Types of Green Manures and Uses
Long term green manures. Usually established for two or three years where considerable organic matter and fertility building is required. They are normally cut monthly during the summer period and mowings/ clippings allowed to remain on the surface as a mulch. Such green manures may be pure clover if nitrogen fixation is a priority or a grass/clover mixture if organic matter build up is also important.
Winter green manures are usually sown in the autumn and incorporated in the following spring. They can be a good way of fitting a fertility building crop into a rotation if they can utilise land that would otherwise be bare. They need to be established early enough to do any good; if harvest of the preceding summer crop is delayed they may be more difficult to establish to be of any benefit. They can be legumes e.g. vetch, but a major use for this class of crop is to minimise nitrogen leaching; when used for this purpose they are often called winter cover crops.
Summer green manures are usually legumes grown to provide a boost of nitrogen in mid rotation. They may be grown for a whole season from April to September or for a shorter period between two crops. These shorter-term green manures can include non-legumes such as mustard and phacelia.
Green manures may also be used in intercropping systems or undersowing – this a way of providing addition Nitrogen during a crops growing period, aiding weed control and helping to prevent soil erosion. It is mainly used in Brassica crops and is sown once the crop is well established and growing well.
Greenhouses and Polytunnels Offering warmer temperatures throughout the year it is possible to sow ‘summer' green manures at any time of year allowing for the crop to be established and benefiting the soil during times it may be left fallow.
Green Manure & Bio-fumigation – Caliente Mustards have been shown to be a good green manure and an equally good bio-fumigant when incorporated into the soil at the correct time. They offer control for the suppression of weeds, soil nematodes and a range of soil-borne diseases.