Soil and Water Conservation Considerations
Conservation Tillage and Previous Research
On-Farm Research Evaluating Four Tillage Systems
Treatments and Methods
Rainfall and Growing Degree Units
Tillage Effects on Surface Residue Cover
Tillage Effects on Plant Populations
Tillage Effects on Yields
Data Summary and Conclusions
Management Tips for Reduced Till Systems
Appendix with Tables
The purpose of this publication is to assist producers and crop consultants in selecting a conservation tillage system for corn in a corn-soybean rotation. It presents results of on-farm yield trials conducted across southern Minnesota and provides management tips for conservation tillage.
Selecting a tillage system requires consideration of many factors, including soil and water conservation, economic return, labor availability, and management capability, all of which are specific to the individual farming operation. For a more complete discussion of soil and tillage management in southern Minnesota, see the University of Minnesota Extension Bulletin for South Central or for Southeastern Minnesota:
Many agronomic and environmental factors affect the impact of agriculture on soil and water quality in Minnesota. Annual row-crops like corn and soybeans do not protect the soil from direct raindrop impact until the leaf canopy closes, which is usually mid- to late June. Because the period from April through June is generally wet in Minnesota, and soil moisture conditions are at or near field capacity while transpiration rates from row crops are low, this period has the greatest potential for water runoff. When the impact of raindrops detaches soil particles, they can be carried in runoff to surface tile inlets and streams. Excessive soil erosion results in the loss of yield potential over time. It also degrades streams and lakes with phosphorus-induced algal growth and sediment, reducing light penetration and depleting oxygen necessary for fish. Maintaining crop residue cover until canopy closure reduces the impact of raindrops that dislodge soil particles, and can reduce the power of runoff water to move soil to streams. Residue is especially effective if left standing, anchored by roots.
Conservation Tillage is defined as tillage systems that leave at least 30% residue cover on the soil surface after planting. Reduced tillage systems have benefits other than soil conservation, such as increased water infiltration, increased or sustained organic matter content, increased water-holding capacity, and continued long-term productivity of the soil. They also require less capital investment in equipment and fewer field passes, which reduces the amount of labor and fuel used.
So why have producers in Minnesota been hesitant to switch over to a higher residue tillage system for corn? One of the biggest concerns is that increased levels of crop residue will result in cooler and wetter soils in the spring, which may delay planting of corn on poorly drained soils. These are typically the glacial till or lacustrine (lake sediment) soils of the state. Delayed planting can reduce yield potential and result in a higher moisture content in grain at harvest. Leaving a high level of residue on the soil has less effect on soybean emergence and growth, since soybeans are planted later, when soils are warmer and drier.
The University of Minnesota has researched several reduced tillage systems to assist farmers and agricultural advisors in making tillage decisions for corn following soybeans. This research showed that reduced tillage systems can enhance residue cover and soil conservation while maintaining or improving corn yields. Small-plot research performed at the University of Minnesota’s Research and Outreach Centers, presented in the two publications cited above, has shown that no-till corn following soybeans on glacial till, heavy clay soils will reduce yields compared with systems that involve some tillage like spring field cultivation, fall strip tillage, or fall chisel plow. However, on the well drained loess soils in southeast Minnesota, research showed no-till corn yields were similar to those of the three reduced tillage systems for corn following soybeans.
The University of Minnesota and Monsanto Corporation, in cooperation with farmers across the state, compared tillage systems for corn following soybeans on farm fields in 2004 and 2005, using producer-owned commercial tillage equipment. Details of the research methods are presented in the box below.
