Soil structure is subject to a raft of influences related to soil type and all aspects of its chemical, physical and biological make-up. But these tiny critters are most influential factor. Their work is crucial because soil structure is directly linked to soil erosion, water intake and crop growth. A compact soil has a low infiltration rate. Whereas a stable, granulated soil allows rapid water intake, drainage, aeration and beneficial microbial activity. Crops grown in such soil respond well to favourable moisture, fertility and cultural practices.

Micro-organisms eat organic matter such as grass clippings, fallen plant leaves, and algae. In doing so, they reduce dead organic matter on Earth’s surface and release nutrients from the decomposing organic matter for living plants to use.

Some of them burrow and channel through soil, improving soil structure and aggregation in the process; while others have the ability to break down resistant organic matter such as lignin, toxins, and pesticides.

During the decomposition of plant and animal remains, micro-organisms produce many organic compounds and release organic substances that influence the stability of soil units. However, the ability of micro-organisms to stabilise soil varies greatly.

Some of the compounds that are produced and released have a tremendous effect on stability; others have little or no effect. Some of the natural products produced by micro-organisms are more effective per unit of weight than synthetic stabilisers.

The soil fauna is an important factor too. For example, earthworm can secrete slimes that render the cast several times more stable than the original soil. Under some mulching regimes, huge quantities of worm casts can be produced and deposited on the soil surface.

Micro-organisms also have the ability to protect plants from antagonistic pathogens, and some can dissolve minerals, making nutrients available to plants.

Earthworms are like "Nature’s tillers". They incorporate dead organic matter into soil, ingest it, and excrete the nutrient rich casts in to the soil. They improve aeration, water infiltration, drainage, and enhance nutrient availability and cycling.

Fungi are able to break down resistant materials such as cellulose, gums, and lignin. They dominate in acidic, sandy soils and in fresh organic matter. Plants roots and the mycelia (vegetative parts) of some fungi tend to push primary particles closer together to form aggregates or structural units in the soil. In other words, they help hold the soil together.

Earthworms, crayfish, ants and many insects also form aggregates, and, in many cases, may stabilise them. Some bacteria produce gums that have similar effects. Burrowing animals separate the soil mass into units. Actinomycetes can decompose resistant substances in soil. One type helps plants get nutrients from the air by breaking triple-bonded nitrogen down into ammonium that plants can use. Antibiotics are made from soil actinomycetes.

Bacteria decompose a wider range of earth material than any other microbe group. Heterotrophs gain their energy and carbon from other organisms, while autotrophs synthesise their own energy from light or by chemical oxidation. Some bacteria can fix nitrogen in to forms plants can use. Beyond the work of the micro-organisms, nature provides a number of examples of ways in which particles, crumbs, granules, lumps, clods and various aggregates are formed from the soil mass into the many-sized units found in the soil.

Changes in the charge of soil particles can account for the bringing together of very small (less than two microns) primary particles. However, this process is of limited importance in aggregation under natural conditions in the soil. When wet soil dries, the particles tend to come together as the attractive charges are brought closer together when water films between the particles are reduced. Drying can also cause unequal stresses that may break the soil into particles. Other physical forces, such as freezing and thawing, can also cause fragmentation on the soil mass into smaller units. While tillage, of course, breaks up the soil mass into various components.

John Barnes is the managing director of Fertilizer New Zealand Ltd. He can be contacted on 0800 fertnz (337869).

Laboratories usually report cation exchange capacity – the energy of the clay and the humus – in terms of milliequivalents. Think of this in similar terms to an electrician measuring electricity in volts and amperes, or a physicist measuring magnetic energy in ergs and joules. It all comes back to principle of positives and negatives. Negative attracts positive. Cation nutrients (which are positive) are attracted to and held on the soil colloids (which are negative), and remain free to move in the soil solution or water. A milliequivalent represents the amount of colloidal energy needed to absorb and hold to the soil’s colloid. For instance, in the top 17-18 centimetres of a 0.4-hectare (one acre) block of soil, the colloid is holding on to 182kg of calcium, 109kg of magnesium, 355kg of potassium – or, simply, 9kg of exchangeable hydrogen.

That’s the big picture, but what does it all mean for individual farmers?

It all comes back to soil analysis, and the need for you to know where your soil is.

