Composts and Fertilisers

Organic gardening requires a very high level of soil fertility, which equates to continual inputs of large quantities of humus. The most economic source of humus is compost made on site from raw organic materials; crop residues, sawdust, animal manures, hay, seaweed, in fact anything that was once living tissue. Composting is the controlled decomposition of the raw material and there are four main methods:

  1. Aerobic composting
  2. Anaerobic composting
  3. Vermicompost
  4. Sheet composting

All four methods require similar preconditions for success. There must be a source of cellulose (carbohydrate for energy), protein (the nitrogen source), lignin (the raw ingredient for humus formation) and water. The carbon to nitrogen ratio must be between 25:1 and 35:1. If there is insufficient nitrogen, the process will be too slow. If there is an excess, you will lose nitrogen in the form of the gas ammonia, readily detected by your nose.

Aerobic Composting

Aerobic composting is far and away the most popular method. It has a number of advantages, chief of which are rapidity and the development of heat sufficient to kill many weed seeds. The raw materials are placed in layers in a compost enclosure 1 - 1.5 metres square, or commercially in a windrow 1.5 - 2 metres wide and 1.5 - 2 metres high. The length is as long as is convenient. The layers should be 25 - 50 mm thick and wetted to the consistency of a well wrung-out sponge. That is, squeezing a handful tightly, one gets the impression water is about to drip from it. If it drips, the material is too wet.

A traditional recipe is one-third animal manure, one-third fibrous material such as straw and one-third wilted green material. A comprehensive description of ingredients and their relevant properties is at the end of this chapter. The heap is initially invaded by the white hyphae of the fungi responsible for breaking down cellulose to simpler carbohydrates, the fuel for the thermophilic (heat loving) bacteria that subsequently take over. The temperature in the heap then rises to as much as 65C.

The compost heap should be protected from rainfall, or it is liable to become too wet. While a covered area would be ideal, this is generally considered too expensive. Polythene covers of various sorts are used, but this reduces the flow of air into the heap, so they need to be put on only in wet weather. Straw thatch allows air to enter and sheds water. When the straw becomes unusable for this purpose, it is incorporated in the next compost heap.

When the temperature of the heap begins to fall, the heap is disassembled and rebuilt, placing the material that was on the outside of the previous heap on the inside of the new heap. The temperature rises again to around 60C and this ensures any undesirable organisms such as weed seeds, or antibiotics are destroyed.

Turning the heap frequently to produce finished material as soon as possible is called the Berkley Method. Turning the heap once, or twice only, the Indore Method.

The material can be used when the original ingredients are only barely recognisable. However, when the material is left for up to twelve months to mature, the humus is more stable and long-lasting in its effect. In practice, we all use much of our compost before it is fully mature. Some composters believe that the compost is superior when the heap is run at the lower temperatures of 35-40C. This would only be workable where there were few weed seeds to cause later problems. One notable common seed that survives the 60C compost heap is that of white clover.

The temperature of the heap is controlled by altering its air content. Less air lowers the temperature - more increases it. Excessive temperatures caused by insufficient moisture can lead to scorching, or even burning of the material. Air content can be increased by inserting a perforated pipe through the centre of the heap, with, or without an air-blower attached. Decreasing air content is achieved by compressing the layers as they are built up. Improving aeration at the bottom of the heap, compacted by the weight of material above, is achieved by using coarser material for the base, or even a simple brush filled trench.

Excessive dryness is indicated by excessive heat. Excessive wetness is revealed by the fouls smells of anaerobic fermentation. Excessive nitrogen content is revealed by the evolution of ammonia, insufficient nitrogen by the low temperature achieved. While it would be entirely possible for you to use tables of nitrogen and carbon content of the various possible materials used in compost, I know of no one other than scientists who would bother. In practice, we all use a restricted range of materials and learn the correct ratios by trial and error. Making excellent compost is as much an art as it is a science.

