Green manures

I have been using grazing rye as a green manure for several years now. My soil is mostly a sandy clay and obviously fairly easy to work once it has been knocked into shape. Grazing rye comes up in thick soft leaves that easily shade out most weeds.  It also has a very thick mat of fibrous roots.  The advantage of this grass is that it rots down very quickly in the soil.  

Green manures, whichever you use, are useful for a number of different reasons.

• They cover the ground in winter so that nutrients are not washed away by the winter rains.
• They shade out weeds that might germinate during the autumn and winter.
• They add organic matter to the soil which eventually rots down to form humus.  Humus is a black oily sticky liquid that forms films around soil particles. 
• They help to recycle nutrients in the soil.  
• If you use one of the plants from the legume family like tares, clover, field bean or lupin then they will add nitrogen to the soil when you dig them in.  Remember that root nodules formed by the rhizobium bacteria help to fix nitrogen and pass it to green plants.  The nitrogen is therefore in the leaves,  stems and roots of the plants.  If you do not dig in all the plant then you will loose some of the fixed nitrogen unless you put the tops onto the compost heap.  If you burn the tops then you are loosing the nitrogen to the air. 

I dig it into the soil in the spring before planting or sowing seeds.  

You don't need to worry about introducing a weed onto your allotment because the only way that rye grass spreads is by seed and whether you dig in or strim you will not get seeds.  It does not have stolons like couch grass.   I sometimes mix it with tares or clover when I am sowing, although grazing rye does tend to shade these plants out as well.