Tillage best management practices for water quality protection in Southeastern Minnesota
On this page
- Using conservation tillage to control erosion
- Conservation tillage today
- How different tillage systems maintain crop residue
- How management factors affect tillage practices
- Reduced tillage risks and benefits
- Using conservation structures to control erosion
- Tillage recommendations for southeastern Minnesota
This publication provides information that can help farmers in the Lower Mississippi River Basin of southeastern Minnesota optimize performance of their tillage system for both erosion control and profitable crop production. It identifies key farm management practices needed to manage production risks associated with reduced tillage and no-till systems. It also draws on more than 18 years of University of Minnesota field trials to help evaluate how particular types of reduced tillage systems perform in different crop rotations in the two sub-regions of the basin: 1) the eastern "Karst" area where wind-deposited (loess) soil overlies fractured bedrock, and where internal soil drainage is generally excellent; and 2) the western "loess-cap" area where loess soil overlies glacial till deposits that often provide poor internal soil drainage.
Using conservation tillage to control erosion
Fortunately, a key method of reducing soil erosion on cropland, conservation tillage, is generally well suited to southeastern Minnesota. If properly managed, conservation tillage can reduce average soil erosion by up to two–thirds. It often lets a farm maintain or enhance profitability through production cost savings. When combined with other common conservation practices, such as grassed waterways, buffers and contour planting, it can help to retard erosion even on the region's steeper, longer slopes where erosion of unprotected cropland is severe. Generally, the conservation tillage benchmark of 30 percent surface residue after planting provides significant erosion control. This is easy to achieve following corn production, but can be a difficult target to attain for crops planted in soybean stubble. Somewhat less surface residue still gives substantial erosion control. Therefore, fields meet crop residue targets if they have greater than 30 percent residue following corn, and at least 15 percent residue cover following soybeans.
Conservation tillage today
Crop residue surveys indicate that farmers' adoption of conservation tillage varies greatly throughout the basin (Table 1). In five counties, no more than one–third of the fields surveyed had adequate crop residue to control erosion, while in three counties two–thirds or more of fields were adequately protected. There appears to be considerable opportunity for increased adoption of conservation tillage across the basin, particularly in areas where adoption rates are currently low.
Table 1. 2000 Minnesota Corn–Soybean Residue Survey Results. Summary for the Lower Mississippi River Basin in Minnesota.
|Fields meeting residue targets1||Residue trend analysis perfect of corn and soybean fields meeting residue targets|
|1Fields meeting residue targets include fields with >30% residue plus fields with >15% residue when following soybeans. Residue is measured after planting.
2A dash indicates no data were collected.
How different tillage systems maintain crop residue
Tillage systems can use tillage implements very effectively to leave various levels of crop residue on the soil surface. The effectiveness of seven tillage systems at protecting crop residue is described below.
Moldboard plowing followed by one or two secondary tillage operations with a field cultivator or disk before planting. This system is an aggressive tillage practice that often leaves less than 10 percent of the surface covered with crop residue after planting.
Fall chisel plowing plus spring secondary tillage with a field cultivator or disk. This tillage practice is quite aggressive and can reduce crop residue to levels that are inadequate for erosion control.
Single pass with a field cultivator in spring before planting corn after soybeans or a tandem disk before planting corn after alfalfa or soybeans after corn. This is a less aggressive tillage system that may leave adequate residue after planting.
Tillage is limited to that performed by the planter (ridge leveling) and one or two in–season cultivations (ridge building). Preformed ridges provide a drier and warmer seedbed at planting. Adequate levels of crop residue remain after planting.
Strips about 4" to 6" wide and 7" to 8" deep matched to the row–spacing of the planter are prepared in the fall with mole fertilizer knives or anhydrous knives mounted on a tool bar. Fertilizer P and K can be injected directly into the strip at the time of strip tillage. Corn is planted into the tilled "residue free" strip without any secondary spring tillage.
Combining deep slit tillage using a zone builder or other narrow subsoil shank and a planter equipped with multiple (2 or 3) fluted coulters cutting residue and preparing a seed bed gives excellent seed-soil contact directly above a deep slit.
No–till (the planter performs all seedbed preparation)
Starter fertilizer placement and cleaning residue from the rows usually are done with the planter, but may be performed separately, sometimes in combination with fertilizer injected into a strip or band.
How management factors affect tillage practices
Soil types vary greatly on the landscape in southeastern Minnesota. It's important to understand these soil differences when deciding which tillage system to use in a farming operation. Failure to match the tillage systems to soil and landscape properties can result in reduced yield, poor erosion control and, eventually, loss of soil productivity.