Ten on-farm trials were completed in 2004 and nine in 2005, with an additional site, Sibley-2, planted but lost to wind in 2005 (See Figure 1 and Appendix: Tables A1 and A2). All sites were on glacial till-derived soils except for those in Fillmore and Wabasha counties, which were on loess-derived soils. Plots were field-length strips ranging in width from 500 to 1,000 ft. and replicated three times in a randomized, complete-block design. The farmer cooperators performed all tillage, planting, spraying and harvesting operations. Generally, experimental sites were chosen that had high to very high levels of soil test phosphorus (P) and potassium (K), and therefore fertilizer P and K was not needed. Nitrogen fertilizer was spring-applied at University of Minnesota recommended rates. Weeds were managed with label rates of herbicides to minimize their impact on corn production. Corn grain yields were measured with a weigh wagon. Percent residue cover, stand counts, grain yield, and grain moisture were measured in each plot at each site. Four tillage treatments were compared at seven sites in 2004 and six sites in 2005. They were no-tillage, spring field cultivate, fall strip tillage, and chisel plow plus spring field cultivate. Two treatments, strip tillage and chisel plow plus spring field cultivate, were compared at an additional three sites each in 2004 and 2005. (See Table F, Table G, Table H, and Table I.) The tillage systems are described in the following section.
The four tillage systems for corn following soybeans compared in this study are described below in order of decreasing residue.
Climatic conditions varied across the state and between years during the study period. In 2004, cumulative growing degree units (GDU) were 5 to 10% below normal at three regional Research and Outreach Centers, and precipitation ranged from 47 to 57% above normal for the months of May through September (Table 1). In contrast, 2005 was an ideal year for crop growth. Precipitation was 28 to 53% above normal and GDUs were 10% above normal (Table 1). Crop producers experienced exceptional corn and soybean yields in 2005.
In addition to the cool and wet conditions in 2004, some Western Minnesota producers experienced a very early frost on August 21. The frost affected maturation, grain moisture, and ultimately crop yields, especially at the Grant County site in West Central Minnesota, where planting and harvest had been delayed.
Residue counts were collected shortly after planting at each site. Average surface residue cover across sites in 2004 for the four tillage treatments was 54, 45, 30, and 22% for no-till, strip-till, one-pass, and chisel-plow-plus, respectively (Fig. 2 and Appendix: Table B). Residue cover in 2005 was 65, 49, 27, and 21% for no-till, strip-till, one-pass, and chisel-plow-plus, respectively (Fig. 2 and Appendix: Table C). On average, chisel-plow-plus left less than 30% residue after planting and, therefore, did not meet the federal standards for conservation tillage. On average, the one-pass tillage treatment just met the requirements in 2004 and was less than 30% in 2005.
An analysis of 13 sites across both years showed that residue cover varied considerably among sites. Residue cover percentages ranged from 30 to 90, 21 to 69, 11 to 54, and 4 to 44% for no-till, strip-till, one-pass, and chisel-plow-plus, respectively (Appendix: Table B and Table C). This variation among sites was attributed to the tillage history of the sites and the row spacing and dry matter production of the previous soybean crops.
Stand counts were taken shortly after corn emergence at each location. Overall, plant populations were very similar among all tillage systems and the average varied by only 600 plants per acre in 2004 and 1,800 plants per acre in 2005 (Table 2).
In 2004, only one location showed a statistical difference among tillage treatments (Appendix: Table D). At this site, strip-till had the highest plant population while no-till had the lowest. In 2005, only one location had a statistical difference in plant population among treatments (Appendix: Table E). At this site, strip-till had the highest plant population while the one-pass and chisel plow plus had the lowest populations. Plant population for strip tillage was never lower than conventional full-width tillage (one-pass or chisel-plow-plus) at any site.
Corn grain yields were significantly affected by tillage treatments at six of the ten sites in the record cool growing season of 2004 (Appendix: Table F and Table G). Averaged across the sites that used four tillage treatments, corn grain yields, ranked smallest to largest, were: no-till (167.8 bu/acre) < one-pass (174.2) = strip-till (174.6) < chisel-plow-plus (177.4), (Fig. 3 and Appendix: Table F). These data are very similar to results from 31 site-years of small plot research at the University of Minnesota‘s Southern Research and Outreach Center at Waseca (Vetsch and Randall, unpublished). They found chisel-plow-plus yielded 13 bu/acre greater than no-till, but only 3 and 4 bu/acre greater than one-pass and strip-till, respectively. At the three sites where only strip-till and chisel-plow-plus were compared in 2004, the chisel-plow-plus tillage treatment yielded 16 bu/acre greater than strip-till (Appendix: Table G).
