Field Residue Decomposition Trials
History: In the late 1990’s, commercial lawn care companies were looking for an
organic thatch reduction material. Several products were screened for this purpose.
The product that proved to be most effective was an OMRI registered emulsified fish
material (Pacific Natural) produced in Vancouver, British Columbia. Pacific Natural was
labeled as both an organic fertilizer and a compost accelerator. It has since been shown to
contain two times the cellulose digesting bacteria as any other fish fertilizer. This is due
to the single species of fish being used to produce Pacific Natural. For the last several
years, Pacific Natural has been commercially sold for thatch reduction in residential turf,
commercial turf and on golf courses.
Starting in 2000, Pacific Natural was introduced into commercial agriculture for field
residue reduction. It was first used on Blue Grass sod. Several pivots of Blue Grass seed
were being rotated into potatoes the following spring. Historically, residual sod requires
hand removal at harvest. After Roundup herbicide was applied to the grass field and the
sod disked, eight gallons per acre of Pacific Natural was applied through the pivot
irrigation system. On fields where this practice was used, we observed the following:
a. All of the sod residue had been completely composted in the soil,
b. The soil was more mellow, less dirt was been removed from the
field,
c. A slight increase in yield due to an increased tuber set.
Pacific Natural has become the standard material used for the decomposition of sod, from
both grasses grown for seed and pasture grasses in fields being rotated into other crops.
In the Spring of 2002, a potato grower in Royal City, Washington planted a field that had
been in wheat the previous year. This field had excessive straw residue. Potato planting
was difficult due to straw plugging the planter. At row closure, late June, 5 gallons of
Pacific Natural and 5 gallons of urea solution (to help adjust the C to N ratio) was applied
through the irrigation system on one-half of the field. In late August, ten feet sections of
row were screened with a ¼ inch mess screen to evaluate residual straw. The following
picture confirmed the activity of this treatment. Note: an increased number of tubers with
smaller size in treated area. This is attributed to a nitrogen flush created by composting
of residue too late in growing season. Also note the bright color of straw in control.
Little decomposition has taken place after 2 months in moist soil.
Field residues, such as sod, straw or corn stubble, cause several problems for the grower
of root and tuber crops:
Potatoes:
Sod and Corn Stubble – must be hand removed at harvest
Cereal Straws – in addition to planting difficulties, can cause an unwanted
nutrient imbalance during the growing season
Sugar Beets:
Any crop residues – interfere with precision planting where seeds are
evenly spaced at a relatively shallow depth. In addition, any straw that
extends from the surface to seed depth becomes a conduit for frost.
In-field composting, decomposition of field residues, offers the following benefits to the
grower:
1. Ability to rotate root and tuber crops into cereal and grass fields
2. Save tillage costs to incorporate residues
3. Improve organic matter and tilth of soils
4. Provide a safe, simple application product (as opposed to sulfuric acid)
It has been noted that some potato processors are rejecting shipments that contain corn
stubble residues. With corn acreages increasing due to ethanol production and the
increased number of cattle on feed in Idaho, decomposition of corn residue is becoming a
priority.
2007 Corn Residue Decomposition Trial
Procedure:
April 24, 2007, approximately two cubic feet of soil, with an abundance of crop
residue, was collected from a field in St. Anthony, Idaho.
Three digester boxes were constructed, interior dimensions of 12”X12”X 8” H
Collected soil was sifted with ¼” mesh screen to remove residue.
A base soil sample was taken from the sifted soil. Approximately 2/3 of sifted
soil was evenly distributed into digester boxes.
Crop residue was divided into three lots, cob and root ball quantities were
equalized. The weight of each lot was noted.
Crop residue was introduced into the digester boxes.
The boxes were noted, from left to right, as control, treatment 1 & treatment 2.
Soil temperature was noted at 56° F at time of treatment.
The control was misted with approximately .10 inch of water, covered with 1/3 of
the remaining sifted soil, and misted with another .10 inch of water.