Well–drained soils warm up sooner and usually require less tillage than poorly drained soils. Warmer soils generally allow earlier planting and let emerging plants withstand greater amounts of crop residues left on the surface. Poorly drained soils often require more tillage and tile drainage systems in order to achieve timely planting. A high level of crop residue on slow–to–drain soils keeps them from warming and drying quickly. Wheel traffic on these wet soils can more easily cause surface compaction and could affect the subsoil as well.
The land's aspect, or exposure to the sun, also affects the warming and drying of soil. The sun's angle of incidence on south–facing slopes in spring is intense, and soils warm up and become drier sooner than soils on north slopes.
Different crops leave different amounts of residue on the soil surface after harvest. Corn harvested for grain leaves a large amount of crop residue that does not readily break down. Much less crop residue is left on fields when corn is used for silage or corn stalks are baled for feed. When alfalfa follows corn in the rotation, tillage may be needed to incorporate fertilizer and/or agricultural lime and to develop a seedbed for the small seeds of forage crops. It is extremely important that small-seed legumes have close seed–to–soil contact for optimum germination.
The residue left following a soybean crop is minimal and does not provide adequate protective residue cover on the steep, loess soils in southeastern Minnesota. Soybean stubble should not be tilled in the fall in order to reduce the potential for soil erosion from fall rains and spring runoff of snowmelt. This leaves an opportunity for limited spring tillage before planting corn. The potential for erosion is greatly reduced when soybean residue is managed by using very limited tillage combined with contour farming and conservation structures. A straw chopper on the combine distributes soybean residue evenly, which helps in managing residue successfully the following spring. Some farmers have reported that special straw chopper knives and other combine attachments may be needed to thoroughly chop and evenly spread residue from some new soybean varieties, the stems of which tend to remain green for a longer time.
When a farmer begins using conservation tillage, starting with a relatively weed–free field greatly improves the likelihood of successful long–term weed management. Using reduced tillage on a weed–infested field requires greater weed management and can become very costly. In fields where tillage has been reduced and crop residue levels have increased, weed pressure may increase and shifts in weed species may occur. In some fields, weed species that were controlled previously with tillage, pre–plant and pre–emerge herbicides begin to sprout and grow, giving the appearance of a "new" weed in the fields. Pre–plant incorporated herbicides are no longer used in fields where little tillage is used; pre– and post–emergence herbicide applications become the primary weed control program. A wide range of effective post–emergence herbicide treatments is available today for crops grown with reduced tillage. As a result of equipment improvements, mechanical weed control can also be combined with herbicides in fields with high crop residue.
Many of the newer generations of planters and drills have options available to handle higher crop residue levels. Most planter tool bars sold today can be modified with row cleaners and/or coulters to ensure optimum seed–to–soil contact. Modern no–till drills are designed to clear residue while dropping and covering seeds as small as alfalfa at precision depths for exceptional contact with the soil, which results in good plant emergence. In recent years, narrow row spacing has become more prevalent and can be a benefit for farmers using conservation tillage. It is more difficult to do row cultivation in narrow rows, particularly on contour strips. However, rotary hoeing, combined with earlier closure of the crop canopy, helps to control weed growth. Farmers with older planters can modify their equipment with row cleaners and/or fluted coulters at a relatively low cost. Also, equipping the planter with starter fertilizer attachments increases the potential for success in high residue situations.
It is critical to establish high soil fertility before starting a conservation tillage system. Fertilizer and manure nutrients, along with agricultural lime, must be managed for optimum crop production. With conservation tillage, moderate–to–poor soil fertility in fields will intensify yield loss and diminish the probability of long–term success. Also, it can be difficult and costly to make great increases in soil pH with lime after very reduced tillage systems have been established.
Nitrogen (N) is the most important nutrient for corn production. Nitrogen needs to be managed for efficient use by the crop and also to reduce environmental risk of runoff and leaching. The Minnesota Nitrogen Fertilizer Task Force recommends that no nitrogen fertilizer be fall–applied on the soils of the Karst geologic area. Surface–applied N fertilizer, such as granular urea and UAN (urea-ammonium nitrate) solution, should be incorporated mechanically or by rainfall within three days of application to eliminate loss of N to volatilization. Any significant loss of nitrogen to the atmosphere or by runoff or leaching will reduce yield and profitability. Anhydrous ammonia is injected into the soil with knives that disturb the soil surface. The injection equipment also provides a minimum tillage pass without destroying the conservation tillage practice. For additional information see University of Minnesota Extension publications: Fertilizing Corn in Minnesota and Fertilizer Management for Corn Planted in Ridge-Till or No-Till Systems.
