Cover crop strategies for intercropping as part of your rotation

Intercropping cover crops can serve a variety of purposes. It may meet regulatory requirements, improve agronomic potential, or increase intercropping production value. Sometimes, a few of these objectives can be met at the same time. But how do you choose the most suitable cover crops from all the species that exist?

Complying with current regulations on intercropping cover crops 

If your main objective is to comply with regulations, you need to be well informed on the rules in force (soil cover, nitrate pollution, etc.). This paragraph gives a general summary of the possible scenarios, but in no way replaces local rules. Are you located in a sensitive area, or subject to specific regulations under the current agricultural policy in your region? Sometimes, only farms in sensitive areas are required to plant cover crops. At other times, current agricultural policies recommend or require that cover crops are planted in non-sensitive areas too. Are there any legal obligations in terms of species to plant? Which are prohibited? Legumes are not always allowed with no-till and direct drilling, for example. They are less effective at fixing nitrates in the soil. Some regulations recommend using them in mixtures or prohibit them altogether.

What to do if it is not possible to seed a cover crop with maize?  

Harvest dates are sometimes too late, or the intercropping period too short, for the biomass to develop properly. If soil cover is an obligation, there are alternatives to intermediate crops in some regions, particularly for maize. As such, it is not compulsory to sow a cover crop, and other practices such as mulching come into play. Mulching covers the field with shredded maize stalks, that are mixed in by ploughing or stubble ploughing just after harvest

example of mulched maize

Choosing cover crops according to botanical families in the rotation 

Taking the previous and following crops into account 

It makes good agronomic sense to choose cover crops that fit in well with the crop rotation. The purpose of a crop rotation is to alternate different botanical species and root systems. This is important in order to fight against pests and weeds by cutting off their development cycle. Species commonly chosen as intermediate crops include grasses, crucifers, legumes and hydrophyllaceous plants.

Intermediate crops that can precede or follow maize and wheat

pea intermediate crop following wheat

As an example, if the next crop is: 

  • Wheat, grass cover crops such as oats, rye, cereal regrowth and moha should be avoided. If there is a risk of take-all, mustard, radish, and rapeseed should also be avoided. Peas and field beans, which are legumes, are perfectly suitable and are beneficial in terms of yield. 
phacelia plant used as intermediate crop preceding maize
  • With maize, do not sow buckwheat (risk of sclerotinia) or Italian ryegrass (risk of regrowth). It is difficult to control Italian ryegrass regrowth with herbicides because it is the same family as maize. In addition, the soil is more likely to dry out if the Italian ryegrass is harvested late.  On the other hand, Italian ryegrass has a positive fertilising effect. Be careful with crucifers too: it's best to destroy them early on as they can have negative effects on maize. On the other hand, legumes such as field beans and peas are ideal for maize crops. Otherwise, you can easily plant phacelia, flax, sunflower or nyger, or even rye, oats, moha, or sorghum.

Choosing the right species according to sowing date

Cover crops should be sown as soon as possible after the previous crop has been harvested. The aim is to give them time to develop and produce as much biomass as possible. Only then will they be able to provide all the agronomic benefits sought (fixing nitrate, increasing organic matter, improving soil structure, and releasing nitrogen when destroyed, etc.). 

Seeding after harvest, before August 15, is possible for most cover crops (oats, moha, ryegrass, rapeseed, radish, legumes, etc.). Some cover crops, such as moha, nyger and buckwheat, must be planted at this time. It is often the case for certain vetches, clovers, and lentils too, and to a lesser extent sunflowers and grass peas. There is still a risk of water and heat stress for these plants depending on soil and climate conditions in the area at the end of summer. It is better to plant white mustard and flax later on, from mid-August to early September. For later planting, oats, Italian ryegrass, rye, and forage turnip are more suitable, but there is no guarantee that they will develop properly due to the lower  temperatures at the beginning of winter.  

Things to consider when choosing your cover crop 

You can use a decision-support grid, based on the factors listed above. 
The first consideration is whether the cover crop is to be used for consumption or for your herd. If so, when will you need the forage? For early winter grazing, opt for cabbage, forage rape, or even Italian ryegrass. For mowing, opt for diploid oats, rye, or triticale + vetch, as well as Italian ryegrass. If needed the following spring, it is easier to mow and make silage with mixtures such as oats, triticale, and rye + protein crops, or even red clover. An Italian ryegrass + red clover mix works well too, with little manure. 

If you don't raise livestock or sell fodder, it's best to think in terms of the benefits for the next crop. If you plan to sow a winter cereal, opt for mustard, phacelia, or buckwheat, etc. If you intend to sow maize, then crucifers, grasses, and phacelia work well. For sunflowers, go with phacelia, buckwheat, oats, or rye. For beet, a good choice is phacelia or buckwheat. These examples are not exhaustive. Local and national organisations can help you choose your cover crops. 
Seeding and crop-destruction methods (shredding, tillage, weeding, etc.) before the following crop can also be an important criterion in your choice of species. These complex subjects are covered in other articles. 

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