Because the clay and humus that make up soil colloids carry negative charges, you need to use the right type of fertiliser. You need to use a fertiliser with a positive charge. Fertilisers with a negative charge will not be attracted to and held by the colloid, and you’ll be wasting your time and money.

Calcium and magnesium from lime compounds have this positive charge. So does sodium and hydrogen (in gas form). Negatively charged elements (called anions), such as nitrogen, phosphorous and sulphur, do not hold to colloids.

In addition the more colloids in the soil, the more negatives there are to attract the positively charged elements (cations). But there is always a saturation point. The soil can hold only so much fertiliser – put on too much, and some will be lost.

Colloids are also very mobile. Because they are the merest pieces of clay and humus (imagine broken-down particle of dust or talcum powder) they are extraordinarily susceptible to erosion.

If you could collect the dust the wind has shuffled around, you would find it has the highest fertility of any part of the paddock. When water or wind is at work, it always moves the most fertile part of the soil first. As a result, soils can not only be torn down, but also built up. Which explains why soil quality and fertility can vary so much in even in a small area. Remember that you cannot see any of this with the naked eye. But, while these colloids are microscopic, they form the bottom line in this positive-negative transfer (trade). They govern most of the chemical reactivity that goes on in soil.

The first thing you need to do for your land is to get a detailed analysis to measure the amount of clay and humus in the soil. You need to know your soils’ cation exchange capacity – a measure of your soil’s capacity to exchange nutrients.

The result will tell you a lot about its capacity to hold nutrients such as calcium, magnesium and ammonia nitrogen. It has a strong bearing on the quantity of nutrients needed to improve their relative levels in the soil.

This knowledge will help pinpoint the amount of fertiliser needed to get the right nutrient balance. It will also tell you about your soils’ capacity to retain fertiliser.

In other words, this analysis arms you with the information to use the correct fertiliser for your soil – and to use in the most effective quantities. The bottom line for you is; whatever you spend you know it will be effective.

John Barnes is the managing director of Fertilizer New Zealand Ltd. He can be contacted on 0800 fertnz (337869).

MAGNESIUM is an extremely important element for all stock. It is defined as a macro element, which means it is required in large quantities. Magnesium is vital for a number of different functions in the body; including relaxation of muscles and nerves, utilisation of calcium and converting sugars to energy. Magnesium is not stored well as a reserve in the body, therefore stock need their daily requirement from feed intake.

Under low magnesium uptake, hypomagnesaemia (or grass staggers) occurs which is most common at peak lactation. A heavily lactating animal requires three times as much magnesium as dry stock. Often with dairy cows you will not see the clinical signs of magnesium deficiency (muscle twitching, convulsions and death) but will suffer a drop in milk production and the cows will exhibit agitated/nervous behaviour.

Most of the soils in New Zealand have adequate levels of magnesium. However due to high levels potassium and nitrogen in pasture and the lack of magnesium fertiliser inputs, magnesium deficiency in livestock is relatively common. With the increasing awareness throughout pastoral farmers of the importance of magnesium nutrition VitaLife Magnesium has been developed. VitaLife Magnesium can supply two thirds of a dairy farms magnesium requirement if applied at 400kg/ha. As part of a well-balanced fertiliser programme VitaLife Magnesium can help in achieving optimum production from animals in optimum health.

Where soil Organic Matter is 10% in the top 7.5 cm, that soil is about 5.8% carbon. The bulk density of soil in the field is generally greater than one, if we use a bulk density of 1, this is 43,500 kg C in the top 7.5 cm, which is quite a large amount. There will be some C further down the profile so it is quite possible in summer moist districts that the C in the top 30cm of soil could easily be 100,000 kg/ha (100 t/ha).

Cultivation to grow one crop or to re-grass is likely to result in the loss of about 3% of the C during that growing season mineralised and released as atmospheric CO2. Repeat cultivation or cropping during successive years will result in a gradually reducing rate of C loss, but loss of C will continue and can be monitored with the soil OM test. Heavy or excessive applications of N fertiliser can eventually have a similar effect.

The good news is that management options can be taken aimed at accumulating soil C. Adoption of crop rotations where soil C (and N) is alternately accumulated under grass pasture and reduced with cropping was the basis of ‘old fashioned’ crop rotations practised before N fertiliser use increased dramatically. Irrigation of pastures has a beneficial effect, increasing plant growth (utilisation of atmospheric CO2) and decreasing the negative effect of summer dry conditions. Soil husbandry aimed at stimulating deep root development, application of lime to enhance soil structure and biological activity all have an effect on the soil C reserve.

