Tillage Research in South-Central Minnesota
Numerous tillage experiments on a corn-soybean rotation have been conducted at the University of Minnesota, Southern Research and Outreach Center at Waseca since 1997. All experiments have been located on Nicollet and Webster clay loam soils that are subsurface tile-drained at a lateral spacing of 75 feet. One experiment was conducted on two low and two high P-testing sites for a continuous 6-year period to determine the effects of tillage system and phosphorus rate and placement on corn and soybean yield and soil test P. Information from this study is presented in Tables 2-8 in the section entitled Tillage Systems and P Management. Another 4-year study was conducted to determine the effects of rotational full-width tillage compared with long-term no-till (NT), strip-till (ST) and deep zone-till (DZT) systems with and without inseason row cultivation on corn and soybean production. Information from this study is presented in Tables 9-12 in the section entitled Rotational Tillage Systems. Two 1- year experiments were conducted in 2004 to determine the effect of tillage system on soybean and second-year corn production in a corn-corn-soybean rotation. Information from these two studies is found in Tables 13 and 14 in the section entitled Tillage for a CCS Rotation. Another 3-year experiment compared effects of tillage system and time and placement of N fertilizer on corn yield. Yield data are shown in Table 15 in the section entitled N Management for Tillage Systems. In summary, average corn yield from 29 and 21 experimental site years are shown in Table 16 and Figure 2, respectively, to illustrate the effect of various tillage systems on corn production across many site-years. This information is found in the section entitled Multi-Site Tillage Performance.
Tillage systems and P management
Tillage studies were conducted on high and low P-testing soils to determine the effects of tillage and phosphorus (P) placement on corn and soybean production. Six-year average corn yields were 5 to 7% lower for no-tillage (NT) compared to one-pass, spring field cultivation (SFC), striptill (ST), and chisel plow-plus (CP+) with no difference between SFC, ST, and CP+ at both the high and low P-testing sites. Corn yields at the high-P site began to respond to the phosphorus treatments after the soil test values in the zero-P treatments had declined into the medium range. At the low-testing site, corn yields were increased 49 bu/A for the 50-lb starter (seed-placed) treatment and 62 bu/A for the 100-lb broadcast treatment. Phosphorus-banded 6 to 7 deep did not improve yields compared with seed-placed P. Six-year average soybean yields were not affected by tillage on either the high or low P-testing sites. At the low-P site, soybean yields were increased 16 bu/A by residual P from the 50-lb starter (seed-placed) and deep-band P treatments and 19 bu/A for the 100-lb broadcast treatment. Surface residue coverage for corn ranked NT>ST>SFC >CP+. Based on 0-2 soil tests, the potential for P loss to surface water is least for deep-banded P, regardless of tillage, and greatest for broadcast P, especially in the shallow SFC/SD tillage system.
A study comparing four methods of P placement for corn (none, seed-placed, fall 6 to 7 deep-banded, and broadcast and incorporated by chisel plow or field cultivator) and four tillage systems [NT, ST, field cultivation or disking (SFC/SD), and CP+] was conducted on a very low to low Ptesting site (4-5 ppm Bray P1) and an initially high P-testing site (19 ppm Bray P1) from 1997 to 2003. Three cycles of a corn-soybean rotation were grown with corn and soybeans planted each year. Corn was planted in 30 rows while soybeans were drilled or seeded in 8 rows. Phosphorus for corn was band-applied either in the seed furrow or in 6-7 deep bands at 30 spacings as 10-34-0 at rates of 40 and 50 lb P2O5/A and broadcast as 18-46-0 at rates of 80 and 100 lb P2O5/A for the high and low P-testing sites, respectively. Soybeans did not receive fertilizer P but responded to residual P from P applied for corn. A nonyield- limiting N rate was applied to all corn plots. Soil samples were taken to a depth of 6 in a transect perpendicular to the crop row with one core directly in the row and the others at distances of 7.5, 15, and 22.5 from the row. Three sets of cores were taken from each plot for a total of 12 cores per plot. Soil samples from the 0-2 depth (which relate better to potential P loss to surface water) were taken from a 3 wide x 2 deep x 30 long zone located perpendicular to the crop row.
