University of Missouri Extension

G1650, Reviewed December 1993

Conservation Tillage and Residue Management to Reduce Soil Erosion

John R. McCarthy
Natural Resources Conservation Service
Donald L. Pfost and H. David Currence
Department of Agricultural Engineering

Crop-residue management through conservation tillage is one of the best and most cost-effective ways to reduce soil erosion. Conservation tillage and residue management may reduce machinery expenses and save soil, labor, fuel and money. Crop residues uniformly distributed over the soil surface will significantly reduce soil losses over an entire field. On terraced land, the resulting reduction in soil losses due to this residue cover can greatly reduce the cost of terrace maintenance.

The erosion process

Two mechanisms are involved in soil erosion: soil detachment and soil transport. Most soil detachment is caused by raindrop impact, a major factor in sheet erosion. The average erosion from cropland in Missouri is about 10 tons per acre per year, equivalent to about 0.07 inches (slightly over 1/16 inch). Sheet erosion can go almost undetected for years, often causing great losses in productivity before the landowner becomes concerned.

Some soil detachment is caused by flowing water, especially where water concentrates to cause gullies. Gullies created by flowing water may be either ephemeral or permanent gullies. Short-lived gullies may be filled in by heavy tillage operations but tend to reform annually in the same location.

How residue reduces erosion

Residue (and crop canopy) can reduce soil detachment by absorbing the impact of falling raindrops. Also, residue may form small dams which retard runoff and create puddles of water that can absorb raindrop energy, thus reducing both detachment and transport of soil particles.

Sufficient amounts of crop residue left on the soil surface can almost eliminate erosion on many fields and greatly reduce erosion on other fields. In areas of concentrated water flow, such as natural or designed drainage ways, crop residues alone generally are not enough to control erosion. Such areas may require permanent grass seedings and/or some structural measures such as diversions or terraces (especially to control gully erosion). On long slopes, detached crop residues may be floated away by the higher water velocities attained in sheet flow. Once removed, erosion due to detachment and transport will accelerate. Terraces and diversions, in combination with crop residues, may be needed to control sheet erosion.

Conservation tillage defined

Conservation tillage is defined to be any tillage/planting system which leaves at least 30 percent of the field surface covered with crop residue after planting has been completed. Figure 1 shows that erosion is reduced by at least 50 percent (compared to bare, fallow soil) if 30 percent of the surface is covered with residue.

Tables showing the effect of percent ground cover on the soil-loss ratio. Figure 1
The effect of percent ground cover by residue (mulch) on the soil loss ratio (compared to a bare, fallow soil)
 

Enhancing residue management

Residue management (through conservation tillage) for erosion control can be enhanced by:

Other conservation tillage benefits

Minor benefits from conservation tillage may result from less tillage leaving the soil surface rougher to retard runoff and increase infiltration. Random roughness may result in shallow puddles, which absorb some of the impact of falling raindrops (water deeper than the raindrop diameter can absorb a considerable portion of the raindrop energy). Contoured furrows, especially from twisted chisel points or ridge planting, may temporarily impound water during heavy rains. This impounded water can absorb raindrop impact and increase infiltration (especially if compared to furrows up and downhill).

However, little credit for soil-loss reduction is given to these factors, since these benefits may be temporary and usually are eliminated by future rains and/or additional tillage. Residue cover therefore is credited as the major factor for reducing soil loss with conservation tillage.

Estimating percent residue cover

Three methods are commonly used to estimate the percent residue cover remaining after tillage/planting operations.

The photo comparison method
Visual estimates may be made by looking straight down on the soil surface and comparing the appearance with photos of known percentages of the same type of residue. Do not try to estimate percent of cover by looking across a field; bare spots behind residue will be hidden from view.

A more time-consuming and accurate method involves projecting photographic slides of the surface onto a grid and determining the percent of grid intersections coinciding with a piece of residue sufficient to absorb the impact of a raindrop. This method is frequently used for research.

The line-transect method
The line-transect method is a practical field method of estimating the residue cover after any operation. This method involves stretching a 50- or 100-foot tape (or cam line) diagonally across the crop rows, and then checking at every foot mark to see if a piece of crop residue is lying under the mark.

When using a 100-foot tape, the percent cover is equal to the number of marks underlain with a piece of residue. When using a 50-foot tape, double the figure to obtain percentage of cover.

To use this method, look straight down at the same side of the tape and when in doubt if there is residue that will absorb the impact of a raindrop under a mark, do not count it. Care should be taken not to overestimate the percentage of cover. Take the average of at least three such readings at typical spots in the field to have a reliable estimate of the percentage of cover.

Calculating residue production

The following amounts of residue are commonly accepted to be produced by various crops:

Crop Residue produced per bushel of crop yield
Corn 60 pounds
Grain sorghum 70 pounds
Soybeans 50 pounds
Small grain 100 pounds

Figure 2 shows the relationship of the percent of surface cover to the amount of uniformly distributed residue mulch for various crops. Ninety-five percent surface cover will be provided by 4,500 pounds of small-grain residue or 6,000 pounds of corn or grain sorghum residue. Increasing weights of residue produce diminishing increases in percentages of surface cover, especially after the surface is 90 percent covered.

