Eyeless, legless, faceless, earless, voiceless, the earthworm is not much to look at — a mere squirming piece of flesh. Yet with its powerful muscles, its two stomachs… its false teeth, it is able to carry out remarkable works”
-- John Stewart Collis
While some aspects of plant nutrition were partially covered in the preceding chapter, it is a complex area beyond the scope of this small book to cover thoroughly. However, it is the author’s belief that some understanding of the underlying principles will enable the improvement of farming beyond that currently considered acceptable.
The classical model of plant nutrition has it that nutrients must be in water solution to be taken up by plant roots. To be absorbable, the molecules must be small. To be water soluble they must be simple salts. All of our current standard mineral fertilisers fit this description. The model further states that these nutrients are taken up in the water from the soil as a result of transpiration of moisture through the plant leaves. While hydroponics is the epitome of this model, when we take a closer look, things start to look distinctly dodgy.
The model implies that for growth to take place there must be transpiration of moisture through the plant leaves to create the flow of nutrient-bearing water. In a terrarium, the atmosphere is saturated with water (100% humidity), so transpiration is almost non-existent, yet plant growth clearly occurs. It would be hard to find growth rates to equal those of steamy tropical jungles, where humidity is high and therefore transpiration rates are low. Conversely, a high transpiration rate should result in faster growth. My observation is that windy conditions and low humidity result in poorer growth.
Let’s look at the soil. A conventional farm soil supporting good plant growth exhibits the high electrical conductivity associated with plenty of ions15 in solution. On the other hand, a good organic farm soil supporting similar growth shows a very low electrical conductivity, indicating that there are minimal numbers of ions in solution. Part of the answer to this conundrum is that the organic farm soil contains more humus which, like clay, has negative electrical charges to hold the positively charged ions out of water solution.
Both humus and clay have surfaces covered in negative electrical charges. Since negative electrical charges attract positive electrical charges16 these surfaces are covered with positively charged ions (cations). These cations include calcium, magnesium, potassium, sodium, copper, cobalt, ammonium, iron, aluminium and hydrogen.
When a plant needs cations, its root hairs emit hydrogen ions. The hydrogen ions displace the cations from the clay, or humus colloids and the cations are then taken up by the plant root hairs. It should be obvious that if the ratio between the cationic nutrients held by the soil colloids is unbalanced, then the nutrition of the plants will also be unbalanced. The plants will be unhealthy.
If all, or nearly all of the plant returns to the soil, as in a forest, the pH will remain pretty constant over time. Where the cationic nutrients are removed in crops, the soil will tend to gradually become more acidic and less fertile unless they are replaced. While our shallow rooted crops exploit very little of the soil profile, deep rooted plants can exploit mineral reserves out of their reach. When the residues of these plants decompose, these minerals are released for use by the shallow rooted crops. Where this occurs to a sufficient degree, the process of acidification can become so slow as to be imperceptible.
The cations required in the greatest quantities are calcium and magnesium, which is why we generally use limestone to correct an acid soil condition. Unfortunately, it is a rare limestone that has the appropriate balance between calcium and magnesium. Unless the ratio between calcium and magnesium in the soil is known, the appropriate liming materials and quantities will also be unknown.
The level to which the Cation Exchange Capacity of the soil is filled is called the Base Saturation and is expressed as a percentage. The higher the humus level, the higher the Cation Exchange Capacity, Base Saturation and consequent capacity of the soil to produce. Since clay also contributes to the cation exchange capacity, soils with more clay and/or humus require much greater amounts of calcium and magnesium to produce a given pH change than a sandy soil, or one low in humus. Cation Exchange Capacities of up to 28 meq% have been recorded in New Zealand. My own very productive market garden soil has a CEC of 20 meq% and good pasture levels are around 10 meq%.
Then there are the negatively charged nutrients, nitrate, phosphate, sulphate and so on. Clearly they are not part of the plant root/colloid interchange. Dr Allan Smith of the CSIRO has written about the interaction between soil micro-organisms, oxygen and ethylene in the soil. At some risk of misrepresenting Dr Smith’s work, we will attempt a very simplified explanation.
