WW-06676     1996  

Tillage Best Management Practices for Corn-Soybean Rotations in the Minnesotata River Basin

Gyles W. Randall Soil Scientist Southern Experiment Station University of Minnesota	William E. Lueschen Department of Agronomy and Plant Genetics University of Minnesota formerly Head of the Southwest Experiment Station at Lamberton
Samuel D. Evans Soil Scientist West Central Experiment Station University of Minnesota now Emeritus Professor at Morris, Minnesota	John F. Moncrief Extension Specialist Department of Soil, Water, and Climate University of Minnesota

Copyright ©  2002  Regents of the University of Minnesota. All rights reserved.

Table of Contents

• Summary
• Introduction
• Factors to Consider When Making a Tillage Decision
  • Crop Rotation
  • Soil Characteristics
  • Nutrient Management
  • Herbicide Program
  • Planting Equipment: Type and Age
  • Management Ability and Risk
• Yield Results From Long-Term Tillage Research
  • Low Rainfall, Glacial Till Sites
    • Corn
    • Soybean
  • High Rainfall, Glacial Till Sites
    • Corn
    • Soybean
  • Manageing Crop Residue With Tillage
  • Tillage Systems
  • Residue Management/Yield Performance Indicators

Summary

A corn-soybean crop rotation presents opportunities for tillage flexibility without sacrificing yields due to the lesser amounts of crop residue produced compared to continuous corn. Numerous reduced tillage practices can be used profitably, with little or no additional risk, in this crop rotation. When accompanied by good management, one-pass tillage with a field cultivator, ridge tillage, and no-tillage systems are appropriate for corn in the lower rainfall area and on glacial till soils throughout the Minnesota River basin. One-pass field cultivation or fall chisel plowing plus spring field cultivation are advisable tillage systems for corn production on the flat, poorly drained lacustrine soils. Soybean production can be accomplished successfully throughout the Minnesota River basin with the chisel plow-plus tillage system. This system also allows incorporation of nutrients, lime, and herbicides. One- or two-pass disk tillage or ridge-till are also advisable on glacial till soils but may require excellent management on wet, level, fine-textured fields. Even then, modest yield penalties are possible. No-tillage for soybeans requires excellent management on all soils in the basin; even then a slight yield penalty is possible. Best results with no-till are obtained when rotated periodically with a chisel plow system. Moldboard plow tillage is not recommended in this crop rotation except when solid manure sources, nutrients, or lime are to be incorporated up to 8 inches deep following corn, or when the risk of sediment losses to surface waters are minimal.

Introduction

Tilling the soil to prepare a seedbed has been a practice used for centuries. Since the mid-1800's 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 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 infiltration of precipitation 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 insulates the soil causing decreased soil temperatures in the spring due to sunlight reflection and increased soil moisture which can reduce soil aeration.

Factors to Consider When Making a Tillage Decision

Selecting the best tillage system should involve a set of specific considerations much like 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:

Crop Rotation

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. The durability of the residue is also crop dependent. Soybean residue is considered to be "fragile" or in other words is easily destroyed. Maintaining an adequate residue cover is a problem following soybeans. Corn residue, on the other hand, is considered "non-fragile" and breaks down quite slowly. Because a corn-soybean rotation generates less residue than corn rotated with most other crops, tillage flexibility is greater. Very reduced tillage, that is, no-tillage, often works well following soybeans. In summary, both crops need to be considered when making tillage decisions for a corn-soybean rotation.

Soil Characteristics

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 land (HEL) require 30% 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 (no-till and ridge-till) systems compared to full-width, deep 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 and short soybeans are evidence of this compaction, which is highly visible in field headlands, spots within fields, and wheel tracks. Primary tillage is often 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.

Nutrient Management

Management of fertilizer and manure nutrients is highly important to the success of conservation tillage systems for corn-soybean rotations. 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. To reduce potential loss by volatilization and runoff, do not surface-apply urea or liquid 28% N solution UAN (urea-ammonium nitrate) unless incorporation can be completed within three days or gentle rains are imminent. Anhydrous ammonia has been the most consistent source of N, but some soybean residue will be incorporated by the knives during application. 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. Grid soil sampling with variable rate fertilizer application will greatly assist farmers to keep soil test P and K within these ranges without over-fertilization of the already high-testing areas. To maintain these soil test levels, broadcast application of fertilizer P and K should be incorporated following corn if at all possible. These nutrients will be available for the corn in the second year of the rotation. 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 could increase the potential for P to be lost to surface water. Recommended application methods include: (1) broadcast and incorporation with a tillage implement following corn; (2) banding 4" to 7" deep within the ridge with ridge tillage; (3) banding 4" to 7" deep randomly or with strip-till (zone-till) systems that prepare a residue-free band for corn; or (4) starter fertilizer. With no-till or ridge-till systems, starter fertilizer should be used for corn when Bray soil test P is <25 ppm. See extension bulletins "Fertilizer Management for Corn in Minnesota" (Minnesota Extension Service FO-3790, 1994) and "Fertilizer Management for Corn Planted in Ridge-Till or No-Till Systems" (Minnesota Extension Service AG-FO-6074, 1993) for more detailed information.