Graph showing the relation of percent cover to dry weight of uniformly distributed residue mulch. Figure 2
Relation of percent cover to dry weight of uniformly distributed residue mulch.
 

Post-operation calculations

To estimate the percentage of residue surface cover remaining after future tillage and planting operations, calculations may be made using the data from Table 1.

Table 1
Influence of field operations on surface residue

Implement Percent residue remaining
Non-fragile (corn) Fragile (soybeans)
Plows
Moldboard plow 0 to 10 0 to 5
Moldboard plow — uphill furrow 30 to 40  
Disk plow 10 to 20 5 to 15
Machines that fracture soil
Paratill/paraplow 80 to 90 75 to 85
V-ripper/subsoiler 12-14 inches deep, 20-inch spacing 70 to 90 60 to 80
Combination tools
Subsoil-chisel 50 to 70 40 to 50
Disk-subsoiler 30 to 50 10 to 20
Chisel plows
Sweeps 70 to 85 50 to 60
Straight chisel points 60 to 80 40 to 60
Twisted points or shovels 50 to 70 30 to 40
Combination chisel plows
Coulter-chisel plows with
Sweeps 60 to 80 40 to 50
Straight chisel points 50 to 70 30 to 40
Twisted points or shovels 40 to 60 20 to 30
Disk chisel plows with
Sweeps 60 to 70 30 to 50
Straight chisel points 50 to 60 30 to 40
Twisted points or shovels 30 to 50 20 to 30
Disk harrows
Offset
Plowing greater than 10-inch spacing 25 to 50 10 to 25
Primary greater than 9-inch spacing 30 to 60 20 to 40
Finishing 7- to 9-inch spacing 40 to 70 25 to 40
Tandem
Plowing greater than 10-inch spacing 25 to 50 10 to 25
Primary greater than 9-inch spacing 30 to 60 20 to 40
Finishing 7- to 9-inch spacing 40 to 70 25 to 40
Light tandem disk after harvest, before other tillage 70 to 80 40 to 50
One-way disk with
12- to 16-inch blades 40 to 50 20 to 40
18- to 30-inch blades 20 to 40 10 to 30
Single-gang disk 50 to 70 40 to 60
Field cultivators (including leveling attachments)
Field cultivators as primary tillage operation
Duckfoot points 35 to 60 30 to 55
Sweeps or shovels 6-12 inches 35 to 75 50 to 70
Sweeps 12 to 20 inches 60 to 80 55 to 75
Field cultivators as secondary operation following chisel or disk
Duckfoot points 60 to 70 35 to 50
Sweeps or shovels 6 to 12 inches 70 to 80 50 to 60
Sweeps 12 to 20 inches 80 to 90 60 to 75
Finishing tools
Combination secondary tillage tools with
Disks, shanks and leveling attachments 50 to 70 30 to 50
Spring teeth and rolling basket 70 to 90 50 to 70
Harrows
Spring tooth (coil tine) 60 to 80 50 to 70
Spike tooth 70 to 90 60 to 80
Flex-tine tooth 75 to 90 70 to 85
Roller harrow (cultipacker) 60 to 80 50 to 70
Packer roller 90 to 95 90 to 95
Rotary tiller
3-inch deep (secondary) 40 to 60 20 to 40
6-inch deep (primary) 15 to 35 5 to 15
Undercutters
Stubble-mulch sweep blade plows with
"V"-blades or sweeps, 30 inches or wider 85 to 95 70 to 80
Sweeps 20 to 30 inches wide 80 to 90 65 to 75
Rodweeders
Plain rotary rod 80 to 90 50 to 60
Rotary rod with semi-chisels or shovels 70 to 80 60 to 70
Strip tillage machines
Rotary tiller, 12-inch tilled on 40-inch rows 60 to 75 50 to 60
Row cultivators (30 inches and wider)
Single sweep per row 75 to 90 55 to 70
Multiple sweeps per row 75 to 85 55 to 65
Finger-wheel cultivator 65 to 75 50 to 60
Rolling-disk cultivator 45 to 55 40 to 50
Ridge-till cultivator 20 to 40 5 to 25
Drills
Hoe opener drills 50 to 80 40 to 60
Semi-deep furrow drill or press drill (7- to 12-inch spacing) 70 to 90 50 to 80
Deep furrow drill with greater than 12-inch spacing 60 to 80 50 to 80
Single-disc opener drills 85 to 100 75 to 85
Double-disc opener drills (conventional) 80 to 100 60 to 80
No-till drills and drills with the following attachments in standing stubble
Smooth no-till coulters 85 to 95 70 to 85
Ripple or bubble coulters 80 to 85 65 to 85
Fluted coulters 75 to 80 60 to 80
No-till drills and drills with the following attachments in flat residues
Smooth no-till coulters 65 to 85 50 to 70
Ripple or bubble coulters 60 to 75 45 to 65
Fluted coulters 55 to 70 40 to 60
Air seeders Refer to appropriate field cultivator or chisel plow depending on type of ground-engaging device used.
Air drills Refer to corresponding type of drill opener.
Row planters
Conventional planters with
Runner openers 85 to 95 80 to 90
Staggered double-disc openers 90 to 95 85 to 95
Double-disc openers 85 to 95 75 to 85
No-till planters with
Smooth coulters 85 to 95 75 to 90
Ripple coulters 75 to 90 70 to 85
Fluted coulters 65 to 85 55 to 80
Strip-till planters with 2- or 3-fluted coulters 60 to 80 50 to 75
Strip-till planters with row cleaning devices (8- to 14-inch wide bare strip using brushes, spikes, furrowing discs or sweeps) 60 to 80 50 to 60
Ridge-till planter 40 to 60 20 to 40
Unclassified machines
Anhydrous applicator 75 to 85 45 to 70
Anhydrous applicator with closing discs 60 to 75 30 to 50
Subsurface manure applicator 60 to 80 40 to 60
Rotary hoe 85 to 90 80 to 90
Bedders, listers and hippers 15 to 30 5 to 20
Furrow diker 85 to 95 75 to 85
Mulch treader 70 to 85 60 to 75
Climatic effects
Overwinter weathering (in northern climates with long periods of snow cover and frozen conditions, weathering may reduce residue levels only slightly, while in warmer climates, weathering losses may significantly reduce residue levels)
Following summer harvest 70 to 90 65 to 85
Following fall harvest 80 to 95 70 to 80
Data provided in Table 1 was developed from available research data, Natural Resources Conservation Service guides and equipment manufacturer trials.

