2.3. Analysis
Yield advantage of intercropping was assessed by calculating
the land equivalency ratio (LER), which is defined as the relative
land area required for sole crops to produce the same yields as
obtained by intercropping [26]. LER values greater than 1.0 indicate
that intercrops are more productive than the two component sole
crops. LER was computed by using the following formula [26]:
LER = Isunflower/Ssunflower + Isoybean/Ssoybean = Lsunflower + Lsoybean
where Isunflower and Isoybean are yields of both crop types when intercropped,
Ssunflower and Ssoybean are the corresponding yields in sole
crops, and Lsunflower and Lsoybean represent the LER components for
the two crops types in the mixture. Partial LER components (L) are
obtained dividing the yield in intercrop (I) by the yield in the sole
crop (S). The averages of sole crop yields of each crop type were
used as divisors in calculating LERs as a standardizing method of
intercrop yields [27]. Grain yields and partial LER components produced
by each crop type in sole crops and intercrops from both
experiments were analyzed using analysis of variance. Data were
square-roottransformed to fulfillthe assumptions of normality and
homogeneity of variance. Means were compared by the Tukey’s significant
difference test at 0.05 probability level. To evaluate if there
was yield advantage in intercrops, LER value was compared to 1
by using one-tail t test (P < 0.05). Since cultivars did not produce
significant effects on yields of both crop types, as well as on the
composition, richness and abundance of weed and insect communities,
this factor was removed from the analysis and data were
considered as replicates.