|Gyles W. Randall
Southern Experiment Station
University of Minnesota
|Samuel D. Evans
West Central Experiment Station
University of Minnesota
now Emeritus Professor
at Morris, Minnesota
|John F. Moncrief
Department of Soil, Water, and Climate
University of Minnesota
|William E. Lueschen|
Department of Agronomy and Plant Genetics
University of Minnesota
formerly Head of the Southwest Experiment Station at Lamberton
A continuous corn cropping sequence can present severe challenges to conservation tillage systems, owing to the extremely high amounts of residue produced. Reduced tillage practices that can be used profitably, with little or no additional risk, in the corn-soybean rotation must be approached with caution with continuous corn. When accompanied by good management, chisel plowing and ridge tillage systems are appropriate for lower rainfall areas and on moderately or steeply sloping fields throughout the Minnesota River basin. However, on fairly level, poorly drained fields with fine-textured soils, chisel plowing or disk-chisel operations are advisable only with excellent management. Even then, modest yield penalties are possible. Moldboard plowing performs best in such conditions, but leaves inadequate residue for erosion protection. Thus, in fairly level, poorly drained, high-rainfall areas where sedimentation is a problem, management practices other than tillage (i.e., vegetative filter strips along rivers, streams, drainage ditches, and other runoff pathways to surface waters) may be required to reduce sediment losses.
Tilling the soil to prepare a seedbed has been a practice used for centuries. Since the mid-1800s the moldboard plow has been used by most farmers to invert the soil-- leaving the soil surface bare of residues. Because the possibility of erosion and sediment loss occurring is higher on bare soils, primary tillage tools that leave some residue on the soil surface were introduced in the 1950s and 60s to reduce soil erosion. Chisel plows and early models of ridge-till planters were the forerunners. Since then many styles and types of chisel plows, including V-rippers, have been developed to prepare a seedbed as well as leave some crop residue on the soil surface. The result has been good seed-to-soil contact for consistent seedling emergence and improved erosion control. With improved herbicides and planters available in the mid-1980s for better weed control and good seed placement, some farmers began to use no-tillage in their crop production system.
Soil erosion that has resulted in sediment loss into the surface waters of the Minnesota River basin has been identified as a key source of nutrient enrichment and turbidity (cloudiness) of the rivers. This nutrient enrichment and cloudiness promotes algal blooms, reduces oxygen levels, and interferes with biological and aesthetic well-being of the rivers. Improved crop residue management on these agricultural soils is one practice that can reduce erosion and subsequent sediment and nutrient losses from these fields. Crop residue on the soil surface protects the soil from the impact of raindrops and minimizes the dislodging of soil particles. Crop residues on the soil surface also may improve the infiltration of the rain into the soil, reducing surface runoff and resulting in more stored water in the soil profile for crop use. However, increased levels of crop residue on the soil surface insulate the soil, causing decreased soil temperatures in the spring due to sunlight reflection and increased soil moisture.
Selecting the best tillage system should involve a set of specific considerations much like those a farmer uses when selecting a hybrid. Often, certain hybrids are chosen to meet specific soil conditions. A similar approach should be taken for tillage. Factors that should be considered in the tillage selection process are:
The amount of residue present in a field before tillage depends on the crop previously grown and the level of production. Corn generates more residue than soybeans; thus it is easier to maintain higher residue levels following corn with a variety of tillage systems. However, corn has a low tolerance to high levels of crop residue on the soil surface, especially under cool and wet conditions, that is, on poorly drained soils. Therefore, continuous corn requires more tillage for residue incorporation. On the other hand, a corn-soybean rotation generates less residue and allows greater tillage flexibility. Little residue exists following soybeans and very reduced tillage, that is, no-tillage, often works well.
Erosion potential --Erosion potential mostly depends on the length and steepness of slope and soil texture. If the erosion potential is high, conservation tillage systems are highly recommended. Fields or acres considered to be highly erodible (HEL) require 30 percent residue cover after planting for conservation compliance. On the other hand, flat fields have a lower erosion potential. Sediment loss can be a problem on these fields, however, if soil detachment occurs during intense rainfall and there are open tile inlets or other channels that serve as direct conduits for the sediment-laden runoff water to quickly reach drainage ditches, streams, lakes, or other surface water bodies.
Internal drainage --Poorly drained soils warm up more slowly and usually require more tillage than do well-drained soils. With high levels of residue, the poorly drained soils often remain cool and wet too long for intolerant crops such as corn, resulting in decreased yields. System tiling helps on soils with poor internal drainage but may not be enough to ensure consistent success with little or no tillage and high levels of crop residue.
