CALU PRESS RELEASE – 10/06
Green manure
usage in horticultural production
The latest in CALU’s series of horticultural technical leaflets looks at
the use of green manures, particularly in horticultural systems. Here
Green manuring involves incorporation into the soil of any field or forage crop while it is green or soon after flowering, for the purpose of soil improvement. Green manure crops are not produced for sale but rather for the benefits they provide for the production of subsequent cash crops.
They are used in many cropping situations and are an integral part of organic growing. They are grown to conserve, accumulate and recycle organic matter and plant nutrients; to improve soil fertility and structure; and to assist in the control of weeds, pests and diseases. The use of green manures is particularly important in horticultural systems where vegetable growing is demanding on the soil in terms of both nutrient depletion and deterioration of soil structure.
The key to the profitable and effective use of green manures is to take advantage of those windows of opportunity when they can be grown to maximum advantage within the rotations. Firstly you have to decide what you want the green manure to do, are you looking for nitrogen fixing, rapid growth, winter or summer, shade or full sun, annual or perennial, what will be planted there next and does it need to have fringe benefits for, example, flowers to attract insects. Consideration should also be given to specific conditions on the farm or holding, in particular soil type, water availability, crop sequencing and cultural practices. There may only be a couple of species suitable.
Although traditionally used in agriculture as a winter cover there are many options in the use of green manures. A summer green manure can be used to fill a niche in crop rotations or simply to fill a gap before a late sowing of crops (Phacelia or mustard). Undersowing green manure into an already established crop is a way of getting ahead of the traditional winter green manure (red clover, vetches). Interplanting is where the green manure and vegetables grow together in the field for all or part of the growing season in order to extend weed control and other green manure benefits (yellow trefoil, clovers). Finally, green manures used as a fallow provide the best rotation benefit in terms of resting the land from cultivation (clovers and cocksfoot).
More details on the use of green manures including varieties can be found in a CALU Technical leaflet. All CALU’s technical leaflets are available at www.calu.bangor.ac.uk or telephone 01248 680450 to request a copy by mail.