Livestock manure should also be incorporated for maximum benefit. However, incorporating manure when in a corn-soybean rotation presents a real dilemma. Greatest nutrient utilization occurs when the manure is applied following soybeans for corn (nitrogen is utilized); however, the small amount of "fragile" soybean residue is almost completely destroyed in the incorporation process. Incorporating manure following corn with either a chisel plow or by injection of liquid manure allows for good residue management, but nutrient utilization by the following soybean crop is inferior to corn. Liquid manure offers more tillage flexibility because it can be knife- or sweep-injected either before planting or sidedressed between the corn rows. 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 offer little flexibility. They should be incorporated by chisel plowing corn ground ahead of soybean or by chiseling very level soybean ground. Solid manure sources should not be applied to sloping land following soybeans.

Herbicide Program

Reduced tillage and increased levels of crop residue may increase weed pressure. Thus, it is extremely important that farmers adjust their herbicide program to fit their tillage system. Herbicide timing and choice are more critical as one relies less on tillage to control weeds. However, with today's wide choice of herbicides, excellent control with little or no tillage is highly feasible, often at little or no additional weed control cost compared to conventional tillage. But starting very reduced tillage systems on weed-infested fields should be avoided. Tillage provides some weed control, offers greater herbicide flexibility, and perhaps some economic savings for weed control. Mechanical weed control, using the rotary hoe or cultivator, is a best management practice and can be an economical choice under many situations. Perennial weed problems often increase with no-till or ridge-till but can be economically and satisfactorily controlled with herbicides. Herbicide incorporation with tillage minimizes herbicide runoff and volatilization losses.

Planting Equipment: Type and Age

Residue management systems require state-of-the-art planters that are capable of providing proper depth control, firm seed-to-soil contact, and good stands. Row cleaning devices that remove residues from a narrow band over the corn row may assist stand establishment, early plant growth, corn maturity, and yield in very reduced tillage systems and, thus, are advisable for high-residue conditions. 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. If considering solid-seeded soybean production with no-tillage, it is essential that a properly designed, heavy duty drill be used that can cut through the residue, place seed at a proper depth without incorporating residue, and firm the soil over the seed. In summary, matching planting equipment with the desired tillage system is very important.

Management Ability and Risk

Economical risk can be increased somewhat as less tillage is used in a corn-soybean rotation. This is especially true over the long term with very-reduced tillage systems. Crop development may be delayed and yields decreased under adverse growing conditions. This long-term risk can be reduced through occasional use of primary tillage and close attention to crop management requirements of very-reduced tillage systems.

In summary, various factors including soil characteristics, erosion potential, nutrient and herbicide management, planting equipment, management ability, and risk must be considered when selecting a residue management system for a corn-soybean rotation. Because crop residue levels are lower in this rotation, tillage options are numerous and reduced tillage systems are practical for a corn-soybean rotation 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 to optimize performance of conservation tillage systems in this rotation.

Yield Results From Long-Term Tillage Research

Long-term tillage experiments on corn-soybean rotations have been conducted at the University of Minnesota agricultural experiment stations at Lamberton, Morris, and Waseca. These experiments allow us to see interactions with climate or trends that may occur during a period of years. These experiment stations are located on glacial till type 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.

Low Rainfall, Glacial Till Sites

Corn

A tillage study comparing moldboard plow, chisel plow, spring disk, ridge planting, and no-till systems for corn following soybeans was started in 1979 at the West Central Experiment Station at Morris and the Southwest Experiment Station at Lamberton. Each year the experiment was moved to a new site. On the somewhat poorly drained Hammerly clay loam at Morris, 6-year average corn grain yields for the 5 tillage systems varied by only 2 bu/A (136 to 138 bu/A) and were not significantly different (Table 1). Within any one year yield differences among the tillage systems ranged from only 4 bu/A in 1979 to 18 bu/A in 1984. However, no single tillage system was consistently better or poorer than another. On the well-drained Ves soil at Lamberton, a similar yield response to tillage was shown (Table 2). Four-year average yields differed by only 1 bu/A with no consistent year-to-year pattern.