Soil fertility level --A high level of fertility is necessary if reduced tillage systems are to perform well. Low fertility conditions offer too many obstacles and generally limit yields more severely in reduced tillage systems. Thus, fields testing low in phosphorus (P) or potassium (K) should be brought to high P and K levels before implementing these reduced conservation tillage systems.
Surface soil compaction --Field activities conducted under wet conditions often result in surface compaction. Short, yellow, and spindly corn is evidence of this compaction, which is highly visible in field headlands, spots within fields, and wheel tracks. Primary tillage is needed to alleviate this surface soil compaction. Without primary tillage, good seed-to-soil contact and rapid root development in the spring will be more difficult.
Management of fertilizer and manure nutrients is critical to the success of conservation tillage systems with continuous corn. If nutrient management is poor, yields and economic return will suffer. In addition, runoff of non-incorporated nutrients applied to fields with no-tillage may actually increase nutrient enrichment of the surface waters. Do not surface-apply urea sources of N without incorporation unless gentle rains are imminent. Urea and UAN should be incorporated within three days to reduce potential loss by volatilization and runoff. Anhydrous ammonia has been the most consistent source of N. Application of ammonia is improved in all tillage systems, and especially in no-till, when covering disks attached to the injection knives are used to close the knife slits and seal in the ammonia. Alternative N application methods with ridge-till and no-till systems include: (1) spoke-injecting UAN into the soil and (2) applying urea 4" to 6" to the side of the seed row with the dry starter fertilizer attachment at the time of planting.
Phosphorus and K should be maintained at high levels (16-20 and 12-15 ppm P for Bray and Olsen extractants, respectively, and 121-160 ppm K) for optimum production with all tillage systems for continuous corn. Fertilizer P and K should be incorporated if at all possible. Results from a 6-year no-till study at Waseca showed a significant accumulation of both P and K in the surface 0-2" layer even when no P or K was applied. Thus, unincorporated broadcast P and K would add to this surface buildup and would increase the potential for P to be lost to surface water. Recommended application methods include: (1) broadcast and incorporation with a tillage implement; (2) banding 4" to 7" deep within the ridge with ridge tillage or randomly with other tillage systems; or (3) starter fertilizer. With no-till or ridge-till systems, starter fertilizer should be used when soil test P is <25 ppm. See extension bulletins "Fertilizer Management for Corn in Minnesota" (MES FO-3790, 1994) and "Fertilizer Management for Corn Planted in Ridge-Till or No-Till Systems" (MES AG-FO-6074, 1993) for more detailed information.
Livestock manure should also be incorporated for maximum benefit. Liquid manure offers more tillage flexibility because it can be knife- or sweep-injected either before planting or sidedressed between the rows with all tillage systems. With strict no-till this will disturb the residue similar to a cultivation, but injection when the corn is 12+ inches tall should not increase the erosion potential greatly. Solid manure sources should be incorporated by moldboard or chisel plowing or disking.
Reduced tillage and increased levels of crop residue may increase weed pressure. It is extremely important that farmers adjust their herbicide program to fit their tillage system. Tillage provides some weed control and offers greater herbicide flexibility and perhaps some economic savings for weed control. Perennial weeds are often economically controlled very satisfactorily with tillage. Herbicide incorporation with tillage minimizes herbicide runoff and volatilization losses.
Reduced tillage systems require state-of-the-art planters that are capable of providing good seed-to-soil contact and good stands. Row cleaning devices that remove residues from a 6" to 10" band over the row may assist stand establishment, early plant growth, maturity, and yield in most reduced tillage systems. Using a light planter designed for moldboard tillage conditions generally will not give adequate stands and uniform seedling emergence when used with no-till or most conservation tillage systems. Thus, matching planting equipment with the desired tillage system is very important.
Management of all the inputs in a manner that fits the soil, climate, and cropping system of the grower is critical if conservation tillage systems are to be profitable. Each of the components must be examined carefully. Seeking information by asking questions and reading educational background material is helpful for improving management.
Economical risk is increased as less tillage is used for continuous corn, especially over the long term. Crop development can be delayed and yields reduced in wet and cool years. The degree of risk is highly dependent on some of the preceding factors. With today's tight farm economy, risk is a factor that needs to be strongly considered by crop producers.