Soils with good aeration are more fertile than those with poor atmospheric gas exchange. There is more oxygen available to the micro-organisms that require it and many of them are implicated in the release of nutrients from the soil. However, even in a well aerated soil there are pockets of low oxygen level. These pockets allow the proliferation of anaerobic bacteria that are suppressed by high oxygen levels. The anaerobic bacteria generate ethylene gas, the gas that ripens fruit. In the soil, ethylene suppresses the aerobic bacteria, decreasing their rate of reproduction at lower levels and putting them into suspended animation at higher levels. When this happens, the aerobes use less oxygen, so the overall level of oxygen in the soil increases. Oxygen has the same effect on the anaerobes as ethylene does on the aerobes, so there is a balancing effect. Neither the aerobes, nor the anaerobes can predominate.
This situation only obtains in a soil that has a continuous source of fresh organic matter for the anaerobes to convert to ethylene. Soil that is tilled too much and becomes over-rich in oxygen disrupts the production of ethylene. We will look more closely at the effect of soil compaction and the overabundance of anaerobic bacteria in the next chapter. Excessive levels of nitrate also disrupt the oxygen/ethylene cycle. This is because the production of ethylene is dependent on the availability of iron and the bacteria that render iron available are suppressed by nitrates. Applying ammonia instead of nitrate is not a solution, since nitrifying bacteria convert ammonia to nitrate.
At the same time iron is released from its chemical bondage by bacteria, so too are the rest of the iron compounds, phosphate and sulphate etc. The now soluble negatively charged phosphate and sulphate become available for absorption into the plant. The iron is adsorbed onto the clay and humus particles after catalysing the production of ethylene. Many plants do not absorb phosphate directly, but do it via an intermediary. Fungi that live on the plant roots, called mycorrhizae, consume the phosphate and then trade the phosphate with the plant root in return for carbohydrates.
This is not the whole story, however. Earthworms are also responsible for the liberation of phosphate and calcium (among other elements) from the silt particles they ingest. Animal manure, dropped on the soil surface by grazing animals, has much of its nitrogen in the form of ammonium carbonate. Fresh manure tilled into the soil has its nitrogen converted to nitrate by the nitrifying bacteria. In effect, it is little different to applying nitrate from the bag. Left on the surface, it is consumed from underneath by manure worms. These little creatures resemble the soil-ingesting pasture earthworm, but are much more active when disturbed. One common variety is called the red wriggler. The nitrogen in the manure they consume is converted to protein.
All of these biological mechanisms require continuous inputs of fresh organic matter — carbohydrates and proteins. Inputs of nitrate and water-soluble phosphate disrupt them. Excessive tillage of the soil produces excessive aeration which in turn allows the organic matter to be consumed at an extravagant rate. When most of the organic matter has been consumed, the soil structure collapses leading to very low levels of aeration and the proliferation of anaerobic bacteria. Excessive tillage, elevated nitrate levels and muriate of potash also reduce earthworm numbers.
From the foregoing it should be apparent that what is required for good biological activity in the soil is the steady, frequent input of small amounts of organic matter and minimal tillage. This leads to optimum use of nutrients in the soil by the crop.
In promoting soil biological activity where the soil is badly out of balance, it would appear to make more sense to apply any shortfall of major nutrients as foliar sprays, rather than disrupt the soil biological cycles further.
Nutrient analysis of soil has become very popular in recent decades. As a guide to fertiliser use, it can be misleading and frustrating — or a useful aid to profitable farming.
The problem is that most analyses rely on the use of a weak acid to dissolve the nutrients out of the soil in order to measure them. The assumption behind this is that plants can only take up fertility elements that are readily soluble in water. While the results from soil analysis are useful in prescribing the amounts of conventional amendments required to grow a crop in the average farm soil, they fall well short when organic fertilisers are used, or when land that has been under pasture for several years is brought into cropping. They are even less useful when the soil has been under an organic regime for any length of time.
A field officer for a vegetable processor told me that he came across a perfect example of this. One paddock that tested as ideal for a crop of peas ended up not being harvested because of the poor crop. Another that tested as mediocre grew the record crop for the season. The differing organic matter levels in the two paddocks explains the apparent incongruity.
The two most difficult to assess major elements are phosphorus and nitrogen. Organic fertilisers and the organisms they feed release phosphorus from the soil not detected by ordinary soil analysis. Much of the nitrogen in a good organic soil is in the form of protein, and the nitrate and ammonium tests for soil nitrogen levels underestimate this important source of nitrogen. Crude estimates based on soil carbon can be used, but the soil carbon level is determined by igniting the carbon and measuring the weight loss. It is not an accurate estimate of the soil’s protein content.
