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Calculating Straw’s True Value

This may seem an odd time for this topic to come up but my thought is that if one understands the potential value of your straw, it might help in your planning process for this fall’s residue management.

Usually, we value straw by calculating the macronutrient content, which disregards micronutrient values and nutrient release rates. What is missed in the calculation is the intrinsic value that comes from the carbon (organic matter) added, increased water holding capacity, enhanced water infiltration rates, mid-summer soil temperature moderation and erosion protection; all of which are extremely hard to place a value on. The full economic value of retaining or removing crop residues from the field depends on the:

present level of soil organic matter.

value of using the residues for other purposes (bedding, coarse feed or fibreboard).

need for extra field operations as a consequence of poorly spread or heavy residues.

early spring soil temperature considerations.

soil’s moisture content.

field’s soil erosion risk.

nutrient levels in the soil and residues.

While the value of the straw is most often calculated based on the nutrients it contains, it is important to understand that the C: N ratio of the residue controls the nutrients availability. Remember the tipping point for nutrient release or tie-up occurs at around 30:1. C: N ratio wider than 30:1 will immobilize nutrients in the short term and ratios lower than 30:1 will release nutrients. The wider the ratio, the longer and more severe the tie up, the narrower the ratio the quicker the release. Potassium (K) in straw is an important exception since straw K is very soluble and leaches out of the straw quickly. Consequently N, P, S, secondary and micronutrient release is directly mediated by microbial breakdown. While this article deals only with select nutrients, please keep in mind that all crop available nutrients can be immobilized and mineralized.

That all said, below is a little spreadsheet I created that helps me get a base value of my farm client’s straw to help them make better decisions of what to do with it. The underlying fertilizer prices came from various sources utilizing winter 2011 fertilizer prices, so you may want to adjust for your costs.

To play with your own numbers, go to http://agrology. agritrend.com/resources (then click on Straw Calculator).

Contemplate this data. Consider straw to grain ratios, cutting heights, chopping and spreading issues, chaff separation, residue analysis, etc. Accordingly, apportioned dollar values reflect future value, not present day value. Cereal residues typically immobilize 10 to 20 pounds of N for breakdown in the year after growth. With N approaching $0.58, this amounts to $5.80 to 11.60 per acre. You may wish to account for this in your straw valuation.

If you have an aggressive fertility program, you will likely findmorenutrients in your straw simply because you target bigger yields and better quality through balanced fertility strategies. As an example, when grain protein (N) increases so does the straw N content. Factor this in too! In other words, N release will be more rapid from a straw with a 45:1 ratio than 80:1. In fact, it could possibly provide much-needed late season N for wheat protein or unwanted late season N for malt. No matter, please factor in the “costs” associated with short-term N immobilization.

FIND MARKETS FOR RESIDUE

For harvested cereals, leave tall stubble (for snow trapping and erosion protection) and find uses/markets for straw. Some of you will be able to separate your residue into chaff (awns and leaves) and stems. Utilize chaff for feed (greater nutrient density) and bale the stems, while leaving adequate stubble height. In my mind, this provides a great compromise, which hedges most issues. Enough stubble is left for erosion control and moisture retention. Residue is utilized in two markets. N immobilization is minimized. Soils will warm more quickly in the spring allowing rapid emergence and early utilization of immobile nutrients.

Other alternatives include baling, silaging or burning (I know, I know, I’m going to a very, very hot place for even suggesting this) every two to four years depending on the severity of residue thatch. Two-pass systems with fall fertilization and spring seeding has several advantages to consider that may avoid all or some of this.

So now, what is your straw worth? Well obviously, it depends on your circumstances and perspective. Proper valuation of your straw resource is helpful, when we attempt to re-allocate scarce input resources to get the most value for your money.

ElstonSolbergispresidentofAgri-Trend Agrologyandasenioragri-coach

———

P2O5

12 15 14 24 30 9 44 6

STRAW VALUE CALCULATOR AVERAGE NUTRIENT CONTENT IN STRAW (POUNDS PER TON)

If

THEN

3.4 5

Crop

Wheat Barley

Oats Peas

Canola Soybean

Nutrient

N

P2O5 K2O

S

Crop

Wheat Barley

Oats Peas

Canola

N

Soybean 25.65

K2O

0.58

0.74 0.45

0.20

3.7 4.1

4.1 43 4.6 30

$/lb based on

insert insert % of

price nutrient

46-0-0 46

11-52-0-0 52

0-0-60-0

0-0-0-90

insert product used

30 2.8 41 2.8

50 9 60 8

%

60 90

S

$/ tonne

590 850

599 390

$N/ton $P2O5/ton $K2O/ton $S/ton

7.00

8.75 8.16

13.99

17.49

2.75

3.05 3.05

3.42

6.69

4.46

13.61

18.61 19.51

13.61

22.69

27.23

Ca Mg

4 5

Total $/ton

0.55 23.91

0.55 30.95

0.67 31.39

0.98 32.01

1.77 48.64

1.58 58.91

4 10

C: N Ratio

80:1 60:1

60:1 25:1

30:1 25:1

5 3 8 2

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