In summary, various factors including soil characteristics, erosion potential, fertilizer and herbicide management, planting equipment, management ability, and risk must be considered when selecting a residue management system for continuous corn. Because corn is sensitive to high levels of crop residue, especially in the cool and wet conditions so common in the poorly drained soils, tillage options are limited for continuous corn production in most areas of the Minnesota River basin. Good tile drainage, high soil fertility levels, a herbicide program that is targeted to the dominant weeds and applied in a timely fashion, and modern planters equipped with row cleaning and/or coulter devices for good seed-to-soil contact are critical management aspects that need to be practiced for conservation tillage systems to succeed for continuous corn.
Long-term tillage experiments on continuous corn have been conducted at the University of Minnesota agricultural experiment stations at Lamberton, Morris, and Waseca. These experiments along with good rainfall records allow us to see interactions with climate or trends that may occur over a period of years. These experiment stations are located on glacial till soils.
There are no data addressing tillage performance (crop response and soil erosion control) on lacustrine soils (see publication in this series that address soil types--"Description of the Minnesota River Basin and General Recommendations of Residue Management Systems for Sediment Control". The recommendations for lacustrine soils are based on the anticipated performance of tillage systems based on experience on other soils that have similar characteristics but have textures that are somewhat coarser and drainage that may be better.
A tillage study comparing moldboard plow (MP), chisel plow (CP), a spring disking (DK), ridge planting (RT), and no-till (NT) for continuous corn was started in 1979 at the West Central Experiment Station at Morris and the Southwest Experiment Station at Lamberton. On the somewhat poorly drained Hammerly clay loam soil at Morris, grain yields were highest in 5 of 6 years with moldboard plow tillage and averaged 8 to 10 bu/A higher than chisel plow, disk, or ridge tillage systems during the 6-year period (Table 1). No-till yields were lowest in 5 of 6 years and averaged 7 to 9 bu/A lower than the chisel, disk, and ridge-till systems. On the well-drained Ves clay loam soil at Lamberton, 4-year average grain yields from the moldboard plow and ridge-till systems were similar and were 8 to 12 bu/A higher compared with the chisel, disk, and no-till systems (Table 2). Yields were not different among the chisel, disk, and no-till systems. The absence of row cleaning devices (sweeps or disks) and fluted coulters on the planter used for all tillage systems in this study should be noted. However, all treatments were cultivated, which may have assisted the performance of the no-till system compared with strict no-tillage where cultivation is not practiced.
|Year||MP||CP||DK||RT 1||NT 1|
|1 All treatments were cultivated. The planter used was not equipped with sweeps, disks, or fluted coulters.|
|Year||MP||CP||DK||RT 1||NT 1|
|1 All treatments were cultivated. The planter used was not equipped with sweeps, disks, or fluted coulters.|
A 6-year (1984-1989) study conducted on a moderately well-drained Tara silt loam soil at Morris showed significant effects of rainfall and substantial differences among tillage systems (Table 3). It should be noted that the 6-month growing season rainfall was above normal and exceeded 15" in 4 of the 6 years. Under these conditions, ridge tillage produced higher yields than the other three tillage systems in three years, and over the six years averaged 6 bu/A higher than the next highest yielding tillage system (chisel plow). Yields with ridge tillage were consistently high in both wet and dry years with the exception of 1988 when yields were very low with all tillage systems. Lowest yields were found with no-tillage in 3 of 6 years. Surprisingly, no-till gave the lowest yield in 1987 (a year with only 8.5" of growing season rainfall) while lowest yields in the wettest year (1986 with over 26" of growing season rainfall) were obtained with moldboard plow tillage. In summary, large yield differences (up to 47 bu/A) were seen among the tillage systems each year, but clear-cut trends during the 6-year period or relationships to growing season rainfall were not apparent.
|Tillage System 1||Rainfall|
|Year||Fall MP||Fall CP||RT||NT||Apr-Sep|
|Grain Yield (bu/A)||Inches|
|1985||91 2||98 2||88||81||19.0|
160 lb. N/A.
2 Spring MP and CP due to wet conditions (10.6") in October, 1984.
3 100-Year average.
A 10-year study (1970-79) comparing four tillage systems--fall moldboard plow (MP), fall chisel plow (CP), a one-pass spring tandem disking (DK), and no-tillage (NT)--was conducted on a somewhat poorly drained Nicollet soil at Waseca. The site had very high soil P and K tests, tile lines at a 75-foot spacing, and a 2-5 percent south-facing slope. A planter equipped with 2" wide fluted coulters was used. Nitrogen was broadcast-applied as ammonium nitrate at 175 lb. N/A. Starter fertilizer was not used.