This does not mean that soil analysis is bereft of utility. We have already referred to the importance of the ratios between calcium, potassium, magnesium, sodium, trace elements and hydrogen ions. The better soil testing laboratories include the percentage cation figures in their analyses, though only for calcium, magnesium, potassium and sodium. The reason for this is that most of the trace cations are expensive to test for. Bringing the ratios of the major cations into the desired range without soil testing is not feasible. When the soil is amended to do so, the consequence is an improvement in crop and stock health. The degree of change is dependent on how far out of balance the soil was prior to amendment.
Soil testing for trace elements is not only expensive, there is little relationship between soil levels and the amount taken up by crops. Again, humus appears to play a role in this, but there is also the issue of interaction between elements. The diagram on the previous page shows some of the known relationships between elements.
This chart shows the effect of various plant nutrients on each other. The solid lines show that one element suppresses another in the direction of the arrow head. For some pairs of elements, both are suppressed when excessive amounts occur. Similarly, the dotted lines show stimulation.
For example, even heavy applications of zinc will not “cure” zinc deficiency if there is an excessive level of calcium. In such a circumstance, there would also be symptoms of phosphorus, magnesium, manganese, potash, boron and iron deficiency.
The soil test results below are from the author’s property and a neighbouring property. The soil type is silty clay, approximately 50% clay and 50% silt; the sand content is less than 5%. Annual rainfall is averages 800 mm. All three sampling sites were within 100 metres of each other. Pasture A is the neighbour’s property and is under a conventional fertiliser regime. Pasture B is my hay paddock. At the time of testing, the paddock had received no fertiliser inputs for twelve years. Despite this, and seven hay cuts that were mostly sold off, the last hay cut was approximately 300 bales per acre which is considered an excellent yield in the district. The market garden block initially received dolomite lime to lift the pH from 5.5 to 6.5 (2.5 tonnes/ha) and muriate of potash (200 kg/ha) as determined by soil test to overcome potassium deficiency. Over the ensuing ten years, only compost has been applied. The crop rotation in the market garden is four crops every three years. Both areas received applications of Bio Dynamic preparation 500 at the rate of 35 gm/acre in 1988 and 1989.
There are several interesting things to note in these soil test results. Despite applications of super every year or so, Pasture A has less available phosphorus than Pasture B which has had no fertiliser inputs for over a decade. Pasture A has a higher organic carbon level than Pasture B, but its lower Cation Exchange Capacity, indicates that less of the organic matter is in the form of humus. Both paddocks have good earthworm activity. Both paddocks also show very low magnesium relative to calcium and this reflects in less than optimum stock health. The claim by some Bio Dynamics proponents that Preparation 500 alone can improve this situation is not borne out by the soil test. However, the topsoil depth in Pasture B increased markedly (from 75 mm to 250 mm) in the two year period following application of Preparation 500.
The market garden area, despite having more than twice the lime content of either Pasture A, or Pasture B, has the same pH. This is because the much higher Organic Carbon level, mostly humus, is buffering the pH. The disparity in lime levels illustrates the folly of liming the soil to change pH while ignoring the contribution of humus.
The Cation Exchange Capacity, expressed here in meq% (percentage milliequivalents), is a measure of the soil’s fertility. That is, it’s a measure of the crop yield that the soil is capable of. We have seen the CEC of the major vegetable producing soils from the NW and NE coasts of Tasmania vary between 10 and 20, most toward the lower end of the range. In New Zealand, CECs of up to 28 have been measured and the best European and United States soils are said to be even higher.
* Estimated as being the
same as Paddock B now since no fertiliser has been added. The estimate ignores
what was exported in the 7 hay crops.
The extraordinary level of phosphorus in the Market Garden sample cannot be explained solely on the basis of the phosphorus content of the applied compost. The soil test indicates that there is now nearly 1.4 tonnes/ha more phosphorus (equivalent to approximately 14 tonnes of superphosphate) than the amount detected in the original soil plus that applied. Also appearing in significant amounts are calcium and magnesium, equivalent to about 5 tonnes/ha more dolomite lime than was applied. Since phosphorus, calcium and magnesium were also being exported in the crops sold, the disparity is even more remarkable. The only rational conclusion to draw is that the increased biological activity associated with the addition of compost has released substantial amounts of phosphorus, calcium and magnesium not detected by the original soil test.