Treatment 1 was the equivalent of 5 gal/ac of Pacific Natural and 5 gal/ac of
20-0-0 urea solution in .20 inches of water, applied directly to residue before
covering with 1/3 of remaining sifted soil. This treatment was to determine the
necessity of having direct contact of residue and treatment.
Treatment 2 was covered with the remaining sifted soil and treated with the
equivalent of 5 gal/ac of Pacific Natural, 5 gal/ac of 20-0-0 urea solution, 8 oz per
acre Wil-Pen soil surfactant in .20 inches of water. This treatment was to
determine if decomposition was as effective if treatment was made after
incorporation of residue.
During the next 50 days, the boxes were kept moist with rainfall and additional
water amounting to approximately 2 inches of water. It should be noted that two
days during this period had daytime temperatures in excess of 90° F. The boxes
were allowed to dry for 5 days prior to evaluation of decomposition.
Due to obvious difference in weed growth between treatments, weeds were
harvested from each box independently, counted and weighed.
Control
Treatment 1
Treatment 2
Contents of control and treatments were sifted across ¼” mesh screen, residues
were analyzed and weighed. Soil samples were collected from the sifted soil for
each box.
Results:
Weed Production
Control
Treatment
Control
Treatment 1
Treatment 2
Treatment 1
Weed Population
134
193
174
Treatment 2
Weight
1.40 oz
2.00 oz
1.50 oz
As the three boxes were sifted, it was obvious that Treatment 2 soil was more
moist. This could have some effect on weight of residue since it was not dried,
before or after treatment. This was done to duplicate field conditions as closely as
possible.
Residue Decomposition
Control
Treatment 1
Treatment 2
Treatment
Beginning Weight
Ending Weight
Reduction
Control
19.00 oz
7.25 oz
12.00 oz
Treatment 1
23.50 oz
8.25 oz
15.25 oz
Treatment 2
28.00 oz
10.00 oz
18.00 oz
Please note difference in color of residue. Composting is definitely in progress
for both treatments. In both treatments, there was good reduction of root stalk
ends, cobs were still intact, but soft, indicating that decomposition would occur
with more time.
Soil Test Results
Change Trtmt 1 Change
-42
73
-52
-10
28
-9
+1
69
-4
+83
335
-30
+1
30
+2
+0.3
6.0
+0.2
-0.10
1.15
+0.03
+0.05
0.70
-0.08
+0.3
8.2
-0-2.0
7.0
-3.0
-0.6
1.6
-0.6
-4
75
+2
-03.2
-0.1
-0.1
0.7
-0.1
Base Control
Trtmt 2 Change
NO3 #/ac
125
83
87
-38
NH4 #/ac
37
27
28
-9
P ppm
72
73
71
-2
K ppm
365
448
398
+33
SO4 ppm
27
28
26
-1
pH
5.8
6.1
5.9
+0.1
OM %
1.12
1.02
.97
- 0.15
B ppm
0.78
0.83
0.79
+0.01
Zn ppm
8.2
8.5
8.0
-0.2
Mn ppm
10.0
8.0
9.0
-1.0
Cu ppm
2.2
1.6
1.6
-0.6
Fe ppm
73
69
65
-8
Ca*
3.3
3.3
3.1
-0.2
Mg*
0.8
0.7
0.7
-0.1
*Meg/100 grams
The changes in soil tests can help explain the difference in weed growth.
Even though additional nitrogen was applied as urea, less NO3 and NH4 was
available in the soil after 55 days in both treatments. Some of this reduction
can be attributed to moisture at the time of sampling.
Economics
Conclusions
Corn stubble residue can be reduced by applying Pacific Natural and urea
solution. Rates are 5 gal/ac Pacific Natural blended with 5 gal/ac 20-0-0.
Resent research also indicates that humic or other organic acids may
accelerate this process.
Best application timing would be in the fall just prior to disking.
Apply through the irrigation system with a minimum of .20 inch of water.
If application is made after disking, use a good quality soil surfactant such as
Wil-Pen at labeled rates.