Phosphorus (P), potassium (K) and soil pH
Soil tests should be used to maintain fertility at optimum levels. For optimum crop production with all tillage systems, soil pH needs to be 6.5 or greater when alfalfa is in the rotation or at least 6.0 when soybean is grown; P should be 16–20 ppm with the Bray test and 12–15 ppm when the Olsen extractant is used; and K needs to be 121–160 ppm. Soil testing should be done every two to three years to maintain soil fertility levels in reduced–tillage fields. If additional nutrients are needed, their placement in relation to the crop is important. Placing the fertilizer close to the corn seed gives the most efficient P and K uptake. Broadcast applications of fertilizer and ag lime are best following corn where some tillage can be used to incorporate the materials and maintain adequate crop residue levels for erosion control. For a soybean–corn crop sequence, two years of requirements for phosphate and/or potash fertilizer may be broadcast and incorporated in the year following corn. Broadcast fertilizer left on the soil surface is recommended for topdressing an existing stand of alfalfa and usually is not a hazard to surface waters when runoff control measures are used. However, soluble phosphorus could enter surface waters if fertilizer is spread on grass waterways.
Continuous corn production provides the best opportunity to apply livestock manure on a consistent basis in conservation tillage systems. Corn residue levels are adequate for erosion control following injection of manure by knife or disk application equipment. Broadcast manure should be incorporated as soon as possible after application to reduce volatilization of N, potential runoff and odors. Farmers who need to apply manure throughout the winter should observe Minnesota Pollution Control Agency rules for land application of manure.
In reduced tillage systems with a corn–alfalfa rotation, using livestock manure gives some flexibility in application timing. Corn is grown for one or two years then is rotated to alfalfa. First year corn following a good stand of alfalfa (4-5 plants per sq. ft.) in most cases requires no additional N, so manure use would be limited. However, manure applied prior to seeding alfalfa, whether in the spring or late summer (by August 15th), gives farmers flexibility in using manure to provide the nutrients required. Regardless of the manure application method, tillage may be needed to prepare the seedbed for alfalfa and to incorporate the manure. If soybeans are in the rotation, manure can also be used effectively when applied at agronomic rates before planting. However, the small amount of soybean crop residue remaining after harvest has a minimal effect on stabilizing soil and controlling erosion, particularly on silt loam soils with steep slopes. Farmers that have substantial amounts of manure for use might consider a rotation of two or more years of corn in order to maintain adequate crop residue cover for erosion control and make the most efficient use of manure nutrients.
Reduced tillage risks and benefits
Many farmers are reluctant to farm with greater amounts of crop residues on their fields. They fear yield loss and don't like the appearance of a crop growing in heavy residue. Their perception is influenced by several factors: 1) upsetting the landlord, business partner or a family member; 2) ridicule from neighbors; 3) lack of crop management skills to adopt conservation tillage; 4) recent purchase of equipment for aggressive tillage; and 5) on–farm research results. Overcoming the aesthetics of crop emergence in a field covered with residue takes patience, time and an understanding of the system. Farmers who have used conservation tillage learn to appreciate the "look" of a crop growing in higher levels of residue and the lower cost of production.
When evaluating potential yield loss that may result from adopting a very high–residue system such as no–till, it is important that farmers compare differences in production costs as well as expected differences in yield to arrive at a sound business management decision. The following example is intended only for illustration. Each farm will have its own production costs and risks based on equipment, management skills, crop rotation and other farm-specific factors.
The risk associated with reduced tillage is most pronounced for no–till production of continuous corn. In the Karst region, over 40 site–years of field research with continuous corn show that the yield difference is only 2 to 6 percent lower for no–till compared to chisel plowing. Following is a brief comparison of average tillage costs for no–till and chisel–plow systems, which can be used as a guide to determine how much of the potential yield penalty from no–till may be offset by cost savings from reduced tillage trips.
All costs above include labor, fuel, maintenance and depreciation. Estimated costs based on William Lazarus' Machinery Cost Estimates for 2013, University of Minnesota Extension, St. Paul.
Table 2. Comparison of estimated field preparation and planting costs for two tillage systems.
|Chisel plow system||No tillage system|
|One pass chisel||8.24|
|One pass disk/finish||8.90|
|Row crop planter||8.96||No-till planter||11.36|
|Estimated use–related costs taken from Machinery Cost Estimates for 2013, University of Minnesota Extension, St. Paul.|
The tillage cost difference in the example is $14.74/A in favor of no–till. Weed control costs and the remaining costs through harvest would be similar for both methods. Assuming a 170 bu/A corn yield at $3.75/bu, the farmer would gross $637.50/A. If yields were 4 percent lower for the no–till system, there would be fewer dollars returned for the no–till system in this example ($11/A). However, the no–till farmer would need less labor, have a reduced line of equipment to maintain and cause less soil erosion and compaction.
Using conservation structures to control erosion
An integrated system of reduced tillage practices and conservation structures is needed for successful soil and water conservation. Crop residues on the soil surface reduce the effect of rainfall intensity and help somewhat to keep sediments in place. However, conservation structures such as diversions, grade control measures, terraces, grass waterways, contour strips and conservation buffers are needed to reduce the velocity of water and sediment transport off fields.