Table 1. Corn yield in a corn-soybean rotation as influenced by tillage on a somewhat poorly drained Hammerly clay loam at Morris.

	Year	Average
Tillage	1979	1980	1981	1982	1983	1984
Yield (bu/A)
Moldboard	137	134	141	148	126	134	137
Chisel	138	124	149	155	130	121	136
Spring disk	136	127	138	154	124	139	136
Ridge 1	135	128	143	151	134	134	138
No-till 1	139	127	136	153	126	136	136
1 All treatments were cultivated. The planter used was not equipped with sweeps, disks, or fluted coulters.

Table 2. Corn yield in a corn-soybean rotation as influenced by tillage on a well-drained Ves clay loam soil at Lamberton.

	Year	Average
Tillage	1979	1980	1981	1982
Yield (bu/A)
Moldboard	128	135	124	146	133
Chisel	130	131	135	138	134
Spring disk	131	138	126	143	135
Ridge 1	138	130	121	148	134
No-till 1	127	135	127	151	135
1 All treatments were cultivated. The planter used was not equipped with sweeps, disks, or fluted coulters.

Another tillage study for corn after soybeans was started on a well-drained Barnes loam soil at Morris in 1980. Again, 5-year yield averages show no difference among the moldboard, chisel, or no-till systems (Table 3). Yields among the three tillage systems never varied by more than 9 bu/A in any year.

In all three of these studies row cleaning devices and fluted coulters were not used, but all tillage systems received cultivation. Under these conditions, when a long-term tillage system had not been in place, corn yields following soybeans were unaffected by tillage.

Table 3. Corn yield in a corn-soybean rotation as influenced by tillage on a well-drained Barnes loam soil at Morris.

	Year	Average
Tillage	1980	1981	1982	1983	1984
Yield (bu/A)
Moldboard	129	139	147	103	139	131
Chisel	131	134	146	105	141	131
No-till 1	134	130	145	106	147	132
1 No-till treatment was cultivated. The planter used was not equipped with sweeps, disks, or fluted coulters.

A 7-year study was started in 1986 on a well-drained Ves soil at Lamberton to evaluate long-term tillage systems in a corn-soybean rotation (Table 4). Three continuous tillage systems--ridge-till (RT), paraplow (PP), and no-till (NT)--were compared to two tillage systems where the tillage varied with the crop. Row cleaners were not used and weed control was a problem in some years. Significant yield differences among tillage systems occurred in five of seven years. Seven-year average yield was highest with the system that involved chisel plow (CP) after soybean and moldboard plow (MP) after corn. Lowest average yields were obtained with continuous paraplowing, continuous no-tillage, and with the system where no-tillage was used after soybean and chiseling was used after corn. Ridge-till yields were intermediate. The performance of the tillage systems did not appear to be related to growing season rainfall. However, a trend of poorer performance with increasing years of continuous no-till use was apparent. In the fourth through seventh years, yields with continuous NT and the NT/CP system averaged 15 and 12 bu/A less, respectively, than with the CP/MP system. These data suggest that corn yields in a corn-soybean rotation may be reduced with the use of no-till systems over time. The reason for this yield reduction is not known. Yields from the spring field cultivation after soybeans and spring disk after corn system averaged 3 bu/A better than the NT/CP system during the last four years.

Table 4. Corn yield in a corn-soybean rotation as influenced by tillage and rainfall on a well-drained Ves clay loam soil at Lamberton.

Year 2	Tillage System 1	Apr. - Oct.
CP/MP	NT/CP	RT/RT	PP/PP 3	NT/NT	Rainfall
Yield (bu/A)	inches
1986	141	138	145	132	142	34.7
1987*	136	125	125	120	132	15.8
1988*	77	70	82	65	74	13.2
1989*	139	128	133	132	122	14.7
1990*	137	120	118	123	114	20.7
1991	132	134	129	133	133	25.4
1992*	154	131	145	137	134	23.9
Average	131	121	126	-----	122
1 Tillage for corn after soybean/tillage for soybean after corn. 2 *Indicates that yields among tillage treatments were significantly different at the 95% level for that year. 3 PP abandoned after 1988 and replaced by spring disk after corn and spring field cultivate after soybeans.

Summarizing the yield data from these 22 site-years indicates little effect of tillage following soybean on corn production. The only exception, but one that is very important, is the reduced yields after three years when no-tillage is used continuously or as part of a reduced tillage system.