Six-year corn and soybean yield averages from the high P-testing site were significantly affected by the tillage and P treatments (Table 2). A yield response to P did not occur in the first few years but did begin to occur when 0-6 soil test P (STP) in the zero-P treatments declined to <15 ppm. The relationship between soil test P at the end of the study and the 6-year average corn yield is clearly seen. This was not true for soybean. Soil test P in the 0-2 depth was greater than in the 0-6 depth because: (1) plant material containing P remained on the surface soil each year in the reduced tillage systems and (2) broadcast-applied P remained more concentrated near the soil surface. Soil test P in the 0-6 depth was affected significantly by P placement but not by tillage system.
Corn and soybean yield responses to tillage at the low P-testing site were similar to the high-testing site, but the responses to P management were markedly greater at the low-testing site (Table 3). Corn and soybean yields were increased 49 and 16 bu/A, respectively, by seed-placement of P in corn. Soil test P values from both depths clearly showed the effect of seed-placed (starter) and broadcast P.
|Table 2. Corn and soybean yields and
soil test P (Bray P1) on a high P-testing soil as influenced by
tillage and P management systems.
|Table 3. Corn and soybean yields and
soil test P (Bray P1) on a low P-testing soil as influenced by
tillage and P management systems.
The effects of tillage on surface residue cover, yield, and STP at both sites are examined in the next five tables.
Surface residue coverage after planting corn averaged across six years was greatest for NT followed closely by ST (Table 4). Spring field cultivation of soybean stubble left 33 to 38% surface coverage, barely achieving the desired 30% minimum. Annual CP+ left inadequate amounts (20%) of residue for effective erosion control on many landscapes. The residue accumulation levels found for the NT, SFC, and ST systems for corn in this study are probably somewhat greater than would be found in most farmers fields in SC MN because most soybeans are grown in wide-rows in the region. In this study, soybeans were no-till drilled into the standing corn stalks for the NT and ST (corn) systems, while a single spring disking (SD) of standing corn stalks was done for soybeans in the SFC (corn) system. Thus, residue accumulation on the surface during the 6-year period was substantial due to minimal disturbance and incorporation by tillage. This is particularly true for the NT and ST systems. Higher crop yields on the high P-testing site consistently gave slightly higher residue accumulations.
|Table 4. Surface residue accumulation
in May after planting corn as influenced by tillage for corn.
Corn yields for each tillage system averaged across the zero P and seed-placed P treatments for the 6-year period are shown in Table 5. Corn yields were significantly affected by tillage system at the low and high P-testing sites. Yields for NT were 8 bu/A (5%) lower at the hightesting site and 9 bu/A (7%) lower at the low-testing site compared to the SFC, ST, and CP+ systems. Yields were not different among the SFC, ST, and CP+ tillage systems.
|Table 5. Corn yield after soybean from
high and low Ptesting soils as affected by tillage system.
Soybean yields for each tillage system averaged across the zero P and seed-placed P treatments for the 6-year period are shown in Table 6. Soybean yields were not affected by tillage system.
|Table 6. Soybean yield after corn from
high and low Ptesting soils as affected by tillage system.
Soil test P (0-2) was greatly influenced by phosphorus placement and tillage on the high P-testing site (Table 7) and low P-testing site (Table 8). Starter (seed-placed) P applied at a total rate of 120 lb P2O5/A to the high-testing site and 150 lb P2O5/A to the low-testing site during the 6-year period increased STP by about 12 ppm and 6 ppm, respectively, compared with the control. When applied in a 6-7 deep-band, STP was increased only 5 ppm at the high-testing site and was not increased at the lowtesting site. Broadcast applications totaling 240 and 300 lb P2O5/A for the high and low P-testing sites, respectively, during the 6-year period greatly increased STP at both sites. Moreover, STP was affected significantly by tillage. When the P fertilizer was incorporated to a greater depth by chisel plow tillage, STP values were 30 to 50% lower compared to the very shallow (2-3) incorporation with the SFC/SD tillage system. These data indicate the potential for P loss to surface water is least for the deep-band P treatments, regardless of tillage, and greatest for broadcast P, especially in the shallow SFC/SD tillage system, where STP is stratified near the soil surface.
|Table 7. Soil test P (0-2) in 2002 on
a high P-testing soil as affected by tillage and P placement.
|Table 8. Soil test P (0-2) in 2002 on
a low P-testing soil as affected by tillage and P placement.
