Manure may be defined as any substance applied to the soil to make it more fruitful a term which may also be applied to fertilizers; so really it is without precise meaning. But we generally think of a manure as a bulky, humus-forming substance that is formed from animal or vegetable origin or in other words, it is a ‘natural’ manure.
Some bulky manures are inconvenient to handle, usually smelly and expensive to buy. So, will we get better plants, more nutritious vegetables and fruit, and do a better job of conserving soils if we use organic manures instead of relying solely on factory made or ‘artificial’ fertilizers that supply plant foods alone? The answer is that bulky organic manures add to the content of organic matter, which plays a vital role in building and maintaining soil fertility. Every time you dig, hoe or cultivate a soil you let more air in. Then the soil organisms become more active and these break down organic matter, which is their food, and soils often lose their structure and become more difficult to work and soils on the sloping ground often erode.
When first applied, the fibrous material opens up all soils making them more porous, better aerated and drained. Small animals and minute organisms break them down and in so doing produce waste products that bind and cement small particles together to form clusters and in some soils porous crumbs. These have large spaces between them that hold moisture yet allow surplus water to run away. The minute spaces within the crumbs hold moisture and plant foods available for plant use. A soil with a good crumb structure does not fall to paste when rained upon nor does it crush easily when cultivated.
Humus is one of the end products of decay. It absorbs many times its own weight of water and this helps sandy soils to hold moisture better—an effect that is most noticeable in dry periods. Close-grained soils, either silts or clays, which tend to pan or are difficult to work, are much improved. Garden compost, farmyard manure and most other organic manures also supply substantial amounts of plant foods—nitrogen, phosphates and potash and many others including trace elements. But being formed from plant and animal residues they differ from most factory-made fertilizers because their nutrients are not in a form that can be used by plants. For example, the nitrogen may be part of a complex protein molecule and as such, it cannot be absorbed by a growing plant as it stands. As the material begins to decay the resident nitrogen in its proteins undergoes a chemical change and is eventually converted into ammonium and nitrate forms that may be absorbed by plant roots. While these forms of nitrogen are exactly the same, whether they come from an inorganic fertilizer or a manure, they are released at a slow and steady rate over a very much longer period. This long-lasting effect is now being imitated in some of the newer synthetic organic fertilizers.
As ‘natural’ manures are long lasting in effect they are not exhausted as quickly as inorganic fertilizers, and generally leave useful residues for crops that follow. This is important to remember when planning vegetable rotations; cauliflowers and many other vegetable crops thrive in soils generously manured with organic manures, while others prefer the residues from a previously well-manured crop—a fact that leads to economy in the use of bulky manures.
Apart from the incorporation of manures in the soil before planting or during the life of the plant these materials are of great value when used as surface mulches. Mulches are like a blanket in retaining moisture. Water vapor from the soil surface diffuses very much more slowly through a loose mulch than it does from the bare soil surface. A wet bare soil can easily lose 1.5cm (1/2in) of rain in a week, whereas a mulched soil will take about six weeks to lose this amount.
Mulches usually allow water to penetrate soils more easily, the raindrops trickle slowly through the fibrous material and do not compact the soil as badly as they do when falling on bare soil. So mulches are of particular value to silty soils that are subject to surface panning through heavy rain. On such soils even a very light mulch will break the force of rain and prevent compaction and, by protecting the surface from exposure to rain, lessen the chance of cracking.
The best-known organic manure is farmyard manure, but rotting plant remains, usually called composts, are manures too, and undecomposed materials like straw may be included. Organic wastes from industrial processes, town refuse and sewage sludges are also offered as organic manures.
All organic manures are not perfect. Some may have a bad effect on plants. For example straw, sawdust and even very strawy farmyard manure. These contain only a very little nitrogen but a lot of carbon and hydrogen, in the form of carbohydrates such as cellulose. But the attacking organisms need supplies of nitrogen while they feed on the carbohydrates and if extra nitrogen is not applied, they will take it from the soil and rob the plants.
This effect can be overcome by adding extra nitrogen to materials of this kind or by allowing them to undergo a partial decay before they are mixed with the soil.
Farmyard manure (FYM) Foldyard manure and dung are names used to describe a mixture of the excreta of farm animals and the straw or other litter used in yards or stalls to absorb the
urine and to keep the animals clean.
If you live in a livestock-producing rural area it is easy to get a load of manure delivered to your garden. The average 3-ton lorry usually holds about 5 cubic meters (yards) of manure which is sufficient for about 500 square meters (yards) of soil so that may be too much for your garden and it is necessary to share the load with a neighbor; a cubic yard weighs anything from 10 cwt to 15 cwt according to the amount of straw contained and the age of the manure. The main trouble, of course, is getting the manure into your garden. You need a gate at least 2.1m (7ft) wide for lorry or tractor and trailer access otherwise the manure has to be dumped outside the garden and barrowed in rapidly to prevent it from becoming a nuisance to passers-by.
