Phytotoxic effects of fresh and decomposing cover crop residues
1996
Breland, T.A. (Norges Landbrukshoegskole, Aas (Norway). Inst. for Bioteknologifag)
The occurrence of phytotoxicity was investigated 16 days after spring grain sowing on a loam soil where treatments with undersown Italian ryegrass, white clover or no cover crop had been introduced in the previous year. Tillage treatments included autumn rotovating, autumn ploughing, no tillage with killing of cover crops by herbicide in autumn, or spring rotovating. Effects of fresh plant materials and of soil incubated (15 deg C) for up to 28 days with plant materials were also studied. Phytotoxicity was bioassayed by the number of radish seeds germinating on filter paper with water extract from plant material or soil and expressed as a percentage of germination with deionized water. Ryegrass incorporated by spring rotovating reduced germination to 45. The other treatments in the field trial were virtually without effect. Germination values in extracts from fresh ryegrass and white clover (13 mg plant dry matter ml-1) were 64 and 15, respectively. At double concentration of plant residues, the corresponding values were 27 and 1.3. Wheat straw had no effect. Germination values in extracts from soil incubated with white clover were 63 and 66 on days 14 and 21, respectively. Ryegrass- and straw-amended soil did not differ significantly from unamended soil but tended to reduce germination on day 21. Plant residues had no effect on days 5 and 28. The results suggest that retarded germination observed in the field was mainly caused by phytotoxic substances indigenous to fresh residues and that these substances were degraded during 3-4 weeks of aerobic decomposition at 15 deg C
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