Figure 2. Crop residue in combination with a waterway or other structure would have protected the soil from erosion damage.
Farmers need to combine tillage systems with crop rotations and conservation structures to control surface runoff and soil erosion effectively. For a corn–soybean rotation in the Karst area, contour farming, contour buffer strips and grass waterways in combination with no–till corn into soybean residue and chisel plowing corn residue could provide sufficient erosion control. However, if tillage is done both after growing corn and growing soybeans, it may be necessary to compensate for the increased erosion potential from the additional tillage by using contour farming and terraces and adding hay or small grain to the rotation. In the loess–cap region, conservation tillage in combination with grass waterways or terraces often can control soil erosion in a corn–soybean rotation. Even if corn is planted no–till into soybean stubble, grass waterways or terraces will often be needed to handle erosion on steeper or longer sloping fields. If tillage reduces residue cover to 20 percent or less, terraces may be needed on steeper or longer slopes.
These typical conservation systems show how combinations of management practices and conservation structures can successfully control erosion in southeastern Minnesota. Individual farms may need site–specific designs that differ from these typical systems. Farmers can contact their local Soil and Water Conservation District/Natural Resources Conservation Service office for help in determining which combination of conservation tillage, crop rotation and conservation structures is best for their farm.
Grass buffers at the edge of a field, drainage ditch or stream should be considered supplemental erosion control for the upper portions of the field, not a replacement for conservation practices. In fact, field buffers are effective mainly against sheet and rill erosion, and can be easily breached by gully erosion that is the result of insufficient erosion control on the uplands.
Tillage recommendations for southeastern Minnesota
Below are the performance indicators used in Table 3 to summarize the tillage recommendations for various cropping systems in the two sub–regions of the basin: the eastern "loess (Karst)" area where loess soil overlies fractured bedrock, and the western "loess–cap (till)" area where loess soil overlies glacial till deposits.
1) Recommended with good management
No yield penalty is expected if the farmer observes all relevant recommended management practices for high residue systems.
2) Excellent management required
Slight yield penalty is possible, even if all recommended management practices are observed. Above average crop management will be needed to ensure good performance.
3) Reduced yield potential
The potential exists for substantially reduced yields, especially on poorly drained soils in wet years.
4) Inadequate residue to minimize erosion
Less than 30 percent of surface is covered after planting. Highest yield may be obtained, however.
Table 3 shows the residue management/yield performance indicators for continuous corn and a corn–soybean rotation using the different tillage systems described earlier. Management to maintain adequate levels of surface residue is more difficult for the corn–soybean rotation. This is clearly shown by the "1/4" indicator for the chisel plow–plus and one–pass systems; in these cases, 1 indicates "recommended following corn" and 4 indicates "inadequate residue following soybeans." However, yield potential is likely to be compromised more easily in continuous corn with some of the very reduced tillage systems.
Table 3. Matrix of residue management/yield performance indicators for continuous corn (CC)and a corn–soybean (C–Sb)rotation grown on loess (Karst) soils and on loess–cap soils over glacial till.
|Loess (Karst)||Loess-cap (Till)1|
|Moldboard plow plus||4||4||4||4|
|Chisel plow plus||1||1/4||2/1||1/4|
|1Tillage recommendations for these soils are also appropriate for the soils just to the west of MLRA 104.
2For corn following silage corn, inadequate amounts of surface residue will exist for all tillage systems.
3No data specific to these soils. Estimates are based on information from somewhat similar glacial till soils.
Continuous corn grain production
Annual residue production is high and some degree of tillage is needed to prevent excessive build–up of surface residue, especially in more poorly drained areas. After corn that is harvested for silage, very reduced or no–till systems are needed to maintain adequate surface residue cover.
In the more well–drained Karst region, spring disk, strip–till and Rawson tillage systems produce yields comparable to chisel plowing. All these tillage systems leave adequate residue for erosion control. In the Karst region, a no–till system may result in an average yield penalty of 2 to 6 percent, but cost–savings from a well–managed no–till system may offset the yield penalty. In the loess–cap till region, moldboard plowing produces the highest yields, but leaves inadequate residue cover. This tillage system, in combination with riparian buffers and grass waterways as needed to retard runoff, may sometimes be appropriate on level fields with poor internal drainage where the potential for erosion is relatively low. Slight yield reductions occur with the chisel plow system, which may be partly offset by lower production costs. More significant yield reductions result from no–till and strip–till systems in continuous corn in this loess–cap till region.