While there is a wide range of compost-inoculants/activators on the market, they are almost all next to useless. The spores of the bacteria and fungi required are present everywhere, especially in the soil the heap is built on. One way to test the need for them is to build one heap from raw ingredients alone and one inoculated with some finished compost and comparing the results. I did run a trial of composting chicken manure with sawdust using the Biodynamic compost preparations. Using them definitely decreased the time required to finish. However, that would only be an issue if you needed to use the compost before allowing it to mature. As to the "special" properties of Biodynamic compost, I am not yet convinced.

A compost heap that should be progressing rapidly, but is sluggish, could be for the following reasons. If the weather is very hot, the flow of air through the heap is probably too slow. Cold air outside the heap allows what is called the chimney-effect to draw air through the heap as the hot air within rises. The other possibility is that the ingredients are too acid. If the ingredients you regularly use fall into this category, you should dust some of the layers with very finely ground limestone, much as if you were dusting a cake with icing sugar. It is not necessary to use builders' lime (calcium hydroxide); it is rapidly converted to limestone (calcium carbonate) in contact with moisture and carbon dioxide, which are abundant in the compost heap. Do not apply the limestone directly on the animal manure, you will convert the nitrogen content to ammonia, with the distinct probability it will be lost to the atmosphere.

Compost making is probably the most energy-consuming task for the market gardener and design of the compost area calls for some planning to make it easier. If possible, the raw materials should be accumulated at the top of a slope. The heap assembled immediately below and the rebuilt heap below that. This allows gravity to assist us. On a large scale, a scoop mounted on the front of a tractor would appear to be essential. While purpose-built machines for composting exist, they are very expensive.

Since the speed of decomposition of the component materials in the compost is dependent on their surface area, shredders are often recommended to pre-process the ingredients. The shredding of materials such as tree branches and cabbage stalks is probably economically justifiable if there is a sufficient amount. In any event, a heavy-duty shredder is more likely to pay for itself than the home garden variety. If you feel you need such, you are probably already using a tractor and this makes the sort run from the tractor's p.t.o a better proposition. Personally, I have never used a shredder, nor have I seen one outside of demonstrations by the sellers of the equipment.

In the home garden, cabbage, broccoli and Brussels sprouts stalks are mashed flat with a heavy hammer, or the back of an axe blade.

Anaerobic Composting

It will surprise many people, but the centre of an aerobic compost heap becomes anaerobic within minutes of assembly. All the oxygen is used up. However, the aerobic portion migrates toward the outside and some part of the heap is always decomposing aerobically. Anaerobic composting is decomposition of all the ingredients in a complete absence of oxygen. This leads to foul smells, so it is just as well that the elimination of oxygen requires sealing the material within a container. Anaerobic composting proceeds much slower than aerobic as the temperature rise in aerobic composting requires an oxygen supply for the thermophilic bacteria.

Having said all this, you may wonder why we are discussing anaerobic composting at all. The special purpose where you may decide to compost anaerobically is when you want the methane gas that evolves for fuel. This I have never done personally, so I do not propose to do more than indicate it as a possibility. The finished material has higher nitrogen content than aerobic compost, but it still needs processing through an aerobic compost heap to stabilise the nitrogen compounds as protein.

Vermicomposting

This imposing word merely means the use of manure earthworms to turn your raw materials into compost. Certain materials, such as sheepskins, are difficult to process any other way. Unlike a conventional compost heap, the materials are generally placed in a container that is vermin-proof. This is a cold-composting process, so the heat generated in a conventional heap is not available to prevent vermin from invading. It is also wise to include a method of preventing the escape of the earthworms, which they are prone to do if you are not spot-on with the provision of ideal conditions for them.

My vermicompost unit is a discarded bathtub with some mesh over the plug-hole. Earthworms require the ingredients to be somewhat wetter than in a normal compost heap, so the volume of material must be considerably smaller in cross-section to prevent the anaerobic condition worms will not tolerate. As well, careful attention to pH is required as earthworms dislike acidity intensely. Frequent additions of lime are generally required. Two materials that worms will tolerate only small amounts of are citrus peel and onion scraps.

The vermicompost unit should be placed where it will remain between 15 and 25C. Worms will not tolerate temperature extremes. Light is another enemy of earthworms, so a lightproof cover is required.