Rotational tillage systems
Similar to crop rotation, tillage rotation indicates the use of rotation of different tillage systems for different phases of the long-term corn-soybean rotation. A 4-year tillage study was conducted to determine if some form of full-width tillage may be needed periodically when using zone-till or NT systems in a high-residue corn-soybean rotation. Surface residues ranged from 31 to 86% for the conservation tillage systems with little difference between the corn and soybean phases of the rotation. Tillage for corn significantly affected yields of corn but not soybean in the subsequent year. Corn yields were greater in 2 of 4 years when CP+ tillage was used for soybeans compared with NT. In some years, row cultivation of corn increased corn and soybean yields when NT was used for soybeans, but not when CP+ was used. When both corn and soybean yields were considered, greatest production occurred when zone tillage systems (DZT or ST) were used for corn and CP+ tillage was used for soybean. Finally, the data suggest some form of rotational fullwidth tillage (even shallow row cultivation) may be needed to disrupt surface soil consolidation that occurs with continuous NT and zone-till systems for corn in rotation with NT for soybean for achieving consistently higher corn and soybean yields. Economic return to these surface-disturbing, full-width tillage systems will likely be highly site-specific (soil and climate).
A study was conducted from 2000-2003 to determine the rotational effects of NT, ST, 14 deep-zone tillage (DZT), SFC, and CP+ tillage systems with and without in-season row cultivation for corn rotated with NT or CP+ tillage for soybean on surface residue accumulation and yield of corn and soybean. Two cycles of a corn-soybean rotation were grown on the same plots with corn planted in 30 rows and soybeans planted in 20 rows each year. One-half of each corn plot received in-season row cultivation in late June each year. Soil test P and K were very high. Starter fertilizer (10-34-0) was used, and N was applied at a non-yieldlimiting rate to all corn plots.
Four-year average corn yields and 3-year average soybean yields were significantly affected by the 18 tillage/row cultivation treatments (Table 9). Surface residue coverage ranged from 24 to 79% in the year corn was grown and from 31 to 86% in the year soybean was grown. The specific effects of tillage for corn, tillage for soybean, and in-season row cultivation of corn are examined in the next four tables.
|Table 9. Corn yield, soybean yield, and
surface residue coverage as affected by tillage systems for corn
and soybeans and in-season row cultivation of corn.
Four-year average corn yields and surface residue coverage averaged across tillage for soybean and in-season row cultivation were significantly affected by tillage for corn (Table 10). Yields for DZT and ST were identical to those for CP+ and were significantly greater than for SFC or NT. Surface residue accumulation was greatest for NT (67%); intermediate for ST (56%), DZT (41%); and SFC (41%); and lowest for CP+ (24%). Three-year average soybean yields and surface residue coverage when averaged across tillage for soybean and in-season row cultivation were not affected by the residual effects of tillage for corn in the previous year (Table 10). Residue coverage exceeded 50% for all tillage systems for corn except CP+ (33%).
|Table 10. Effect of tillage following
soybeans on corn yield and surface residue coverage and on soybean
yield and residue coverage in the following year.
Three-year average soybean yields shown in Table 11 when averaged across all tillage and row cultivation treatments for corn were significantly greater for CP+ (56.5 bu/A) compared with NT (55.5 bu/A). This 1 bu/A advantage for CP+ is not considered to be economically significant, since it is offset by the costs of additional machinery, time, and fuel associated with the CP+ tillage operation. Surface residue coverage was considerably greater for NT (79%) compared with CP+ (33%). Four-year average corn yields shown in Table 11 when averaged across the tillage and row cultivation treatments for corn were significantly greater when CP+ tillage was used for soybean in the previous year (159 bu/A) compared with NT (154 bu/A). However, a significant year by tillage interaction occurred showing a yield advantage of 4, 1, and 1 bu/A in 2000, 2001, and 2003 but a 15 bu/A advantage in 2002. These year-to-year yield differences were not explainable when examining monthly and growing season temperature and precipitation. Similar results showing periodic yield reductions with NT systems on these soils were reported by Randall et al. (1996). Surface residue accumulation for corn in the year following NT for soybeans was greater (57%) compared to CP+ (46%).
|Table 11. Effect of tillage following
corn on soybean yield and surface residue coverage and on corn
yield and residue coverage in the following year.
