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Accepted for publication 11 April 2006. Published 26 June 2006.

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

Michael S. DeFelice, Paul R. Carter, and Steven B. Mitchell, Pioneer Hi-Bred International, Inc., Johnston, IA 50131-1150

Corresponding author: Michael S. DeFelice. michael.defelice@pioneer.com

DeFelice, M. S., Carter, P. R., and Mitchell, S. B. 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.

Abstract

An extensive literature review was conducted of corn and soybean research that compared yields of no-tillage to conventional fall tillage systems. The objective was to test the hypothesis that no-till has a different effect on corn and soybean yields in different regions of the United States and Canada. The trial results were mapped to look for geographic and environmental patterns in the relative performance of no-tillage to conventional tillage on corn and soybean yield. The national average difference in corn and soybean yield between no-tillage and conventional tillage was negligible. A map of the tillage yield comparisons was created for the U.S. and Canada. 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-tillage had greater corn and soybean yields than conventional tillage on moderate- to well-drained soils, but slightly lower yields than conventional tillage on poorly drained soils. Corn and soybean yields tended to benefit more from crop rotation in no-till as compared to continuous cropping. Future tillage research should focus on optimizing successful high residue no-tillage or strip-tillage production systems instead of making comparisons to conventional tillage systems.

Introduction

No-tillage crop production has been increasing in the United States for many years (12,62). The desire to reduce input costs, manage larger acreages with the same or less labor and equipment, conserve valuable soil resources, and maintain compliance with government conservation programs has driven crop producer interest in conservation tillage practices (96). The potential for increased government and private sector incentives to practice no-till for carbon sequestration may cause additional adoption of high-residue no-till and strip-tillage crop production in the near future (75,57).

There has been considerable debate over the relative merits of no-till as compared to conventional tillage over the years. Many tillage experiments have been conducted in the United States and Canada comparing yield and economic return between no-tillage and conventional tillage. The results of these research projects often appear to be contradictory. A general perception has arisen that no-tillage is more favorable in the southern United States, but does not perform as well in the northern United States or Canada (63). Soil classification by soil moisture characteristics – especially drainage – has also been used to define areas as suitable or unsuitable for no-tillage (14). Farmers, crop advisors, extension agronomists, and seed breeders are all concerned about managing crop production to obtain optimum yield and economic returns. Seed breeders are particularly interested in developing genetics that produce maximum yield while maintaining the sound agronomic traits that are required to produce a successful crop under various environmental conditions. The recent increase in no-tillage in the United States, Canada, and other parts of the world invites an analysis of the influence of geography, soils, and crop rotation on yield response to tillage, and the resulting optimization of genetic traits in crops that may be required for optimum economic return in conservation tillage systems.

The objective was to test the hypothesis that no-till has a different effect on corn and soybean yields relative to conventional tillage in different regions of the United States and Canada. An extensive literature review was conducted of published corn and soybean research that compared yields of no-tillage to conventional fall tillage systems. These trials were then mapped to look for geographic and environmental patterns in the relative performance of no-tillage to conventional tillage on corn and soybean yield. This review also attempts to summarize some of the factors that might explain these regional differences. Some observations on the strengths and weaknesses of the existing data and how tillage research could be improved in the future are also summarized. 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 can vary by so many factors. The current literature indicates a wide variety of both positive and negative economic comparisons of no-tillage to conventional tillage systems. The comparative economics of tillage can vary by region, cropping system, variable input costs, risk aversion, and management experience among other factors. The economics of studies utilizing older technology also do not apply very well to current conditions (8,11,15,21,26,38, 63,64,65,74,78,79,80,82,86,96, 106,108,109).

Background

Crop breeders are keenly aware of the effects of environment on the performance of individual cultivar or hybrid seed lines. Previous research indicates there is little effect of tillage on the yield potential of high-performing genetics (13,30,34,36,40, 55,68,72,80,84,90). 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 (1,10,19,24,37,40,55,66,100). 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 (53,71).

Seedling emergence and development can be delayed in no-till compared to conventional tillage because spring soil temperatures tend to be lower, and soil moisture levels tend to be higher under residue. A delay in seedling emergence often leads to postponement in vegetative growth, silking or flowering, and grain dry-down. These delays can result in significant yield loss in shorter season growing areas, or where the relative maturity is long for the region (2,6,9,10,16,17,19,27,40,44,45, 51,58,62,67,93,97,110).

The relative importance of crop traits 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 (2,7,14,20,21,23,27,33,43,46,47, 54,55,62,73,79,80,99, 101,103). An understanding of the influence of geography and environment on the relative performance of no-till compared to conventional tillage will help crop breeders develop soybean cultivars and corn hybrids that are optimized for high-residue tillage. An understanding of the impact of regional differences on no-tillage corn and soybean yield compared to conventional tillage will also help crop producers, crop advisors, and government policy makers to make better informed management and legislative decisions related to tillage options.

