Influence of Tillage on Soybean Yield in the United States and Canada

• An extensive literature review was conducted of soybean research that compared yields of no-tillage to conventional fall tillage systems in the U.S. and Canada.
• The trial results were mapped by region to look for geographic and environmental patterns in the relative performance of no-tillage vs. conventional tillage on soybean yield.
• The national average difference in soybean yield between no-tillage and conventional tillage was found to be negligible with a 0.7% advantage to no-till.
• No-till tended to have greater yields than conventional tillage in the south and west regions. The two tillage systems had similar yields in the central U.S., and no-till typically produced lower yields than conventional tillage in the northern U.S. and Canada.
• No-till had greater soybean yields than conventional tillage on moderate- to well-drained soils, but slightly lower yields than conventional tillage on poorly drained soils.
• On a regional basis, soybean yields tended to benefit more from no-till in crop rotation than in continuous cropping.
• Pioneer researchers have assigned a High Residue Suitability rating for all Pioneer® brand soybean varieties. The goal of this rating is to give customers guidance on selecting varieties suitable for high residue tillage systems.

No-tillage crop production has been increasing in the United States for many years. The desire to reduce input costs, manage more acres with less labor and comply with government conservation programs has driven this increase. Additional adoption of high-residue no-till and strip-till crop production is expected in the near future due to rising energy costs and increased incentive payments to producers. These increased payments may come from both the government and private sector to encourage no-till farming for carbon sequestration and compliance with World Trade Organization (WTO) requirements.

In spite of the advantages of no-till in reducing costs and labor and providing incentive payments to farmers, there arealso challenges with this production system. In fact, the merits and drawbacks of no-till vs. conventional tillage have been debated for many years by farmers, crop advisors, extension agronomists and seed breeders intent on managing crop production for optimum yield and economic return. One reason for this prolonged debate is that tillage experiments comparing yield and profitability between these systems have often given contradictory results. A general perception has arisen that no-till is more favorable in the southern United States, but does not perform as well in the northern United States or Canada. Soil classification by soil moisture characteristics – especially drainage - has also been used to define areas as suitable or unsuitable for no-till. This Crop Insights will present data to help determine if no-till has a different effect on soybean yields than conventional fall tillage in different regions of the United States and Canada.

An extensive literature review found 43 full-season soybean trials representing 455 site-years of data that compared soybean yields by tillage system. All of the trials summarized used a close variant of a true no-tillage system with minimal surface disturbance only at planting and/or during fertilizer application. The conventional tillage systems varied from a maximum of fall moldboard plowing followed by multiple spring tillage passes to a minimum of fall chisel plowing followed by one or more spring tillage operations prior to planting. Strip tillage was not included because there were very few published studies on strip till, and the methods varied too widely to make valid comparisons.

Yield differences between tillage systems in the studies were mapped and analyzed to determine if geographic and environmental patterns were evident. An economic analysis was not attempted because many of the studies did not provide enough information for such an analysis, and because the economics of tillage vary by so many factors.

The national average difference in yield between no-tillage and conventional tillage soybean was small with a 0.7% advantage for no-till (Table 1).

Table 1. Soybean yield advantage of no-till over conventional tillage.

The map of soybean experiment locations also clearly shows regional differences in tillage effect on yield (Figure 1).

Figure 1. Soybean yield advantage in no-till vs. conventional tillage by experiment location and region.

Data plotted in Figure 1 were used to identify three areas where there appeared to be a different impact of no-tillage compared to conventional tillage on soybean yield and these regions were overlaid on the map.

Averaging the yield data from the experiments in these three areas provided a numerical cross-check and an estimate of the tillage impact on soybean yield in these areas. No-tillage had greater average soybean yields than conventional tillage throughout the southeastern, southern, and western regions of soybean production in the United States (Table 1, Figure 1). The area of positive soybean yields for no-tillage extends into the Ohio and Missouri river valleys of the Midwest and Great Plains. A narrow transition zone extends from the northeastern United States to the upper Midwest. Soybean yields in no-tillage tend to be lower than conventional tillage in the upper Midwest and Canada (Table 1, Figure 1). The percent of total U.S. and Canadian soybean acres in the southern/western, transition, and northern regions is 47, 40, and 13 percent, respectively.

Poor soil drainage tends to have a negative impact on no-tillage soybean yield as compared to conventional tillage (Table 1). The trend was similar in the southern/western and northern regions, but was neutral in the transition area (Table 2). Crop rotation (corn-soybean versus continuous soybean) appeared to have little effect on soybean yields in the two tillage systems averaged over all the data with a slight trend favoring continuous soybeans (Table 1). However, no-till soybeans tended to perform better under rotation than continuous cropping on a regional basis

(Table 2).

Table 2. Interactions of soil drainage and crop rotation by geography on soybean yield.

A number of observations were collected during the analysis of the existing literature on tillage effects on soybean yield. Several studies indicated no-tillage yields improve after several years of continuous no-till have been in place. This time effect was thought to be the result of improved soil tilth over time in the no-tillage plots caused by increases in organic matter, soil enzyme activity, microbial biomass, and changes in soil porosity and aggregation. Drainage in new no-tillage plots is often poor until old tillage pans and lack of soil structure is corrected over time. Experiments conducted for a short number of years (less than 4 or 5) without prior years of no-tillage in the no-till plots probably do not provide a completely fair comparison to conventional tillage because the no-till soils have not had time to stabilize.

