Fertilisers are made soluble, but it’s a damn fool idea. They should be insoluble but available. Most of our botany is solution botany, the first rain takes out the nutrients. There’s a big difference between the laboratory and the farm.
-- William Albrecht
Pelletised poultry manure, with or without additives such as fish and seaweed, is readily available and not excessively priced for use in mainstream farming when purchased in bulk. The nitrogen in fresh poultry manure is in the form of ammonium carbonate, which is caustic. Prior to the pelletising process, the manure is fermented or composted, converting the ammonium carbonate to bacterial protein. The pellets are then steam sterilised to kill any pathogenic organisms, or weed seeds. Some growers have observed that “new” weeds have arisen following the use of this material and have believed the seeds arrived in the manure. This is not necessarily the case as the increase in biological activity, or pH change can stimulate germination of dormant weed seeds.
One manufacturer makes the claim that they use only pure poultry manure, not deep litter. A sample placed in water and left overnight revealed the presence of sawdust particles. The sawdust is not necessarily a bad thing, however. The bacteria that ferment the raw manure need the cellulose in the sawdust as an energy source to convert the lignin in the sawdust to humus. There being no significant amount of lignin in pure poultry manure, there would be no humus formation when fermenting pure poultry manure. As well, much of the nitrogen that would otherwise be lost as ammonia is tied up in the humus.
Application rates for pasture are between 150 and 400 kg per hectare. The much higher rates used in cropping have created some difficulties. Modern fertiliser spreaders are built to spread low volumes of high analysis fertilisers. As well, the pelletised poultry manure takes longer to start working than artificial fertiliser and is best applied to the soil four to six weeks earlier. While banding works best with artificial fertilisers, as it “allows the plant roots to dodge them” in Albrecht’s words, broadcasting is preferred with organic fertilisers. This is because the goal is to stimulate the soil biology to release nutrients in the soil, rather than feeding the crop directly.
In two trials on peas, there were noticeably less peas left on the ground following harvest when compared with artificial fertiliser alone. Both of the trials used a 50% mixture of pelletised poultry manure and super. One crop had a yield close to average, the other was almost 50% higher than usual. A nearby crop grown on conventional fertiliser alone had many pods left behind after harvest.
Liquid fish is readily applied to soil by boom spray, injection into irrigation, or field jet in place of the boom spray. Foliar applications seem to work best at dilution rates of at least 50:1, and preferably 100:1 or higher. There is a wide variation in price and quality of fish emulsions. One of the most expensive we have used needed filtration prior to use, to remove what appeared to be scallop frill. It also smelled foul. The best we have used is the least expensive and has the most acceptable smell. Fish can be liquidised by a number of processes, heat, chemicals, or enzymes. The enzyme approach appears to produce the best end result, though all liquid fish fertilisers used have proved beneficial.
Application rates on pasture vary between 10 and 20 litres per hectare. Soil drenching at the rate of 60 litres per hectare for crops has given excellent results, though it appears that there has been very little, if any, work to determine optimum application rates at this time. Foliar applications of 10 litres per hectare to crops in place of urea appears to promote a high level of resistance to fungal disease and mites. Stock health is noticeably improved with less scouring due to parasitic worms.
Results from the use of liquid seaweed have been much more variable than with fish emulsion. This may be because of seasonal variation in the components of the kelp used in its manufacture. Dutch research shows spring harvested seaweed to be higher in auxins (plant growth hormones), autumn harvested is higher in abscissic acid. Abscissic acid is the hormone that stimulates leaf fall in deciduous trees and appears to confer pest and disease resistance. More work needs to be done in this area.
Like liquid fish, liquid seaweed can be manufactured by a variety of processes. Some products contain a certain amount of urea, the manufacturers claiming that it is necessary to stabilise the material. However, since some manufacturers do not use urea and their products are stable, this appears to be untrue. It is more likely that the urea is included to give a pronounced visual response. A crop of potatoes treated with liquid seaweed responded with a greater amount of foliage, but no measurable difference in the yield of tubers. An orchard trial at the rate of 9 litres per hectare promoted the growth of laterals in young apple trees.
There would appear to be little justification for the use of these materials for pasture production. Applications of water soluble nitrogen suppress the fixation of atmospheric nitrogen by clovers. Until the amount of fixed nitrogen is exceeded, there is no noticeable benefit and the cost is not only measurable in spending on fertiliser. The grass grown with water soluble nitrogen has more free amino acids and a higher water content. Some of the nitrogen taken up as nitrate is converted to nitrite in the sap of the pasture plants and this cause methaenoglobanaemia in the stock consuming it. This is a condition where an animal’s blood is unable to carry sufficient oxygen. High levels of nitrate in the soil suppress copper, resulting in steely wool, scours and parasitism (eg barbers pole worm).