Soybean

A comprehensive study to evaluate tillage systems for soybeans in a corn-soybean rotation was started in 1982 at the Morris, Lamberton, and Waseca experiment stations (Table 5). The soils were primarily moderately and well-drained Aastad and Barnes clay loams at Morris and moderately and well-drained Normania and Ves clay loams at Lamberton. Each year a new site was used; thus the tillage methods were one year in length and were not repeated as part of a long-term tillage system. Stalks were chopped in the spring for the ridge-till and no-till treatments. Cultivation was not done on any of the plots. Both 10" and 30" rows were planted in the moldboard, chisel, and disk plots. A planter equipped with fluted coulters was used to plant all plots except the ridged plots where a ridge planter, which scalped 1" to 2" from the ridge, was used. Weed control was perfect with a combination of herbicides and hand weeding.

Yields shown in Table 5 indicate no significant difference among tillage systems in two of four years at Morris and two of three years at Lamberton. In the three years when differences existed, yields among the 5 tillage treatments never varied by more than 4.5 bu/A. Four-year average yields at Morris were slightly lower with the double spring disk treatment compared to the chisel, ridge, and no-till treatments. Average yield with moldboard plowing was intermediate probably a result of the low yield in 1982, a very dry spring. At Lamberton, 3-year average yields were not different among the tillage treatments. A tillage by row spacing interaction was not found at either location, which indicates that yields among the tillage systems were not affected by row spacing. Surface residue coverage after planting averaged about 14% for the fall moldboard plow treatment, 40% for fall chiseling, 50% for spring disking, 59% for ridge-planting, and 76% for no-tillage at the two sites.

Table 5. Soybean yield in a corn-soybean rotation and surface residue cover as influenced by tillage at three locations in the Minnesota River basin, 1982-1985.

Location	Tillage	Year	Average	Surface Residue 1 Cover
1982	1983	1984	1985
Yield (bu/A)	%
Morris	Moldboard	30.0	55.5	39.4	49.8	43.7	14
Chisel	32.3	55.4	41.2	49.2	44.5	37
Spring disk	32.9	52.5	38.9	45.8	42.5	51
Ridge	32.4	54.6	40.7	49.2	44.2	58
No-till	34.5	55.5	40.6	47.7	44.5	74
LSD (.05)	2.3	NS	NS	2.4	1.4
Lamberton	Moldboard	45.5	41.1	36.8	-----	40.7	15
Chisel	46.2	40.3	33.2	-----	39.3	43
Spring disk	45.9	42.0	34.7	-----	40.4	48
Ridge	43.9	46.0	33.0	-----	41.0	60
No-till	42.0	43.5	35.3	-----	39.6	79
LSD (.05)	2.2	NS	NS	-----	NS
Waseca	Moldboard	44.0	43.4	42.1	40.0	42.4	14
Chisel	44.0	41.5	41.9	38.2	41.4	40
Spring disk	44.6	40.3	42.3	40.6	41.9	48
Ridge	41.8	43.0	40.1	39.2	41.0	40
No-till	43.0	40.7	40.2	38.8	40.7	84
LSD (.05)	2.0	2.1	1.6	NS	1.0
1 Between 30 inch rows after planting and averaged over years.

Another study was started at these same three locations in 1986 to evaluate the effect of five tillage systems for a corn-soybean rotation on both corn and soybean yields (Table 6). Soils were similar to those described in the previous study. Stalks were chopped in the fall for the ridge-till and chisel treatments only. Eight soybean varieties were planted in 30" rows on each tillage plot. Weeds were controlled with herbicides applied to all plots; cultivation of the moldboard, chisel, and ridge plots; and by hand-weeding all plots.

Yields shown in Table 6 indicate significant differences among the five tillage systems in 4 of 6 site-years at Morris and Lamberton. Three-year soybean yield averages at Morris show a significantly lower yield with moldboard plow tillage primarily because of 1988 (a very dry year in which yields from the moldboard plots were 6 to 8 bu/A poorer than from the other tillage treatments). Yields among the chisel, ridge, paraplow, and no-till treatments were not different. At Lamberton, 3-year average yields contradicted those from Morris and were significantly higher for the moldboard treatment compared to the other treatments. Again, this difference was due primarily to 1988 which was dry at Lamberton but not quite as dry as at Morris. Surface residue coverage after planting averaged 9% for moldboard plowing, 51% for chiseling and ridging, 65% for paraplowing, and 82% for no-tillage.