A fully functioning vermicompost unit will process the addition of approximately 25 mm of fresh material per week. To access the finished material, the fresher material on top is pushed to one side and the worm-casts removed. This material is an effective amendment to the soil at a considerably lesser rate than ordinary compost.

Sheet Composting

In sheet composting, the raw ingredients are spread over the area you wish to compost. The total thickness of the material should be no more than 300 mm, or it is difficult to wet thoroughly. If it is less than about 200 mm, it is difficult to maintain at a high enough moisture level. While it eliminates double-handling of materials, it is harder to manage than aerobic composting in a heap. Decomposition is slower, as less heat is generated. Weed seeds can also be a problem. In market gardening, it is most likely to be used at the beginning, before the beds are raised.

Compost Ingredients

One of the most important ingredients for compost is protein (for its nitrogen), as it is the most expensive. Many gardeners believe that the disease resistance of crops is due to animal protein rather than vegetable protein in the compost, others disagree. Nevertheless, animal manures are a staple ingredient in most compost heaps.

Blood'n'bone

Despite its popularity in the home garden, it is difficult to justify the expense of what would otherwise be an excellent source of phosphorus, calcium and nitrogen. The problem is, it is such a valuable protein source for poultry and pigs and this generally keeps the price too high.

Cottonseed Meal

This is an excellent nitrogen source if you can get it.

Cow Manure

This is rated second only to horse manure in value for the compost heap, though The Git rates it above all other manures. It is just as fibrous as horse manure, but is lower in nitrogen content. In the paddock, it retains much more of its nutrient content than horse manure. Biodynamic practitioners would not dream of making compost without it.

Fish

Fish, like seaweed is full of trace elements. Fresh fish is best, rotten fish smells deplorable, but it's just as good for the compost heap. Dehydrated fish-meal is expensive. Liquid manure made from any fish you can get is probably a better use than in the compost heap. Commercial fish emulsion (liquid fish) is too expensive to use as a compost activator.

Grass Clippings

Grass clippings from lawns are a good source of nitrogen. They have a tendency to form a slimy, impervious mat if layered too thick. Keep layers of grass clippings no more than about 25 mm thick.

Hay

On the surface, hay looks like an ideal compost ingredient. It is high in fibre and lignin, and has significant protein content. However, much hay is made with grasses at the seeding stage, so weed seeds are a very real potential problem. I have used hay extensively, and with care, it has been invaluable. Lucerne hay is much less of a problem in this regard, and it has higher protein content than grass hay. In districts where a second hay cut is taken, the second cut contains far less seeds.

Horse Manure

Horse manure is very high in both fibre and nitrogen content as horses are very inefficient users of the nutrients in their food. A good source of horse manure is from racing stables. As very high protein diets are fed to racehorses, the manure is also highest in nitrogen. The manure will in all likelihood come already mixed with fibre of some sort, generally sawdust, or wood shavings. Care must be taken to ensure it is not contaminated with wood preservatives, such as copper-chrome-arsenate. Horse manure is generally rated number one for market gardening.

Human Manure

It is illegal to use human manure in compost used to grow food for human consumption, due to the possibility of contamination with several intractable human diseases. This doesn't stop people from using it. With care, long periods of decomposition, and attention to where it's used, under trees for instance, they seem to experience no difficulties.

Leaves

Most tree leaves are low in nitrogen and high in tannin, which slows decomposition. Use only moderate amounts in compost, or let them decompose in their own heaps without additives for two years or so. The resultant material, called leaf mould, is an excellent substitute for peatmoss. Eucalypt leaves contain oils and other substances that render them much less useful than European deciduous trees, so treat them with caution. Pine needles contain terpenes, the raw ingredient for turpentine, so use them sparingly, if at all.

Paper

Newsprint contains cellulose and lignin, so it is a better bet than higher quality papers. Paper should be shredded before use, to prevent it forming impervious layers.

Pig Manure

Pig manure is considered little better than poultry, as it is devoid of fibre. Past pig-farming practice was to include a copper supplement to make the pigs grow faster. As a consequence, pig manure often had an excessive copper content. Caution is advised.