The low nitrate levels in Pasture A and Pasture B would probably lead to conventional agronomists advising applications of urea, or ammonium nitrate. However, neither paddock shows the slightest sign of nitrogen deficiency. In both paddocks there is more than adequate nitrogen, in the form of protein. These low nitrate figures indicate that very little leaching of nitrogen can occur. The higher nitrate level in the Market Garden sample is probably due to the fact that it had recently been tilled following a harvest of beetroot. Tillage oxidises humus, releasing nitrogen in the form of nitrate.
All three samples show magnesium needs to be increased relative to calcium. While the Market Garden sample indicates that dolomite limestone has ameliorated the situation, a source of magnesium without calcium would have achieved a better result. Epsom salts (magnesium sulphate) would be the best source as it would improve the low sulphur levels (not shown). Unfortunately, it is too expensive. Magnesite, or magnesium oxide would be more economical.
The high potassium level in the market garden indicates that the original application of potash was a complete waste of money. Had I waited for the increased biological activity to make the potassium available, I could have eliminated the expense. Ah! The wisdom of hindsight.
Insects and diseases are the symptoms of a failing crop, not the cause of it”
-- William Albrecht
If the approach taken by most agricultural scientists and books written by them were a guide, then pests and diseases are the result of a deficiency of pesticides and fungicides. Of course this is not so. Pests and diseases are almost always the result of plant stress. These stresses include:
Not a direct stress, but also important, is the decimation of predators caused by pesticide use.
All of these factors are at least partially under the farmers' control. If the stresses are avoided, or diminished, then many plant pests and diseases either simply do not occur, or fall below levels that justify control. The question then arises of the economic viability of avoiding plant stress versus using pesticides and fungicides. All of the stresses listed above decrease crop yields, not just through crop loss caused by the pests and diseases they encourage, but more directly.
Let's take spider mites as an example. You will probably have noticed that they are much worse in periods of hot, dry weather. Plants under stress from water deficiency are what spider mites demand. Of course a plant that is suffering from water deficiency is also not going to yield as well as it would were it supplied with adequate levels of water. Is it more economical to allow crops to suffer water deficiency, reducing yields and use miticide, or to supply more water, increasing yields and eliminating the cost of the miticide?
One way to supply more water without the necessity of additional irrigation or rainfall is to improve the water-holding capacity of the soil and also the infiltration rate of water falling onto it. Increasing the humus level will accomplish this. Humus is important in utilising water to its utmost. Water that runs off is not just wasted, but also carries topsoil and nutrients away from the crop.
Another common pest, one that is almost ubiquitous, is the aphid. These little suckers probably cause more damage than any other insect. The first thing to consider is their nutritional needs. Aphids cannot digest complete protein; they require free amino acids (the building blocks of protein). Excessive amounts of water-soluble nitrogenous fertiliser creates the condition of high levels of free amino acids in plant sap, effectively a dinner invitation to aphids. Conversely, feeding protein to plants reduces the level of free amino acids and minimises the attractiveness of plants to aphids.
Many insect problems are caused by monoculture, that is the growing of vast areas of a single crop. In a polyculture, such as a natural ecosystem, insects have the problem of finding the next plant to feed on. Not only is it likely to be some distance away, its odour, essential for insects to find it, is masked by the odours of all the other plants in the insect's vicinity. Not only that, some of those other plants harbour predators on the insect, so it is more likely to be consumed in a polyculture than in a monoculture.
Insecticides, natural or synthetic, are a poor answer to the problem of excessive insect pests. This is because insect predators necessarily reproduce more slowly than their prey. If it were otherwise, then they would eat themselves into starvation. Most insecticides kill pest and predator alike, so unless they are used continuously, they give pests an edge over predators. Unfortunately, continuous use is not just expensive, it leads to pesticide resistance. Then, when a pest outbreak occurs, there is one less insecticide in the arsenal.
Some predatory insects can be encouraged by providing attractive food sources. For instance, hoverflies whose larvae consume aphids are attracted to flowering umbelliferous plants whose nectar they consume. Traditionally, Britain's hedgerows provided habitat for many predators on insects. It is no coincidence that the decline of hedgerows in Britain has been accompanied by dramatically increasing pest problems. Many Australian farmers have discovered the virtues of leaving some bush to provide a predator reservoir, or reintroducing bush to their farms where similar problems are occurring.