Corn following soybeans
Maintaining 30 percent surface soybean residue after planting corn often is a challenge. Strip–till and the Rawson system leave adequate residue and prevent yield losses if managed well. If the field cultivator is used for one–pass spring tillage before planting, equipment must be carefully outfitted and operated to avoid burying too much soybean residue. In the more well–drained Karst region, yield penalties associated with very reduced tillage are generally small or nonexistent. However, substantial yield reductions can occur in some years, especially under cooler and wetter growing conditions or after several years of continuous no–till farming. On more poorly drained soils in the loess–cap till region, results show slightly lower corn yields (3-8%) with no tillage compared to chisel plowing, the highest–yielding treatment. Savings in production costs with excellent management of a no–till system might offset slight yield reductions. Very small yield differences occurred among the chisel, strip-till and field cultivation systems.
Soybeans following corn
Very reduced tillage and no–till systems can be used to maintain high surface residue levels without incurring significant yield reduction in the Karst region. However, excellent management is needed to optimize performance of ridge–till and no–till systems. In the loess–cap till region, chisel plowing and spring disking produce yields very similar to moldboard plowing, while leaving much more crop residue on the surface. No–till systems resulted in average yields similar to other tillage systems in long–term field studies in Nashua, Iowa, within the same soils region. However, field trials in Waseca indicate that a very slight yield penalty (maximum of 5%) may result from no–till planting or drilling on glacial till soils.
Corn following alfalfa
Fall–killed alfalfa that was later planted to corn using no–till methods produced yields comparable to corn planted following primary tillage. However, where alfalfa was not fall–killed, no–till corn planting resulted in large yield losses compared to tilled treatments, while use of the chisel plow or disk in the spring resulted in small yield reductions compared to moldboard plowing.
Long-term Research in Southeastern Minnesota
Loess soils over Karst bedrock
Numerous long–term tillage experiments on continuous corn and corn–soybean rotations have been conducted on farmer–cooperator fields in southeastern Minnesota. Fewer studies, some being short–term, were conducted using manure and in–season cultivation as treatments or alfalfa as the previous crop. These studies were conducted from 1982–2000 in Fillmore, Goodhue, Olmsted, Wabasha and Winona counties.
Tillage studies for continuous corn have been conducted on more than 40 site–years since 1982 on loess soils over Karst in southeastern Minnesota. Although corn yields were generally lower with no tillage, the difference between the consistently higher–yielding chisel plow system and no tillage ranged between 3 and 10 bu/A for only a 2 to 6 percent yield loss with no tillage. These small yield differences may be more than offset by economic and/or logistic reasons specific to each farm operation. Disturbance of the soil surface and residue cover in a no–till system, by either sweep injection of liquid dairy manure or in–season cultivation, lessened the yield difference between these two tillage systems. Spring disk, strip–till and Rawson tillage systems gave continuous corn yields very comparable to chisel systems.
A study comparing chisel plow (CP+), ridge–till (RT) and no–till (NT) systems was conducted from 1982–1987 on a Mount Carroll silt loam soil in Goodhue County (Table 4). Statistically significant differences in corn grain yield were found in 3 of 6 years with greatest yields with RT in two years (1983 and 1984) and with CP+ in one year (1985). Corn yield, averaged across all six years, was 3 bu/A lower with no tillage compared to chisel plow or ridge tillage. Even though fluted coulters were used with no tillage, significant amounts of residue still remained in the row area, delaying growth and contributing to stand loss in some years.
Table 4. Continuous corn yield as influenced by tillage on a Mount Carroll silt loam soil in Goodhue County.
|1S=Significant; NS=Not significant|
Continuous corn studies comparing various tillage systems were conducted at four sites on Port Byron and Seaton soils in southeastern Minnesota as part of a Nitrogen Management/Water Quality effort from 1987-1991 (Table 5). Corn yields averaged across years were 3 to 6 bu/A higher with chisel plow (CP+) compared to no tillage (NT) at the Olmsted #1, Goodhue and Winona County sites. Although these average yield differences were not large, in some specific years there were large yield differences. In 1990 at the Olmsted #1 site, yields for no tillage were 15 bu/A less than for chisel plow tillage. Weed control was perfect for all tillage systems, but April–July rainfall totaled 28.2" in 1990 compared to the normal of 13.9". At the Olmsted #2 site, yields for the moldboard plow (MP+) and chisel plow systems averaged about 9 bu/A greater than for the ridge–till and no–till systems. Fluted coulters mounted directly ahead of the planter unit were used, and anhydrous ammonia was the N source on all tillage systems in these studies.