Poultry Manure

Like horse manure, poultry manure is rated as "hot". That is, it is very high in nitrogen. Unlike horse manure, it is devoid of fibre, which is why market gardeners generally rate it last in the list of desirable animal manures. However, my garden has thrived on compost made from chicken deep-litter (poultry manure mixed with sawdust) and crop residues. Poultry manure is generally free of weed seeds. Antibiotics are a common additive to poultry diets in modern intensive units. As they are very unstable compounds in an aerobic compost heap, they generally are not a problem.

Sawdust

Sawdust gets a pretty bad press in gardening circles. However, it is a great source of fibre and lignin. Softwood sawdust contains terpenes and resins that are growth inhibitors, so we have only used eucalypt hardwood sawdust. Sawdust from workshops may contain synthetic glue residues, so we have always used sawmill waste. Sawdust from decades old heaps is nearly all lignin, but it is generally wet and therefore harder to move than dry, green sawdust.

Seaweed

Seaweed contains neither cellulose, nor significant nitrogen. Nevertheless, it is an important ingredient in gardening. It is full of trace elements and a moderate source of potassium. If you are lucky enough to be near the seaside, you can collect the material yourself. Bull kelp is said to be the best. Unfortunately, wet seaweed is nearly all water. Seaweed for sale is dehydrated. We have used both and the convenience of seaweed meal outweighs the inconvenience of heavy, wet, smelly seaweed half an hour's drive away.

Analysis of kelp meal by Mount Pleasant Laboratories of Tas. Dept. Of Agriculture. File H047. Lab. No. 20172.

Nitrogen 0.750%
Sulphur 0.695%
Phosphorus 0.196%
Zinc 88.3 ppm
Potassium 1.36%
Boron 70.0 ppm
Calcium 1.08%
Iron 53.9 ppm
Magnesium 0.882%
Manganese 61.5 ppm
Sodium 2.93%
Copper 2.50 ppm

Sewage Sludge

This otherwise excellent source of nitrogen is often contaminated with heavy metals due to sewage and stormwater sharing the same drains. As we become more aware of the waste of this resource, the situation is likely to change.

Sheep and Goat Manure

To all intents and purposes, sheep and goat manure are the same material. It is fibrous and moderately endowed with nitrogen. When we kept goats, my wife made perfect compost on her first attempt from goat manure mixed with hay. Due to their dietary habits, these manures are nearly always full of undigested weed seeds, so careful attention to turning the heap to kill them is required.

Straw

This is a major source of fibre and lignin. Except for legume straw, it has virtually nil protein content. Seeds are rarely a problem in straw. Cereal straw contains substances called mucins that act as a glue to improve the stability of soil crumbs.

Vegetable Scraps

Your market garden will produce an abundance of material unsuitable for sale; leaf trimmings, pea haulm etc. This material is best wilted to accelerate decomposition.

Weeds

Weeds are wonderful accumulators of various trace elements. Before incorporation in the heap, they need to be wilted, or they take longer to break down. Weeds at the seeding stage can be a source of weed contamination if they are not heated sufficiently, or if their seeds can tolerate compost heap temperatures. For instance, wild white clover seeds can survive 65C.

Wool

We compost all the loose bits and dags following shearing our sheep flock. Wool is an excellent nitrogen source.

Using Compost

As referred to earlier, compost can be used when the original ingredients are only just barely recognisable. Compost at this stage is far from fully humified, and the nitrogen content is still susceptible to leaching by rainfall and irrigation. Consequently, it is best used on crops that are greedy feeders, such as corn, cabbage tribe, pumpkins, lettuce and potatoes. As compost matures, it turns into a black, colloidal material in which none of the original components are recognisable. This material will last longer in the soil and is required for seed-raising mixtures.

In practice, we all use some compost before full maturity, even though we would prefer not to. The amount required depends very much on the fertility of the soil, its type and the crop. Sandy soils require heavier and more frequent additions than heavier soils. Some crops abhor fresh compost, particularly carrots which fork. Peas and beans require little if any compost in the average garden; they are usually more than happy with what's left over from the preceding crop. Onions, like carrots, peas and beans, prefer to subsist on the compost residues from a previous crop.