If NZ is serious about managing C emissions and involving horticulture and agriculture, then monitoring of soil C is essential. There should be some incentive for land-based industries to be good guardians of the soil C ‘pool’. It could be worked into a carbon credit system. However this would be a ‘two edged sword’, if loss of C occurred, a debit would be incurred…

Food for though

The potential is BIG

If Carbon leaves the soil it has to go somewhere.

Yes…into the air.

If Carbon builds up in the soil it comes from somewhere…

Yes…the air

Credits: John Turner

•    John Barnes is the managing director of Fertilizer New Zealand Ltd. He can be contacted on 0800 fertnz (337869).

Nitrate losses to the environment were identified as “a key challenge for farming” in the 2004 findings presented by the Parliamentary commissioner for the environment, Morgan Williams, in his report, ‘Growing for Good: Intensive farming, sustainability and the New Zealand environment’. Williams drew on the words of Australian CSIRO researcher Barney Foran to an international grasslands conference in Palmerston North more than a decade previously:
“The biggest challenge at the moment is to produce a vision of why we produce products from grasslands. If we are worried by the energy consumption of our developed economies, then we must develop low-energy, integrated pasture systems that give high-quality products with no downstream pollution effects – a “cradle-to-grave” concept.
“Our experimental methods must now be redesigned to reflect product quality rather than product quantity. We must re-examine why production per hectare is seen as the holy grail. In many areas, land is overvalued in terms of its productive worth, rather than limiting in amount. We could do better by helping to crash land prices rather than developing technologies to run the land harder to make it pay.
“Grasslands give much more than production. Using our grasslands are people who are real, and have life goals. Many of our landscapes are beautiful and biodiverse, and our technologies must accommodate these other uses.”
Eleven years on, Williams reinforced Foran’s synopsis as being “even more pertinent”. “Unfortunately,” Williams adds, “New Zealand has made glacial progress in addressing (or even fully acknowledging the issues, opportunities and needs…in particular, the need for a new vision and to redesign farming systems seems to have gained little traction”.
“We cannot continue to respond so slowly and in such a piecemeal fashion.”
Williams says the redesign of farming “ranges along a spectrum from tools for remedy and mitigation of adverse environmental impacts, to the development of new farming systems which deliver environmental sustainability and economic wealth (i.e. sustainable agriculture), to approaches which promote sustainable agriculture and seek to integrate farming into the wider environment”.
“Hear, hear,” you will hear from us at Fertilizer NZ. Just like Barney Foran and Morgan Williams, our aim is to help farmers towards sustainability and wealth. We do it by providing them with products designed to keep the soil nutrients in balance, and, therefore, keep the soil healthy.
We know that healthy soil produces healthy crops and healthy pastures, which, in turn, produce healthy animals and healthy products, and, ultimately, healthy humans.
One of the secrets to Fertilizer NZ’s success is our access to special microbes that are renowned internationally for their ability to bring added value to soil.
These microbes – mycorrhizal fungi – have been shown to increase plants’ ability to absorb soil nutrients. There is a best balance of micro-organisms for each type of plant. If it’s right, the plant lives at its healthiest, and often yields to higher levels.
By judicious use of these fungi, phosphate in the soil can be used more efficiently, less nitrogen fertiliser needs to be used – and, all the time, production is maintained.
While several million microbes live in the soil, even more – up to 100 times more, in fact – live near and in the roots of plants. These microbes give phosphate to roots and, in return, receive carbon dioxide. In other words, they do naturally what nitrogen fertiliser is intended to do.
Mycorrhizal fungi are widespread in New Zealand’s native forests, native tussock, and agricultural and horticultural soils. They spread out into the soil, increasing the area of the host plant’s root system and stimulating soil phosphorus uptake. This improves clover growth at low to moderate soil-phosphorus levels and ryegrass growth at high soil-nitrogen levels.
Some strains of these fungi are more efficient than others, and some soils contain only inefficient species. The introduction of the more efficient fungi to these soils will increase plant growth through enhanced uptake of phosphorus.
It’s easy to overlook microbes. They’re infinitesimal beings so tiny you need a high-powered microscope just to sight them. They are so numerous that a teaspoon of soil contains more bacteria than there are people in the world.
And our entire existence depends on these unseen earthlings.
Obviously, at Fertilizer NZ, we are aware of the crucial significance of microbes. We are not alone. Many scientists and soil specialists around the world are aware of how much we depend on these mites, even though it is believed that barely 6% of soil microbes have been discovered out of potentially 1.5 million species of fungi, 1 million species of nematode worms, and similar multitudes of bacteria.
One is Landcare Research scientist Graham Sparling who sums up soil succinctly: soil is soil only if it has biological activity, otherwise it’s dead like moon dust – and we are lucky to have it in New Zealand. He is adamant humans have gone too far in their abuse of the soil that is their life-blood.
“We think soil comes for free,” he says. “It’s our repository for waste, it cleans up our excess liquids, contains out contaminants, and we use it for sports fields, golf courses and cricket pitches. We do all that, and think soil is miraculously going to take it all.”
No, he says, New Zealanders’ habits are coming home to roost as we tread down the same path as the European and Americans – unless we take action.
Which is where Fertilizer NZ comes in. Our philosophy of restoring and maintaining nutrient balance in soils, and fostering microbe populations, is designed to slow down the degradation Sparling speaks of and to reverse the trend.
Sparling, who has issued dire warnings on the state of New Zealand’s soils and natural environment, briefed Morgan Williams. Many of Sparling’s sentiments are echoed in Williams’ report which pinpoints the management of nitrogen fertiliser use as a key plank in the redesign of farming.
We believe Fertilizer NZ is capable of cleaning up New Zealand’s water – much of which is under threat from nitrate run-off and leaching.