Table 6. Soybean yield in a corn-soybean rotation and surface residue cover as influenced by tillage at three locations in the Minnesota River basin, 1986-1988.

Location	Tillage 2	Year	Average	Surface Residue 1 Cover
1986	1987	1988
Yield (bu/A) 3	%
Morris	MP/CP	45.5	39.2	15.8	33.5	12
CP/NT	44.3	40.0	22.3	35.5	52
RT/RT	42.0	40.3	24.3	35.5	62
PP/PP	45.3	36.9	23.4	35.2	62
NT/NT	45.2	40.0	25.1	36.7	80
LSD (.05)	2.5	NS	4.9	2.1
Lamberton	MP/CP	47.9	38.8	32.0	39.6	6
CP/NT	46.7	39.5	26.3	37.5	50
RT/RT	47.3	38.7	26.7	37.6	40
PP/PP	48.9	37.0	26.2	37.4	68
NT/NT	47.4	39.3	26.9	37.9	84
LSD (.05)	2.0	NS	2.4	1.3
Waseca	MP/CP	46.6	42.0	38.8	42.1	11
CP/NT	45.1	42.3	36.3	40.9	42
RT/RT	40.2	42.4	34.6	38.9	51
PP/PP	44.1	42.6	34.7	40.1	72
NT/NT	44.5	42.0	37.6	41.1	82
LSD (.05)	4.6	NS	NS	2.0
1 Between 30" rows after planting and averaged over years. 2 Tillage for soybean after corn/tillage for corn after soybean. MP = moldboard plow, CP = chisel plow, RT = ridge tillage, PP = paraplow, and NT = no-tillage. 3 Each yield is an average of 8 varieties.

The study described above and shown in Table 6 was continued at Lamberton for four additional years. The only change was substituting the spring disk after corn/spring field cultivate after soybean treatment for annual paraplowing. Yields shown in Table 7 indicate significant differences among the tillage systems in three of four years. Beginning in 1989 (the fourth year of the study) and continuing through 1991, soybean yields with continuous no-tillage were 5.2 bu/A lower than for the other tillage systems. In 1992 (year 7) when yields were relatively low, yield differences among the tillage systems were not found. Four-year averages show highest yields with the moldboard plow/chisel and chisel/no-till systems, intermediate yields with the ridge till and spring disk/spring field cultivate systems, and lowest for the continuous no-tillage system.

Based on the 17 site-years of data from these two low rainfall, glacial till locations, it is very clear that little yield difference exists among any tillage methods for soybeans after corn until at least three years into continuous no-tillage. After three years, yields from the continuous no-till began to decline. Although the exact reason for this decline is not known, we can speculate that surface soil compaction may be at least partially responsible. Surface residue coverage was ideal with all tillage systems except moldboard plow.

Table 7. Soybean yields in a corn-soybean rotation as influenced by tillage on a well-drained Ves clay loam soil at Lamberton.

	Year 2	Average
Tillage 1 System	1989*	1990*	1991*	1992
Yield (bu/A)
MP/CP	48.8	51.8	48.0	37.3	46.5
CP/NT	45.8	51.6	46.2	37.7	45.3
RT/RT	49.2	48.7	41.4	35.4	43.7
SD/SFC	47.1	45.4	44.4	36.5	43.4
NT/NT	40.9	44.7	40.3	35.9	40.4
1 Tillage for soybean after corn/tillage for corn after soybean. SFC = spring field cultivate. 2 * Indicates that yields among tillage treatments were significantly different at the 95% level for that year.

High rainfall - glacial till sites

Corn

A 5-year study was started in the fall of 1972 on a poorly drained Webster clay loam at Waseca to compare time and methods of tillage for a corn-soybean rotation (Table 8). Fluted coulters were used to plant the treatments that did not receive primary tillage, but were removed for the rest of the treatments. Nitrogen as ammonium nitrate was broadcast at a rate of 150 lb. N/A each spring. Starter fertilizer was not used on this high testing soil. All tillage treatments were cultivated once in 1975-1977. However, high surface residues prevented cultivation of the no-till plots in 1973 and 1974.

Four-year average yield data shown in Table 8 indicate substantially lower corn yields with continuous no-tillage, and somewhat lower yields when primary tillage (moldboard plow or chisel) was done in the spring.

Table 8. Corn and soybean yields in a corn-soybean rotation as influenced by time and method of tillage on a poorly drained Webster clay loam at Waseca.

