III. SOILS, AGRICULTURE, AND ENVIRONMENT
Tillage and Cropping Management Next Section>>
In practice, various tillage and cropping systems are combined in farm operations. Here, individual tillage systems and cropping systems are described, then combinations of them commonly used in Indiana are explained. The soil evaluation rules are listed at the end of this section.
Subsections:Tillage systems | Cropping systems | Tillage-cropping practices
Tillage is the preparation of land for planting. Depending on the cropping system to be used, the soil may be tilled every year, or it may never be completely tilled. The more often it is tilled, the more subject the soil is to erosion. For years, the standard tillage method has been to turn under residues with a moldboard plow and then to till the soil to a shallow depth with a disc harrow or other implement to prepare the seedbed. In recent years, however, conservation tillage techniques have become more popular, largely because of the development of new herbicides that provide weed control without plowing as well as the development of planters that can drill or slice through heavy residue cover. Erosion control by leaving residue on the surface is one of the chief benefits of conservation tillage systems. Conservation tillage includes all tillage systems that leave at least 30% of the soil surface covered with live plants or crop residue at planting time. It includes no-till, strip-till, and ridge-till, which are described below.
Any traffic over the land can cause soil compaction. The amount of compaction depends greatly on how wet the soil was when it was tilled or driven on. Thus, any reduction in the number of trips across a field with heavy machinery will reduce the risk of compaction. It is also very important to stay out of the fields when they are wet.
In no-till planting, the crop is planted in soil that has a residue cover (Fig. 24). The residue may be left from a previous row crop such as soybeans or corn or from vegetation, such as a cover crop, that was recently killed with a herbicide spray. No-till double cropping is planting soybeans into small grain stubble immediately after harvesting the small grain crop, usually in early July. No-till planting saves fuel because of fewer tillage trips over the land.
Fig 24. Corn growing in crop residue illustrates the no-till system.
No-till planting is especially well suited for erodible, well-drained soils where the increased cover greatly reduces erosion and moisture loss through evaporation. Corn and soybeans planted in a no-till system generally yield more on these soils than when a moldboard plowing system is used. Wheat can also be seeded by the no-till method, but a special drill is needed. No-till wheat is usually grown in a rotation with other crops. No-till is also used in renovating a pasture.
On many poorly and somewhat poorly drained soils, however, corn grown in corn residue under no-till yields less than if grown under moldboard plowing. This occurs because wetter soils warm up slowly in the spring if they are covered with heavy residue from previous crops. These cool, early season soil temperatures, and perhaps other factors, retard crop growth and result in a yield reduction. The cost of the yield reduction, however, may be offset by lower fuel and equipment costs. Yields for corn planted no-till after soybeans, on the other hand, are only slightly reduced. For this reason, farmers first began no-till operations by planting corn after soybeans. When better seeding machinery and herbicides became available, more farmers planted soybeans directly into soil with crop residue.
Less than 10% of all cropland was managed in a no-till system in 1990, but no-till crop production grew rapidly during the 1990s. Initially, corn was considered to be better suited to no-till than soybeans, but the development of the no-till drill to plant soybeans in corn residue and better herbicides resulted in steady increases in the acerage of no-till beans. The percent of corn land in no-till increased until 1994, then decreased for several years, and returned to 1994 levels in 2000 (Fig. 25). Acres of no-till beans increased fairly regularly for 10 years. In 2000 about 60% of the soybeans and 21% of the corn in Indiana was planted by no-till methods.
Fig 25. Adoption of no-till planting of corn and soybeans.
In soil evaluation, no-till systems are marked YES for many soils with slopes of 6% or less because they control erosion adequately. No-till might not be feasible, however, for some wet soils when planting into heavy crop residue cover such as corn stalks or wheat stubble. No-till without a cover crop is somewhat low in residue cover after the soybean crop, and is not quite as effective in erosion control as it is when combined with a cover crop.
Strip-till planting is similar to no-till except that residue is cleared from a narrow strip, the strip is tilled, and then seeds are planted in it. Usually the residue is just pushed out of the row, leaving the same amount of total residue, but some of it could be buried in the operation. Strip-till has the same soil requirements as no-till.
