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Selling nutrients: the last straw

Practical Research: How to degrade productive cropland by selling the nutrients after the harvest season

When you sell straw or hay off your farm, have you ever considered the fate of the nutrients contained in the hay or straw?

Sandy soil areas are not uncommon on the Canadian Prairies, especially west and north of Edmonton, my home area. It made me wince when I saw endless lines of wheat straw bales on countless sandy fields this fall. Technically speaking, straw should never be sold on any kind of cropland unless there is a very good reason. A good reason is if potatoes are the next crop — straw is conducive to higher scab levels in potatoes. Perhaps the straw was unduly heavy in a given year and occasional removal would make seeding and soil management much easier. Otherwise why would any farmer sell straw? Unless the farmer is renting the land on a temporary basis, and the straw sale adds to income while debilitating nutrients in the rented land?

The average straw yield per acre from a 60-bushel crop of wheat would be from 1.5 to 2.0 tonnes (3,000 – 4,000 lbs) per acre. This straw would make 1½ to two large bales. Baled wheat straw is usually worth around $30 a tonne in good hay years, but in years of hay shortage wheat straw can be priced as high as $75 a tonne.

How much nutrient moves off the field in the straw per acre from a 60-bushel wheat crop? On average this amounts to around 30 pounds of nitrogen, 10 lbs. of phosphorus, 65 lbs. of potassium and 7 lbs. of sulphur. Current prices are: for N, $0.55/lb; $0.66/lb for P; $0.50/lb for K; and $0.55/lb for S. Total that up per acre, and it’s $16.50 for N, $6.60 for P, $32.50 for K and $3.85 for S.

The average value of nutrient removal per acre in the wheat straw = $59.45

At an average of 1½ bales per acre = $39.63 per one-tonne bale.

Baling costs, per round one-tonne bale: about $12 per bale.

Hauling and stacking round 1 tonne bales: about $3 per bale.

So, at $39.63 worth of nutrients and $15 in costs, the farm cost of a one-tonne bale are about $54.63. With a selling price of $75/tonne, there is some profit, if the price is any lower, let’s say $50 for the wheat straw bale, you’ve lost $4.63 per bale. Would you call that good business?

Would you, as a farmer be far better off using a straw chopper and leaving the baling to the hay and green-feed growers? Recent British research shows that chopped straw significantly reduces soil erosion.

Coffee shop chatter says returning wheat straw to cropland burns up the nitrogen. Plain nonsense. The chopped-up straw, at 1½ tonnes per acre will release very little of that N to the next crop and it will also tie up about 50 to 60 lbs. of additional N. This tie-up of N at about 100 lbs/ac will be released from the wheat straw and the microbial biomass (fungi, bacteria, etc.) over the next two to three years. You do not lose nutrients from your cropland since all of the N, P, K and S will be returned as nutrients to the cropland soil. This is how the prairies built up fertility (organic fraction) over the last 10,000 years. Do not forget that the 60-bushel crop of wheat also removed about 75 lbs N, 39 lbs. P, 24 lbs. K and 5 lbs. S from the soil. These are the actual nutrients that you lost per acre on your cropland in the form of 60 bushels of 12 per cent protein wheat. The actual cost of the nutrients lost in the 60 bushels of wheat that you grew is around $83 per acre, not including the nutrients in the straw. Thus, selling your cereal straw on an annual basis results in loss of organic matter, loss of water holding capacity, loss of nutrients, soil erosion and many other soil degrading factors.

Fate of the nutrients

When you sell straw or hay off your farm, have you ever considered the fate of the nutrients contained in the hay or straw? Much of the nutrients in the straw and hay go to feed dairy and beef cattle as well as horses and sheep. The livestock retain nitrogen for protein as well as lesser levels of P, K, calcium and magnesium as well as the hay and straw micronutrients. Much of the K and lots of the other nutrients will pass through these animals in the form of manure and urine.

As a consequence, dairy, beef and other livestock farmland actually becomes loaded with P and K but unfortunately both the N and S can leach out, and the N may become denitrified under some conditions. Such manured land, along with the end produce of other feed stuff in the manure become inundated with crop nutrients. Such cropland particularly in higher rainfall areas is prime land for the canola 100 competition.

I have soil tested dairy cropland in central Alberta and I have come across soils with as high 600 lbs/acre of available N in the top 12 inches, as well as high levels of other macro and micronutrients. What would your fertilizer inputs be for canola? Nothing. But, instead of putting six lbs. of canola seed per acre, two lbs. would be optimal to prevent severe lodging and consequently very high levels of sclerotinia.

I have seen beef cropland soil tested for nutrients at eight per cent organic with over 3,000 lbs of K and 300 lbs. of P with less than 10 lbs. of N in the top 12 inches and very low levels of available copper. In this instance the cattleman insisted that he applied cattle manure to this particular field every second year and insisted on adding 100 lbs annually of 15-10-15 per acre, saying this is what he’s done for the last 25 years. He blamed herbicide injury for his less-than-80 bu/ac yield of continuous barley. His solution resulting in a 150-bushel barley crop the following year, under strong advice, was 100 lbs. of N and 5 lbs. of copper in the form of bluestone or copper sulphate.

I hope this article does not confuse you. We need to resort to facts and figures, since crop production is a strict science not art by any imagination. There are no bio-miracles just plain cropland management.

In a subsequent article I will try to demonstrate to you the excellent benefits of crop residue and manure and compost to any and all cropland. I tend to speak (write) my mind because its hard to bite my tongue all the time.

About the author


Dr. Ieuan Evans is a forensic plant pathologist based in Edmonton, Alta. He can be reached at [email protected]

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