The study aimed to uncover the mechanism of how cover crops versus autumn tillage influences the competition of succeeding barley crop and thistle. By the difference in their effects on the N distribution, this gave barley or thistle an advantage to uptake more soil N than the other during the growing season of barley

Phan, Hong TT

Thorup-Kristensen, Kristian

Organic Eprints

18th European Weed Research Society Symposium, Slovenia 2018    Upward N redistribution - Postharvest effect of cover crops on  creeping thistle (Cirsium arvense)  Hong TT Phan and Kristian Thorup-Kristensen   Abstract  Weed control is important in organic farming to improve crop yield. In Northern European countries, the need for mechanical weed control restricts the use of green manure-based cover crops, a key resource of N supply. In a two-year experiment repeated in three seasons, we aim to compare the effect of cover crops and autumn tillage on the N uptake and N competition of barley and thistles growing in the following year. In the autumn, 15NO-3 tracer was applied to the topsoil and made subject to leaching or cover crop uptake. 15NO-3 content in the soil profile was measured in the following spring, followed by measurement of 15N uptake by barley and thistles during crop growth. Cover crops reduced leaching of the residual 15NO-3 from the topsoil to the deeper soil layer (1.0−1.5 m) by a factor of >18 compared to the tillage treatment. A significant effect of cover crops on soil N distribution was observed: 67−85% of the total recovered 15NO-3 was found in the upper 0.5 m under the cover crop treatments, while in the tillage treatment only 4−27% of the recovered 15NO-3 were found in this upper soil layer. By keeping the 15NO-3 in the topsoil, cover crops shifted 15N availability away from the deep-rooted thistles and towards the shallow rooted spring barley, and strengthened the competition of barely against thistles. In contrast, the deep N redistribution following the autumn tillage practice enhanced N uptake of thistles. Therefore, intensive autumn tillage used as a tool of perennial weed control should be removed or reduced and cover crops can be part of the integrated perennial weed management in organic cereal production.   

Upward N redistribution - Postharvest effect of cover crops on creeping thistle (Cirsium arvense)

http://orgprints.org/35206/1/Conference%20Abstract.pdf

Upward N redistribution - Postharvest effect of cover crops on creeping thistle (Cirsium arvense)

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