Tillage for: 1	Yield Average
1974-77	1973-77
Corn after Soybean	Soybean after Corn	Corn	Soybean
bu/A
No-till	No-till	113	38.6
Fall moldboard	Fall moldboard	135	45.5
Fall chisel	Fall moldboard	138	46.4
Spring chisel	Fall moldboard	129	44.8
No-till	Fall moldboard	137	45.2
Spring moldboard	Spring moldboard	124	45.3
Fall chisel	Fall chisel	130	43.2
No-till	Fall chisel	125	43.9
Spring chisel	Spring chisel	128	43.2
Spring disk	Spring disk	136	44.0
LSD (.05)		10	2.5
1 Corn was grown on all plots in 1972.

Periodic poor weed control with continuous no-tillage and a poor, cloddy seedbed resulting from spring primary tillage in some years were the primary causes of these reduced yields. Highest yields were obtained with the fall chisel/fall moldboard and the no-till/fall moldboard tillage combinations and the continuous spring disk system for the corn-soybean rotation.

Table 9. Corn yields and surface residue cover in a corn-soybean rotation as influenced by tillage on a poorly drained Webster clay loam soil at Waseca.

Tillage System 1	Yield 2	Residue cover 3
1986	1987	1988	Average	1986	1987	1988
(bu/A)	%
CP/MP	134	161	92	129	9	11	8
NT/CP	141	151	100	131	32	59	49
RT/RT	137	158	98	131	4	36	14
PP/PP	136	154	90	127	21	45	41
NT/NT	135	148	92	125	29	76	58
LSD (.05)	NS	7	NS	-----	-----	-----	-----
1 Tillage for corn after soybean/tillage for soybean after corn. 2 Average of 5 hybrids grown each year. 3 Average of 16 measurements taken after planting but before anhydrous ammonia application.

Tillage systems similar to those discussed earlier for Lamberton (Table 4) were also evaluated on a poorly drained Webster clay loam at Waseca (Table 9). After soybean, only the chisel plow plots received a field cultivation before planting. Five hybrids were planted on each plot. Nitrogen as anhydrous ammonia was sidedress-applied at the 4-leaf stage at a rate of 160 lb. N/A each year. None of the treatments were cultivated except to build the ridges when the corn was about 30" high in the ridge treatment. Weed control was excellent.

Yields shown in Table 9 indicate no significant difference among tillage systems for corn after soybeans in two of three years. However, in 1987 yields with no-tillage and paraplowing were lowest. Three-year average yields were highest with the no-till/chisel plow system and ridge-till system and were 6 bu/A lower with the continuous no-till system. A companion study indicated yields were optimized at rates of 80 lb. N/A in two years and 120 lb. N/A in the third with no-tillage by N rate interaction. Surface residue coverage was poor in all three years when the moldboard plow was part of the tillage system. Ridge tillage also gave inadequate residue cover, largely because scalping the ridge buries most of the fragile soybean residue. In 1986, when the tillage treatments for corn had not been in place earlier (1984), residue coverage was marginal for all tillage systems. However, in 1987 and 1988 (corn was grown in 1985 and 1986, respectively, on these plots), residue coverage was much higher and averaged 43% with paraplowing, 54% with the no-till/chisel system, and 67% with continuous no-tillage.

From the results of these two studies (7 site-years), adequate residue coverage and optimum corn yields can be obtained with no-tillage after soybeans as long as some primary tillage (chiseling or moldboard plowing) is done following the corn. Ridge till or a single spring one-pass tillage operation (field cultivator or disk) would also result in optimum yields but residue coverage could be less than desired. Continuous no-tillage results in somewhat poorer yields but does give excellent surface coverage.

Soybean

Soybean yields were also obtained in the 1973-1977 study conducted at Waseca and described above (Table 8). Lowest yields were obtained with continuous no-tillage partially due to inadequate weed control in some years. Those tillage systems that contained either fall or spring moldboard plowing yielded 2 bu/A higher than those that contained either fall or spring chiseling.

Five tillage methods described in the low rainfall discussion for Morris and Lamberton were also compared at Waseca on a poorly drained Webster clay loam (Table 5). Yields were affected by tillage in three of four years with the 4-year average showing highest yield (42.4 bu/A) with moldboard plow tillage and the lowest yield (40.7 bu/A) with no-tillage. Surface residue coverage ranged from 40% with the chisel and ridge systems to 84% with no-tillage while moldboard plowing only had 14% coverage.