Corn and soybean yields, when averaged across years, tillage for corn, and tillage for soybean, were not affected by in-season row cultivation of corn (Table 12). However, significant interactions among year, tillage for soybean, tillage for corn, and row cultivation occurred. In two years, row cultivation increased corn yields by as much as 10 bu/A when NT was used for the previous soybean crop and decreased yields by as much as 10 bu/A when CP+ was used for the previous soybean crop. Weeds were not a factor as chemical weed control was excellent in all plots each year. These positive and negative effects of row cultivation were confined to the NT, DZT, and ST systems for corn but not the full-width SFC tillage system. Similar interactions between row cultivation for corn and tillage for soybeans, suggesting small yield responses to row cultivation when combined with NT for soybeans, were also found in the soybean phase of the rotation.
The 4-year corn yields and 3-year soybean yields for each of the 18 tillage system treatments shown in Table 9 were combined to evaluate crop production for the corn-soybean rotation. Although the combined yield differences among tillage systems were not large, production was greatest for treatments 4, 6 and 13, which are characterized by some form of zone tillage (DZT or ST) for corn and CP+ tillage for soybean. Row cultivation for corn was not needed for optimum production. Lowest production occurred for treatments 1, 3, 5, 7 and 10, which are generally characterized by a combination of no row cultivation for corn and NT for soybean regardless of tillage for corn. Thus, these data, containing many significant interactions, suggest that some form of full-width tillage (even shallow row cultivation) may be needed to disrupt surface soil consolidation and/or disturb accumulated surface residues in continuous NT and ST or DZT systems in rotation with NT for soybeans. This disturbance appears to enhance early plant growth and gives greater consistency of slightly higher corn and soybean yields on these soils.
|Table 12. Effect of in-season row cultivation
on corn yield and soybean yield in the following year.
Tillage for a corn-corn-soybean rotation
Two studies were conducted to determine the effect of tillage on second-year corn and soybean in a corn-cornsoybean rotation. Second-year corn yields were highly related to surface residue coverage and ranged from 212 bu/A for MP+ tillage (10% residue coverage) to 155 bu/A for NT (91% coverage). When surface residue coverage ranged from 50 to 76%, yields averaged 200, 191, 189, and 180 bu/A for DZT, CP+, ST, and SD tillage, respectively. All soybeans were NT drilled into six tillage systems that had been in place for corn in the two previous years. Soybean yields averaged 50 bu/A for a 3-year NT system, which was 4 to 8 bu/A less than for tillage systems that included ST, CP+ MP+, SD, and DZT for corn during the 3-year rotation.
Two studies were conducted in 2004 to determine the effect of tillage on yield of second-year corn and soybean in a corn-corn-soybean rotation. Tillage for second-year corn in 2004 was the same as for first-year corn in 2003 and consisted of NT, DZT, ST, CP+, SD (SFC was used in 2003), and moldboard plow plus (MP+) systems. Soil test P and K were very high. Row cleaners and starter fertilizer (10-34-0) were used for corn, and N was applied at a nonyield- limiting rate. Soybeans were no-till drilled in 8 rows into the same tillage treatments for corn as described above.
Second-year corn yields were greatly influenced by surface residue cover (Table 13). Highest yield was obtained with MP+ tillage (212 bu/A) where surface residue coverage was only 10%. When surface coverage ranged from 50 to 76%, yields ranged from 200 bu/A (DZT) to 180 bu/A (SD). At 91% surface coverage, yield for NT was only 155 bu/A a 27% yield reduction.
|Table 13. Second-year corn yield and
residue cover in 2004 as affected by tillage system for corn in
2003 and 2004.
A similar trend was shown for soybean where a 3-year NT system yield (50 bu/A) was significantly less than the 54 to 58 bu/A yields from the other treatments (Table 14). Soybean yields for the DZT, ST and SD tillage treatments applied for corn were not different from the CP+ and MP+ treatments. Residue amounts were not measured, but they likely were similar to those shown in Table 13, except for the MP+ treatment. In summary, these data show that continuous NT resulted in soybean yields 4 to 8 bu/A less than where NT for 2004 followed DZT, ST, SD, CP+ or MP+ tillage applied for corn in 2002 and 2003. These highly significant second-year corn and soybean yield differences among tillage systems in a corn-corn-soybean rotation probably were exacerbated by the cool and very wet conditions that prevailed in 2004. Earlier research showed a 3 bu/A average yield advantage over a 10-year period for MP+ tillage compared with CP+ on a well drained, sloping Nicollet soil at Waseca (Randall et al., 1996a). Thus, CP+ tillage is a recommended tillage practice for second-year corn to minimize erosion on soils with slopes >4%.
|Table 14. Soybean yield in 2004 after
second-year corn as affected by tillage system for corn in 2002
N management for tillage systems
A 3-year study comparing late October vs. spring, preplant application of anhydrous ammonia across four tillage systems (NT, ST, SFC, and CP+) indicated that corn yield response to N timing was greatly affected by April-June rainfall. Under normal to slightly below-normal rainfall, yields were not different between fall and spring-applied ammonia. But when rainfall was above normal, corn yields were reduced an average of 36 bu/A, regardless of tillage system. These results do not support late October application of anhydrous ammonia without N-Serve and should be a warning to those desiring to apply N with their fall strip-till operation.
