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 3). 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 3. Continuous corn yield as influenced by tillage on a Mount Carroll silt loam soil in Goodhue County.
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 Man-agement/Water Quality effort from 1987-1991 (Table 4). 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 4. Continuous corn yields as influenced by tillage at four southeastern Minnesota sites.
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 5). 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 5. 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.
1/ 150 lb 9-23-30/A.
2/ 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 am-monium nitrate and injected liquid dairy manure, during an 8-year period on a Timula silt loam in Goodhue County (Table 6). 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 fertili-zer 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 much as a chisel plow does in this experiment.
Table 6. Continuous corn yield as affected by tillage and injected manure vs. fertilizer N on a Timula silt loam in Goodhue County.
1/ 200 lb N/A as ammonium nitrate, surface broadcast in spring.
2/ Liquid 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 7). 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 7. Continuous corn yield as influenced by tillage and in-season cultivation on a Tama silt loam in Fillmore County, 1985-1989.
1/ S tine cultivator with no coulters or disks.
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 8). 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 8. 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.
1/ 150 lb 9-23-30/A
2/ 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 9). 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 9. Corn yield following soybeans as influenced by tillage on a Fayette silt loam in Wabasha County.
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 4) 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 10). 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 10. Corn and soybean yields as influenced by tillage on a Port Byron silt loam in Goodhue County.
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 11). 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 11. Corn yield after alfalfa as influenced by tillage and in-season cultivation in Winona County, 1988-89.
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 12). 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 10).
Table 12. Soybean yields following corn as influenced by tillage on a Fayette silt loam in Wabasha County.
1/ All 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.
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