Table 5. Continuous corn yields as influenced by tillage at four southeastern Minnesota sites.
|Location and years|
|Tillage system||Olmsted #1 Port Byron 1987-91||Olmsted #2 Port Byron 1987-91||Goodhue Port Byron 1981-90||Winona Seaton 1987-90|
|Average corn grain yield (bu/A)|
A study comparing chisel plow (CP+) strip tillage (ST), Rawson system (Rawson) and no tillage (NT), with and without starter fertilizer (150 lb 9–23–30/A), was conducted on a high–testing Port Byron silt loam in Olmsted County in 1997–2000 (Table 6). Fluted coulters and row cleaners were used for all tillage systems. Soil test P (Bray P1) and exchangeable K were 25 ppm (VH) and 149 ppm (H), respectively. Urea + Agrotain was broadcast applied at 160 lb N/A to all plots after planting. Surface residue coverage after planting, averaged across years, ranged from 54 percent with the Rawson system to 87 percent with no tillage. The chisel plow system resulted in less–than–desirable 26 percent residue coverage. Averaged across tillage systems, with and without starter treatments, highest yields were obtained with chisel tillage (166 bu/A). Statistically lower yields were found for the Rawson (163 bu/A), strip–till (162 bu/A) and no–till (155 bu/A) systems. A 9 bu/A response to starter fertilizer was obtained when averaged across all tillage systems, and there was no interaction between tillage and starter fertilizer.
This is somewhat surprising. Perhaps the small amount of N in close proximity to the germinating seed, coupled with the P and K, was instrumental in getting the plants off to a faster start in these years with high yield potential. Because of the comparable yields and much greater surface residue levels, the Rawson system appears to be an excellent alternative to chisel plow tillage on these soils, especially where incorporation of manure is not necessary.
Table 6. Continuous corn yield and surface residue as influenced by tillage and starter fertilizer on a high–testing Port Byron silt loam in Olmsted County, 1997–2000.
|Tillage system||No||Yes||Avg.||Surface residue2|
|1150 lb 9-23-30/A.
2Residue measured after planting.
Continuous corn: Effect of liquid manure application
Liquid manure can be injected into either no–till or chisel plow systems without negatively affecting either corn yield or surface residue coverage.
Two tillage systems, chisel plow (CP+) and no tillage (NT), were compared using two N sources, fertilizer N as ammonium nitrate and injected liquid dairy manure, during an 8–year period on a Timula silt loam in Goodhue County (Table 7). The chisel plow had 3"-wide twisted shovels while the manure applicator had 8"-wide sweeps on 36" centers. Fluted coulters on the planter were used for all treatments. Surface residue coverage between the corn rows was reduced from 64 percent with no tillage to 35 percent when sweep–injecting manure and 27 percent when chisel plowing. Averaged across all years and fertilizer and manure treatments, there was no yield difference between the chisel and no-till systems. However, sweep-injecting manure into the no-till system gave 8 bu/A greater yields compared to broadcast fertilizer N. The manure applicator apparently disturbed the soil as much as a chisel plow does in this experiment.
Table 7. Corn grain yield as affected by tillage system and nitrogen source.
|Year||Fert N1||Manure2||Fert N1||Manure2|
|1200 lb N/A as ammonium nitrate, surface broadcast in spring.
2Liquid dairy, spring-applied with 8" sweep injectors on 36" centers.
Continuous corn: Effect of in-season cultivation
In-season cultivation becomes more important as tillage intensity is reduced. Corn yield response to in-season cultivation varies from year to year, but positive benefits may be obtained in the absence of weeds on soils that crust easily.
A study on a Tama silt loam in Fillmore County compared in-season cultivation with a S-tine cultivator to no cultivation on spring moldboard plow (MP+), spring chisel plow (CP+), spring disk (SD) and no tillage (NT) systems (Table 8). Cultivation reduced the density of giant foxtail, especially as tillage was reduced, but had no effect on velvetleaf. Velvetleaf density was reduced most with moldboard and chisel plowing and least with no tillage (data not shown). Corn yields, averaged across the five years, were affected by both tillage and in-season cultivation. No-till yields were about 8 bu/A lower than moldboard plow yields when in-season cultivation was conducted and 13 bu/A lower when no cultivation was practiced on no-till.
Table 8. Continuous corn yield as influenced by tillage and in-season cultivation on a Tama silt loam in Fillmore County, 1985-1989.
|1S-tine cultivator with no coulters or disks.|
Corn after soybeans
Field research in the Karst region indicates that yield penalties associated with very reduced forms of tillage are small or nonexistent, on average, for corn following soybeans. However, substantial yield reductions have occurred in certain years, particularly under cooler and wetter growing conditions, or after several years of continuous no-till farming.
A study comparing spring field cultivation (FC), strip tillage (ST), Rawson system (Rawson) and no tillage (NT), with and without starter fertilizer (150 lb 9-23-30/A), was conducted on a high-testing Port Byron silt loam in Olmsted County in 1997-2000 (Table 9). Soil test P (Bray P1) and exchangeable K were 28 ppm (VH) and 143 ppm (H), respectively. Fluted coulters and row cleaners were used for all tillage systems. Urea + Agrotain was broadcast-applied at 120 lb N/A to all plots after planting.