A reasonably fertile loam to heavy soil will need about 25mm of compost preceding a heavy feeder. This amount can be increased with benefit; there is none of the toxicity problem with overfeeding that can occur with artificial fertilisers. Availability is more of a factor than overfeeding when using compost. Compost is unique in that it allows plants to take nutrients as they are needed and usually at the rate they require.

Compost consists of living organisms, mostly microbes that are readily killed by sunlight. Consequently, it is somewhat wasteful to use compost as mulch. It is best lightly tilled into the top 100mm of soil for its optimum benefit to be realised.

Producing Your Own Compost Ingredients

We have produced our own hay, goat manure and chicken manure. Goat manure is convenient due to the habit of goats defecating in the sheds they require for shelter from inclement weather. As well, they are very wasteful of hay and this becomes mixed with the dung. It is unfortunate that goats spend 95% of their intellectual abilities planning the best way to invade your garden.

We kept chickens for eggs in a shed on sawdust during the morning, allowing them free-range in the afternoons after they had finished laying. The shed was cleaned out once a year in the summer and this material was our profit margin, due to the low price for eggs and the high price of wheat at the time.

We would like to establish a paddock of lucerne, far and away the best fixer of atmospheric nitrogen, but our soil is too heavy. We plan to try cow grass, a heavy yielding red clover, one of these days. We do grow comfrey and stinging nettles, both being of inestimable value in compost and liquid manures as well as compost ingredients.

Home Made Liquid Fertilisers

Some organic practitioners are very much against the use of liquid fertilisers, either as soil drenches, or as foliar applications. The nitrogen in liquid manures is much more available than in regular compost and so is more akin to artificial fertiliser. They dislike foliar applications of fertiliser on the grounds that plants were designed to absorb nutrients through their roots, not their leaves.

The first point is an important one. It is entirely possible to replicate the disadvantages of artificial fertilisers with either raw animal manure, or liquid organic fertilisers. However, soil drenches of highly diluted material have effects far beyond the analysable nutrient content.

The second point is really ideological. If plants were not designed to absorb nutrients through their leaves, then it would not be possible for them to do so. Some plants, notably Spanish moss, have no roots in the soil and clearly make a living from atmospheric nutrients. In any event, what we apply as foliar feeds are nutrients in vanishingly small amounts. We do this not to supply the plants' needs for major nutrients, but for trace elements and the effect of these nutrients on certain micro-organisms that live on the leaves of crops and protect them from undesirable fungi and frost.

Liquid manures are easily prepared from the ingredients by steeping them in water for a period of several days to several weeks, depending on their nature and air temperatures. On a small scale, the best vessels to use are plastic 200 litre drums with the tops cut off. Make sure that the drums you get were not used to store toxic materials. Plastic has pores that tend to hold on to the materials that were stored in them. Steel drums are useless, as they rapidly corrode, and the iron goes into solution.

Loosely woven bags to hold the ingredients are useful to avoid later filtration, but require regular squeezing to ensure complete decomposition. The foul smells of anaerobic decomposition are reduced by regular vigorous stirring to incorporate air, which drives off the smelly nitrogenous compounds. This also, incidentally, reduces the nitrogen content, which somewhat takes away from the argument of the anti brigade. The inclusion of chamomile is also said to reduce bad odours.

In use, the material is strained to remove particles that could block application equipment, and diluted as required. Some materials, notably seaweed, are noticeably more effective at a dilution rate of 1000:1 than at 50, or 100:1. The optimum rates will need to be determined by trial and error, there having been little formal research. In any event, the ingredients you use are hardly likely to be consistent with those used by others, or even from season to season.

Comfrey and Nettles

We use a mixture of comfrey and nettles, for the stimulation that nettles provide plants growing sluggishly in cold spring soil and the potassium content of the comfrey. We fill the drum with equal parts of both and top up with water. It smells very much like pig slurry - awful! However, we find it of great benefit as a soil drench, particularly for tomatoes.