Williams spells out specific tools and practices to achieve this management:

• Matching total nitrogen applied to attainable yield goals to avoid excess applications;
• Applying nitrogen only during suitable weather conditions  -  for example, late-autumn and winter fertiliser applications have the greatest risk of direct-leaching loss of nitrogen fertiliser;
• Timing nitrogen applications to fit pasture and crop needs, such as high nitrogen-demand periods;
  monitoring soil nitrate so that fertiliser rates can be adjusted appropriately;
• using nitrogen-stabilisation techniques to slow the formation of nitrate;
  specific placement of nitrogen-containing fertilisers;
• applying fertilisers with irrigation water for controlled plant uptake;
• balancing fertility to maximise nitrogen-use efficiency;
• application of nitrification inhibitors.

Which is very much what Fertilizer NZ’s philosophy and practice is all about.

•    John Barnes is the managing director of Fertilizer New Zealand Ltd. He can be contacted on 0800 fertnz (337869).

•    John Barnes is the managing director of Fertilizer New Zealand Ltd. He can be contacted on 0800 fertnz (337869).

Our ancestors were well aware that this “dust” of the soil is what determines vigour and health. Well before metabolism and enzymatic functions were known about, our forebears looked at what they saw around them, and declared that “the animal is a product of the soil”.Scientific discovery now allows us to put this belief in more modern terms which are, however, no more than a copy of the olden words – “The living organism (animal or human) is the biochemical photograph of the environment in which it lives, particularly of the soil which manufactured the nutrients for it.”

While our increasingly globalised world blurs this “biochemical photograph” for humans (it’s now more an album of many pictures of very different environments), the grass continues to maintain a close connection between soil and animals for most of the year.And this relationship reveals the profound influence of the soil on the cell metabolism of animals (which, incidentally, is very similar to that of humans). Between the grass and the grazing animal, we get an excellent “biochemical photograph” of the soil, which demonstrates how the elements of the soil control the functioning of the cells of living organisms.
All of the mineral elements in soil impact on the quality of the plants and animals that depend on the soil for life and survival. The mineral matter of the soil is a profound force in modifying the organic matter and metabolism of cells, vegetables and animals.

The traditional NPK – nitrogen/phosphorus/potassium – mix has long been the staple of the fertiliser industry. These elements are important and necessary in the soil to increase the level of organic matter in grass. But so, too, are the minor and trace elements – so named because they appear in very small quantities (parts per million or less). They play crucial roles in the manufacture of living matter. Some of them are names we know; others are less familiar. We’re talking of minor nutrients such as calcium, chloride, iron, magnesium, sodium and sulphur, and trace elements such as boron, cobalt, copper, iodine, manganese, molybdenum, selenium and zinc.

