225 
ation of the 
•ibed by equa- 
lation of the 
the ratio of 
ind of infra- 
the soil at 
l to one. The 
ition in the 
1 explicitly. 
1 to be a more 
ared reflec- 
:e the actual 
various spec- 
method 1 com- 
¡asurements in 
rhich the green 
) for calcu- 
nce, whereas 
1 reflectances 
(1 and 2) may 
tance cannot 
the recording 
s explicitly 
Results for 
le 2 and fi- 
2 gave sim 
arse results 
is indicates 
ail reflec- 
!S. The con- 
id by method 2 
d 0 or 1 was 
i of LAI is 
asymptotic 
:ance, and it 
.g. from a 
is an ex- 
¥s in consid- 
.ues, but with 
LAI 
Figure 3: Regression of LAI on corrected infrared 
reflectance, using method 0. Field trial 116, vege 
tative stage, 1982. 
LAI 
Figure 4: Regression of LAI on corrected infrared 
reflectance, using method 1. Field trial 116, vege 
tative stage, 1982. 
LAI 
the regres- 
.ectance for 
it measure- 
esulting in 
did not vary 
: of the curve, 
¡reals and in 
leasurements 
malysis of 
er treatment 
nteractions 
ients (LAI), 
1 out on re- 
i spectral 
itter vari- 
;ly smaller 
can be as- 
;ans of con- 
sis of vari- 
¡timated LAI 
results of 
ile with the 
riginal LAI 
ime variable. 
:or correcting 
:ly estimating 
efficient of 
1 of 
[duals 
figure 
.217 
3 
.230 
4 
.214 
5 
Figure 5: Regression of LAI on corrected infrared 
reflectance, using method 2. Field trial 116, vege 
tative stage, 1982. 
Table 3 lists the means, estimated coefficients of 
variation (CV) of residuals and the critical levels 
in testing for treatment effects for the LAI (field 
measurements) during the vegetative stage of the 
crop, resulting from an analysis of variance. The 
variance was determined by means of appropriate 
averaging of inter-plot and intra-plot variances. 
The CV is the ratio of the square root of the mean 
squares of residuals and the mean value of the de 
pendent variable. The critical level (often called 
P-value) is the smallest level of significance at 
which the observed result would just lead to rejec 
tion of the null hypothesis (that a treatment has no 
effects). On 19 May the interaction effect between 
sowing date and nitrogen nutrition was significant 
at the 5 % level (meaning that the effects of nitro 
gen nutrition were dependent on the sowing date). 
The nitrogen nutrition effect was significant on 
17 June. 
The results of the analysis of variance for the 
infrared reflectance data obtained are listed in 
table 4 (the infrared reflectance relates best to 
LAI). On most dates, critical levels in testing for 
treatment effects by means of infrared reflectance 
measurements were smaller than those obtained by 
means of LAI measurements, with the exception of a 
large critical level for sowing date effect on 
10 June. Thus treatment effects could be ascertain 
ed with larger power with reflectance measurements 
than with LAI determination in the field. This is 
the main reason for preferring reflectance measure 
ments over sampling in field trials. This conclu 
sion is also confirmed by the magnitude of the co 
efficients of variation. CV values in the infrared 
band were considerably smaller than CV values for 
LAI. However, one has to keep in mind that infra 
red reflectance and LAI are different characteris 
tics and therefore one should be careful when com 
paring these results. 
With the results of table 2 it is possible to 
estimate the LAI per plot from the reflectance mea 
surements (method 2) and subsequently to apply an 
analysis of variance on these LAI estimates. The 
results of such an analysis of variance are listed 
in table 5. Results for 28 April 1982 are not list 
ed, because bare soil predominated on that date. 
Similarly to the results for the infrared reflec 
tance, the critical levels in testing for treatment 
effects in LAI estimates were smaller than those in 
the LAI measurements (table 3) on most dates. Thus, 
treatment effects on LAI could be ascertained with 
larger power by reflectance measurements than by 
taking samples in the field. This was confirmed by 
Table 3: LAI: means, CVs and critical levels in 
testing for treatment effects, obtained on conse 
cutive sampling dates. Field trial 116 in 1982. 
date 
mean 
CV 
critical 
interaction 
level in 
sowing 
dates 
testing: 
nitrogen 
nutrition 
19 
May 
0.99 
0.215 
0.030 
0.003 
0.011 
3 
June 
3.67 
0.363 
0.474 
0.092 
0.277 
17 
June 
5.27 
0.256 
0.920 
0.123 
0.004 
Table 4: 
critical 
obtained 
in 1982. 
Infrared reflectance (%): means, CVs and 
levels in testing for treatment effects, 
on consecutive missions. Field trial 116 
date 
mean 
CV 
critical 
interaction 
level in 
sowing 
dates 
testing: 
nitrogen 
nutrition 
28 April 
13.8 
0.056 
0.587 
0.012 
0.885 
17 May 
15.4 
0.021 
0.003 
0.001 
0.001 
27 May 
33.6 
0.034 
0.000 
0.001 
0.000 
10 June 
47.9 
0.071 
0.864 
0.465 
0.001 
17 June 
53.0 
0.033 
0.565 
0.013 
0.000 
Table 5: LAI estimated by reflectance measurements: 
means, CVs and critical levels in testing for treat 
ment effects, obtained on consecutive missions. Field 
trial 116 in 1982. 
date mean CV critical level in testing: 
interaction sowing nitrogen 
dates nutrition 
17 
May 
0.48 
0.099 
0.000 
0.002 
0.000 
27 
May 
2.42 
0.075 
0.000 
0.001 
0.000 
10 
June 
4.47 
0.152 
0.906 
0.814 
0.002 
17 
June 
5.70 
0.073 
0.279 
0.110 
0.000