Animal Manure

Fill a bag with animal manure and steep in the drum of water, squeezing daily for three to five days. Dilute and use as a foliar application to combat fungal disease. It is also useful as a side dressing, or pre-plant soil drench.

Compost

Fill a bag with finished compost and steep in the drum of water, squeezing daily for three to five days. Dilute and use as a foliar application to combat fungal disease.

Fish

Home made fish emulsion smells even worse than comfrey and nettle. As a consequence, we use a better smelling commercial fish product (see below).

Seaweed

Liquid seaweed is the single most popular liquid fertiliser. It contains substances, such as abscissic acid, the plant hormone that tells deciduous trees to drop their leaves. This material is implicated in seaweed's ability to confer disease and frost resistance to crops. Seaweed also contains plant growth hormones that influence cell elongation and division. To cap all this off, it also contains the full range of trace elements in a form readily available to plants.

To make a liquid fertiliser with fresh seaweed, fill the drum completely and top up with water. To use seaweed meal, use about 10 kg or so to 200 litres. Seaweed breaks down very rapidly as it contains alginate, rather than cellulose. We use it diluted to the colour of very weak tea.

Weeds

Weeds contain a wide variety of trace elements that are useful to our crops. Biodynamic practitioners claim that making liquid manure out of your weeds and spraying it where they are a problem reduces the problem. Even if this is not true, you will be doing your crops a favour.

Organic Fertilisers

There are many materials commercially available that can be used directly on the soil, or the foliage of crops. You will often find that you will obtain more benefit from mineral fertilisers when they are included in the compost heap.

Blood 'n' bone

This is the most famous of all organic fertilisers. Unfortunately it has a number of disadvantages. Competition for it as stock food keeps its price far too high. The nitrogen in it is quickly made available in all but very cold soil, so it is a useful side dressing. Its fibre content is nil, so it is not a substitute for compost. The bone component releases phosphorus and calcium slowly.

Cottonseed Meal

Cottonseed meal is very bulky for its weight and so is uneconomic to transport over long distances. Where cheap transport makes the cost realistic, it is a useful nitrogen source, both directly in the soil, or as a compost addition.

Fish Emulsion

Fish emulsion is the most useful of organic fertilisers. It is sold in a range of qualities and at a range of prices. The best we have used, Vitec, was much cheaper than liquid seaweed and unlike some we have used, pleasant smelling. The worst (smelliest) and most expensive we have trialled, needed filtration prior to use. Fish emulsion applied as a soil drench at rates of around 6 ml per square metre releases many nutrient s from the soil. Applied as a foliar at dilution rates of 50 to 1000:1, it inhibits many fungal diseases. Regular application at 10-14 day intervals is more beneficial than less frequent, more concentrated applications.

Lucerne Chaff

Lucerne chaff is lucerne hay that has been chopped up small for use as stock food. It can be applied directly to the soil and lightly tilled in for a quick nitrogen boost. It also contains hormones that increase the rate of growth.

Phosphate Rock

The phosphate rock that is used to manufacture superphosphate was all that was available in years past. Now we can buy reactive phosphate rock, in which the phosphorus is more readily available to crops.

Pelletised Poultry Manure

Materials such as the well-known Dynamic Lifter and Organic Life, consist of chicken deep-litter composted, pelletised and steam sterilised. Some products are blended with fish, seaweed, blood 'n' bone, other animal manure, or zeolite to improve the material. These products are necessarily more expensive than the compost you can make for yourself. However, they do have the advantage of being easier to handle and spread. They are generally most useful when your own composting program has fallen behind.

Rock Dusts

Various crushed rocks can now be had for use in improving soil fertility. Basically, the theory is to emulate the effect of glacial action on rocks that form silt. Rather than wait for another ice age, we crush the rocks containing the desired minerals and apply them either directly to the soil, or via the compost heap. To be effective the rock has to be very finely powdered so as to present as great a surface area to the soil organisms as possible. You may find that the nearest road-metal quarry will let you take the fine stuff away for free. It tends to accumulate below conveyor belts and such like. Some unscrupulous vendors mix clay with rock dust to improve their profit margins, so beware.