Table 9. Corn yield and surface residue after soybeans as influenced by tillage and starter fertilizer on a high-testing Port Byron silt loam in Olmsted County, 1997-2000.
|Tillage system||No||Yes||Avg.||Surface residue2|
|1150 lb 9-23-30/A.
2Residue measured after planting.
Surface residue, averaged across all years, ranged between 41 percent (Rawson) and 67 percent (no tillage) for the three conservation tillage systems. Field cultivation resulted in 23 percent residue coverage, inadequate for erosion control. Corn grain yield was not affected statistically by tillage, but was improved 9 bu/A with starter fertilizer when averaged across tillage systems. The study found no interaction between tillage and response to starter fertilizer, indicating a consistent yield response to starter fertilizer for all tillage systems.
A study comparing chisel plow (CP+), spring disk (SD), ridge tillage (RT) and no tillage (NT) systems was conducted on a Fayette silt loam in Wabasha County (Table 10). Corn yield was affected significantly by tillage in only one year (1989) when yields for the chisel plow and spring disk tillage system were about 13 bu/A greater than for the ridge-till and no-till systems. Averaged across six years, yields with chisel plow or spring disking were about 4 bu/A greater than for ridge tillage or no tillage.
Table 10. Corn grain yield as influenced by tillage on a Fayette silt loam in Wabasha County, 1984-1989.
|1S=Significant; NS=Not significant|
A chisel plow system was compared to no tillage on a Port Byron silt loam in Goodhue County for continuous corn from 1987-90 (Table 5) and soybeans in 1991. Following soybeans, the chisel plots were disked and compared to continuous no-till. Corn yields in 1992 were reduced 36 bu/A after five years of continuous no tillage (Table 11). Grain moisture at harvest was 6.5 points higher with no tillage (data not shown). Corn growth was retarded all season long by the large amount of residue in the no-till plots in this cooler-and-wetter-than normal year. Weed control was excellent in all plots.
Table 11. Corn and soybean yields as influenced by tillage on a Port Byron silt loam in Goodhue County.
|1987-90 Corn||1991 Soybean||1992 Corn||1991 Soybean||1992 Corn|
Corn after alfalfa
Field research indicates that small yield reductions may result from using the chisel plow or disk as a substitute for moldboard plowing alfalfa fields in preparation for corn planting in the spring. Fall-killed alfalfa that was subsequently no-till planted to corn produced yields comparable to corn planted following primary tillage. However, where alfalfa was not fall-killed, no-till corn planting resulted in large yield losses compared to tilled treatments.
A two-year (1988 and 1989) study comparing moldboard (MP+), chisel (CP+), spring disk (SD) and no tillage (NT) combined with in-season cultivation was conducted in Winona County (Table 12). All tillage treatments were performed in the spring. Fluted coulters (2") were mounted on the planter. A conservation cultivator equipped with coulters and large sweeps was used. Corn yields averaged across the two years show only a small (6 bu/A) difference between the moldboard plow, chisel plow and disk systems; however, yields were reduced about 32 bu/A with no tillage when averaged across, with and without in-season cultivation. In-season cultivation was of great benefit for all tillage systems, resulting in an average yield increase of 23 bu/A. Lower yields with no tillage were due primarily to wooly cupgrass and giant foxtail competition.
Studies conducted on 10 silt loam sites in Wisconsin from 1985–1989 convincingly showed fall-killed alfalfa no-till planted to corn produced yields equal to or greater than moldboard or chisel plow tillage systems or spring-killed alfalfa that was NT planted (data not shown). Spring-kill NT resulted in 10 to 50 percent lower yields compared to fall-kill NT in 3 of 4 years and the most inconsistent weed control. Yield differences were not found between the fall and spring plow tillage systems.
Table 12. Corn yield after alfalfa as influenced by tillage and in-season cultivation in Winona County, 1988-89.
|1S-tine cultivator with no coulters or disks.|
Soybeans after corn
Soybean is much more tolerant than corn of very reduced tillage systems so long as weeds are controlled and row spacing is similar.
A study conducted from 1984-1989 on a Fayette silt loam in Wabasha County compared chisel plow (CP+), spring disk (SD), ridge tillage (RT) and no tillage (NT) for soybean production after corn (Table 13). Soybean yields were affected significantly by tillage in 5 of 6 years. Lowest yields in those years generally occurred with either ridge tillage or no tillage. Averaged across all six years, very little yield difference was found among the chisel, disk and no-till systems. Yields with ridge tillage were about 10 percent lower, likely because of the 38"/30" row spacing compared to 10" rows in the other tillage systems. In Goodhue County, soybean yields in 1991 were not different between chisel plow and no tillage systems that had been used for continuous corn from 1987-1990 (Table 11).
Table 13. Soybean yields following corn as influenced by tillage on a Fayette silt loam in Wabasha County.
|1All tillage treatments had 10-inch rows except RT, which had 38" in 1984 and 1985, and 30" from 1986-89. The NT treatment was not cultivated, whereas the RT treatment was cultivated twice.