A study was conducted from 1997-1999 to determine the effect of time and placement of N in a wide range of tillage systems for corn after soybean with particular emphasis on concerns with applying N at the same time as strip tilling. Tillage consisted of NT, ST, SFC, and CP+ with ST performed in the last week in October. Chisel plowing was performed in early November. Anhydrous ammonia without nitrapyrin (N-Serve) was the N source. Fall N was applied near the seed-row zone for the coming crop in the last week in October. Soil temperature at the 6 depth on the date of application was 47°, 48°, and 55° for each of three years and averaged 40°, 43°, and 50° in the subsequent 10-day period, respectively. Spring N was applied midway between the 30 rows in mid- to late April. Soil test P and K were very high and high, respectively.
Corn yields shown in Table 15 were separated into: a) 1997 and 1998, b) 1999, and c) 1997-1999 average because of large differences in precipitation among years.
In 1997 and 1998, when April-June rainfall totaled 8.5 and 11.8 respectively, corn yields were influenced by tillage system but were not affected by time/placement of N. Yields were highest for CP+ (193 bu/A) intermediate for ST and SFC, and lowest for NT (184 bu/A). In 1999, when April-June rainfall totaled 15.8, corn yields were not significantly affected by tillage but were reduced 36 bu/A when N was fall-applied. Unusually wet conditions, especially in April and May, likely caused significant leaching and denitrification, resulting in substantial yield loss. Across the 3-year period, corn yields were highest for CP+ (184 bu/A) and slightly lower for ST (180 bu/A), SFC (178 bu/A), and NT (176 bu/A). Yields for spring-applied ammonia averaged 186 bu/A compared to 174 bu/A for ammonia applied in late October. An interaction between tillage system and time/placement of N application was never found, indicating the effect of fall vs. spring application was the same for all tillage systems.
|Table 15. Corn yield as affected by tillage
system and time/placement of N.
Multi-site tillage performance
Twenty-nine site-years of tillage research on sites yielding from 92 to 216 bu/A showed that NT yields as a percent of CP+ yields were reduced more when overall yields were limited by inadequate soil fertility. Yields for the 21 nonyield- limited site-years averaged 183 bu/A for CP+ and were reduced 2% for ST (180 bu/A) and SFC (179 bu/A) and 6% for NT (172 bu/A).
Twenty-nine site-years of tillage research, comparing NT, ST, SFC, and CP+ tillage systems for corn after soybean, were conducted under tile-drained conditions at Waseca between 1997 and 2004. Twenty-one site-years were conducted under conditions where nutrients were not yield-limiting and eight at sites where low soil test P levels were yield-limiting. Average yields across tillage systems for the 29 site-years ranged from 92 to 216 bu/A. Yield ranges from 92-135 bu/A (Low, 7 sites), 136-159 bu/A (Med., 7 sites), 160-175 bu/A (High, 7 sites), and 176-216 bu/A (V. high, 8 sites) were arbitrarily established to determine if yield differences among tillage systems changed with yield level (Table 16). With the exception of the seven sites in the high yielding group, yields for the tillage systems ranked: CP+ > SFC >= ST > NT. But, NT yields as a percent of CP+ increased as the yield level increased, i.e., 90% for the low-yielding sites and 94-95% for the high- and very high-yielding sites. These findings point to the advantage for establishing high-fertility conditions before switching to NT.
|Table 16. Corn yield as affected by tillage
system and yield level across 29 site-years.
Averaged across all 21 non-yield-limited sites, yields averaged 183, 180, 179, and 172 bu/A for the CP+, ST, SFC, and NT systems, respectively (Figure 2). Yield reductions as a percent of CP+ were 2% for ST and SFC and 6% for NT. Economic return may or may not be significantly different for these tillage systems, depending on farm-specific factors.
|Figure 2. Average corn yield across 21
site years with four tillage systems for corn after soybean.