Green Manures booklet - Institute of Organic Training and Advice

8. Glossary of terms
Legume is any plant in the leguminosae family. This includes lupins, clovers, vetches, peas, trefoils and
many others. Under appropriate conditions, most of these will fix nitrogen in association with
Rhizobium bacteria (see N fixation).
Green manure refers to any short term crop grown primarily to add nutrients and organic matter to the
soil. It is usually grown for a fixed term before being incorporated.
Cover crop is grown primarily to protect and improve the soil during time when it would otherwise be
vulnerable to erosion.
Alleochemicals are chemicals released by plants that suppress the growth of other species
Alleopathy is the suppression of one plant species by another through the release of inhibitory substances.
Leaching is the loss of water soluble nutrients from the soil through rain or irrigation.
Rhizobium is a genus of bacteria that forms an association with the roots of legumes in nodules and fixes
nitrogen.
N fixation is the process of converting nitrogen (N2) from the air into biologically useful compounds. It is
carried out by Rhizobium bacteria in association with the roots of leguminous species
Mineralisation is the conversion of a mineral (e.g. nitrogen) from an organic form to a mineral form (e.g.
nitrate). In this form it is more readily available to be taken up by plants but also more prone to being leached
out of the soil.
Deposition is the conversion of gaseous elements from the atmosphere into biologically useful forms in the soil.
Denitrification is the conversion of nitrates in the soil into gaseous nitrogen in the atmosphere. It is carried out
by denitrifying bacteria.
Mineral nitrogen is nitrogen in inorganic soluble forms (nitrate or ammonium). In this form it is more readily
available to be taken up by plants but also more prone to being leached out of the soil.
Immobilisation is the conversion of a nutrient to an unavailable form through uptake of the microbial
population
Glucosinolates are organic compounds found in brassica species. When plant tissue is macerated, glucosinolates
are converted into isothiocyanates which are thought to have biocidal properties against pests, pathogens and
weeds.
The use of green manures
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