Many birds are avid consumers of insects and insect larvae. In the New England Tableland, there has been an interesting study of a species of bird that consumes grass grubs. It is the female that consumes the grubs, while her male counterpart consumes the nectar of flowering gums. The females will not feed more than 150 metres or so from the males, so the maximum distance of pasture from trees needs to be no more than this distance for natural grub control. Growing belts of trees and shrubs on farms has other benefits apart from pest control. They keep groundwater under control and reduce evaporation of rainfall by reducing wind speed. Stock chilled by wind have to consume more feed to keep warm, so windbreaks can provide increased productivity. The shade from hot summer sun they provide reduces heat stress.
Insects that appear to be pests at first glance can also be seen in a quite different light. Japanese agricultural researcher, Masonabu Fukuoka, was trialing a pesticide to control a stem borer that afflicts rice. Much to his surprise, the first trial showed a yield decrease in the paddy treated to control the stem borer. A repeat trial also showed that killing the pest decreased rice yield. He came to the conclusion that plant density was the issue. The stem borer thinned the rice plants to produce a higher yield than when they were too crowded. The funds for this research came from a pesticide manufacturer who forbade publication of this interesting result. After all, it would have reduced sales of their products! Fukuoka, having drawn a number of conclusions from his years of agricultural research, took up organic farming and put his ideas into practise18.
When we look at a natural ecosystem, which by definition is devoid of pesticide and fungicide inputs, we see very little pestilence and disease. Note that there is not a complete absence, just a very low background level. Of course, such a system is not very productive from the human economic viewpoint, which is why we developed farming. What organic farmers are attempting to do is bring the control mechanisms in the natural system into our more productive farming systems. The problem here is that the more we improve productivity, the further removed from the natural ecosystem we get. Maintaining the mechanisms of the natural ecosystem alongside improved productivity requires considerable effort and expertise.
Ironically, peasant populations the world over have achieved this, yet we have been trained to perceive peasants as ignorant. Miguel Altieri, who coined the term agroecology, took a group of botanists and a group of peasants into a Central American forest. Each group was required to identify as many different plants as they could. The peasants won by a country mile.
In the UK, there was an archaeological experiment carried out at a place called Little Butser. The idea was to equip students only with the resources available to Britons of the Bronze Age and observe the way they lived. Some of the outcomes were quite remarkable and certainly unexpected. The Little Butser Bronze Age village produced 15 times more food than historians estimated such a village could produce at the time. This implies that either the population was 15 times greater than previously believed, or that excess food was exported.
We knew from archaeological digs that wheat was stored in pits dug in the chalk subsoil, capped with clay. The experiment revealed that carbon dioxide generated by the wheat killed any insects that would have consumed the stored grain. The wheat varieties chosen for the experiment were those known to have been grown in that period. They were much higher in protein than modern varieties and one turned out to be unpalatable to rabbits. Today's wheat farmers have an ongoing battle with rabbits and I wonder if there has been any research into breeding a less rabbit-susceptible modern wheat variety.
What we are trying to do here is establish, not that imitating peasant practises is the way to go, but that there are important lessons to be learned from them. World food production increases are slowing down; conventional agriculture has gone just about as far as it can. We must either improve the technology of food production, or decrease population growth. Since the latter is outside the scope of this book, we are concentrating on the former. We also believe that there are many other reasons for improving our farming.
We referred in the previous chapter to the oxygen/ethylene cycle and its effects on soil biology. It is a feedback mechanism for maintaining the balance between aerobic and anaerobic microorganisms. Its existence was discovered in natural ecosystems and appears to be what the best organic practises can achieve.
Ethylene is a gas produced by ripening fruit and decomposing vegetables. When we wrap tomatoes to ripen them, we are capturing the ethylene and preventing its escape, thus accelerating the ripening process. Ripe bananas are prolific producers of ethylene, so this is why we put a banana in a bag with tomatoes to accelerate their ripening.
Disease organisms are organisms that decompose organic matter and can be looked at from two differing viewpoints. When they are attacking our living food crops they are a problem. When they are decomposing crop residues, they are converting them into food for the next generation of plants. What is it about our current agricultural practises that allows what are usually benign organisms to run out of control? What keeps them in check under natural conditions and in organic farming? Let's look at what happens to organic matter under the systems of organic and conventional production.
