This study was conducted to evaluate the weed suppressing effects of two winter cover crops, hairy vetch and rye in foxtail millet and sorghum fields in 2010. Crop growth and development and weed occurrences in the fields were examined to know the efficiency of proposed cropping system. In hairy vetch treated plots, heading of minor cereals occurred early. The heading date was earlier by 1 day and 2 days in sorghum and foxtail millet, respectively. However, rye treatment delayed heading by 12 days and 8 days in sorghum and foxtail millet, respectively. Besides the effect of cover crop on ear emergence of crops, the residues changed growth-related characteristics. Plant height, chlorophyll content and chlorophyll fluorescence of sorghum were increased in hairy vetch treatment by 46.4% 88.7% and 7.9%, respectively. In foxtail millet, the characteristics were also increased by 45.6%, 50.9% and 37.8%, respectively, as compared to control. Yields of sorghum and foxtail millet were increased by 105.1% and 135% as compared to control by hairy vetch treatment, respectively. However, the yields of cereal crops were decreased by rye cover crop treatment, the yields of sorghum and foxtail millet were decreased by 25.8% and 119.1%, respectively. Rye cover crop treatment inhibited crop growth suggesting nitrogen starvation in rye treated plots. In rye treatment, plant height, chlorophyll contents and chlorophyll fluorescence of sorghum were slightly decreased by 7.1%, 10.8% and 10.8%, respectively, as compared to control whereas the inhibitory effects were greater in foxtail millet. Weed occurrences based on weed number in hairy vetch and rye plots were reduced by 27% and 20%, respectively. The smothering effect was weakened or disappeared after heading of crops. Weed number and dry weight in hairy vetch plot were increased by 159% and 55.2%, respectively, as compared to control. The results implied that weed suppressing of cover crops could be reduced drastically after heading of crops.
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