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Assessing the value of organic matter

It may be important, but why?

November 13, 2007  By Ralph Pearce

48aGrowers understand the economics of farming. Most have an excellent grasp of heat units and which varieties and hybrids grow best. The basics of soil nutrients, particularly nitrogen, potassium and phosphorus, are well-engrained.

But ask about soil organic matter, and most growers agree it has a very important place in overall plant performance. Understanding why or trying to quantify it is a different matter.

As the 2006 growing season approaches, the economics of planting corn and soybeans is being scrutinized like never before. Some growers are talking about opting out of corn altogether, as a means of saving on fertilizer. But others, like Dr. Fred Magdoff and Dale Cowan, are encouraging growers to get down to the basics of soil management, including organic matter. Whether an individual understands the inner workings of chelation or the finer points of ‘the living, the dead and the very dead’ is not the key. Realizing there are options to improve crop performance and the bottom line.

Is there a value?

According to Dale Cowan, president of Agri-Food Labs in Guelph, growers have a basic idea of what soils with good organic matter contents look like, with darker colours and deeper profiles. “There’s an innate awareness that’s important, but for us to actually put our finger on it and say, ‘This field has four percent organic matter and this is two percent, and the four percent gives me $200 more per acre in income,” says Cowan. “That’s pretty hard to get evaluated, but that’s exactly what comes out of it.”

Again, the economics of farming in that part of the pricing cycle where cost per bushel is at or below the cost of production places less of a value on ‘the little things’. Yet they are the ones that add up the fastest and have the greatest benefit to soil health. “The thing about organic matter is what it does for a soil: where you can still get compaction but it allows the soil to heal itself very quickly,” says Cowan. Yet in spite of its benefits, organic matter is hard to build and maintain. Studies he knows of cite 25 tonnes per acre of dairy manure per year, just to balance the organic carbon losses and gains. “It’s a continuous process, and it’s not your organic matter level that’s important, it’s the fact you’re doing these things that enhance organic matter, to break it down as much as you build it because it’s the process that creates the benefits to the soil.”

Some confusion in C and N

When it comes of organic matter basics, Dr. Fred Magdoff is considered a leading authority. A professor and soil researcher at the University of Vermont, in Burlington, Magdoff believes there are perception problems with organic matter. In the current economic climate in southern Ontario, where hog farming has increased in intensity in the last decade, nitrogen is a valued component. Especially at a time when so many growers are trying to reduce fertilizer costs or considering dropping corn from their rotations.

Yet it is the carbon in dairy manure and in plant residues that are vital to organic matter development. Thus organic matter increases with the application of dairy manure, more so than with hog manure. The inclusion of a sod-type or forage crop in rotation also helps. “There are growers who are not using nitrogen fertilizer because they’re producing their own nitrogen with cover crops or by rotations with legume forages,” relates Magdoff, citing the challenge of balancing the ideal with reality. Economics and the rise in hog farming make it hard to dismiss nitrogen in Canada. “It does help break down the carbon, which you want because it’s during that decomposition process that so many things happen. It’s food for lots of different organisms in the soil that help maintain the balance.”

Reality forces some growers

It is often true that dairy farms have some of the better soil types and organic matter levels, just by their rotations and forage requirements. But it does not make it impossible to build organic matter without dairy manure. The use of green manures, in the form of a forage crop that is suppressed prior to planting, is one method of compensating for a lack of cattle manure. Magdoff agrees dairy producers have a head-start on organic matter levels, just by the nature of their farms. “Partially, you have an economic reason to have crops like hay, so you’re not plowing the soils every year, just two years out of five or six,” he says. “That really helps to build up soil organic matter and soil structure, but even that doesn’t guarantee anything. And then there’s all that manure from dairy farms that helps to maintain or build soil organic matter.”

Asked if the scenario he typically sees in Vermont can be applied to farming in Ontario, Magdoff concedes it is harder to use only hog manure, especially if there is no carbon substrate like sawdust or wood shavings for bedding. “Then it doesn’t have the same effect,” he says. “You’re getting nitrogen out of it, you’re getting phosphorus out of it, you’re getting potassium, but the contribution to organic matter, while it’s there, is probably not very large.”

Better to change… now

All the more reason, adds Magdoff, for growers to look closer at management decisions like applying large amounts of fertilizer without scientific justification. Economics will no longer allow growing corn according to tradition. In an ideal situation, a grower would assess what the soil provides in terms of nutrients and organic matter, then grow the crop or crops best suited to those conditions. Yet too many growers are still applying fertilizer in spite of the cost. One operation Magdoff knows of spent an average of US$14,000 annually on fertilizer, despite tests that showed no yield response in corn.

It is commonly possible, he concludes, to grow crops using reduced fertilizer applications, and for very fertile soil, without any at all. But it requires more precision and a determination to ask ‘why’ of each management decision to be made. “Use of better rotations, cover crops, and judicious use of animal manures or other sources of organic materials result in a lot of intangibles that add up. There’s better water storage and nutrient availability as well as control of soil borne disease and parasitic nematodes, so it’s a package of practices, and it’s going to be somewhat different on each farm,” says Magdoff.

Every farm is unique, as is the grower, the soil, the climate and the need for highest economic return. “But those that do a good job of organic matter management have a leg up, as far as soil health.”

The bottom line

Soil organic matter is of great concern to us. Our North Gower clay soil is very prone to compaction. We do not have access to dairy manure so all cereal straw is worked back into the soil. Hay is not an option, so we are underseeding on a rotational basis with a clover plowdown. Rotation seems to be the key to helping the soil keep its health. – Grahame Hardy, Inkerman, Ont.

‘Soil health’ is the message. Our challenge is to attempt to restore our soils to where they once were, while coping with the reality of making a living from every acre we farm.

In a droughty year, you can tell the soils that have had manure applied, that have had a proper rotation and have had a balanced fertility program. The crops are greener, further advanced, are more forgiving to compaction and have better ‘staying power’ as a result of having the right things done to it. – Andy van Niekerk, Stayner, Ont.



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