Town gardeners are hindered by the problems of access and the high cost of transport. Even so, many town gardeners do buy FYM, either directly through manure contractors or through garden centers. Composted farm manures that are sold in bags are an obvious alternative to the fresh bulky material direct from the farm.
Quality Like all organic manures farmyard manure can vary in many ways from load to load, in contrast to inorganic fertilizers that have a fixed and definite composition.
The type of animal producing the dung has a big effect on quality. The dung (the solid excreta) of horses is the richest in all nutrients and it is drier than that of cows or pigs, so that the bacterial changes during rotting are much more rapid and a greater amount of ammonia is produced. Horse manure when stacked soon begins to steam showing that fermentation is going on; so it is called a ‘hot’ manure, specially suitable for mushrooms and for greenhouse work.
Pig dung is the next richest, followed by cow dung; both of these are much wetter than horse dung and in consequence heat up more slowly and are referred to as `cold’ manures.
So far as nutrients are concerned, farmyard manures are weak; for example you need about 25kg (50lb) of horse manure to supply as much nitrogen as there is in .5kg (1lb) of sulphate of ammonia. The average analysis of most farmyard manures is about 1/2 percent nitrogen, 1/4 percent phosphates and 1/2 percent potash. All animal manures contain in addition useful amounts of magnesium and calcium and are very good suppliers of trace elements, together with other substances which are believed to have growth-promoting properties.
Quality also depends upon the kind of litter used for bedding. The most commonly used litter is straw, which absorbs about three times its own weight of urine and of course provides additional humus-forming matter. Peat moss is an even better absorber of urine and makes a manure which is easily spread and mixed with the soil. Sawdust and wood shavings are poor absorbers of liquids and are very slow to break down in the soil.
Benefits of manure In view of the foregoing you may well think that in a space age it is an archaic practice to use farmyard manure at all. But the results of experiments with good quality products show that it is the yardstick for comparing all other organic manures. In addition to its content of plant nutrients it is a humus supplier and for every ton you buy you will get about 3 to 5 cwt of organic matter which soon becomes humus in the soil and gives all the benefits associated with humus. It supplies its nutrients in a slowly available form and, therefore, has a long-lasting effect; the benefits of a single dressing can last for 3 or more years.
Using farmyard manure If you have some ground ready when the manure comes in, you will lose less of your manure by digging it in right away; but it is often a question of getting a load when you can and storing it until the ground becomes vacant. If you buy a ton of manure now, you will only have about
a ton in six months time because the microbes change parts of the manure into carbon dioxide and ammonia gases which blow away in the wind; nutrients are also washed out of the manure during heavy rain, forming the brown liquid which you often see round the bottom of a dung heap.
While in the heap it is best kept under cover and always kept trodden down tightly to exclude air, and if the drainings can be collected in a bucket or tank a great waste of precious plant nutrients can be avoided.
In very dry weather, moisten the heap periodically. By stacking fresh manure straight from the stable or piggery for a few months the product is improved; you get a better balance in nutrient content, the nitrogen part becomes slower-acting and is less likely to burn seedlings or the delicate roots of tender plants. The well-rotted manure is much easier to spread and mix in with the topsoil. You can tell if it is well rotted by the absence of unpleasant smell and even texture of the product—the straw part will no longer be recognizable. Fresh manure is much more difficult to spread and mix; if you intend to sow or plant soon after an application you have to bury it deeply otherwise it interferes with plant bed preparations.
Deeply buried manure does not give the best results; ideally it is spread on well-broken soil and then worked in to a depth of 7 or 10cm (3 or 4in) with a cultivator, then turned with a spade or fork. Take care not to turn the soil completely upside down, but rather at an angle wide enough just to cover the surface material. Manure covered with slabs of wet soil merely prevents humus formation. By mixing it with 7 or 10cm (3 or 4in) of topsoil, hard crusts which prevent seedlings from pushing through easily, are obviated. To do any real good to soil that is low in humus it is essential to cover the soil with a layer thick enough to obscure the soil beneath it; this will need at least 5kg (101b) of well-rotted manure per square yard. For vegetables this is done every 3 years before you plant crops such as brassicas that respond to generous dressings of manure.
Well-rotted farmyard manure can be applied at any time of the year before sowing or planting, but fresh or ‘long’ manure as it is called, is best dug in during the autumn or early winter so as to allow it to break down and lose its caustic nature in time for spring plantings.
For mulching during the summer the manure is useful for suppressing weeds and retaining moisture; when dug in at the end of the season it adds to the humus content of the soil.
Since large dressings of farmyard manure supply appreciable amounts of plant nutrients you can reduce your fertilizer dressings by half if 5kg (10lb) of well-rotted farmyard manure per square meter (yard) has been added.
Composted manures There are a number of products derived from fresh animal manures that are sold in bags under brand names. Large heaps of the fresh manure are allowed to decay under cover for several months during which time the coarse material is broken down and the heat of decomposition drives off much of the moisture.
The resultant dark brown spongy manure is applied at the rate of 180-240g (6-8oz) per square meter (yard) and is lightly forked in or mixed with the topsoil by means of a rotary cultivator.
These products are clean and convenient to handle.