As well, application of water soluble nitrogen in excess of the amount plants can use is either leached from the soil, or taken up by soil micro-organisms. In order to balance their diet, the micro-organisms consume organic matter in the soil. The result is that more and more water soluble nitrogenous fertiliser is needed to achieve the same result and soil structure deteriorates as organic matter levels decline.
Since the amount of nitrogen available to a crop from organic fertiliser is proportional to the amount of bacterial activity, a very poor season may very well justify the application of judicious amounts of artificial nitrogen. While it is clear that used alone these materials encourage fungal disease, aphids and acidify the soil, these negative effects may be ameliorated to some extent when used in conjunction with organic fertilisers. While the cost per unit of artificial nitrogen is much less than organic, the additional cost of pesticides, fungicides, and tractor fuel (to overcome the reduced organic matter content of the soil) must be taken into account. These costs are not just the purchase price and application costs. Since markets are now demanding residue-free produce, some pest and disease control materials are becoming severely restricted.
Organic farmers are often particularly injudicious in their assessment of the most commonly used fertiliser. There is no substitute for super when bringing eucalypt bushland into farmland. On the other hand, there would appear to be little benefit from excessive, long-term use. The main problem is that the bulk of applied superphosphate becomes locked up by chemical reaction in the soil.
The micro-organisms responsible for liberating phosphorus from the soil, making it available to crops, are suppressed by high levels of water-soluble phosphorus. Continual applications of superphosphate (or ammonium phosphate) keep these organisms inactive. Consequently, the farmer needs to apply all the phosphorus needs of the crop.
When a farmer stops applying superphosphate, there is usually a lag of 2-4 years during which the phosphorus liberating micro-organisms re-establish. This process is accelerated by applying proteinaceous fertilisers, such as animal manures and fish emulsion. The degree of recovery is dependent on the amount of locked-up phosphorus in the soil. Nearly always, pasture production returns to what it was prior to stopping. Heavy feeding crops often need more phosphorus than the soil biology can supply to produce the yields that are decreed necessary to remain economically viable. There appear to be three ways out of this double bind. The first would be to apply small amounts of super alongside organic fertiliser. The second, and probably better approach, would be to apply phosphorus as a foliar. This would allow better control of the amount applied and the soil micro-organisms would not be affected. The last would be to include reactive phosphate rock in the composting process used to manufacture pelletised poultry manure, or in vermicomposting with manure earthworms.
Where there is a demonstrable deficiency of phosphorus, rock phosphate offers several advantages over superphosphate. It is less expensive, contains a higher percentage of phosphorus, does not inhibit the soil micro-organism that liberate phosphorus and it doesn’t acidify the soil. The reason it has not been more widely used in the past is it is not water-soluble. On this basis, conventional agricultural theory said it could not possibly work. In more recent times, this attitude has been modified to “it works, but only in acid soils”. Organic farmers have known for years that it also works in biologically active soil. Trace elements are removed in the acidification process of super manufacture. Reactive phosphate rock, being unacidified, retains any trace elements in the original material.
There are only a few potassium fertilisers available in Australia. The most common is muriate of potash (potassium chloride) which is mined from natural deposits in Germany. Many plants are sensitive to excessive chloride and overuse of muriate of potash on crops, particularly potatoes, has led to levels that are cause for concern.
Sulphate of potash (potassium sulphate) is much preferred. Unfortunately, this material is manufactured from muriate by chemical reaction with sulphuric acid, and so it costs significantly more. In some districts, kiln dust, a by-product of cement manufacture, is available and contains significant amounts of potash. While seaweed contains significant amounts of potassium, it has been used to manufacture potassium oxide by burning, it is generally far too expensive to be used for its potassium content alone.
Lime is said to not be a fertiliser by conventional agronomists. Its use is merely to reduce soil acidity. From the foregoing it should be apparent that the two major constituents of lime, calcium and magnesium, have much more important roles than this gross oversimplification would allow. The relative proportions of calcium and magnesium in the soil should dictate the type and quantity of lime used, rather than adjusting pH using the cheapest source of lime regardless of its analysis. This latter approach often leads to a severe imbalance.
When the imbalance is a serious deficiency of magnesium relative to calcium, then the usual source of magnesium, dolomite, cannot be used. While there are sources of magnesium without calcium, they are relatively expensive. They include Epsom salts, Kieserite, magnesite and magnesium oxide. All of these sources are acceptable from the point of view of improving soil fertility, the same cannot be said regarding price. The least expensive is magnesium oxide, followed by magnesite. The most expensive is Epsom salts, followed by Kieserite.