It seems clear from this summary that the most important factor governing the success or failure of no-till compared to conventional tillage is soil moisture. No-till provides greater yields in the eastern, southern, and western United States where high temperatures, soils with low water holding capacity, and/or unfavorable rainfall patterns often cause drought stress. No-till yields are equal or slightly less than conventional tillage in the northern United States and Canada where cold, wet spring conditions and poorly drained soils cause slower emergence and crop development in short maturity zones.

The tillage regions outlined in this review do not have absolute or rigid boundaries. There are pockets of well-drained soils and local climate in the north where no-till works very well, and areas with poorly drained soils and local climate conditions in the south and west where no-till is more challenging. However, the general boundaries and trends are reasonably clear.

Over 40% of soybeans in the United States are now produced using no-tillage practices. It is apparent from this summary that a majority of the soybean producing regions of the U.S. would see a yield benefit or at least no yield reduction from no-tillage production. Even in the northern region the yield penalty to no-till soybeans is often more than out-weighed by the labor and fuel reductions and improvements in soil quality and conservation.

Although environment often affects the relative performance of individual soybean varieties, university and private research indicates there is little effect of tillage on the yield potential of high-performing soybean genetics. However, agronomic traits such as disease resistance or early season seedling vigor and emergence can cause some genetics to perform more poorly under no-tillage than under conventional tillage. Some stresses like Sclerotinia stem rot [Sclerotinia sclerotiorum (Lib.) de Bary] and Septoria brown spot (Septoria glycines Hemmi) in soybeans have even been reported as lower in no-tillage than conventional tillage while others have reported the opposite.

The relative importance of crop traits for high residue cropping systems varies by geography or environmental factors such as soil drainage or frequency of drought stress. Excessive or deficient soil moisture appears to be a significant factor in the relative performance of no-till compared to conventional tillage. Soil moisture conservation and retention is a benefit for no-tillage under dry conditions and on moderate- to well-drained soils. However, wet springs and poorly drained soils tend to reduce yields in no-tillage compared to conventional tillage.

No-till soybeans emerging in previous corn residue.

Pioneer provides a High Residue Suitability rating for each of its soybean varieties based on field observations and a weighted calculation of key trait scores that are important for high residue growing conditions. This rating is available in Pioneer seed catalogs and on the Pioneer GrowingPoint® website. Your Pioneer sales professional can help you determine the most suitable soybean varieties for your tillage and management conditions.

Our next Crop Insights will investigate the response of corn yield to no-till vs. conventional tillage.

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Conservation Tillage Information Center, 2004. National Crop Residue Management Survey – Conservation Tillage Data. West Lafayette, IN.

Cosper, H. R. 1983. Soil suitability for conservation tillage. J. Soil and Water Conserv. 37:152-155.

Deibert, E. J. 1989. Soybean cultivar response to reduced tillage systems in northern USA dryland areas. Agron. J. 81:672-676.

Guy, S. O. and E. S. Oplinger. 1989. Soybean cultivar performance as influenced by tillage system and seed treatment. J. Prod. Agric. 2:57-62.

Kurle, J. E., C. R. Grau, E. S. Oplinger, and A. Mengistu. 2001. Tillage, crop sequence, and cultivar effects on Sclerotinia stem rot incidence and yield in soybean. Agron. J. 3:973-982.

Leuschen, W. E., S. D. Evans, J. H. Ford, T. r. Hoverstad, B. K. Kanne, J. H. Orf, J. A. Staricka, W. C. Stienstra, D. D. Warnes, and D. R. Hicks. 1991. Soybean production as affected by tillage in a corn and soybean management system I. Cultivar response. J. Prod. Agric. 4:571-579.

Mueller, D. S., G. L. Hartman, and W. L. Pedersen. 2002. Effect of crop rotation and tillage system on sclerotinia stem rot on soybean. Can. J. of Plant Path. 24:450-456.

Popp, M. P., T. C. Keisling, R. W. McNew, L. R. Oliver, C. R. Dillon, and D. M. Wallace. 2002. Planting date, cultivar, and tillage system effects on dryland soybean production. Agron. J. 94:81-88.

Uri, N. D. 2000. Perceptions on the use of no-till farming in production agriculture in the United States: an analysis of survey results. Agric., Ecosystems and Environ. 77:263-266.

Webber, C. L. III, M. R. Gebhardt, and H. D. Kerr. 1987. Effect of tillage on soybean growth and seed production. Agron. J. 79:952-956.

Yusuf, R. I., J. C. Siemens, and D. G. Bullock. 1999. Growth analysis of soybean under no-tillage and conventional tillage systems. Agron. J. 91:928-933.

¹Note: This Crop Insights is based on the recently published journal article: DeFelice, M. S., P. R. Carter, and S. B. Mitchell. 2006. Influence of Tillage on Corn and Soybean Yield in the United States and Canada. Online. Crop Management. doi:10.1094/CM-2006-0626-01-RS. ©2006, PMN. (www.plantmanagementnetwork.org.)