Agriculture in Brittany, in the north-west of France, is known for fish, beef, pork, poultry, vegetables and milk. Cover crops are used by farmers of Mauron, and the example described here is from a farm located in Morbihan in the basin known as Ploërmel. In this warm temperate area the average annual rainfall is 650-700 mm with an annual temperature of around 11°C.
There are three types of cover crops included in the rotation. These are selected on the basis of their benefits in relation to soil fertility and fodder production, in order to improve the farm's food self-sufficiency. There are three basic types of cover crops, as follows.
1) “Protein mixes” are composed of 35% faba (broad) beans, 26% oats, 17.5% peas, 17.5% vetch, and 4% clover. These are sown in early October after grass or maize are made into silage at the end of April.
2) "Green manure" cover crops are sown at the beginning of September after cereals, and are composed of various complementary species with the main objective of preserving and strengthening soil life (i.e. worm abundance), and winter feeding of heifers. For example, the commercial "Biomax" mix contains seeds of broad bean, vetch, clover, phacelia and radish. These cover crops are enriched by the presence of approximately 50% ryegrass regrowth, supporting the development of soil life.
3) Rapeseed is sown after cereals as a crop rotation feedstock and are made into silage.
Cover crops are either broadcast and rolled, or direct seeded depending on the conditions of the post-harvest plots. The seed drill used is equipped with discs to minimise soil disturbance as a reduced tillage technique, but more important in this respect is the presence of crop residues (i.e. straw). The seed drill is also equipped with tines.
The cover crops are grazed by heifers in a rotational 2-day paddock set-up. After grazing and regrowth of the ryegrass present, the fields may be left to develop into pasture, or seeded to crops using a minimum tillage drill.
The purposes are:
•Improved production
•Countered land degradation
•Protected watersheds
•Preserved biodiversity
•Adaptation to climate change/extreme events
The benefits are:
•Sustained ecosystem health: no pest and disease problems, good herd health
•Enrichment of the soil by the addition of carbon in organic matter and by the work of earthworms - favouring ecosystem functioning
•Protection of the soil and surface biodiversity because of maintained plant cover
•Increased weed control due to plant canopies and fertilisation effect of green manure
•Planted cover crops used as livestock feed during winter
The challenges are:
•Potential difficulties in establishing plant cover (especially in dry areas)
•Late sowing of cover crops reduces beneficial effects
•High costs of seed mixtures with high protein cover crops
