17.73 Table 1. Average Nutrient Content In Straw*
* straw with 10 per cent moisture
** based on fertilizer prices of 60/lb N; 55/lb P2O5; 26/lb K2O; and 25/lb S.
Peas N (pounds per ton)
12 15 14 24 P2O5 (pounds per ton)
K2O (pounds per ton)
30 41 43 30 S (pounds per ton)
Total $/ ton**
Straw and chaff from annual grain crops hold a very tangible and lasting value for the soils that produce it. Baling this residue for feed or bedding it or burning it has a cost.
“Weigh the options and try to estimate the value of that crop residue we sometimes call trash,” says Ron Heller, Alberta Reduced Tillage Linkages (RTL) program agronomist, Vermilion. Heller is cautious about selling crop residue for removal from the field. “The decision will always come back to soil quality. For example, the drier you are, the more you need that residue in place to catch snow or slow down evaporation. Water is a growing crop’s most essential nutrient.”
In addition to conserving soil moisture, the actual value of crop residue depends on the existing soil organic matter level, soil erosion risk, nutrient levels in the residues and the soil, problems caused by excessive or poorly managed residues, including reduced tillage, and alternative uses such as livestock or industrial supplies.
Climate sets the stage for soil quality, crop production and for crop inputs. Climate also built the soil base. Whether coarse sand, brown clay or black loam, in all regions crop residue has three important soil quality functions. It prevents moisture evaporation, protects against wind and water erosion, and provides nutrients for soil fertility.
HOW MUCH RE SIDUE DOYOU NEED?
Scientists estimate that preventing erosion on gentle slopes requires 700 pounds of residue per acre. That requirement soars to 1,500 pounds per acre on moderate slopes. Similarly, most soil needs 30 per cent ground cover to prevent wind erosion. Sandy soils may need 60 per cent cover. Standing stubble anchors soil. Mulched crop residues reduce wind speed and drying at the surface.
In the moisture-challenged brown soil zone, Heller says, “somebody would have to pay you a lot” to make selling crop residue from your field a worthwhile proposition. “If somebody wanted to buy it from me, I’d say show me the money to replace the long term value. I value residue because I want my soil to remain productive. To me, soil quality is associated with sustain-ability.”
EXCEPTIONS TO EVERY RULE
The occasional sale of crop residue may be acceptable where the Prairie climate generally permits production of generous amounts of crop residue. Heller points out that it comes down to the crops we grow and practical implications for our seeding systems.
Peas for example are unlikely to leave excess amounts on the ground, nevertheless pea vines can be troublesome sometimes for direct seeding and can be more favorably viewed as quality livestock feed. Cereal crops may leave more than enough residue for ground cover requirements, assuming it isn’t a drought year. Certain crop residue, such as flax, can be difficult to handle, and may be better off removed and sold rather than left in the field.
Crop residue management is an important component of reduced tillage systems, and direct seeding equipment will be a factor. “Calculate the seedbed utilization, or how much soil disturbance is happening and the stubble knock-down potential. Can you retain at least 30 per cent residue for soil cover after seeding?”
Whether the harvest excess should be sold off or managed differently requires some thought. Erosion risk should never be ignored. Heller suggests it may be wiser to invest in a better seeding system that will cope with the extra residue rather than use tillage. The true “investment” opportunity to improve soil quality over time might be in maintaining sufficient residue on the field.
“When it comes to estimating the value of crop residue, there’s certainly good reason to leave it in the field. Why get rid of it?” Heller asks. “In some cases, if you sell it today, you’ll be buying additional fertilizer later, and at what cost?”
On the other hand, for good soils with low risk of erosion and after a high-residue crop like wheat or barley, straw removal once in three or four years may not be detrimental. These highly productive soils with decent rainfall will retain enough residue from other crops in the rotation to sustain high yielding, high quality crops in normal situations. Rotational removal of crop residue may sometimes be required in order to avoid problems, especially with a poorly designed no-till seeding system. “Go ahead, bale and sell it to a needy neighbour with cattle, or even a strawboard company if the price is right,” says Heller.
Livestock producers can also manage crop residues used for feed and fodder needs in a manner that respects soil. “Done right, swath grazing, winter field feeding, and composted manure applications do not compromise direct seeding,” Heller states. Each practice holds merit to optimize the retention, return or recycling of valuable nutrients. Both soil and crop benefit.
HOW TO CALCULATESTRAW VALUE
In much of Manitoba and across the moist Parkland region of Saskatchewan and Alberta, climate determines tall, heavy straw production on a regular basis. Some farms have 18 inches of black loamy soil, more than six per cent organic matter, and produce substantial crop residue virtually every year. In these conditions, many crop residues decompose more quickly than in drier, low organic matter soils where nutrient cycling is slower.
New crops gain nutrients from the previous residue, reducing part of the current fertility requirements. The value of that nutrient contribution from residue can be calculated, but will vary with the type of straw, fertilizer prices, and the baseline soil analysis. See Table 1.
Carbon content of crop residues may be another evaluation element for growers to consider in light of what’s happening with climate change and carbon trading. Heller thinks it should be worth more, but points out that currently carbon can be traded for somewhere between $5 to $10 annually per acre netback to direct seeders.
By default, when we produce residue we cycle carbon, but sequestration is not well understood and is very climate specific. It’s hard to scientifically specify the amount of soil carbon gained from each residue, or just what that means, but it is there. Heller suggests, ask yourself, why would you destroy, remove, or sell someone else the credit?
“If a farmer ignores the value of his crop residue, he’s going to lose money somewhere,” Heller says. “It has a very intrinsic value in terms of nutrient management. Soil moisture is the most essential crop nutrient we can have. Retaining or returning adequate amounts of crop residue in a direct seeding system will pay dividends over time.”
For more information about residue management, direct seeding, and other reduced tillage practices, go to RTL’s website atwww.reducedtillage.ca.