My Green manures are kept in a tin in the allotment shed and they are always sown insitu and currently I don't have a clue what I have left. Note to self do Green Manure audit when next on the plot.
Green manures are usually sown in late summer
or autumn and mop up any nutrients, preventing them being washed away by winter
rain. When dug in the following spring, they release these nutrients back into
the soil. Winter grazing rye and winter tares are hardy green manures that will
carry on growing all winter before being incorporated back into the soil in
spring.
Green manures can also be used to cover bare patches of soil in the
spaces between crops, or during intervals between one crop and the next.
Fast-growing mustard sown before mid-September can be incorporated in October,
for example, or the frosted remains left as mulch.
Summer-grown green manures such as buckwheat and fenugreek form dense foliage that will effectively suppress weeds.
Green manures belonging to the pea and bean family (legumes) have the additional capacity of storing (fixing) nitrogen from the air to their root nodules, but only in summer. Nitrogen is a valuable plant nutrient.
Other benefits of green manures include protection of the soil surface from compaction by rain and shelter for beneficial insects such as ground beetles.
How
to use green manures
- Sow seeds in rows, or broadcast them across the soil and rake into the surface
- Once the land is needed for cropping, chop the foliage down and leave it to wilt
- Dig the plants and foliage into the top 25cm (10in) of soil After digging in, the site should be left for two weeks or more before sowing or planting out as decaying green materials can hamper plant growth
Cultivar
selection
Alfalfa (Medicago
sativa): This perennial legume can be dug in after two or
three months or left for one to two years; sow in April to July; good for
alkaline soils. Nitrogen fixing may only occur if the seed is inoculated with
nitrogen fixing bacteria prior to sowing.
Alsike clover (Trifolium
hybridum): This perennial legume can either be dug in after
two or three months or left in for one or two years; good for wet, acid soils;
sow in April to August.
Bitter blue lupin (Lupinus angustifolius): This
perennial flowering legume suits light, sandy, acid soils; sow in March to June
and leave for two or three months before digging in.
Buckwheat (Fagopyrum
esculentum): This half hardy annual will only grow in spring
and summer best sown in April to August, it can be left for two or three months
after sowing; grows well on nutrient-poor soils.
Crimson clover (Trifolium
incarnatum): This perennial legume is good for light soils; sow
in March to August and leave in for two or three months up to flowering.
Essex red clover (Trifolium
pratense): This hardy perennial legume overwinters well and
can be left in for two or three months or for one or two years after sowing;
good for loamy soils; sow March to August.
Fenugreek (Trigonella
foenum-graecum): This annual legume will only grow in the spring
and summer; it is unlikely to fix nitrogen in the UK.
Grazing rye (Secale
cereale): This annual crop is good for soil structure and
overwinters well; sow in August to November and dig in the following spring.
Mustard (Sinapis
alba): This annual crop from the brassica family should
not be followed by other brassicas, as it could encourage build-up of the
disease clubroot; sow in March to September and leave for two or three months
before digging in.
Phacelia (Phacelia
tanacetifolia): Later sowings of this annual crop may overwinter
in mild areas, but it is generally best sown in April to August and dug in
after two or three months; its flowers are very pretty.
Trefoil (Medicago
lupulina): This legume can be annual or biennial and overwinters
well but needs light, dry alkaline soil; it can be dug in after two or three
months or left for one or two years after sowing; sow in March to August.
Winter field bean
(Vicia faba): This annual legume can be left for two or three
months after sowing (up to flowering) and is good for heavy soils; sow in
September to November.
Winter tares (Vicia
sativa): This annual legume is hardy and overwinters well,
even in heavy soils; sow either in March to August and leave for two or three
months before digging in, or sow in July to September for overwintering.
Problems
A dense carpet of green makes
a perfect environment for slugs and snails so control measures may be needed after green
manuring.
Decaying green manures can
suppress plant growth, so allow at least two weeks between incorporation and
planting or sowing.
Club Root can be a problem with green manures in the cabbage
family such as mustard.
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