Ridge-till planting is a once-over springtime operation. Typically, the first step in establishing this system is taken the previous year by making ridges with a disk- or sweep-type cultivator. This is usually done when corn is 12 to 18 inches tall in early summer or after soybeans have reached sufficient height (12 to 15 inches) that the ridged soil will not seriously affect yield by covering up too many of the lower pods. No further tillage is done until the planting pass the following spring. All crop residue is left in the field, but some of it may be buried when ridges are formed.
In the planting operation, the top 1 to 2 inches are cut from the ridge to provide firm, moist soil for planting, while residue and clods are pushed into row middles. A narrow slot is then made in the cleared strip, the seed dropped, and the slot covered and firmed.
The ridge-till planting system is repeated by once again making or reforming the ridges at cultivation time or after harvest. On sloping land, however, ridges should be made only at cultivation time because ridging after harvest will increase the erosion hazard. Rows remain in the same place each year.
Ridge-till planting is intermediate between moldboard plowing and no-till in protection against erosion on sloping soils. On wet soils, ridge-till planting performs better than no-till because the bare soil on the leveled ridges warms up sooner in the spring-time. On well-drained sloping soils, water flow is concentrated in the furrows left between the rows. If these furrows are on the contour they will reduce down-slope water movement, but if the furrows run up and down the slope they may concentrate flow and cause erosion. Therefore, the practice is limited to soils with less than 6% slope.
Soybeans produce little residue for surface cover compared with corn, and some of the residue they do produce is buried when ridges are formed or when the ridge tops are leveled. Thus, after soybeans, ridge-till planting does not provide enough residue to adequately control erosion on sloping soils unless the ridges are contoured.
Ridge-till is not considered in soil evaluation competition because it is not widely used in the state. One reason for the decline is that many soybean fields are planted in narrow rows that do not fit the ridge-till system. The requirements are similar to those for no-till, except that ridge-till is not well suited to soils with sandy surface textures because the ridges will not hold up well in these soils.
Chisel tillage utilizes a chisel-type implement that can be adjusted to a desired depth, for example, 8 to 10 inches. Chisel tillage does not invert the soil but rather leaves it rough and cloddy. Chisel plows are equipped with chisel points spaced 12 to 15 inches apart. Some types have a gang of discs in front of the chisel to cut the residue and to avoid clogging the chisel. Straight or twisted chisel points or sweeps may be used, depending on how much residue incorporation is desired. Narrow, straight chisels leave as much as 80% of the corn residue on the surface, while wide, twisted points leave very little residue.
Chisel tillage after corn is usually most successful if it is done in the fall. Then soils are chiseled 8 to 10 inches deep. In the spring a field cultivator, disc harrow, or similar implement is usually used for secondary tillage because chisel plowing leaves the soil very cloddy. If chisel plowing is done in the spring, it should be done to a depth of only 4 to 6 inches to avoid the deeper layers that are often wetter. The runoff and erosion control effectiveness of chisel tillage depends on the amount of residue left on the surface, tillage direction (down or across the slope), and degree of soil roughness. The importance of residue cover is discussed and illustrated in Chapter VI.
For many years, moldboard plowing was the usual method for primary tillage. It is considered a “clean tillage” practice. It inverts the surface soil, to a depth of 7 to 10 inches, and covers the previous crop residue so there is no cover to protect against erosion. Much of the organic matter is placed in the lower part of the plow layer. Often moldboard plowing is followed by several other shallow tillage operations with a disc harrow or field cultivator. Moldboard plowing can be done in the spring or in the fall. It leaves the soil bare and very subject to erosion, but the bare soil warms more quickly in the spring than soil under a heavy residue cover. The only soils on which moldboard plowing can be used safely are those with very little wind or water erosion hazard and those less likely to become compacted.