Plants consist of mainly carbohydrate (starches, sugars, cellulose) and proteins. When plant matter is incorporated in the soil, it is decomposed by the soil microorganisms. In the presence of oxygen, the carbohydrates are decomposed by fungi to generate carbon dioxide and water. The carbon dioxide displaces oxygen. These fungi are just as happy without oxygen, but now decompose the carbohydrate to alcohol and carbon dioxide. Under this condition, anaerobic bacteria come into the picture and decompose the carbohydrate to methane and ethylene. The ethylene suppresses the aerobic bacteria so they consume less oxygen. Consequently, oxygen levels increase, suppressing the anaerobic bacteria and the ethylene level then decreases. This allows the aerobic bacteria to revive and they transform the alcohol to acetic acid which dissolves nutrients from the silt. Proteins are decomposed to generate the free amino acids they require and some is converted to ammonia. Other aerobic bacteria convert ammonia to nitrate which is absorbed by plant roots. In the process these aerobic bacteria also convert oxygen to carbon dioxide. Plants convert carbon dioxide and water to carbohydrate, liberating oxygen. The plants then die to begin the cycle once more.
This is a grossly simplified view of what happens; there are over 2,000 different species of interacting micro-organisms in a healthy soil. However, it is enough to give us some insight into what we can do to ensure these process occur and what happens when our farming practises interfere to create undesirable consequences. It illustrates the principle of the dynamics of a functioning ecosystem. Each micro-organism has a different purpose and also provides the checks and balances to maintain the system. As farmers, we must either provide conditions that allow these processes to occur, or accept the consequences of hindering them.
What we call disease organisms are part of this ecosystem. They only become a problem when they are allowed to predominate over organisms that in a natural ecosystem keep them in check. Our farming practises, tillage, fertilisers, pesticides, herbicides and fungicides, all affect the system. Nitrate fertilisers suppress ethylene production, the feedback mechanism for keeping fungal "diseases" in check. Many fungicides kill bacteria, and as we have seen, bacteria are an essential part of the soil ecosystem. The speed of gas diffusion is a function of soil structure. Insufficient air in the soil is a stimulant to the anaerobic organisms and suppressant of the aerobes. Excessive aeration leads to the rapid depletion of organic matter, the food source of microorganisms. Herbicides are implicated in the chemical lock-up of trace elements needed by plants and micro-organisms for the formation of essential enzymes.
Does this mean we are advocating the immediate cessation of all synthetic inputs? Not at all! The establishment of a healthy soil ecosystem requires time and effort, which is a cost. The consequent reduced need for the supposedly necessary external inputs is a cost reduction. The difference between the two may be a profit, or a loss. For ecologically acceptable farming to be viable, a profit is essential. For a fortunate few farmers, the profit need not be monetary, but a sense of well-being engendered by not using toxic, or potentially toxic chemicals. The majority of farmers caught in the financial squeeze between high input costs and low returns must trial these techniques carefully to assess their economic viability.
A further factor is the changes in external economic conditions. The origin of our current farm economy woes was the demand for abundant and cheap food. Having succeeded in supplying that demand, we now find that requirements are changing. The consumer is expecting abundant cheap food without the chemical inputs. It has not yet occurred to them that they could be requiring a decrease in the standard of living for farmers in order to maintain their own. We need to inform them of these and other issues vital to the well-being of farming and bring them into the decision-making process. In some European countries, where the negative impact of farm chemicals is more pressing, governments are subsidising the farm conversion process19, or requiring the cost of damage caused by agricultural chemicals be included in the purchase price20.
Another factor to take into account is the small, but growing number of consumers who are aware of the problems of agriculture and many of them are sympathetic to farmers' needs. They have shown a willingness to pay significant premiums for organically grown produce. Ian McLaughlin, when he was shadow minister for primary industry, called for cooperation between farmers and the public in solving farmland degradation. Revegetation in the form of trees on farms is a cost most farmers can't meet unaided. McLaughlin's suggestion is that farmers donate the 10-15% of the farm that need to be in trees and the public provide the trees and labour. The farmer benefits from improved productivity and reduced land degradation. The public benefits in improved landscape, water quality and reduced costs of production.