Grain yields averaged over the 10-year period were 12 to 16 bu/A higher with the moldboard, chisel, and disk systems compared with the no-till system (Table 4). Although a hard, compacted soil layer (disk pan) was found at the 3" to 4" depth at the end of the study with the continuous disk tillage system, yield was not affected. Yield differences among tillage systems in the first few years of the study were not large, probably due to the favorable site characteristics of a south-facing slope and close tile spacing. However, in the last two years of the study, under both average and wet conditions, yields with no-till were dramatically less than with the other three systems. Weed control, with the exception of some late-emerging fall panicum in the disk and no-till plots, was good in all years.
|Grain Yield (bu/A)||Inches|
Another study comparing ridge tillage with fall moldboard plowing, fall chiseling, and no-tillage was started on a poorly drained (but tiled) Webster clay loam at Waseca in 1975. All plots received 175 lb. N/A as broadcast ammonium nitrate each year and 150 lb. 9-23-30/A as starter fertilizer in 1975-1978. Beginning in 1979, one-half of each plot did not receive starter fertilizer, while the other half received 12 gal. of 7-21-7/A. Soil test P and K were high at the beginning of the study and tested very high at the conclusion of the study due to broadcast P and K additions. Weeds were controlled with a pre-emergence application of Lasso + atrazine plus post-emergence atrazine and oil in 1979 and 1980. Weed control was excellent on the moldboard plow, chisel, and ridge-till plots, which were cultivated each year, but weed pressure and lack of control increased with time in the no-till plots. Corn yield results shown in Table 5 indicate a 5 bu/A average yield advantage for moldboard plowing compared with ridge tilling and a 10 bu/A advantage over chisel plowing. Lowest yields occurred with no-tillage. This was primarily due to slow early plant growth, which delayed maturity, and inadequate weed control due to foxtail pressure. Yields of the chisel, ridge-till, and no-till plots were increased by 5 to 6 bu/A with starter fertilizer, but starter fertilizer did not increase yield with moldboard plowing.
Moldboard plow tillage was compared with no-tillage to determine if tillage for continuous corn affected nitrate losses from tile lines. This study was conducted on a poorly drained Webster clay loam at Waseca from 1982-1992. Soil test P and K were very high. Starter fertilizer and row cleaners were not used. Nitrogen was broadcast-applied as ammonium nitrate just prior to planting at 180 lb. N/A. The moldboard plots were cultivated. Weed control with the pre-emergence herbicides was excellent in all plots up until 1992, when some grasses and milkweed were found in the no-till plots. Average corn yields for the 11-year period showed a 21 bu/A advantage for moldboard plowing compared with no-till (Table 6). Each year, no-till yields were less than with moldboarding, even in the drier years when no-till was expected to perform better. The yield advantage for moldboarding increased as the study aged. In the 8th through 11th years of the study, yields averaged 42 bu/A lower with no-tillage. These extreme differences occurred under both wet and dry conditions. Early plant growth was much slower with no-tillage and resulted in a 5- to 7-day average delay in silking date and higher grain moisture at harvest. Nitrate losses in the tile drainage were not different for the two tillage systems.
|Grain Yield (bu/A)||Inches|
In summary, yield results from these long-term continuous corn studies indicate clear advantages for moldboard plow and ridge tillage on the normally drier glacial till soils at Morris and Lamberton, while moldboard plowing was superior on the flatter, poorly drained soils at Waseca. The sloping, somewhat poorly drained soil at Waseca produced almost equal yields among the moldboard, chisel, and disk systems, indicating greater tillage flexibility under these soil conditions.
Tillage implements combined into tillage systems can be used very effectively to create various levels of corn residue remaining on the soil surface. However, as seen from the previous discussion, corn yields following a previous crop of corn may be impacted greatly, depending on the amount of crop residue, internal drainage of the soil, soil texture, and growing season rainfall.
Five tillage systems shown below are categorized in Table 7 according to the residue management/yield performance indicators also shown below:
Moldboard Plow: Fall moldboard plowing followed by one or two secondary tillage operations before planting.
Chisel Plow-Plus: Fall chisel plowing plus spring secondary tillage.
One or Two Pass: Single or double pass with tandem disk in spring before planting corn.