While dolomite is relatively more expensive than ordinary limestone (it’s harder and more expensive to crush), it is cheaper than allowing the soil to become so magnesium deficient that straight magnesium materials become necessary.
Bio Dynamic farming places great store in what is known as BD500, or “horn manure”. This material is manufactured from cow manure placed in cow horns and buried over the winter months. The resultant material is black colloidal humus, rather than the green, smelly original manure. Between 25 and 35 gm is stirred rhythmically in 13.5 litres of lukewarm water for an hour. This liquid is then sprayed onto the paddock in the evening, the amount being sufficient for one acre. The BD500 is claimed to enhance the soil digestion process. That is, the raw organic matter in the soil is converted to humus and many BD proponents claim that fertility elements that are absent or deficient are created from existing elements in the soil.
While this sounds like the “muck and mystery” that organics has been labelled with for decades, there is no doubt that Bio Dynamic practitioners achieve remarkable results. Dr Doug Small of the Victorian Department of Agriculture and Rural Affairs has compared conventional and Bio Dynamic dairy farms and provided much food for thought. The Bio Dynamic practitioners, for instance, needed dramatically less irrigation than their conventional counterparts.
The foregoing preamble was not so much to spark interest in Bio Dynamic practices, but more an introduction to the proliferation of various materials that purport to achieve the same results. Unlike BD500, which costs between $1 and $3 per acre (ignoring the cost of stirring), these other soil activators cost significantly more. There is little doubt that many are no more than “snake oil”, but some have proved worthwhile. One such soil activator the author trialed, with rather a lot of scepticism, produced yield increases of between 15 and 50%.
Curiously, this material was being applied at the same rate as the amino acid betaine in trials conducted by the Tasmanian Department of Primary Industry. When the manufacturer of the soil activator was asked to comment on the similarity of results and application rates, he became extremely defensive. I imagine this was because betaine, a cheap by-product of beet sugar production, is much less expensive than the material he was manufacturing and I became somewhat sceptical of his explanations about his products.
Betaine, incidentally, confers some frost resistance to crops. Bill Hinchcliffe, head of the Riverina Ricegrowers Co-operative, says that organic rice is less susceptible to frost.* Trials of several strains of grass with varying levels of cold tolerance revealed that the more tolerant strains had a higher betaine content. Perhaps organic growing methods increase the betaine content of crops and this in turn may also explain why many organic food aficionados perceive better flavour than in conventionally grown produce.
Apart from carefully trialing these materials yourself, there is no way to tell in advance if they will work. The author submitted several materials for comparative trials to the Tasmanian Department of Primary Industry. I was asked what my attitude to a negative outcome would be and I said that the results should still be published. The manufacturers of some products being trialed wanted any negative results suppressed.
Soil fertility can either decrease, remain constant, or be increased. The humus level, or Cation Exchange Capacity of the soil are the best indicators to use. The quickest way to decrease soil fertility is to use only water soluble fertilisers and to till the soil too often, especially when it is too wet. Soil fertility is conserved with minimum tillage, using water-soluble fertilisers only when strictly necessary, and by including green manure crops in a diverse crop rotation. Soil fertility can be increased by balancing the major nutrients, calcium, magnesium, potassium and sodium as described earlier, and by including a pasture phase in the crop rotation.
A cow generates 20% more manure than is required to grow the food she needs. Consequently, pasture accumulates fertility that can be converted to a cash crop for export without decreasing the net fertility of the farm. One Tasmanian dairy farmer admitted to the author that his best paddocks had been sown down by his father with a horse-drawn plough and never fertilised as there was no response to fertiliser strips.
Organic farmers use rotation of pasture with crops as an economic alternative to importing fertiliser. The relative lengths of the pasture and cropping phases are determined by the capacity of the soil to accumulate fertility and the particular crops that the farmer grows. The 100 kg/ha of nitrogen fixed by a sward of white clover is a sufficient amount to grow a worthwhile crop. Lucerne fixes even more nitrogen and can be applied as chaff to be harrowed in for a nitrogen boost to a crop. Lucerne also contains growth hormones that give increased yields beyond the result expected from its nitrogen content alone.
When a paddock is ploughed under for cropping, it is important to plough shallow. Organic matter buried too deep is decomposed by mainly anaerobic bacteria, so the process is fermentation, rather than humification. For optimum results, the organic matter should also be completely decomposed before sowing the crop. Many plants, particularly those we call weeds, contain growth inhibitors (phyto-toxins) and until they have decomposed, they will inhibit seed germination and reduce the vigour of the crop.