The unusually cool growing season of 2004 undoubtedly had an effect on the performance of the three reduced tillage systems in this study. Other research has shown (Randall and Vetsch, 2005) that reduced tillage systems can have significantly lower yields compared with conventional tillage in unusually cool or wet growing seasons, especially when long-term no-till or reduced tillage systems are used. In the six sites in 2004 where chisel-plow-plus increased corn yields compared with strip-till, four of the six sites had a long-term no-till or reduced tillage history.
In contrast, corn yields were not significantly affected by tillage treatments at eight of nine sites in the warmer-than-normal growing season of 2005 (Appendix: Table H and Table I). Yields were 195.8, 202.2, 196.5, and 200.5 bu/acre for no-till, strip-till, one-pass, and chisel-plow-plus, respectively, when averaged across the six sites with four tillage treatments (Fig. 3 and Appendix: Table H). These data show strip-till and chisel-plow-plus having significantly greater yields than one-pass or no-till for corn. At the three sites where only strip-till and chisel-plow-plus were compared, there was no significant difference in yield (Appendix: Table I). The trials in 2005 demonstrated how reduced tillage systems, like strip-till, can produce excellent corn yields while maintaining adequate residue cover to protect the soil from erosion.
Average of 2004 and 2005:
Corn yield averages across the 13 sites of 2004 and 2005 that compared all four tillage systems are: chisel-plow-plus (190 bu/acre) = strip-till (188) > one-pass (185) > no-till (180). As stated earlier, these data are quite similar to those found in small-plot tillage research averaged across years at Waseca, with little difference among the treatments that include some tillage.
Tillage research for corn following soybean conducted on farmer’s fields in 2004 and 2005 has shown:
Conservation tillage can greatly reduce soil erosion, with minimal effect on crop yields and often at lower production costs than conventional tillage. With appropriate adjustments to crop management, conservation tillage offers a low-risk means of achieving substantial reductions in sediment and phosphorus losses from cropland to streams, rivers, and lakes.
Tillage systems that leave more than 30% residue after planting corn work for many producers; however, adjustments to management may be required throughout the whole cropping system, in addition to a change in tillage implements. Successful producers have made the following observations and suggestions:
The project could not have been accomplished without the site management carried out by the producers and research coordinators listed in Appendix Table A. We wish to thank the staff of USDA-NRCS and Soil and Water Conservation Districts for their contributions to site management in the following counties: Cottonwood, Grant, Pope, Rice, Sibley, Stearns, and Wabasha.
This project was funded by an EPA 319 grant awarded by the Minnesota Pollution Control Agency and managed by the University of Minnesota Water Resources Center, Les Everett project manager. In addition, the Monsanto Corporation provided funding and management of seven on-farm trial sites.
This publication was reviewed by Gyles Randall, edited by Tracy Wilson and Les Everett, and designed by Amy Baker.
Al-Kaisi, M. M. and M. Hanna. 2002. Consider the strip-tillage alternative. Iowa State University Extension publication PM 1901c.
Hill, P. R. Fall strip-till systems for corn production: Results from Monsanto’s Center of Excellence, 1998. 1999 No-Till Farmer Conference.
Randall, G. W. and J. A. Vetsch. 2005. Optimum tillage systems for corn and soybean production and water quality protection in South Central Minnesota—Minnesota River Basin. University of Minnesota Extension Service publication BU-08315.
Randall, G. W., T. L. Wager, N. B. Senjem, L. M. Busman, and J. F. Moncrief. 2002. Tillage best management practices for water quality protection in Southeastern Minnesota. University of Minnesota Extension Service publication BU-07694.
Randall, G. W. and P. R. Hill. 2000. Fall strip-tillage systems. Conservation Tillage Systems and Management. MidWest Planning Service. MWPS-45 Second Edition. Chapter 23.
Randall, G. W., W. E. Lueschen, S. D. Evans, and J. F. Moncrief. 1996. Tillage best management practices for corn-soybean rotations in the MN River basin. University of Minnesota Extension Service publication FO-6676.
Senjem, N. B., J. F. Moncrief, G. W. Randall, and S. D. Evans. 1996. Sediment problems and solutions for the Minnesota River. University of Minnesota Extension Service publication FO-6671
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