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United States Department of Agriculture

Agricultural Research Service

Title: Cover Crops Affect Sorghum Seedling Growth

Authors
item Dabney, Seth
item Schreiber, J
item Rothrock, C - UNIV. OF ARKANSAS
item Johnson, J - MAFES

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 4, 1996
Publication Date: N/A

Interpretive Summary: Seedling stunting and death often occurs when crops are planted soon after killing winter cover crops, so planting is usually delayed 3 to 4 weeks. Shortening this interval would allow a longer period of cover crop growth without delaying planting of the summer crop. Longer cover crop growth would be beneficial for several reasons: increased organic matter addition to the soil, improved soil erosion control, and additional legume biological nitrogen fixation. Some cover crops might also be able to mature seed so they would not have to be replanted every year. In this research, a combination of controlled environment and field studies were conducted to characterize the nature and persistence of factors causing stand and growth reduction of sorghum [Sorghum bicolor (L.) Moench] planted following winter cover crops and to test several management alternatives which might improve growth of sorghum planted soon after killing cover crops. Results indicated legumes cover crops were more detrimental to seedling growth than were non-legume cover crops and that both sub-surface residues and surface-residue leachates contributed to the deleterious effects. When legume residues were removed from the soil, growth retardation and increased disease incidence disappeared by 7 to 14 d after killing cover crops, but when residues were mixed into soil, detrimental effects persisted through 32 d. Using planter attachments that move residues away from the row combined with selected seed protectants may allow the interval between cover crop killing and successful no-till planting to be reduced to less than 7 days.

Technical Abstract: Controlled environment and field studies were conducted to inves- tigate the interference associated with planting sorghum [Sorghum bicolor (L.) Moench] into recently killed cover crops. Germina- tion, root and shoot length, and disease incidence of sorghum germinated at 25**oC for 5 d in soil collected 2, 4, 7, 14, 23 and 32 d after killing cover crops indicated legumes cover crops were more detrimental to seedling growth than were non-legume cover crops. Both sub-surface residues and surface-residue leachates contributed to the deleterious effects. When legume residues were removed from the soil, growth retardation and increased disease incidence disappeared by 7 to 14 d after killing cover crops. When residues were mixed into soil or placed on top of soil, some detrimental effects persisted through 32 d. Pathogenic organisms isolated from lesions on seedlings indicated legume cover crops increased damage due to Rhizoctonia. In a no-till field study, stand and seedling growth were reduced when sorghum was planted 0 to 7 d after killing crimson clover (Trifolium incarnatum L.) compared to planting 21 d or longer after killing. Insecticide, activated charcoal, or CaO2 seed coating improved sorghum stand. In-furrow fungicide drench had no effect on stand, but phytoxic effects reduced shoot and root growth rates in both field and controlled environment studies. Residue removal combined with selected in-furrow treatments may allow the interval between cover crop killing and successful no-till planting to be reduced to less than 7 days.

Last Modified: 11/1/2014
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