the subjective validation the simulated progress of ontogenesis was compared visually
with the observed BBCH growth stages in the field. The classification of the cases in correct,
overestimated and underestimated was the same used for the type 2 model validation. In
total 215 data sets were analysed by this validation method. 88.4% of the cases were
simulated correctly, 9.8% were underestimated and 1.9% were overestimated.
For the statistical validation the model output (dependant variable) was compared to the
field data (independent variable) with the help of a regression analysis. The average of the
coefficient of determination was 0.984 and the slope b was in all cases not significant.
BBCH stage
n
too early
correct
too late
229
0 % 86.0 % 14.0 %
69 22.7 % 75.5 % 1.7 %
Table 13. Evaluation of the deviation in days (% of the cases with early, correct or late
classification) between the date of the BBCH stage observed in field and the simulated for
BBCH 61 (begin of flowering) and BBCH 69 (end of flowering) (n=229).
61
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