Most tillage practices residue cover. The amount of residue lost varies considerably due to the type of implement used, depth of operation and speed of travel. Tillage in the northern plains is done for a number of reasons. They are:

1. Weed Control
2. Residue reduction
3. Seedbed preparation
4. Incorporation of fertilizer and pesticides
5. Dry out the soil

Current research and producer experiences have found that many of these reasons for tillage are not valid. Most weeds can be controlled with chemicals and crop rotations, and many types of seeds are available that will work in high residue conditions. Many farmers feel that they must prepare a seedbed. This is sometimes difficult to determine. If the seedbed was looked at from a seed standpoint, it would probably desire a warm, moist, and firm environment. Two of these are available under no-till conditions. With no-till, the soil may remain cooler longer , but the extra moisture saved will usually more than compensate for the cooler soil by saving more soil moisture that can be used later in the growing season when rainfall tends to decrease. No till does provide a firm seedbed. The third desirable aspect of a warm seedbed is partially met by being able to plant shallow with no-till. In the northern plains, soil moisture is usually available near the soil surface in the spring. Spring tillage will dry the soil to the depth of tillage. In the northern plains, soil moisture usually is the major limiting factor to maximum crop production. If spring tillage is completed, it is best to keep it shallow to keep drying of soil to a minimum. Shallow tillage will usually control most weeds. Tillage for fertilizer and pesticide incorporation is often done in the fall and is especially common for anhydrous ammonia. The remainder of the fertilizer can be applied at seeding time with the drill in a one pass operation which includes fertilizer placement along with the seeding operation. Pre-emergent pesticides can usually be replaced with post-emergent types and many newer brands of seeders are capable of placing large quantities of fertilizer, including anhydrous ammonia, a short distance from the seed at planting time. In the Great Plains, it is extremely important to save as much moisture as possible if maximum crop protection is going to occur.

Considerable variation in residue loss occurs with tillage. The approximate percentage of residue cover remaining on the soil surface after a single pass of a tillage implement and seeding equipment is listed in the following chart.

Operation % Residue Left After Each

Operation

Spraying (chem fallow) 100

Undercutter (Sweeps 24" or wider) 70-90

Chisel Plow

Sweeps 50-80

Straight spikes 40-70

Twisted Points or shovels 20-50

Undercutter

V-Blade >30" wide 80-90

V-Blade 20"-30" wise 70-80

Subsoiler 80-90

Chisel Plow or Coulter-Chisel with:

Sweeps 50-80

Straight Chisel – 2"points 40-70

Twisted points or shovels 20-50

Disk – Chisel plow with:

Sweeps 45-60

Straight Chisel-2"points 35-55

Twisted points or shovels 15-40

Disk (tandem or offset)

Blade less than 23" diameter 40-70

Blade 23" to 28" in diameter 20-50

Blade over 28" diameter 10-40

One-way disk

12"-16" blades 40-50

18"-30" blades 20-40

Single gang disk 50-70

Field Cultivator 40-70

Harrows

Springtooth 60-80

Spike Tooth 70-90

Spring tooth with rolling basket 70-90

Rotary Tiller

Secondary operation – 3"deep 40-60

Primary operation – 6" deep 15-35

Rod Weeder

Plain rotary rod 80-90

Rotary rod with chisels 70-80

Anhydrous applicator 75-80

Rotary hoe 85-90

Mulch treader 70-85

Drills

Hoe opener drill 50-80

Single Disc drill 80-90

Double disc drill 70-80

Air seeder 50-80

Moldboard plow 5-10

Overwinter weathering 70-80

Many factors affect the amount of residue left after a pass with a tillage implement or seeding unit. Residue levels are sensitive to depth and speed of equipment operation and to the number of shanks or discs that are stirring the soil. When selecting values from the table for a specific machine, consider the following general rules. (1) At shallower operating depths, greater amounts of residue are left on the surface while at deeper operating depths, more residue is buried. (2) Slower operating speeds tend to leave more residues on the surface while at faster speeds more residue is buried. In the residue reduction ranges provided, usually the higher values can be used at 2" to 4" operating depth along with 3 to 4 mph speed ranges. If operating depths are 5" to 10" deep and travel speeds of 5 to 7 mph are used, the lower values are usually more accurate. Under some conditions field cultivators, some other implements and drills may return some residue to the surface that was incorporated at shallow depths by previous operations.

A chisel plow can leave as little as 20 percent or as much as 80 percent of the crop residue depending on the condition of the residue, tillage point, speed and depth. A chisel low with wide low rise sweeps operating at a low speed and shallow depth may be able to maintain a 70 to 80 percent cover. If twisted spikes are operated 8-10 inches deep and at 5.5 to 5 mph, only 20 to 30 percent of the residue may be retained on the surface. An undercutter with a 24 inch or wider blade will usually leave 70 to 90 percent of the residue. A tandem disk with small blades operated at a slow speed (3-4 mph) and shallow depth (3-4 inches) may retain 50 to 70 percent of the residue. But, operating a heavy disk with large blades 6 to 7" deep at a fast speed (6 mph) may retain only 20 percent of the cover.

Many farm operators think when they have an unworked stubble field after harvest, they have 100 percent cover. This usually is not the case. If base soil can be seen among the stubble, there is not 100 percent cover on the field. Typically most fields will have 80 to 90 percent cover after harvest.

The climate in the northern plains is usually dry and moisture conservation is extremely important. Maintaining a residue cover is one of the best methods of storing additional moisture in the soil profile. An additional inch of stored soil moisture can often result in a wheat yield increase of 3-5 bushels per acre.

Estimating residue cover in a field can be difficult. Calculating the amount of residue cover remaining after a tillage trip may or may not be accurate due to a number of variables. Some are the original amount of residue, the percent loss due to a tillage trip across the field, and the affect of weathering. Another means of determining residue is with a picture that is compared to the amount of residue on the soil surface. Again, this may or may not be accurate. Another method is determining percent cover by the line transect method. Usually, this is the most accurate but is the most time consuming as compared to the calculated or picture comparison methods. The following procedure explains use of the line transect method.

1. Use a 50 or 100 foot tape measure.
2. Select an area that is representative of the field and stretch the line out across the crop rows or tillage travel direction. The line may be oriented perpendicular to the row, or 45 to 90 degrees off the row direction.
3. Walk along the tape stopping at each mark. Position yourself directly over the foot mark and look down.
4. Determine the percent residue cover by counting at each one foot mark along the tape under which residue is seen. Count only on one side of the tape at each mark and only if a piece of residue is 3/32" or larger in size. If a piece of residue is smaller than 3/32" under the one foot mark, do not count it. Do not move the tape while counting.
5. When using a line with 100 points, the percent residue cover is equal to the number of points, under which a 3/32" piece of residue is seen. If a 50 foot tape is used, multiply the number of points times 2.
6. Three to five transects should be done in each field, using the procedure described in steps 1 through 5.