Technology has turned some of agriculture's trash, cereal straw, into an economic commodity in today's market place. Cereal straw is now being used as fiber. Cereal straw as a feed stock for bio-ethanol is almost a reality and who knows what is next? A dilemma is that direct seeders had already decided that straw was not "trash" but that it had some value and were developing their production systems around those values. Is technology going to pay enough for cereal straw to cover those values and a margin?
Many producers traditionally thought of their cereal straw as trash and not calculated the value of the benefits in the selling price for straw. One of the benefits of cereal straw is the nutrients it contains for future crops. A Farm Facts sheet entitled "Best Management Practices When Harvesting Surplus Cereal Straw" was put out this fall by Sask Ag & Food (SAF). They have confirmed that an average tonne(t) of wheat straw contains: N 12-15 lbs, P2O 4.5-5 lbs, K2O 27-34 lbs, S 2-3 lbs. The value of these nutrients are about $9.30 to $11.75. Another benefit of residue is its ability to prevent the processes of erosion. Over time there could be a substantial value put on this benefit. The next benefit is that straw contributes to the organic matter content of our soil. It is an important component of direct seeders ability to "build up" our soil. It is hard to put a dollar value on this benefit. A price for carbon sequestration would be part of this dollar value. Another benefit of straw in direct seeding is its insulating value conserving moisture. Again, very difficult to put a dollar value on this benefit.
Most straw in the past has been priced in baled form. This is the only way it can be transported. SAF's Custom and Rental Rate Guide gives a custom baling rate of $9.30/bale if you put 90 hours annually on your baler (this gives you $1.15 margin or profit). Considering the heaviest straw bales made, 2 of them could weigh a tonne. This makes $18.60/t for baling. Farmers know this rate guide is usually the high end of the scale. The local alfalfa dehydrating industry says they can get baling done for $12 - $13/t. That is about $7.30 a bale and it includes stacking the bales in rows in the field. That puts you at $15/t for baling straw.
In SAF's October issue of the Feed Grain and Forage Listing Service the lowest price for this year's wheat and durum straw is listed at $22/t. Although this producer might not think he needs to make a margin on baling he is still just getting paid for the nutrients in his straw. Isobord Enterprises, a large strawboard manufacturing company operating at Ellie, just east of Winnipeg, buys their straw in windrows in the field. They buy their straw for $8 - $9/t and they have had no problem procuring straw.
For the most part, the farmers that have survived to date are business men. There must be a reason why they are ready to let straw go for such a seemingly low return. About half of the nutrient value of wheat straw is in potassium. In most Saskatchewan soils (except some sandy and sandy gray soils) we have an excess of potassium and maybe we can afford to mine some. This will only go so far but maybe we justify selling potassium to buy other nutrients that will give us a yield increase next year.
Agriculture and Agri-Food Canada researchers have some long term comparisons showing productivity and soil quality differences after years of harvesting surplus straw or leaving it spread in the field. The best comparison for the purposes of this article is being carried out at Indian Head. This is in the black soil zone on heavy clay soils. After 40 years of returning cereal straw in one set of trials and baling it off in another, there was no significant difference between the amount of organic matter and nitrogen in the soil in the two trials. These plots were in a fallow-wheat-wheat rotation and were properly fertilized. The baled plots had the straw removed every year a crop was grown. In a discussion with Dr. Con Campbell, a former Agriculture and Agri-Food Canada researcher, he says that there was no effect on yield in this comparison. He does point out that they only removed an average of 22% of the above ground residue with their baling operation. The Best Management Fact Sheet gives these ratios: above ground material other than grain in a typical western Canadian wheat crop is 1.66 times the amount of grain produced. (However this ratio can vary from 1 to 4 t of residue to 1 t of grain.) They suggest that baling removes 0.6 - 0.8 t of residue per t of grain removed. This is a removal of 36 to 50% of the above ground residue. Another factor to keep in mind is the organic matter root production returns to the soil. When all these are added together, it is obvious that baling straw takes away a fairly small portion of the biomass produced by the wheat crop.
A low disturbance direct seeding system provides us with excellent erosion control. Leaving the stubble standing is what provides this control. Chopping and spreading straw doesn't add a lot to the erosion protection of standing (6" or higher) cereal stubble. This broad generalization should probably not apply to erodible soils such as sandy soils. If you have sandy soils you probably do not have too much surplus residue to harvest. You want to protect that light soil from wind and use as much residue as possible to build up organic matter levels. Also, soils with any amount of topography need all the protection they can receive against water erosion. If somehow it would be feasible to leave residue on eroded knolls even where straw from the rest of the field is being harvested a lot can be gained from trying to build these areas up. A certain quantity of residue is needed to protect any soil from erosion. The Best Management Practices fact sheet suggests that you need 750 lb/ac of standing stubble and 250 lb/ac of loose residue after seeding to protect your soil. A 40 bu/ac wheat crop cut at 6² high will leave 750 lb/ac of standing residue. As long as sufficient quantities of residue are produced baling will still leave enough behind to protect the soil.
A number of researchers seem to agree that surplus cereal straw is produced on many of the non-erodible soils of the black soil zone. In the gray soil zone organic matter contents are lower, the soils are more fragile and probably not a lot of straw should be harvested. In the brown soil zone a much lower quantity of residue is produced and most if not all of it is probably needed to protect and build up the soil and to conserve moisture. Wetter areas of the dark brown soil zone may produce sufficient residue for some straw harvesting.
The Best Management Practices suggest that in black soils, straw can be harvested every year that a cereal crop is produced. In the gray and brown soil zone, they recommend that a frequency of 1 in 5 - 7 years may be acceptable. One of the important understandings in these guidelines is that crops need to be fertilized to soil test recommendations. The fact sheet cites research work done in Alberta where soil organic matter improved even when all crop residue was removed as long as fertilizer was added to soil test recommendations.
Best Management Practices points out that harvesting residue form canola, mustard or pulse crops needs to be avoided. These residues decompose faster so maintain as much of these residues as possible for soil protection.
One of the benefits of residue that has only been touched on is that crop residue conserves moisture for the following crop. There certainly are instances in some growing seasons when this is a hindrance to the following crop. If a producer finds that there is often a time in his rotation when there seems to be excess moisture the previous fall, this would be the time to harvest residue. Here in the northeast, the most likely time this scenario happens is when canola is to be planted early into cereal residue. Probably the most beneficial time to harvest straw is at this point in the rotation.
There are a lot of community benefits and spin-offs to the ventures that are or would like to utilize straw. I believe that it is right for producers to do a lot to support these ventures. However, straw is not trash and I think that the market today is not quite or just paying for the value of the straw. Optimistically, I think the market will begin to recognize this and it will respond to give producers a margin. Until this response comes, I would rather error on the conservative side of protecting our soil resource by, even in the black soil zone on non-erodible soils with decent top soil levels, harvesting cereal residue 1 out of 4 years. SSCA recommends a basic cereal broadleaf rotation so that means straw from every other cereal crop would be harvested.