The five tillage systems for a continuous corn-soybean rotation described for Morris and Lamberton were also compared at Waseca on a poorly drained Webster clay loam (Table 6). Very little yield difference was found among the tillage systems during the 3-year period except for the ridge-till yields being about 5 bu/A lower in 1986. The 3-year average yields reflected this with a ridge-till yield of 38.9 bu/A compared to yields from 40.1 to 42.1 bu/A with the other tillage systems. Surface residue coverage was inadequate for the moldboard plow/chisel system, averaged about 45 to 50% with the chisel/no-till and ridge-till systems, and over 70% with the continuous paraplow and no-till systems.

In summary, these studies also indicate that excellent soybean yields and surface residue coverage can be obtained on high rainfall, glacial till soils with very little or no-tillage in a corn-soybean rotation as long as good weed control is practiced.

Managing Crop Residue With Tillage

Tillage implements combined into tillage systems can be used very effectively to create various levels of corn residue remaining on the soil surface. However, any tillage following soybeans almost completely destroys the residue because of the small amount present and its fragile nature. As seen from the previous discussion, corn and soybean yields in a corn-soybean rotation are not impacted greatly by the amount of crop residue present.

Five tillage systems shown below are categorized in Tables 10 and 11 according to the residue management/yield performance indicators also shown below:

Tillage Systems

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: No fall primary tillage. Single pass in spring with field cultivator before planting corn. Single or double pass with tandem disk in spring before planting soybeans.

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 for corn, but may be performed separately, sometimes in combination with anhydrous ammonia injection or other fertilizer injected into a band.

Residue Management/Yield Performance Indicators

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.

Corn

The matrix of performance indicators shown in Table 10 indicates that corn following soybeans is not very sensitive to tillage system when grown on medium and fine-textured glacial till and lacustrine soils. Moldboard plowing does not result in higher corn yields than other tillage systems and leaves inadequate surface residue (often <10%) to minimize soil erosion. Thus, this tillage system should not be used for corn after soybean in the Minnesota River basin. The chisel plow-plus system will also leave inadequate amounts of surface residue in all soil-rainfall scenarios, and will not give higher corn yields than other reduced tillage systems. This tillage system should be used only on level (0 to 3% slope) soils when broadcast manure is to be incorporated or if severe surface soil compaction occurred during the last year when soybeans were grown.

Table 10. Matrix of residue management/yield performance indicators for corn following soybean on glacial till and lacustrine soils under high annual precipitation (>28") or low annual precipitation (<28") conditions in the Minnesota River basin.

Tillage system	Glacial till	Lacustrine
Rainfall
High	Low	High	Low
Moldboard plow	1	1	1	1
Chisel plow plus 1	2/1	1	2/1	1
One pass	2	2	2	2
Ridge-till	2	2	3	3
No-till	3/2	2	3	3
1 Even if straight shanks are used, this system cannot reliably achieve the 30 percent surface residue target, and must be used in a rotation where corn residue levels are at least 40 percent after planting.

One pass, field cultivator tillage in the spring levels the field, provides a good seedbed, incorporates surface-applied fertilizers and preplant herbicides, and kills early-germinating weeds. However, little soybean residue is left on the soil surface, and erosion control is minimal. Use of flat, wide, low-crown cultivator shovels can help to minimize destruction of fragile surface residues. Corn residue left on the soil surface from the previous crop can be helpful in attaining slightly higher surface residue coverage. A disk should not be used unless absolutely necessary because more residue will be incorporated and soil cloddiness can develop under wet conditions in these fine-textured soils. This tillage system performs best on 0 to 4 percent slopes.

Ridge-till also maintains inadequate surface residue coverage when corn following soybeans, especially when soil is removed (scalped) from the ridge at planting. The accumulation of residue between the ridges/rows from the previous corn crop will not be helpful because it will have been destroyed in the ridge-building process. However, the ridges themselves which act like mini-terraces every 30-36", allows this tillage system to be used successfully on 0 to 6 percent slopes provided that the row orientation is not consistently up and down the slopes. 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 may result in wetter and slightly colder soils at planting. Row cleaners attached to the planter may be necessary to minimize these potential negative effects on crop growth. This system has been successful when used up to three consecutive years in this rotation or where primary tillage (moldboard plow or chiseling) has been used following corn. However, the consolidated nature of the surface soil with long-term 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 needs to be high and fertilizer must be injected for optimum efficiency. Starter fertilizer should be applied when Bray soil test P is <25 ppm. Burndown herbicides should be applied before crop emergence to minimize weed competition and optimize yield. This practice works best on fields with 0 to 8 percent slopes.