For soil evaluation, clean tillage includes moldboard plowing, which buries all plant residue, as well as chisel tillage that buries most plant residue. If the soil is cleanly tilled in the fall, the bare soil is subject to erosion in the winter and early spring. Clean tillage exposes the soil to more erosion than any other tillage method. Therefore, clean tillage is not suitable for soils with slope more than 2%. It should be used only on soils with very little erosion potential, such as those with medium or finer surface texture, and poor or somewhat poor drainage. It should not be used on soils with sandy or moderately sandy surface textures because they are very subject to wind erosion.
In contour tillage, all the farming operations are performed on the contour, that is, at the same elevation, like the lines on a contour map. In this way, surface roughness features are across the direction in which water flows and water movement is retarded. Contour tillage can be used effectively when slopes are long and fairly uniform. Where slopes are short and choppy it is impossible to follow the contour with farm implements.
back to topThe kinds of crops and cropping systems commonly used on Indiana farms are described in this section, especially as to how well they protect soils from erosion. The potential for soil erosion largely determines the kind of cropping system that can be used on a certain soil. Cropping systems are closely related to the tillage practices described in the next section.
Permanent pasture is land with perennial vegetation that is used for grazing rather than for harvesting hay. It provides almost as much cover and erosion protection as natural vegetation such as forest. In addition to surface cover, the roots anchor soil material in place. Pastures must occasionally be renovated, however, and during renovation, the soil might be more vulnerable to erosion than if it were continually covered by trees. Also, traffic by livestock might lead to some soil compaction and erosion problems. Thus, pasture is usually not quite as effective as forest in controlling erosion.
Forage crops include perennial crops grown for animal feed as hay or pasture. They might be used in permanent pasture, in a permanent hay field, or in a rotation with row crops. In contrast to row crops, they provide continuous soil cover throughout the growing season. Forage crops can be safely used on all but the steepest soils.
Cover crops are grasses, legumes, or small grains grown when the soil would otherwise be bare (usually after corn or soybeans) for the purpose of protecting the soil from erosion and taking up nutrients, such as nitrates. If no cover crop is grown, these nutrients might be leached from the soil. Cover crops can be seeded in the fall or in the spring. Crops usually seeded in the fall are rye, wheat, annual rye grass, and hairy vetch. Normal spring-seeded crops are oats, red clover, and crown vetch.
Cover crops are used with row crops to control water and wind erosion. Soils erode more readily after soybeans than after corn. Therefore, cover crops should be considered for use on sloping soils, especially after soybeans. As evident from the rules in the Tillage-Cropping Systems section, use of a cover crop after soybeans in a corn-soybean rotation extends the range of slope on which no-till planting can be used. Corn provides more residue, so continuous corn, without a cover crop, can be used on the same slopes as a corn-soybean rotation with a cover crop after soybeans. If a crop is grown and then plowed under to add organic matter to the soil, it is called a green manure crop.
Small grains Winter wheat is the most common small grain crop in Indiana, but oats and barley are also grown. These crops are often grown in a rotation with row crops and forage crops. Fall-seeded small grains grow to a height of several inches before winter and thus provide good protection against erosion, especially if residue from the previous crop is left on the soil surface. After harvest, around the first part of July, the stubble continues to provide protection for the soil.
Row crops The main row crops in Indiana are corn and soybeans. They are often grown in a rotation with each other, but continuous corn is also common. A corn-soybean rotation is assumed for the continuous row crop culture in soil evaluation. If residue is not left on the soil surface, erosion by water is a severe problem on sloping soils. Erosion by wind is a severe problem on sandy soils because the field is bare during times of frequent rain storms and high winds. Soybeans provide less erosion control than corn. This is partly because soybeans are smaller plants than corn and therefore leave much less residue in the field after harvest. Also, soils seem to be more erodible after soybeans than after corn, but we do not know why.