2S=Significant; NS=Not significant
Loess soils over glacial till
Two long-term tillage experiments on continuous corn and corn-soybean rotations have been conducted on loess-cap soils over glacial till at the Iowa State University Northeast Research Center, Nashua, Iowa. Because tillage studies have not been conducted on these soils in Minnesota, data from somewhat poorly drained, high organic matter, glacial till soils at Waseca, which are somewhat similar to the Kenyon-Floyd soils, will be cited. Results from the Waseca studies are likely quite appropriate for the more poorly drained soils in the loess-cap area over till in southeastern Minnesota.
Yield penalties of 10 bu/A or more are frequently found for ridge-till and no-till systems compared to moldboard and chisel systems on loess-cap soils with poorer internal drainage.
A 15-year study conducted on a Kenyon silt loam soil at Nashua, Iowa compared moldboard plow (MP+), chisel plow (CP+), ridge tillage (RT) and no tillage (NT) (Table 14). The yield average was greatest for moldboard plow (134 bu/A), intermediate for chisel plow (130 bu/A) and ridge tillage (124 bu/A), and lowest for no tillage (121 bu/A). This ranking of yields is very similar to some of the long–term data obtained on the Nicollet and Webster soils at Waseca.
Table 14. Continuous corn yield as influenced by tillage on a Kenyon silt loam in Northeastern Iowa, 1978-921.
|Tillage system||15-Yr Yield Avg.|
|1Personal communication, Ramesh Kanwar, 2000.|
Corn after soybeans
Results from four studies on poorly drained soils consistently show slightly lower corn yields (3 to 8%) with no tillage compared to chisel plowing, the highest yielding treatment. Very small differences occurred among the chisel, strip-till and field cultivation systems.
A 15-year corn-soybean study conducted at Nashua compared the same tillage systems as the above continuous corn study. Corn yields averaged across the 15-year period were not greatly affected by tillage, ranging from a high of 145 bu/A with chisel tillage to 139 bu/A for ridge tillage (Table 15). A 30-inch row spacing was used for all treatments. A 6-year study conducted from 1993-1998 showed a 10 bu/A advantage for a single, spring field cultivation (FC) prior to planting corn (128 bu/A) compared to no tillage (118 bu/A).
Table 15. Corn and soybean yields in rotation as influenced by tillage on a Kenyon silt loam in Northeastern Iowa1.
|Crop, Number of years2|
|1Personal communication, Ramesh Kanwar, 2000.
215-Yr = 1978-92; 6-Yr = 1993-98.
3Tillage for corn = spring field cultivation (FC); tillage for soybean = fall chisel plow plus spring field cultivation (CP+).
At Waseca, tillage studies were conducted to compare nitrogen (N) and phosphorus (P) management strategies on chisel plow (CP+), strip-till (ST), field cultivation (FC) and no–till (NT) systems. The 3-year yield average ranged from 184 bu/A with chisel tillage to 176 bu/A with no tillage (Table 16). The optimum time for N application varied greatly from year to year. In 1997 and 1998, with normal rainfall amounts, yields were identical (188 bu/A) for fall and spring-applied anhydrous ammonia. However, in 1999, very wet and warm April and May conditions led to large losses of fall-applied N. As a result, corn yield was 36 bu/A less for fall-applied N compared to spring application, but was similar for all tillage systems. A 4-year study on high P-testing soils showed no yield difference between the chisel (CP+) and field cultivation (FC) systems, no yield difference between the strip till (ST) and FC systems, and lowest yields for no tillage (NT) (data not shown).
Table 16. Corn yield after soybean as influenced by tillage and time of N fertilizer application on a Nicollet-Webster clay loam soil complex at Waseca, 1997-99.
|Tillage system||1997-98 Avg.||1999||3-Yr Avg.|
|Time of N app.1|
|Fall, under row||188||145||174|
|1N applied as anhydrous ammonia at 110 lb N/A.|
Soybeans after corn
Results from three studies show very little yield penalty (maximum of 5%) for no tillage when soybeans follow corn.
Tillage studies conducted in Nashua, Iowa show no difference in soybean yield averaged across 15 years among moldboard plow (MP+), chisel plow (CP+), ridge-till (RT) and no-till (NT) systems (Table 15). Similar results were obtained during a 6-year period when chisel plow was compared to no tillage (Table 15).
At Waseca, 3-yr yield averages show significantly higher yields (56 bu/A) when some tillage was performed after corn–either chisel plowing (CP+) or spring disking (SD) of the corn stalks compared to no tillage (53 bu/A) (Table 17).
Table 17. Corn and soybean yields in rotation as influenced by tillage system on a Nicollet- Webster clay loam soil complex at Waseca.