These trace elements are needed to activate the enzymes which, in turn, are the catalysts in the synthesis of living matter. In other words, the trace element is the catalyst that unleashes the catalyst.There are numerous examples to illustrate the beneficial influence of the correct use of mineral fertilisers – and, in particular, the strategic use of trace elements – on plant quality. Mineral fertilisers not only have the capacity to increase the yield of crops, but clearly also to improve the quality.
But it is crucial that they are used correctly and in the correct proportions. If fertilisers are used incorrectly, the quality of the produce is likely to be lowered.

These elements provide essential nutrients in the soil. The mineral matter of the soil obviously has a profound effect on the organic matter and the metabolism of cells, plants and animals.They also help the constituents of the soil to do their job. Take the amino-acids, for example. They’re the bricks from which proteins are constructed. Calcium, phosphorus, boron and nitrogen enhance the level of tryptophan, one of the essential amino-acids; sulphur helps raise the levels of two other amino-acids, methionine and cysteine.

Then there is catalase, an enzyme that comes to the aid of and plays a decisive role in helping cells that are struggling for life. A complete dressing of fertiliser enriches the soil’s carotene content; so does iron. And thiamine, one of the most important vitamins, thrives through the addition of phosphorus and potassium.But, be cautioned. The application of nutrients is all about balance. Balance is achieved by thorough analysis to establish what is lacking in the soil in question. The nutrients, or fertiliser, should be formulated specifically to remedy these identified shortfalls. It should be formulated with precision to achieve balance and health in the soil, rather than merely piled on quantity in the hope something will stick in the right place.

John Barnes is the managing director of Fertilizer New Zealand Ltd. He can be contacted on 0800 fertnz (337869).

The average person will assume that water simply moves downwards. But, in fact, if water is applied to soil at a single point, it defies the law of gravity and moves sideways just as fast as it goes down. The result – it soaks into the soil in a spherical pattern.

Of course, rain normally falls all over the soil surface rather than on a single point, so a horizontal "front" of water will generally soak in.

However, differences in soil texture – a subsoil hardpan or even just a change from fine to coarse, for instance – produce a barrier effect to water penetration. When water encounters this change, its rate of penetration slows considerably, and, in reverse, later rise of water to supply roots will also be slowed.

The role of porous matter, such as plant residue, in absorbing water can also be important under some conditions. Organic matter (a mixture of dead, decomposed humus and the living soil organisms) that has been thoroughly incorporated into the upper layers of the soil or is partly exposed to the surface acts as a wick to increase water penetration. A compact sloughed-under mass or organics matter will also act as a barrier.

Indeed, organic matter is of crucial importance in soil – it has been described as the "constitution" of soil.

The "humus" component of organic matter is a structureless material formed through the decomposition of mostly plant residues and manures. It’s a complex chemical mixture that includes proteins, lignin (originally part of plant-cell walls), fats, carbohydrates and organic acids.

Its colloidal nature gives it great ability to hold nutrients, which leads to a number of beneficial qualities:

• It stores essential plant nutrients – 95% of the nitrogen, 60% of the phosphorus, and 98% of the sulphur available to plants.

• It helps make some nutrients more soluble and available to plants. It stores nutrients and releases them when plants need them most. Acids in humus also dissolve soil minerals slowly and release nutrients.

• It contains substances that stimulate plant growth and improve both crop quality and resistance to pests and diseases.

• Its spongy nature allows it to absorb and hold large quantities of water.

• It contributes to good soil structure (tilth) by helping make the soil crumbly and porous. It also reduces wind and water erosion, and makes soil easier to work.

• It acts as a protective buffer to plants against high salt levels, toxic chemicals and drastic changes in pH.

• It’s a source of food for beneficial soil organisms, especially during fresh organic matter’s pre-humus form.

Now to the living part of the soil.

Fertile soil teems with a variety of plant and animal life, most of it microscopic and therefore little known and little appreciate by most people. But these life-forms – which include bacteria, actinomycetes, fungi, algae, protozoa, nematodes, worms and insects – are a valuable "work force" that performs a multitude of chemical transformations as well as many other services.

Bacteria, actinomycetes and fungi are the most important:

• Bacteria are single-celled organisms that can live in conditions with or without oxygen, but usually not in very acid soils. Soil bacteria help decompose organic matter to form humus, convert inorganic chemicals into useful plant nutrients, break down manmade toxic chemicals (herbicides and pesticides), and trap nitrogen from the air for later use by plants.

• Actinomycetes are thread-like organisms, somewhere between bacteria and fungi, that require aerobic, neutral or slightly alkaline soils. They help produce humus.

