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Changes of Field Establishment and Growth in Cover Crops Sown at Different Times

In organic farming systems, integration of cover crops into cropping system are recommended to im-prove the soil quality, to prevent soil erosion, and to pro-vide biological control of weeds. The aim of the present study was to evaluate the optimal seeding dates of major cover crops. To know optimal seeding dates, crimson clover, alfalfa, rye and hairy vetch were sown on 20. Sep., 27. Sep., 4. Oct., 11. Oct., 18. Oct., 25. Oct. Rye could ger-minate and grow well in all the tested sowing dates. Hence, it was concluded that the sowing of rye could be conducted later in fall or more earlier in spring than any other cover crops tested in this study. Growth and ground covering capacity were significantly decreased by late sowing in alfalfa and crimson clover. For safe overwintering, alfalfa and crimson clover should be sown before late September. Similarly, field emergence of hairy vetch was found to be sensitive to soil temperature, however, its growth and ground covering capacity after overwintering was enough to com-pensate the delay in sowing. Germination tests in labora-tory revealed that hairy vetch grew faster at 25℃ compared to 20℃. The result suggested that germination and growth rate of hairy vetch was rapidly decreased at low tempera-ture. Therefore, it is recommended that hairy vetch should be sown as soon as possible in September for improving stand establishment after overwintering.