|
The Soil Tillage Intensity Rating's Purpose
The USDA-NRCS Soil The Soil Tillage Intensity Rating's allows
you to calculate Soil Tillage Intensity Ratings based on the Crop Management
System that is being employed on that land.
The Soil Tillage Intensity Rating is intended as a replacement for the Soil
Disturbance Rating component in the Soil Conditioning Index and to function
as a stand-alone rating to evaluate tillage and/or planting systems on
parameters other than the traditional ground cover and surface disturbance
parameters. It replaces the subjective ratings contained in the Soil
Disturbance Rating component of the SCI with more scientifically supported
parameters. It utilizes the various operations database parameters in RUSLE2
to calculate a soil tillage intensity rating for the system used in growing a
crop or a rotation. STIR ratings tend to show the differences between systems
across the spectrum from true no-till all the way to
conventional plow systems. It does so, better than do surface cover or
surface disturbance criteria since the kind, severity and number of ground
disturbing passes is evaluated rather than just the end result or a snapshot
of conditions after planting.
The components of the STIR rating are the following parameters from the
RUSLE2 operations database:
1. Recommended Operating Speed:
This process represents the recommended speed for this operation. RUSLE2 can
compute how speed of an implement affects residue burial. Speed between the
range of a minimum and maximum can be entered in the management screen. The
recommended speed is the generally is the recommended speed that the
manufacturer suggests for the implement. This speed is the default speed for
this operation, and indicates the assumed condition under which the
flattening, burial, and re-surfacing values are defined.
2. Tillage Type:
Tillage type describes how the operation mixes the soil and associated
residue. This variable refers to the type of mechanical disturbance on the soil,
and how that affects the distribution of residue within the soil. The
distribution of material, like plant residue, incorporated into the soil
depends on the type of mechanical disturbance, referred to as tillage type.
Also, tillage type affects the distribution of material within the soil as
subsequent mechanical disturbances, i.e. tillage operations, occur.
The following values are assigned to individual tillage types in the STIR
rating:
1.0 Inversion some mixing
0.8 Mixing + some inversion
0.4 Lifting and fracturing
0.7 Mixing only
0.15 Compression
Inversion with some mixing places most of the surface material in the lower
half of the depth of soil disturbance (tillage depth). In effect, the soil in
disturbance depth is “flipped over” with some mixing in the soil. Several
subsequent operations result in the material being somewhat uniformly
distributed in the soil. A moldboard plow is an example of an implement that
inverts the soil with some mixing.
Mixing with some inversion places most of the surface material in the upper
half of the depth of soil disturbance (tillage depth). The next operation
leaves a somewhat uniform distribution of the material in the soil. The
material becomes increasingly concentrated with subsequent operations and
moves down in the soil in a “lump”. Tandem disk, chisel plows, and field
cultivators are examples of implements that are a tillage type of mixing with
some inversion.
Mixing only places most of the surface material in the upper three tenths of
the depth of soil disturbance (tillage depth). The next operation or two
leaves a somewhat uniform distribution of the material in the soil. The
material becomes increasingly concentrated with subsequent operations and
moves down in the soil in a “lump”. Rotary tillers are examples of implements
of mixing only.
Lifting, fracturing places most of the surface material in the upper three
tenths of the depth of soil disturbance (tillage depth). The next operation
or two leaves a somewhat uniform distribution of the material in the soil.
The material becomes increasingly concentrated with subsequent operations and
moves down in the soil in a “lump”. Subsoilers,
fertilizer and manure injectors, and scarifiers are
examples of implements of lifting, fracturing.
Compression “pushes” surface material into the soil without the soil being
disturbed. The initial distribution of material in the soil is the same as
the mixing only tillage type. Examples of implements that are a compression
type include sheep foot’s rollers used on construction sites and cattle
trampling.
3. Recommended Tillage Depth:
Many site operations disturb the soil, causing changes in soil properties and
incorporation of surface residue. One of the key parameters is the depth to
which the residue is incorporated. Note that this may or may not be the same
as the actual depth of tillage. Typical implements work best at a particular
tillage depth recommended by the manufacturer.
4. Surface area disturbed:
The value sought here is used to determine the impact of the operation on
long-term soil consolidation. A plow assumed to completely invert the surface
layer would receive a value of 100%, while a no-till planter which cuts a
3-inch slot every 30 inches could be assumed to disturb 10% of the surface.
Disturbing the soil causes erosion to increase. Soil that has not been
disturbed for an extended period, (the time to soil consolidation—typically
assumed to be seven years), is assumed in RUSLE2 to only be about 45% as erodible as soil that has been recently disturbed.
Operations like planters and drills typically disturb the soil in strips. The
fraction (percent) of the total soil surface that is disturbed is the value
entered.
Selection of a value for the fraction of the surface disturbed sometimes
requires special consideration. In general, the area actually disturbed plus
the area receiving soil “thrown” (displaced) by the soil disturbance is used
for the input. However, if the displaced soil is very thin, the area of
disturbance may be limited to the fraction of the soil surface (source area)
that produces (generates) the displaced soil. This consideration is
especially important in certain no-till cropping systems where the displaced
soil doesn’t interfere with the typical effects of no-till with a buildup of organic
matter in an upper surface layer of soil of about 2 inches (50 mm).
Another special consideration is in the Northwest Wheat and Range Region
(NWRR) where most of the erosion is by surface runoff. Erosion by surface
runoff, which is rill erosion, is concentrated on much less than the total
surface. In this situation, a value less than the surface actually disturbed
and that actually receives displaced soil can be used so that the proper
effects of no-till are represented by RUSLE2.
The fraction of surface disturbed is an important variable for disturbed
forestland and similar lands are disturbed in a “patchy” pattern. This input
is used to represent the portion of the surface disturbed and it should not
be used to represent percent ground cover. Percent ground cover should be
based on the entire area, not just on the area disturbed.
The STIR rating for an individual operation is calculated by multiplying the
individual parameter values and by applying "weighting" factors for
each. All of the operations involved in tilling, fertilizing, planting,
controlling pests, harvesting the crop and managing residues are evaluated in
the STIR rating for a tillage system for a given crop. STIR ratings can be
calculated for single crops or for crop rotations. Higher STIR ratings are
shown for systems with greater disturbance and more frequent operations.
Comparison of STIR ratings for different tillage and planting systems
provides insight into the carbon loss, moisture depletion, and fugitive dust
issues related to tillage of the soil.
|
Example
STIR rating for a 3 year rotation:
|
|
Operation
Name
|
STIR
|
|
no
operation
|
0.0
|
|
Plow,
moldboard
|
52.0
|
|
disk,
tandem light finishing
|
19.5
|
|
Cultivator,
field 6-12 in sweeps
|
23.4
|
|
planter,
double disk opnr
|
2.4
|
|
Harvest,
killing crop 50pct standing stubble
|
0.5
|
|
no
operation
|
0.0
|
|
chisel,
sweep shovel
|
45.5
|
|
disk,
tandem light finishing
|
19.5
|
|
planter,
double disk opnr
|
2.4
|
|
Harvest,
killing crop 50pct standing stubble
|
0.5
|
|
Disk,
tandem heavy primary op.
|
39.0
|
|
Disk,
tandem secondary op.
|
32.5
|
|
Drill
or airseeder, double disk
|
13.8
|
|
Harvest,
killing crop 50pct standing stubble
|
0.5
|
|
Average
Annual Soil Tillage Intensity Rating (STIR):
|
83.9
|
|
|