• Fungi, or moulds, are thread-like, mainly aerobic, and able to tolerate fairly acid conditions. Many of them help produce humus, and one particular group is especially because it lives inside plant roots helping absorb nutrients (especially phosphorus and nitrogen), secrete growth-promoting hormones and protect roots from disease.

• Soil organisms "tie up" nutrients from minerals and organic matter temporarily in their bodies and counteract the loss of soils nutrients through leaching into groundwater. When the organisms die, the nutrients become available to plants, which are fed slowly over the growing season.

• Soil organisms, along with humus, produce the "glue" – a sticky carbohydrate – that holds soil particles together and forms a loose, crumbly, porous soil.

Humus and soil life work together as a team to perform these valuable services – and, best of all, they work for nothing if given the chance. So why would anyone want to dump toxic materials on the land that will kill or inhibit this volunteer army?

More information: John Barnes, phone 0800 337869, mobile 021 2203944 email info@fertilizernz.co.nz


John Barnes is the managing  director of Fertilizer New Zealand Ltd.

Tiny flower buds are actually formed long before they become obvious. In corn, for example, the cob and tassel buds form when the plant is only about knee high. In apple trees, the buds that will produce next year are formed this year.

The quantity and quality of fruit and seeds depends partly on the number and health of the flower buds – along with other factors such as weather, light, nutrients and pollination. Farmers clearly have no control over some of these, but they can certainly influence plant nutrition and health. Once again, this reinforces the importance of fertile soil.

After flowers have been pollinated, seed and fruit development begins – and the nutrition and health of plants are critical during this time. Water, sugars, amino acids, organic acids, inorganic nutrients, and hormones from roots, stems and leaves are redistributed to the developing seeds and fruit.

Plants’ needs for some soil nutrients peak at this time – similar to the demands of human pregnancy. If plants are to cope properly with this demand for nutrients, their "plumbing" (xylem and phloem) must be in good condition, and all their metabolic and photosynthetic activities must be in top nick.

Remember the xylem and phloem. They’re the two tubular vascular tissue systems (like pipes) that transport water and nutrient molecules around the plant. The xylem tissue takes them mainly upward, while the phloem carries food and minerals from one place to another.

When water and nutrients get into the xylem, they are carried upward through hollow, tubular vessels by a pulling force from above. Those parts of the plant, such as leaves and actively growing areas, that need water create a water deficit and pull the water up through the xylem.

Both the xylem and phloem systems can be plugged if plants are not healthy. A lot of poor health in plants can be traced to soil problems – not enough nutrients; nutrients not available or not in the correct form; the wrong balance of nutrients (when nutrients interact, too much of one and not enough of another can have drastic adverse effects).

These problems can very often be traced to insufficient humus and soil organisms in the soil.

Now, imagine you’re inside a phloem cell and gliding down a leaf, back into the plant’s stem and out into, say, a developing corn cob. It’s a beehive of activity.

In the earlier stages of seed and fruit development, a lot of new cells are produced by cell division; later, the existing cells simply enlarge as the seed and fruit swells. Now, large quantities of food and other chemical substances from the leaves are moving into the seed or fruit for storage. Later, in grain crops, much of the moisture in the kernels is, or should be, removed, producing a "dry" grain that can be stored without turning mouldy.

In both seeds and fruit, there are also chemical transformations in the type of stored food, from sugars to starches, organic acids, proteins, and fats or oils.

These are all metabolic activities, and they all require cell energy (supplied by phosphate-containing energy carriers), enzymes and, often, hormones.

If the reproduction process is to occur normally and result in top-quality seeds and fruit, plants must be healthy, and well fed with water and nutrients.

If there are trace-element deficiencies, for example, there may be a shortage of the enzymes that regulate vital metabolic steps. This will lead to low test-weight, low yields or low-quality (low biological value) animal feed.

Or, if the all-important plumbing is blocked, the food the seeds and fruit need may not get through. Or water may not be removed, and the grain will not be "dried down" naturally – which will leads to additional grain-drying expense for farmers.

As with so many living organisms, most of these problems can be prevented quite easily. Prevention in this case comes down to maintaining a healthy soil with good tilth, adequate humus and soil organisms, and proper fertilisation.

 John Barnes is the managing director of Fertilizer New Zealand Ltd. He can be contacted on 0800 fertnz (337869).