Method of Analysis

A literature review was conducted of published research comparing yields of corn and soybean in no-tillage and conventional tillage in the United States and Canada. The search revealed 61 experiments that compared corn yields representing 687 site-years of data (Table 1). The search located 43 full-season soybean trials that compared soybean yields by tillage representing 455 site-years of data (Table 2). Three published corn experiments and two locations of a fourth corn experiment were disqualified because the Materials and Methods indicated significant management problems with tillage operations, weed control, or population stand in these studies (8,33,65,86). Four soybean studies were disqualified for the same reasons (8,31,65,86). The research studies summarized were conducted using a variety of treatments and variables, and reported their data in many different ways. Yield data were normalized by reporting the percent difference in yield of no-till over (or under) the yield of a conventional fall plus spring tillage system. The level of statistical significance between these yields reported in each experiment was also recorded.

Table 1. Individual corn experiment data

Prior no-till: N = No, Y = notilled or undisturbed such as CRP or grass pasture with no data on number of years, number = number of years in no-till or undisturbed pasture prior to experiment.

 * Used yield means from last 5 years of the experiments.

Table 2. Individual soybean experiment data.

Prior no-till: N = No, Y = notilled or undisturbed such as CRP or grass pasture with no data on number of years, number = number of years in no-till or undisturbed pasture prior to experiment.

All of the trials summarized used a close variant of a true no-tillage system with minimal surface disturbance only utilized at planting and/or during fertilizer application. The conventional tillage systems varied from fall mold-board plowing followed by multiple spring tillage passes to a minimum of a fall chisel plowing followed by one or more spring tillage operations prior to planting. Data on crop rotation was also recorded, and was usually a corn-soybean rotation or continuous corn or soybean. The soil series at each location was categorized as poorly drained or moderate-to-well drained using the USDA-NRCS soil series description database (3). The number of years prior to the initiation of the trial the no-till plots had been no-tilled, row spacing, and if a soil insecticide was used in the corn studies was also recorded. Notes were recorded if the study included a comparison of genetics, and if any comments in the Materials and Methods on management issues were mentioned that affected the study. Management issues were noted that would significantly affect the validity of the tillage comparisons such as weather preventing tillage or planting operations, or weed control failures. Many of the authors were first-time no-tillers and apparently had some "learning curve" issues with their no-tillage plots. Only a few experiments seemed to have confounding effects large enough to make the tillage comparisons questionable as previously mentioned.

Each experiment was located by zip code for mapping purposes. These locations were plotted on a map in three categories: (i) no-tillage yields significantly greater than conventional tillage yields, (ii) no-tillage yields not significantly different from conventional tillage yields, and (iii) no-tillage yields significantly less than conventional tillage yields. A regional pattern of yield differences was apparent from the plots. Three corn and soybean yield regions were visually defined by observing the plotted data on the maps. A line separating the northern region from the southern/western region was drawn approximately along the most southerly locations with a negative no-till response for each crop. Then the transition regions were defined for each crop by an iterative process of including trials along a widening band along this border where mean yield differences between tillage systems were similar.

Discussion

The national average difference in yield between no-tillage and conventional tillage corn was negligible (Table 3). However, the plot of corn experiment locations clearly shows regional differences in tillage effect on yield (Fig. 1). The data plot in Figure 1 was used to identify three areas where there appeared to be a different impact of no-tillage compared to conventional tillage on corn yield and these areas were overlaid on the map. Averaging the yield data from the experiments in these three areas provided a numerical cross-check and estimate on tillage impact on corn yield in these areas. These maps show that no-tillage tends to have greater corn yields than conventional tillage in the southeastern, southern, and western United States (Fig. 1, Table 3). A "transition zone" can be seen that extends from the northeastern United States through the northern Ohio valley and Missouri river valley where corn yields are generally the same in both tillage systems (Fig. 1, Table 3). No-tillage tends to have slightly lower corn yields in the north central United States and Canada (Fig. 1, Table 3).

Table 3. Corn and soybean yield advantage of no-tillage over conventional tillage.

 * Six corn studies and four soybean studies not used because data was pooled across rotations, or the rotation could not be determined from the Materials and Methods.

Fig. 1. Corn yield advantage in no-till versus conventional tillage by experiment location and region.

This data plot agrees with the general opinion that no-tillage corn performs better in the southern United States than in the north. However, this summary indicates no-tillage is equivalent in performance compared to conventional tillage into the central United States with only the most northerly areas of the corn belt showing a negative yield response to no-till. The yield advantage to no-till in the southeastern, southern, and western United States is quite substantial at about 12%. However, the yield disadvantage to no-till in the north-central U.S. and Canada is less at about -6%. The percent of total U.S. and Canadian corn acres in the southern/western, transition, and northern regions is 28, 28, and 42% respectively, with 2% of corn in the far west not mapped (4,5).

