| dc.description.abstract | Resource demand between the reproductive phases of intercropped soybean and maize was staggered both genetically, with cultivars and isolines of differing maturity and photo periodic response, and agronomically, with a range of absolute and relative planting dates in a two year study at Elora, ontario. The objective of the study was to relate
soybean yield, yield component, and seed quality responses to the degree of synchrony between the reproductive phases of the' two intercrop components.
In the genotype trial, intercropped soybean planted to 70% of the available land, yielded 45 to 50% that in monoculture, while maize, which occupied 30% of the land base,
yielded 55 to 57% that in monoculture. Soybean yield reduction did not vary consistently with cultivar maturity.
In the agronomic trial, intercropping reduced soybean yield by 30 to 40% in 1990 and by 50 to 6O% in 1991. However, yield component compensation served to stabilize relative
intercrop soybean yields within a year, obscuring responses to seeding date or relative maize seeding date.
The cause of the deleterious effect of maize on soybean yield appeared to be more subtle than expected. The PAR received by intercropped soybeans was not different from that
received by monocropped soybeans until R5 or R6 - beginning or full seed. The maximal measured reduction in PAR availability to intercropped vs. monocropped soybeans did not exceed 20%.
The timing and magnitude of PAR reduction owing to the intercropped maize are difficult to reconcile with the magnitude reduction in intercropped soybean yield. Similarly,
within the intercrop, soybeans in rows adjacent to the maize received 20 to 40% less than soybeans three rows over. Yet, the disparity in PAR among rows translated into only a 9 to
18% range of yield among rows, suggesting some other overriding factor.
Evidence was interpreted to suggest that drought stress, could have contributed to the relatively large yield losses experienced by intercropped soybean, as well as the difference in yield expressed between the two years of the study.
Dayneutrality appeared to cause soybean developmental responses to temperature to vary in a less predictable way. As a result, the correspondence between soybean and maize developmental status varied unpredictably between years,
particularly for the dayneutral isolines. In addition to suggesting some caution in employing dayneutral materials when breeding for intercrop systems, this observation emphasized a fundamental difference between performance in monocrop vs.
intercrop systems. A slight shift in timing of development may be of no importance in monoculture, but shifting the timing of reproductive phases in one component of an intercrop can incur stress at different and unpredictable points, from
year to year or from site to site. soil temperature, which differed substantially between
years of the study, may also have interacted with air temperature to influence growth and development. Hence it was not possible to clearly relate soybean yield and yield
components to degree of overlap with the intercropped maize.
Recommendations for future research include: 1) either synChronize soybean and maize developmental responses to temperature, to stabilize or fix the pattern of reproductive
overlap, or 2) emphasize the formidable compensatory capacity of the soybean, such that varying the timing or degree of reproductive overlap will not introduce yield variability.
Additional research is needed to clarify the role of soil temperature and dayneutrality on the developmental responses of soybean. | en |