Ridge-Till: Tillage is limited to that performed by the planter (ridge-leveling) and one or two in-season cultivations (ridge-building).
No-Till: All seedbed preparation is performed by the planter. Starter fertilizer placement and clearing residue from the rows usually are done with the planter, but may be performed separately, sometimes in combination with anhydrous ammonia injection or other fertilizer injected into a strip.
1) Inadequate Residue to Minimize Erosion. (less than 30 percent of surface covered after planting). Highest yield may be obtained, however, on poorly drained, fine-textured, high organic matter soils.
2) Recommended with Good Management. No yield penalty is expected if the farmer observes all relevant recommended management practices for high-residue systems.
3) 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.
4) Reduced Yield Potential. The potential exists for substantially reduced yields especially on poorly drained soils in wet years.
|Tillage System||High Rainfall||Low Rainfall||High Rainfall||Low Rainfall|
|Chisel Plow Plus||3||2||3||2|
|One or Two Pass||3||3||4||3|
|1 For corn following silage corn, inadequate amounts of surface residue will exist for all tillage systems.|
The matrix of performance indicators shown in Table 7 indicates that corn following corn is very sensitive to tillage system when grown on medium- and fine-textured glacial till and lacustrine soils.
Moldboard plowing often results in highest corn yields, especially on poorly drained soils, but leaves inadequate surface residue (often <10 percent) to minimize soil erosion. Thus, this tillage system should be restricted to the flat, poorly drained, fine-textured soils if both yield/profitability and erosion are to be optimized.
The chisel plow-plus system will leave adequate residue in all soil-rainfall scenarios, but will require excellent management and may result in a slight yield penalty in the higher annual precipitation area (>28") of the Minnesota River basin. Residue clearing attachments should be mounted on the planter to minimize yield loss. Fields that are better drained in lower rainfall areas, or landscapes with 3 to 8 percent slopes, are ideal for this tillage system.
One or two pass, tandem disk tillage is usually a rescue spring tillage treatment for continuous corn because conditions the previous fall were either too wet or cold for fall tillage. This system evenly distributes a large amount of corn residue across the soil surface but does little seedbed preparation below 2" to 3". Delayed planting may be a problem, and corn yields can suffer markedly, especially on poorly drained, flat fields. This tillage system performs best on 3 to 8 percent slopes and when row cleaners are used.
Ridge-till maintains excellent surface residue coverage in continuous corn cropping systems, especially when very little soil is removed (scalped) from the ridge at planting. The accumulation of residue between the ridges/rows coupled with the ridges themselves every 30"-36", which act like mini-terraces, allows this tillage system to be used very successfully on 3 to 10 percent slopes. Soil erosion is minimal because infiltration is optimized and runoff is minimized. Maintaining high soil test P and K with band injection of fertilizer 4" to 7" deep into the ridge is necessary for optimum yield and profit. This practice also minimizes loss of soluble P from the landscape. Ridge tillage can be practiced on glacial till soils without a yield penalty. Although we do not have long-term yield data with ridge-till on lacustrine soils, we speculate that greater management may be required and some yield loss could occur on these very flat, poorly drained landscapes.
No-tillage leaves all of the residue on the soil surface, which often results in wetter and colder soils at planting. Row cleaners attached to the planter are necessary to minimize these negative effects on crop growth. However, the consolidated nature of the surface soil with continuous no-till appears to slow root growth when the plant is small. This results in slower plant growth, delayed maturity, and lower yields, especially on wet, poorly drained soils. Soil test P and K also need to be high and fertilizer must be injected for optimum efficiency. Starter fertilizer is usually necessary. This practice works best on fields with 4 to 10 percent slopes.
In summary, soil characteristics such as slope, drainage, and texture must be carefully considered when choosing a tillage system for continuous corn. On flat, poorly drained, fine-textured soils, moldboard plow tillage is usually best. On the other hand, conservation tillage practices can be used on those landscapes with 2 to 10 percent slopes, but management is critical for these systems to perform well.
To order other publications in this series, contact your Minnesota County Extension Office, or outside of Minnesota, contact the Extension Store at (612) 625-8173. Titles in this series include:
This set of publications was the result of a joint effort between Minnesota Extension Service, Minnesota Agricultural Experiment Station, and Minnesota Pollution Control Agency. This information was first presented February of 1995 at the Sediment Control Solutions Conferences in Mankato and Montevideo, Minnesota.
In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request. Please contact your University of Minnesota Extension office or the Extension Store at (800) 876-8636.