In any event, while a wholesale overnight change is impossible, small incremental changes are not only possible, but highly desirable. What works well on one farm does not necessarily work well on another. What may have a negative impact on profit in one location may have a positive impact at another. By proceeding slowly and sharing our experiences, we can expect to develop agricultural systems that are better and more organic than those predominating now, but they will not necessarily be identical to what we currently call organic. It would be a foolish person indeed who declared that current organic farming practise is a panacea for all our agricultural problems. After all, as we discussed in the early part of this book, our pre-industrial agricultural practises were just as capable of massive land degradation as our currently much maligned conventional agriculture. It's just a lot quicker with tractors than slaves. And it's worth noting that nature, unassisted, takes geological ages to repair the damage we can cause. If we expect to continue supporting a large human population on planet earth, we have a lot of hard decisions to make over the next decade, or two.
While the mechanisms of pestilence and disease as we currently understand them appear complex, the solutions to them, generally speaking, are not. While we cannot create the diversity in farm ecosystems that occur in natural ones, any move to increase diversity will help. An example from the Lockyer Valley in Queensland will illustrate. Broccoli growers adopted a number of strategies to reduce their pesticide inputs. One was the growing of a row of canola every few metres among the broccoli. The canola harbours a predator on one of the target pests and coincidentally provided some wind shelter, since it is taller growing than the broccoli. Another strategy was not growing broccoli when the market was flooded and prices so low that it wasn't really profitable to produce. This discontinuity created a feeding problem for the pests and reduced overall numbers. Dipel (Bacillus Thuringiensis) was adopted for some caterpillar control. This is a living organism, so it has the capacity to breed in the environment and infect subsequent generations of the target pest. Since the bacterial toxin is highly specific to caterpillars, only the target organism is killed. The last strategy was to rotate among a group of chemically unrelated pesticides to reduce the problems caused by target pests developing immunity to the spray, an invariable consequence of using a single pesticide continuously.
This illustrates a number of organic principles:
As has already been indicated, organic methods are rarely single-shot. Nearly always, a number of strategies are adopted. One of the simplest ways to reduce fungal disease on leaves is to ensure that adequate sunlight and air movement occur in a crop. Most fungi thrive where there is high humidity and shade. Soil fungi are more troublesome where there is inadequate humus in the soil and poor drainage.
Another strategy almost universally adopted by organic growers is varietal selection. The more cynical organic producers believe that many modern crop varieties are promoted because of their dependence on synthetic inputs. While older varieties yield less under a conventional regime, they can outperform modern varieties in an organic context without the expensive necessity for spraying.
Nearly all fungal diseases are controlled by the stimulation of bacterial activity21. The bacteria appear to be competitors for the same ecological niches as fungi. Sclerotinia, botrytis, phytopthera, mildews and apple scab have all been controlled by applications of fish emulsion and a liquid extract made from compost. Increasing the pH of the leaf surface prevents spores of some fungal diseases from germinating. Examples of the use of this technique include control of botrytis and apple scab with applicationsof a 3% solution of sodium silicate22 or a saturated solution of calcium hydroxide (Limil).23 Also organically acceptable are most of the copper sprays, such as Bordeaux and Burgundy mixtures, sulphur, lime sulphur and sodium bicarbonate (baking soda). Where seed rotting is a problem, potassium permanganate (Chondy’s Crystals) is used as a seed dressing. Damping-off of seedlings is generally controlled by lightly dusting the soil surface with sifted wood ashes, or hydrated lime. Covering seeds with sand rather than seed raising mix also helps by improving drainage around the stem where the infection occurs. Mildews can be controlled with phosphorous acid.
Many diseases are a response to unbalanced plant nutrition. The emphasis on providing for the plants’ nutritional requirements mitigates against most fungal diseases being a problem for the organic grower.
Research is currently under way to develop biological controls for a number of pest and disease problems. While this is laudable for its potential to reduce the level of synthetic pesticide use, this research is of more use to the users of these chemicals than to farmers whose management precludes their necessity.
One aspect of organic production that is remarked upon with some frequency is the claim for longer shelf-life of organic produce. Opponents of organic production say that because organic produce is not protected with chemicals, it is more subject to bacterial and fungal contamination. Therefore, they say, organic produce is more hazardous to the health of the consumer than the chemical residues in conventionally grown produce. This is not borne out by scientific research.
