Horse manure has many uses, not least being just the thing to dump on Jeremy Clarkson’s front lawn if you are concerned about his attitude to global warming, as campaigners did in early September. In the USA you can even subscribe to and immerse yourself in Manure Manager magazine, if you so wish.
Manure mulch on a raised bed
Manure contains a wide range of minerals and nutrients, including large amounts of the three main chemicals that plants need for growth: nitrogen, phosphorus and potassium. It also contains trace elements.
Manure is good for the soil structure. The animal waste and the straw or hay form 'humus' which help the soil to retain moisture and its microbes provide good growing conditions for the roots of the plants, on which their healthy development depends.
Part rotted manure used as a mulch
Horse or Cow manure?
Cows’ digestive systems are more effective than those of horses as they have a number of stomachs. This means that you are less likely to transmit weed seeds to your plot by choosing cow manure. However, for me an even greater consideration is the origin of the manure, since I do not want it to contain anti biotics, and I do not like the idea of intensively reared cattle or them being under cover for more of the year than is absolutely necessary. For this reason I prefer to collect my own from a stable where I can be sure that pesticides have not been used on the grass and where I can see the conditions in which the animals are kept. The risk of weed seeds is, for me, is the lesser of two evils. However, while I have so far avoided the recent outbreaks of contamination, this is not guaranteed, for I understand that stables from where infected manure has originated have blamed the straw or hay rather than their grazing land.
How and when to use manure
Because of the high nitrogen content, which is so desirable, placing fresh manure next to plants can scorch them. This is why fresh manure is best left for a few months until it is well-rotted. Fresh manure generates heat, especially in the centre, so by covering and turning it every week or so the process can be speeded up and the risk of weed transference reduced. Covering is also beneficial since it stops nutrients leaching away with the rainwater.
Some old timers manure their plots in the Autumn, when they dig it over and close down for the winter. However, because this results in the loss of nutrients, it is generally felt to be more efficient and eco friendly to use it in spring when it is spread and forked it in about three weeks before planting,
Well-rotted manure does not smell, it just looks like ordinary soil, except it will probably contain some brandlings ( aka bramblings), the little red worms that assist the rotting down process. Bits of hay or straw should have vanished as they will have rotted down. The length of the process depends upon the air temperature (the higher the faster), the time of year (faster in summer) and the size of the manure heap ( the bigger the better). The larger the heap the more heat is generated in the centre. Ideally the heap should be turned regularly for six months before the manure is ready to use.
How much to use.
The amount you need is astonishingly small, especially when you consider the vast amounts used by some plotholders, largely I suspect because the amount of a trailerload takes them by surprise and they don’t know what to do with it. The DEFRA recommendation for maximum manure application is around 40 tonnes per hectare (10,000 square metres) in any one year. This translates down to one barrow load for about 10 square metres. Using more than this can cause pollution of surface and ground water. I aim to use about a barrow load on each of my raised beds for crops which need it.
This end half rotted, far end well rotted
Which crops benefit from manure?
The simple answer is those which need to attract a lot of water to increase in size: Potatoes like manure and so do concurbits and sweetcorn.
Not only do carrots and parsnips not need manure, they do not even like it. Manure causes their roots to spread out or ‘fang’, not what you want at all.
Legumes – peas and beans – don’t need manure, they are happy to follow on from the potatoes, just as brassicas are content with the nitrogen rich soil left by the legumes.
Aliums – the onion family – will benefit from compost being added but do not benefit from too much enrichment since it is the base of the plant which you want to develop and not the upper foliar part. Over manuring can lead to ‘shanking’, a very thick neck, which makes the onions less likely to store successfully.
In the last year many plotholders have used manure infected with a pesticide which has adversely affected their crops in a number of ways. The use of the chemical aminopyralid is to blame, the manufacturers, Dow Agrosciences marketed the product under the trade name Forefront and Pharaoh. If you are interested in this follow these links.