The bacteria responsible for humification need the right working conditions to perform to the best of their not inconsiderable abilities. The most important of these conditions are warmth (10-20°C), air and moisture. Of secondary importance, but still vital for best results, is a source of protein. Quite small inputs of protein can produce results seemingly out of all proportion to the amount applied. While solid fertilisers, such as pelletised poultry manure, are cheap to buy, the convenience of fish emulsion applied by boom spray or field jet can give a more economic result. The soil activators that are touted as “essential” have already been discussed above.
Tillage of the ploughed paddock should be the absolute minimum required for weed control. Each time the soil is tilled, the organic matter is reduced by oxidisation. The humus is converted to nitrate (among other substances) and in the absence of a crop, this nitrogen can be lost through leaching. Tillage also reduces earthworm numbers, damages the crumb structure and the diversity of microorganisms decreases.
A green manure is a crop grown specifically for fertility enhancement. Quite often, green manure is confused with cover cropping. The latter is specifically grown for weed suppression and prevention of soil erosion when the ground would otherwise remain bare for a period of three months, or more. Of course, a crop can be grown for both purposes, but the type of crop grown is determined by the most important purpose.
European organic farmers have brought green manuring to a state approaching perfection. They almost invariably sow a mixture of a legume, a cereal and a crucifer. The legume fixes nitrogen. The cereal straw produces soil binding materials when it decomposes, called mucins. They bind the soil in the crumb structure that is essential for good drainage, aeration and ease of tillage. The sulphur compounds in the crucifers are believed to enhance the health of the soil.
Typical legumes include lupins, tick beans, field peas and tares (vetch). Typical cereals include oats, rye and barley. Typical crucifers include oilseed radish, rape and mustard.
The optimum time to plough a green manure under is when the flowers are just starting to form. At this point, the protein content is at a peak. Afterward, the fibre content increases, necessitating the application of additional protein, or a longer wait for complete decomposition. The effectiveness of a green manure is enhanced when the carbon to nitrogen ratio is between 25 and 35 to 1. That is, the protein content complements the fibre. Looked at from the point of view of using pelletised poultry manure, its effects too are greatly enhanced when used in conjunction with a fibrous green manure due to the low fibre content of the poultry manure. The remarks above applying to ploughing in pasture also apply to green manures. Wilting the green manure by rolling or mowing prior to turning under promotes an increase in decomposition rate.
Cover cropping requirements are rapid establishment to get ahead of the weeds, and for plenty of fibrous roots that will hold the soil together. Usually this is a cereal, or annual ryegrass. One suspects that a mixture of species would perform better from the point of view of the soil biology vastly preferring a mixed diet, but this may not be as economic as using a single species.
Organic fertilisers are generally considered to be more expensive than artificial fertilisers. On the face of it, this is true. In Tasmania in 1994, a tonne of Dynamic Lifter cost approximately $400; the equivalent nutrients as artificial fertiliser cost approximately $170 per tonne.14 In reality, the Dynamic Lifter was better value for money on several counts.
According to the Soil Handbook that comes with the La Motte soil testing kit, the following table of nutrient use obtains:
Percentage obtained by crop in one season
| Nitrogen | Phosphorus | Potassium | |
| Animal manure | 30 | 30 | 50 |
| Artificial fertiliser | 60 | 30 | 50 |
Artificial fertiliser seems to be ahead, but there is a marked difference over several years. The artificial fertiliser needs to be applied at the same rate, year after year. While 30% of phosphorus in artificial fertiliser is used by the crop during a season, 40% of it is chemically locked up, or lost through erosion, contaminating groundwater and streams. The 70% balance of the phosphorus in the animal manure remains for use by the subsequent season’s crop. The first year of applying Dynamic Lifter would cost $400 versus $170 for the artificial fertiliser. Subsequent applications of Dynamic Lifter to maintain the equivalent input of nutrient would cost only $120. After ten years, the total cost of artificial fertiliser is $1700; the equivalent Dynamic Lifter would have cost $1480.
But this is not the whole story. Dynamic Lifter stimulates the proliferation of bacteria and other micro-organisms that render the locked-up phosphorus available for use by plants. On a paddock with a long history of superphosphate use, these reserves of phosphorus are quite significant. Build-up of the necessary organisms to fully exploit “unavailable” phosphorus generally takes three to four years. The farmer then has the choice of increasing yield, or reducing fertiliser input to maintain the same yield.