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Joint International Conference on Long-term Experiments ...

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The b = 1.7 value recorded for Treatment 7 can be explained partly by the lower extent<br />

of weed interference in a favourable envir<strong>on</strong>ment.<br />

The main effects of year and treatments and the interacti<strong>on</strong>s were also examined<br />

using AMMI analysis, which combines ANOVA and principal comp<strong>on</strong>ent analysis<br />

(Table 3). The first and sec<strong>on</strong>d principal comp<strong>on</strong>ents (PCA1, PCA2) explained 71.4%<br />

of the interacti<strong>on</strong> SS. The results of the AMMI analysis are illustrated in Figure 4, with<br />

the yield average <strong>on</strong> the X axis and the value of the first principal comp<strong>on</strong>ent <strong>on</strong> the Y<br />

axis, for seven treatments in 42 envir<strong>on</strong>ments (years). The higher the value of the<br />

principal comp<strong>on</strong>ent, the greater the c<strong>on</strong>tributi<strong>on</strong> of the treatment to the interacti<strong>on</strong>, i.e.<br />

the lower the yield stability. It can be seen that Treatments 7, 6, 1 and 4 made the<br />

greatest c<strong>on</strong>tributi<strong>on</strong>s to the interacti<strong>on</strong>, while Treatments 2, 3 and 5 had the greatest<br />

yield stability.<br />

First principal comp<strong>on</strong>ent scores<br />

3<br />

2<br />

1<br />

0<br />

-1<br />

-2<br />

G1<br />

G7<br />

.<br />

E40<br />

E27<br />

E33 .<br />

E32<br />

.<br />

E26<br />

E42 E3 7<br />

E22 .<br />

E38 G3 E30<br />

E17 E35 E23 .<br />

.<br />

E19 E16<br />

. E39 E10 E41 G2<br />

E34 E14 .<br />

. . . . .<br />

. . . . . G5 E36<br />

. . . . . . E21 . . . . .<br />

. . .<br />

. . . E28 . . . . . . . .<br />

E18<br />

E31<br />

.<br />

E1 E20<br />

.<br />

E4E13<br />

E8<br />

.<br />

E24<br />

E15<br />

.<br />

. E1 2<br />

E9<br />

E11<br />

E5 E7<br />

E25<br />

E6<br />

.<br />

.<br />

E2<br />

E29<br />

E3<br />

.<br />

.<br />

G4<br />

G6<br />

2 4<br />

6<br />

8<br />

Mean yields t ha -1<br />

Figure 4. Plot of the mean yields and first principal comp<strong>on</strong>ent scores of crop<br />

producti<strong>on</strong> factors in 42 envir<strong>on</strong>ments<br />

ACKNOWLEDGEMENTS<br />

This research was supported by a grant from the Nati<strong>on</strong>al Committee for Technological<br />

Development (OMFB-00895/2005).<br />

27<br />

10<br />

12

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