The destruction of nitrate-fixing intermediate crops is often regulated and not possible before a specific date. To find out, check local regulations. In Europe, the rules are related to the Nitrates Directive, which includes sensitive areas. In agronomic terms, the more developed the cover crop, the greater its nitrate-fixing capacity. That’s why cover crops should be destroyed as late as possible. Often 2 to 3 months after planting. What destruction methods are used?
The frost and a roller as a destruction technique
Some cover crops, such as legumes, are highly sensitive to frost. They can be used in areas where the use of chemical products is restricted in agriculture. However, this technique is not possible in all regions and is dependent on weather conditions. When the technique is possible, it is sometimes combined with a roller which increases the destruction effect. Grasses are insensitive to frost, and when winter cover crops are destroyed, regrowth often follows.
Mustard and phacelia freeze at -7 or -8°C. Oats, vetch and sorghum freeze at 0°C.
Shredding cover crops boosts decomposition
Shredding intermediate crops destroys them and improves decomposition by exposing more of the plant’s surface to external elements and micro-organisms. It is also easier to work the soil (stubble cultivation or ploughing) when the cover crop is shredded. A shredder can be used, or even a cutter roller, which can have the same effect. This technique is not recommended for grasses though. Grain-crop regrowth can compete with the following crop.
Shredding is very effective with mustard, phacelia, and buckwheat, but should be avoided for grasses.
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Dive into the Details of BP 8300 shredderWorking the soil: stubble cultivation or ploughing to destroy nitrate-fixing intermediate crops
Stubble cultivation or ploughing makes it possible to destroy nitrate-fixing intermediate crops and work the land, at the same time, before planting the next crop. A shredder can be used first to prevent clogging, or a roller if the cover crop is mature. Winter weather conditions can enhance the effect of the roller. The depth of burial varies according to the tine tool’s working depth. Stubble cultivators with discs are used for mulching. The plough is used to bury residues. It is recommended to remove the skimmers to avoid sending the residues to the bottom of the furrow.
Stubble cultivation or ploughing works well with oats and rye, without a roller, and with a harrow. Dry conditions are best. The technique is suited to clover, vetch, mustard and phacelia.
Ploughing works well if residues are completely buried.
Destroying nitrate-fixing intermediate crops with chemical products to facilitate planting the next crop
It is possible to use a herbicide such as glyphosate to destroy intermediate crops. This technique is often used as part of a minimum tillage system or with direct seeding. It works well with grasses, although some are resistant. To destroy dicots, 2.4D can be added.
Cautionary notes to bear in mind:
- Make sure the doses and time limits are respected before re-entering the plot
- Destroying nitrate-fixing intermediate crops with chemical products is forbidden in some regions, especially before the plough.
Chemical destruction is quick and easy with mustard, oats, sorghum, and buckwheat. It is slightly less effective, but still possible, with turnip rape, rye, clover and vetch.