Soil drainage also had an effect on corn yield in no-tillage relative to conventional tillage (Table 3). No-tillage had slightly greater corn yields than conventional tillage on moderate to well drained soils, but lower corn yields than conventional tillage on poorly drained soils. Sorting the data to show soil drainage by geography indicated this relationship was similar across all regions (Table 4). It is apparent from USDA soils maps that there are more poorly drained soils in the north than in the south or west (3).

Crop rotation (corn-soybean versus continuous corn) had a small effect on corn yields in the two tillage systems with rotation providing greater corn yield advantage for no-tillage than continuous corn (Table 3). Sorting the data to show rotation by geography indicated this relationship was similar across all regions (Table 4).

Table 4. Interactions of soil drainage and crop rotation by geography on corn yield.

 * Six corn studies not used because data was pooled across rotations, or the rotation could not be determined from the Materials and Methods.

The national average difference in yield between no-tillage and conventional tillage soybean was small (Table 3). The map of soybean experiment locations also clearly shows regional differences in tillage effect on yield although the differences are not as great as with corn (Fig. 2). Data plotted in Figure 2 was 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 (Fig. 2). Averaging the yield data from the experiments in these three areas again 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 (Fig. 2, Table 3). 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 (Fig. 2, Table 3). The percent of total U.S. and Canadian soybean acres in the southern/western, transition, and northern regions is 47, 40, and 13%, respectively (4,5).

Fig. 2. Soybean yield advantage in no-till versus conventional tillage by experiment location and region.

Poor soil drainage tends to have a negative impact on no-tillage soybean yield as compared to conventional tillage just as it does in corn (Table 3). The trend was similar in the southern/western and northern regions, but was neutral in the transition area (Table 5). 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 3). However, no-till soybeans tended to perform better under rotation than continuous cropping on a regional basis (Table 5).

Table 5. Interactions of soil drainage and crop rotation by geography on soybean yield.

 * Four soybean studies not used because data was pooled across rotations, or the rotation could not be determined from the Materials and Methods.

Observations

A number of observations were collected during the analysis of the existing literature on tillage effects on corn and soybean yield. Several studies indicated no-tillage yields improve after several years of continuous no-tillage 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 (21,22,23,32,43,62,83). Drainage in new no-tillage plots is often poor until old tillage pans and lack of soil structure is corrected over time (21,22,23,32,43,62,83,102). 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. To be fair, the first two authors have also conducted tillage comparison studies without sufficient time for the no-tillage plots because of the time and budget constraints common in this area of research, and the lack of long-term sites in areas of low no-tillage adoption (10,18,44). Some researchers may also still have been learning how to manage no-tillage while conducting this type of research for the first time. Other than tillage itself, it was apparent that some researchers used the same management practices in both tillage systems. Planting rate, fertilizer rate and application, and sometimes even weed control practices were the same in both tillage systems. No-tillage and conventional tillage usually require distinctly different management practices for planting rate and date, fertilizer rate and placement, irrigation management, herbicide weed management, and insect control. Some of the early experiments conducted prior to the 1980s also had problems maintaining seeding rates and planting depth in no-tillage because they lacked the improved high-residue planter technology introduced after that time. Using uniform management practices across tillage systems is probably not a fair comparison of the overall tillage management systems. It is interesting that no-tillage still managed to provide equal or better yields than conventional tillage in many of these studies despite the short life span and less than optimal management practices sometimes used in the no-tillage plots. This is an indication that the comparisons in this review are somewhat conservative towards the performance of no-tillage relative to conservation tillage.

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 clearly 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. This may be the reason various methods of ridge-till and strip-tillage are being used in this region (2,11,48,58,62).

The tillage regions outlined in this review are not 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.

Overall, it is the authors’ opinion that conducting additional side-by-side comparisons of no-tillage and conventional tillage corn and soybean production systems are probably not widely needed in the United States. Producers practice no-tillage crop production for a variety of reasons that go beyond yield. Management costs, farm size, labor and time constraints, soil conservation, and government programs all influence the decision to practice high residue systems like no-till or strip-till. This review indicates corn and soybean producers in most of the United States will not suffer a yield disadvantage to switching from conventional tillage systems to no-tillage. Even in areas where no-tillage yields are lower, the economics of no-tillage and other factors such as soil conservation and government incentives probably make the switch to no-tillage a small economic issue. It is likely other factors such as environmental stewardship, personal experience, equipment availability, switching costs, farm size, time and labor availability, fuel prices, and government incentive programs will be a far greater influence on the decision to no-till than the effect on crop yield. Future tillage research would most profitably focus on optimizing successful high residue no-tillage or strip-tillage production systems instead of making comparisons to conventional tillage systems. Research comparing reduced irrigation regimes in no-tillage compared to fully irrigated conventional tillage are needed in the west.

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