In summary, characteristics such as slope of the field, soil test levels, condition of the field following soybeans, and previous years' tillage must be considered when choosing a tillage system for corn after soybeans. On flat, poorly drained, fine-textured soils, a one-pass secondary tillage is usually best. On the other hand, no-tillage can be used on those landscapes with 0 to 8 percent slopes, but management is generally more critical for this system to perform consistently well.

Soybeans

The matrix of performance indicators shown in Table 11 indicates that soybean following corn is only slightly sensitive to tillage system when grown on medium and fine-textured glacial till and lacustrine soils. Moldboard plowing generally does not result in higher soybean yields than other tillage systems and leaves inadequate surface residue (often <10%) to minimize soil erosion. Thus, this tillage system should not be used in the Minnesota River basin unless manure or fertilizer P and K are to be incorporated into the surface 8-inch layer. The chisel plow-plus system will leave adequate residue in all soil-rainfall scenarios, will minimize surface compaction, will allow incorporation of nutrients and herbicides, and will result in optimum yields when good management is practiced. Residue clearing attachments mounted on the planter may be helpful but are not usually necessary to optimize yield. This tillage system also facilitates the use of narrow soybean rows and no-tillage in alternate years when corn follows soybeans. Fields or landscapes with 0 to 8 percent slopes are ideal for this tillage system.

One or two pass, tandem disk tillage can be used successfully for soybean after corn especially on glacial till soils. This system kills early spring weed growth and evenly distributes a large amount of corn residue across the soil surface but does little seedbed preparation below 2" to 3". Soybean yields may suffer some on poorly drained, wet, flat lacustrine fields. This tillage system performs best on 3 to 8 percent slopes.

Table 11. Matrix of residue management/yield performance indicators for soybean following corn on glacial till and lacustrine soils under high annual precipitation (>28") or low annual precipitation (<28") conditions in the Minnesota River basin. ¹

Tillage system	Glacial till	Lacustrine
Rainfall
High	Low	High	Low
Moldboard plow	1	1	1	1
Chisel plow plus	2	2	2	2
One or two pass	2	2	3	3
Ridge-till	2	2	3	2
No-till	3	3	3	3
1 When following silage corn, inadequate amounts of surface residue will exist for all tillage systems.

Ridge-till maintains excellent surface residue coverage when soybeans follow corn, 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 0 to 6 percent slopes. Soil erosion is minimal because infiltration is optimized and runoff is minimized. 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, especially under wet conditions. The opportunity to use narrow rows, unless no-till drills or special planters are used, is a disadvantage of this tillage system.

No-tillage leaves all of the residue on the soil surface, which often results in wetter and cooler soils at planting. Soybean yields with both wide and narrow rows can be optimal with this system if excellent management is used. However, the consolidated nature of the surface soil with long-term, continuous no-till may lead to some stand reductions and disease problems. This may result in slightly lower yields, especially on wet, poorly drained soils. Burndown herbicides coupled with post-emergence herbicides are necessary to control weeds. Soil test P and K also needs to be high. Starter fertilizer and stalk chopping are not necessary for soybeans. This practice works best on fields with 2 to 10 percent slopes.

In summary, soil characteristics such as slope, drainage, texture, and condition of the field after corn must be considered when choosing a tillage system for soybean. On flat, poorly drained, fine-textured, lacustrine soils, chisel plow plus tillage is usually best, but with excellent management, one- or two-pass, ridge-till, or no-till systems can be used successfully. These latter conservation tillage practices can be used on glacial till landscapes with 0 to 10 percent slopes, but good management is necessary for these systems to perform consistently well. For continued long-term success with reduced tillage systems for a corn-soybean rotation, farmers are encouraged to practice tillage rotation. Research on glacial till soils suggests that no-till planting of corn into soybean stubble and fall chiseling corn ground for either wide or narrow row soybean production is a good example of this rotation. The tillage choice must be based on the current soil properties, that is, wet and compacted vs. dry and non-compacted, the crop to be grown, and the soil/field characteristics. Properly matching the tillage system with the soil and cropping conditions will lead to successful conservation tillage systems that minimize erosion losses and optimize profit.

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:

• Sediment Problems and Solutions for the Minnesota River (FO-6671).
• Tillage Best Management Practices for Continuous Corn in the Minnesota River Basin (FO-6672).
• Description of the Minnesota River Basin and General Recommendations of Residue Management Systems for Sediment Control (FO-6673).
• Tillage Best Management Practices for Small Grain Production in the Upper Minnesota River Basin (FO-6674).
• Economic Comparison of Incremental Changes in Tillage Systems in the Minnesota River Basin (FO-6675).

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.

Produced by Communication and Educational Technology Services, University of Minnesota Extension.

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.