What is the value of crop residue?

There is lots of talk about crop residue removal for bio-energy purposes. We have gone through the first wave of trying to make it very clear to those less familiar with agriculture that this crop residue has real value.

Crop Residue Value Components

Crop residue value hinges on a few components:

  1. Crop residues are critical for maintaining the organic matter fraction of the soil. This in turn impacts everything from yield potential to water holding capacity, to resistance, to compaction.
  2. When left on the surface or incorporated in shallow surface soil layers, residues are critical to prevent soil erosion.
  3. Crop residues have value based simply on the nutrients that would be lost if these residues were removed from the field.
  4. Value is attributed to residues based on the current price being paid for crop residues for traditional uses, i.e. straw for bedding, mushroom compost, etc.

So what are crop residues worth? The simple answer would be to pick up the phone and find out what someone would pay you for the wheat straw or corn stalks on your land. This would take care of item #4 above.

NPK Removal Value

Slightly more complicated is determining the value of the nutrients in the residue. Table 1 estimates nutrient concentrations in a tonne of corn stover, the fertilizer costs and the resultant fertilizer replacement value. At relatively modest fertilizer prices, the NPK (nitrogen, phosphorus, potassium) removal is valued at $22.73 per tonne of stover.

How Much Crop Residue Is Needed To Maintain Soil Organic Matter?

What are the key questions when considering the value of the residue as it relates to long term soil health, organic matter levels and sustainable productivity? How much crop residue does it take to fuel the organic matter furnace that exists in your soil? Organic matter is constantly being broken down by a variety of processes. Crop residues need to feed the cycle in order for soil organic matter levels to remain steady in an agricultural soil. The estimates for crop residue requirements are fairly wide ranging, depending on soil factors. However, a reasonable estimate is 10,000 kg/ha/year! That is 10 tonnes of crop residue (including roots) to keep soil organic matter levels from declining.

Crop Residue Availability

The University of Guelph evaluated crop residue availability (Table 2). On average, the crop residue produced in the corn – soy – wheat scenario was 11,575 kg/ha/year. If it takes 10,000 kg/ha/year to just maintain soil organic matter levels, the amount of crop residue you could remove without some impact on productivity would be quite small. Higher crop yields, manure additions, cover crops and tillage could all play a part in assessing the value of crop residue. However, it is clear that underestimating the amount of crop residue required for stable organic matter levels, may contribute to undervaluing the crop residues.

Table 1 – Nutrient removal and values from 1 tonne of dry corn stover.

Nitrogen
P205
K20
Total
Removal (kg/ha)
19
8
34
61
Removal (lb/ac)
17
7
30
54
Price of Fertilizer ($/tonne)

$500.00

(46-0-0)

$500.00

(11-52-0)

$500.00

(0-0-60)

Value of Nutrient in Stover ($/tonne)
$8.51
$2.98
$11.24
$22.73
Price of Fertilizer ($/tonne)

$750.00

(46-0-0)

$750.00 (11-52-0)

$750.00

(0-0-60)

Value of Nutrient in Stover ($/tonne)
$12.77
$4.46
$16.86
$34.09

Table 2 – Total crop residue production (above and below ground components) from a three crop rotation. Estimates provided by Hilla Kludze et al., University of Guelph, 2010.

Corn
Soy
Winter wheat
Grain Yield (bu/ac)
162
44
80
Total Residue (kg/ha)
17, 147
5, 658
11, 919