Production Method and Storage Loss24
Potatoes 24.5% 16.5%
Beetroot 59.8% 30.4%
Carrots 45.5% 34.5%
It is easy to see from results like these that yield could be lower in the paddock, but more produce be saleable at the all important market end of the production process.
My friend Ted Sloane was an agricultural extension officer in New Zealand when he decided to take up farming. He decided to put his conventional agricultural training to practical use by growing kiwifruit. The results in terms of yield were extremely gratifying; they were the best in the district. Unfortunately, the keeping quality of the fruit was poor and losses in storage were over 20%. Consequently, his income was well below the district average.
It was fortuitous that one day when Ted was burying the recently deceased domestic cat that he noticed the prolific number of earthworms in the home garden in contrast to their complete absence in the orchard. It was then that Ted decided to replace his conventional fertiliser program with organic fertiliser. He chose a liquid fish product that was available locally. The earthworms proliferated and the wind-drifts of leaves that previously banked up against the windbreaks for many months were rapidly consumed by the improved soil biology. Ted managed to reduce his spray program from thirteen, or more per season down to two, or three. As a consequence of this, Ted went on to develop his own fish fertiliser and become a manufacturer25. Despite solving the kiwifruit growing problem, he was unable to control the ever decreasing price he received for the fruit.
Dr Mike Walker of Watercress Valley Herbs trialed a range of fertiliser programs on parsley. Not only was the fully organic patch yielding better than the fully chemical, but the storage life of the organic was way ahead. From his customers’ point of view, it was more economical to purchase longer storing herbs at a higher price less frequently than to pay less and have to buy more frequently.
Here again the organic grower has a multiple strategy of defence. The first line is to create as ecologically diverse an environment as possible. The few remaining pest problems can then be controlled by relatively innocuous materials. Aphids are controlled by soft soap (potassium stearate, Clensil), or garlic sprays, caterpillars by Bacillus thuringiensis (Dipel), mites with potassium permanganate (Chondy’s Crystals) or salt solution, slugs and snails with metaldehyde baits (protected from consumption by birds, or other non-target animals) and codling moth by pheromone traps. Neem is starting to take off as an effective non-residual broad spectrum insecticide with pest-repellent and fungicidal properties.
The traditional organic broad spectrum insecticide, pyrethrum can be used against a wide variety of insect pests, including pear and cherry slug. Commercially, pyrethrum is almost always mixed with the synergist piperonyl butoxide. The organic standards demand that pyrethrum be used without this additive as it is a suspected carcinogen. Its inclusion appears to be to give faster knockdown of the pest, rather than increasing its kill rate. Other traditional broad spectrum natural materials include derris, rotenone and ryania.
One pest control method of note that is remarkably effective is making a spray from the target pest and spraying the crop. Caterpillars, slugs, or whatever, are finely minced in a food blender, strained and diluted. The application rate per hectare is extremely low (around 1 kg of insects will treat 30 Ha). The theories as to why this works abound, but to the best of my knowledge no work has been conducted to ascertain which is correct. They include spread of disease from the few organisms infected through the whole population, interference with breeding patterns due to spreading the pests’ pheromones onto all the plants in an area and repulsion due to the odour of deceased organisms of the same type.
Before predators brought the slugs under control in my market garden, I used a similar technique. Hand-picked slugs were killed by dehydration in dry sugar and the resultant slimy mess fermented for a few days in a warm place. The resultant even slimier mess was strained, diluted and sprinkled throughout the market garden area (approximately 0.5 ha). The slug population dropped to a tolerable level in a matter of a week or so and returned only briefly three years later. A repeat application has seen no necessity for further control during a period of ten years. The effect also appears to have spread beyond the area treated.
Much work is being conducted on alternative methods of pest control and most is in the field of biological control. Predators and diseases are being bred for many of the more recalcitrant pests. While this is commendable, it is important to realise that they are generally more expensive than chemical controls and often no more effective than providing a biologically diverse environment that produces its own predators and other checks on pest proliferation.
A very new method involves saturating the environment with pheromones, the chemicals that insects use to find each other for the purposes of reproduction. As biotechnology increases its efficiency, we will likely see the day when it is economical to spray a paddock with a pheromone to dramatically reduce the rate at which specific pests can reproduce. A compelling benefit of this approach is that it is highly specific to the target pest.
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© Jonathan Sturm 2002 - 2011
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