The aim of planting nitrate-fixing cover crops between two crops is to trap nitrogen in the form of nitrates so that it does not pollute surface water and ground water during the winter. One crop can be planted or a mix (e.g., grasses / legumes). A good nitrate-fixing cover crop also provides other agronomic advantages for a farm.
Natural nitrogen boost
Nitrogen-fixing plants—such as legumes like clover, alfalfa, vetch and soybeans—naturally convert atmospheric nitrogen into a form that crops can use. This process enriches the soil and supports healthier, more productive fields. For producers, the benefits include reduced reliance on synthetic fertilizers, improved soil structure and enhanced microbial activity, all contributing to long-term soil fertility.
Rotation and cover crop advantages
These plants also play a valuable role in crop rotations, often improving yields in subsequent crops like corn or wheat. Many nitrogen-fixers help suppress weeds and reduce erosion while building soil health. Popular options include alfalfa for deep-rooted forage and soil building, hairy vetch for strong nitrogen contribution in winter, field peas for quick spring growth, and red clover for versatility across systems.
Nitrogen-fixing cover crops, a nitrogen reserve
Crop residues left on the field, which are sometimes shredded, return a certain amount of nitrogen to the soil. This can reduce the need to add mineral fertilizers, which means economic benefits with the next crop. This is known as the “green manure” effect. However, nitrogen-return-to-the-soil depends on certain species (especially if legumes are in the mix) and their C/N ratio. If it is too high, it can even cause nitrogen starvation, i.e., nitrogen in the soil is needed to decompose woody residues.
Improving soil structure with intermediate crops
Planting winter cover crops has a positive effect on the structure of the soil. It protects against slaking and reduces erosion. The root development of nitrate-fixing cover crops enhances the soil’s bearing capacity. When the cover crop is destroyed, the organic matter enriches the soil with humus and improves biological activity.
Increased biodiversity in terms of the microfauna, macrofauna, insects, and wildlife is one of the positive consequences of planting nitrate-fixing intermediate crops.
Nitrate-fixing cover crops: a rotation effect on crop protection
By alternating plant families in the rotation, such as nitrate-fixing cover crops, and choosing different cash crop families from one season to the next, it is possible to combat pests. Mustard (crucifer) works well against nematodes. Phacelia (hydrophyllaceae) is also a good option as it does not belong to the same family as any of the cash crops.
Plant a nitrate-fixing cover crop to keep weeds under control
As with pests, planting cover crops that are different from cash crops can limit the development of certain weeds. Nitrate-fixing cover crops can reduce regrowth and weeds by competing with them.
Nitrate-fixing cover crops can also be used as catch crops to provide additional forage for the herd.