COMPETITION BETWEEN BARNYARDGRASS AND SOY BEAN CULTIVATED IN HYDROMORPHIC SOIL .2. EFFECT ON SOME AGRONOMIC CHARACTERISTICS

The objective was to study the interaction between duration of competi tion of barnyardgrass (Echinocloa spp.) and row spacing on some agrono mic characteristics of soybean grown in a hydromorphic soil. The resul ts indicated that as the competition period increased there was a redu ction in plant height and insertion of the lower pods, stem diameter a nd leaf area index. However, the reduction rate was affected by row sp acing and weed population. The narrow row spaces, by decreasing intras pecific competition, resulted in higher plants and greater leaf area i ndex. The duration of competition after which there was a significant effect on plant height was 20 days for the 40 cm rows and 30 days for the 60 cm and 80 cm rows, whereas for leaf area index this period was 22 days. Among the agronomic characteristics studied, the one that was most related to seed yield was stem diameter.