Crop rotation Crop rotation refers to growing a certain sequence of different crops in a field, in contrast to continuous cropping. There are many possible combinations of kinds of crops and the length of time they are grown in a crop rotation. The rotation assumed for the rule below provides almost continuous cover and protects the soil from erosion on slopes as steep as 18%. In year 1, corn (C) is no-till planted in residue of a forage crop that was killed by herbicide. Corn residue is left in the field and a small grain (G) and grass-legume mixture is planted in this residue. After the small grain is harvested, in year 2, the grass-legume forage mixture (F) gets started and becomes productive in years 3, 4, 5, and 6. This forage crop is killed with a herbicide the following year to begin another cycle. Alternatively, the small grain is seeded alone and the grass-legume mixture is seeded into the small grain stubble. The rotation can be designated C-G-F-F-F-F.
back to topThe tillage systems and cropping systems described in previous sections are combined into five tillage-cropping practices that are considered for soil evaluation. The No-till with Cover Crop practice combines a tillage practice and a cropping practice that are more effective together they than either is individually. The clean tillage, no-till, and no-till with a cover crop practices assume that a corn-soybean rotation is used.
It is impossible to completely eliminate erosion, because some erosion occurs with all farming systems. The goal is to keep the amount of erosion small enough so that farming will not be harmed in the long term. This limit is called the “tolerable soil loss,” which is four to five tons per acre each year for most Indiana soils. In Fig. 21, the amount of erosion is calculated using the Universal Soil Loss Equation, USLE, described in Chapter VI. The values needed to make the calculation are typical for central Indiana. The graph shows that the amount of erosion increases with slope for all tillage-cropping practices, but it increases, for example, much more rapidly for spring plowing (clean tillage) than for permanent pasture. The tolerable soil loss, T, is plotted as a horizontal line that represents four tons/acre. As long as the line representing a tillage-cropping system is below the T line, the system will not result in excessive erosion. Slope limits in the rules for the five tillage-cropping practices were selected to keep erosion less than four tons per acre (T line). The slopes at which the practice line rises above the tolerable limit (T line) are: 1% for spring plowing, 7% for no-till, 11% for no-till with a cover crop, 19% for rotation with one year of six in row crops, and 31% for permanent pasture. The soil evaluation rules set the upper slope limits at 2%, 6%, 12%, 18%, and 25%, respectively, for these practices. They approximate the limits shown in the graph. Forest always keeps erosion much less than T.
The effect of cover crops on erosion is illustrated for a corn-soybean rotation. No-till alone can be used on slopes as steep as 6%, but the combination of no-till and cover crop can be used on slopes as steep as 12%. In this practice, corn is planted directly in the residue from soybeans and the residue from the cover crop that was killed with a herbicide. After harvest, the corn residue is left in the field and soybeans are no-till planted directly into it in the spring. In the fall, just before or after soybean harvest, a cover crop such as rye is seeded. This crop is killed with a herbicide the following spring to start another cycle. In practice (but not considered in soil evaluation), crop yields on medium to fine-textured, poorly and somewhat poorly drained soils may be reduced by using a cover crop with no-till because the heavy crop residue cover keeps the soil too cool in the spring which slows plant growth.
Practices are listed below in decreasing order of their capacity to control soil erosion. As indicated earlier, natural vegetation (forest), is suitable for all soil conditions. Permanent pasture, the first practice listed in this section, is suitable for almost any soil condition. However, the last one in the list, clean tillage, is suitable for very few situations. From another viewpoint, nearly level soils can be tilled in many different ways, but steeply sloping soils can be used safely for only one or two tillage-cropping systems.
Some practices that reduce soil erosion can also reduce the hazard of soil compaction. For example, systems that require fewer trips over the land than moldboard plowing reduce the chance of compaction.
These rules follow the same principles used by scientists in the Natural
Resources Conservation Service (NRCS) and the Purdue Cooperative Extension
Service (CES). However, they are greatly generalized and their use on specific
farms should be carefully evaluated prior to adoption. Note that many of the
practices apply only to cropland.
Soil Evaluation Rules—Tillage-Cropping Practices
| Mark Permanent pasture YES for soils with slopes
25% or less. |
| Mark Crop rotation YES for soils with slopes 18% or less. |
Mark No-till with cover crop YES for soils with both properties: 1. 12% or less slope, and
|
Mark No-till YES for soils with both properties: 1. 6% or less slope, and
|
Mark Clean tillage (chisel tillage and moldboard plowing) YES for soils with all these properties: 1. 2% or less slope, |