For a given implement, residue coverage is influenced by speed and depth of operation, soil moisture, texture and condition, plus the type and height of the residue. A disk or chisel will cover considerably more of a flat, fragile residue such as soybeans than of a sturdier, more erect residue such as corn or milo (grain sorghum).

High-yielding corn, grain sorghum and small grains generally leave about 95 percent of the soil surface covered with residue after harvest, if spread uniformly behind the combine. High-yielding soybeans typically produce an 80 to 85 percent residue cover.

The following examples illustrate how to use the data from Table 1 to predict the percentage residue cover remaining after various operations (use chain multiplication and convert percentages remaining for each operation to decimal equivalents).

Example 1
Assume a field of corn in northern Missouri yielded 100 bushels per acre. From Table 2, the residue produced is 60 pounds per bushel (total residue produced = 6,000 pounds per acre).

Table 2
Relationship of residue production to crop yield

Crop Pounds of residue produced per bushel of crop yield
Corn 60
Grain Sorghum 70
Soybeans 50
Small Grain 100

From Figure 2, 6,000 pounds of uniformly distributed residue per acre will cover 95 percent of the soil surface after harvest. Assume the following operations: Fall chisel with straight points, 10 percent residue decay over winter, spring disk (finishing) and drill soybeans with double-disc openers, conventional drill.

initial residue cover x chisel x winter decay x disk x drill = final residue cover

95 percent x 0.75 x 0.90 x 0.70 x 0.90 = 40 percent

The 40 percent residue cover remaining will qualify as conservation tillage (30 percent or more cover after planting) and will reduce erosion to about 40 percent of that from a fall plow system.

Example 2
Assume a field of soybeans yielded 40 bushels per acre. From Table 2, the residue produced is 50 pounds per bushel (total residue produced = 2,000 pounds per acre). From Figure 2, 2,000 pounds of uniformly distributed residue per acre will cover about 72 percent of the soil surface after harvest. Assume the following operations: 20 percent residue decay over winter, apply anhydrous ammonia and no-till plant corn with a fluted coulter.

initial residue cover x winter decay x ammonia applicator x plant = final residue cover

72 percent x 0.80 x 0.70 x 0.80 = 32 percent

The 32 percent cover after planting in the soybean stubble will reduce erosion to about 55 percent of that from a fall plow system.

The calculation points out the problems associated with keeping 30 percent residue cover after planting following soybeans due to the fragile nature of the residue. Obviously, no-till planting is the only system that can be relatively certain to qualify as conservation tillage following soybeans.

The calculations of predicted residue aren't as accurate as measurements after planting but do allow one to compare various systems on paper. By calculating the estimated percentage of cover remaining after planting, the corresponding "Soil Loss Ratio" can be estimated for each year of a crop rotation and the average "Soil Loss Ratio" can be calculated for the rotation. Thus, various rotations and tillage regimes can be compared to aid in selecting the most desirable system for a specific conservation plan.

G1650, reviewed December 1993

G1650 Conservation Tillage and Residue Management to Reduce Soil Erosion | University of Missouri Extension

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