Seaweed Meal

Seaweed meal is available in various grades. The powdery sort sold as stock feed is less satisfactory than the coarser grades that are less inclined to blow everywhere in the wind. Application rates between 75 and 150 gm per square metre are ample. Rates much higher than this have the lamentable effect of depressing yield. The benefits to expect are improved trace element availability and water-holding capacity of the soil.

Costs

You will read that organic fertilisers cost much more than artificial. When I first commenced market gardening, I went shopping. The most expensive nutrient is nitrogen. While you can obtain it "for free" from the use of legumes, this will only provide for a fraction of the needs of an intensive organic garden, unless you have a separate legume pasture for hay production. A one hectare paddock of white clover will produce about 100kg of N per annum, sufficient for . When I looked at off-farm nitrogenous fertilisers, blood 'n' bone was far and away the most expensive. The cheapest was chicken deep-litter (poultry manure mixed with sawdust) trucked from 70 km away. It must be pointed out that this was much bulkier than urea, a popular artificial nitrogenous fertiliser. On the other hand, chicken deep-litter contains phosphorus, potassium and the essential precursors of humus: cellulose and lignin. It also has an abundance of trace elements.

My friends Ian and Caryl Cairns have a neighbour with a dairy farm down the road where they obtain cow manure. In any farming district, you will come across crop residue that is available, for little cost that is a valuable source of major nutrients and humus. On one occasion I emptied a disused jam-factory of cow manure, it had been converted into a hay shed cum feeding area. On another occasion, I emptied a friend's goat shed. Both of these sheds were full of manure that had been aging for years and was used direct on the soil. Most important, it was free apart from my labour and transport. We have also, in the past, taken the trailer to a beach and collected copious quantities of seaweed that is in abundance following storms. Until my farming neighbours woke up to the fact that they could be doing the same as us, we were given spoiled hay, either for nothing, or the cost of baling.

It is important for the economics of organic market gardening that you locate accessible, inexpensive sources for your compost. Other materials we have come across at little, or no cost, have been hop mark, pyrethrum mark, cocoa bean shells, pea straw, cereal straw, pig slurry, spoiled fish meal, lawn clippings, sawdust, spent barley malt, spoiled vegetables and trimmings from shops, barber shop hair, sheep manure from underneath shearing sheds and apple pomace.

Even an organic fertiliser that looks expensive on the surface may be better value when looked at closely. A friend who compared the effect of superphosphate to blood 'n' bone on pasture, noted that while the effect of super was confined to the season of use, the blood 'n' bone treated section was well ahead in the year following its application. This prolonged and cumulative effect is noticeable with all organic fertiliser programs. In the writer's garden, after a decade soil testing showed the equivalent of an additional one tonne per hectare of super, above the phosphorus applied and ignoring what was exported in crops. This phosphorus was locked up by the chemistry of conventionally managed soil.

Percentages of Nitrogen (N), Phosphorus (P) and Potassium (K) in Common Organic Materials

Material N P K
Cow 0.4 0.3 0.4
Horse 0.7-0.8 0.3-0.6 0.5-0.7
Pig 0.3 0.3-0.4 0.5
Sheep and goat 0.7 0.5 0.2
Chicken 1.1-1.8 1.0 0.5
Turkey 1.3 0.7 0.5
Rabbit 2.0 1.0 0.5
Blood'n'bone 5.0-7.0 4.0-7.0 Nil
Fish emulsion 5.0 2.4 1.2
Fish meal 8.0-10.5 4.0-9.0 2.0-3.0
Granite dust nil nil 3.0-5.0
Hard rock phosphate nil 25-33 nil
Soft rock phosphate nil 15-20 nil
Kelp meal 0.8 0.2 1.4
Sawdust 0.2 0.1 0.2
Wood ashes nil 1.0-2.0 4.0-10.0
Seaweed 0.5-3.3 0.1-2.0 1.0-5.0
Lucerne hay 3.0-4.0 n.a. n.a.
Red clover hay 2.0-3.2 0.3-0.5 1.3-2.0
Broiler litter 2.6 2.7 2.0

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Jonathan Sturm 2003 - 2011

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