Yield-Limiting Factors in Continuous Corn Production

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Crop Insights by Andy Heggenstaller, Pioneer Agronomy Research Manager

Summary

It is generally more difficult to maximize yield of continuous corn (CC) than corn rotated with soybean (CS). This is true even in intensively managed CC systems, as yield-limiting factors are not fully understood.
A recent study in Illinois reported that CC yielded 25 bu/acre less than CS. The study identified 3 factors that collectively explained > 99% of the CC yield penalty: soil N supply, CC history and weather.
Soil nitrogen supply was by far the most important factor explaining the difference between CS and CC yields. The CC yield penalty decreased as intrinsic soil N supply capacity increased.
History of CC was the second most important component of the CC yield penalty. The difference between CS and CC yields increased with years in CC.
Factors related to weather were the third driver of the difference between CS and CC yields. The CC yield penalty increased as weather conditions limited N availability to CC to a greater degree than to CS.
The results of this study indicate that positioning CC on highly productive soils and effectively managing corn residues are 2 of the most important practices for consistently achieving high CC yields.

Continuous corn yielded 25 bu/acre less than corn rotated with soybean in a recent 6-year study in Illinois.

Identifying Factors that Limit Continuous Corn Yield

Numerous studies have documented yield reductions when corn follows corn rather than soybeans, even when all yield-limiting factors appear to have been adequately addressed. Better understanding of factors that limit CC yield can help to improve management of this production system.

A recent study in east-central Illinois compared CC and CS yields over a 6-year period (Gentry et al., 2013). With the exception of N fertilizer rates, which were varied as part of the study, high-yield management practices were applied uniformly to both CC and CS systems - this included the use of soil-applied insecticides for rootworm control. In general agreement with previous research (Erickson, 2008), the Illinois study reported a significant yield penalty and generally higher N fertilizer requirement for CC compared to CS (Table 1). On average over 6 years, CC yielded 25 bu/acre less than CS and required 10 lbs/acre more N fertilizer to achieve optimum (but lower than CS) yields.

Table 1. Agronomic optimum N fertilizer rate and yield of continuous corn (CC) and corn following soybean (CS) in a 6-year study in east-central Illinois. (Gentry et al., 2013).

Agronomic optimum N fertilizer rate and yield of continuous corn and corn following soybean.

The authors of the study used their field data to develop a regression model that identified the most important combination of factors contributing to reduced yields in the CC system. Of 11 potential yield-limiting factors that were evaluated, 3 factors were identified as collectively explaining more than 99% of the difference between CC and CS yields: soil N supply; CC history; and weather (Table 2).

Table 2. Factors identified as explaining the yield penalty for continuous corn (CC) compared to corn rotated annually with soybean (CS) in a 6-year study in east-central Illinois. (Gentry et al., 2013).

Soil nitrogen supply was by far the most important factor explaining the difference between continuous corn and corn rotated with soybeans yields. Overall, the ability of soil to supply N explained 85% of the CC yield penalty. Soils with higher N mineralization capacity supported higher CC yields, as was evidenced by a negative relationship between unfertilized (0-N) corn yield and the CC yield penalty (Figure 1). Soil N mineralization is reduced in CC systems due to the slower rate at which corn residues break down and release N relative to soybean residues. Soils also tend to warm more slowly in the spring when the previous crop was corn, which reduces activity of soil bacteria responsible for N mineralization. The fact that the CC yield penalty was smallest in situations where relatively high corn yields were achieved, even in the absence of N fertilizer, demonstrates that soils with high intrinsic N supply capacity are generally best suited for CC.

Relationship between unfertilized CC yield and the CC yield penalty. — **Figure 1.** Relationship between unfertilized CC yield and the CC yield penalty (adapted from Gentry et al. 2013).

Continuous corn history was identified as the second most critical component of the continuous corn yield penalty. Soil N supply and CC history together explained 97% of the difference between CC and CS yields. While many growers report that their CC yields approach CS yields over time, this study found that the CC yield penalty increased with years in CC (Figure 2). While producers typically alter management as they gain experience with CC, management remained relatively constant over time in the Illinois study. Therefore, this study likely reflects the underlying effects of large quantities of corn residues accumulating in and on the soil over time in the CC system. Corn residues exert negative effects on nutrient cycling, early-season soil temperature and moisture, and increased disease pressure for subsequent corn crops.

Relationship between years in CC and the CC yield penalty. — **Figure 2.** Relationship between years in CC and the CC yield penalty (adapted from Gentry et al. 2013).

High Residue Corn Field — High-residue levels following high corn yields.

Weather was found to be the third driver of the continuous corn yield penalty. Collectively, soil N supply, CC history and weather explained more than 99% of the difference between CC and CS yields. While weather has profound effects on all aspects of crop production, weather-related factors were found in this study to have a particular effect on N availability to CC relative to CS (Table 3). Specifically, the CC yield penalty was greatest in years in which the difference between unfertilized yield and agronomic optimum yield was greater for CC than for CS (Figure 3). This N response differential reflects the extent to which environmental conditions limited soil N availability in CC more so than in CS, and demonstrates that CC was generally more sensitive to negative weather effects, including drought or leaching.

Precipitation patterns observed during the years of the study (Figure 4) highlight the relationship between weather effects on N availability and the CC yield penalty.

Table 3. Corn yield with no N fertilizer, yield response to agronomic optimum N fertilizer rate, and N response differential for CC and CS over the course of a 6-year study in east-central Illinois (Gentry et al., 2013).

CC is often more sensitive than CS to environmental conditions that limit N availability, such as drought and leaching.

**Figure 3.** Relationship between differential (CC vs. CS) response to agronomic optimum fertilizer N and the CC yield penalty (adapted from Gentry et al., 2013).

**Figure 4.** Growing season precipitation in Urbana, Ill, 2005-2010 and 30-yr average.

The difference between CC and CS yields was the lowest (low CC yield penalty) in 2005 and 2006. While these 2 years were different in many ways, both exhibited generally favorable conditions with respect to N availability - dry springs followed by normal to dry summers. Notably, yields were very low at the study location in 2005 due to sustained high summer temperatures, but very high in 2006 due to generally favorable growing conditions. The CC yield penalty was greatest in 2007 and 2010. Both of these years were characterized by wet spring conditions with high potential for N leaching followed by very dry summer conditions that limited N mineralization and crop uptake. The CC yield penalty was intermediate in 2008 and 2009. Both of the years had wet spring and summer conditions with high potential for N leaching followed by little or no drought stress.

Managing Factors that Limit Continuous Corn Yield

There are numerous management factors that must be taken into consideration in order to maximize CC yields, including hybrid selection, tillage, soil fertility, and weed and insect control practices. The following review focuses on just those factors that relate directly to the findings of Gentry et al. (2013) described in this article. A complete review of Best Management Practices for Corn-After-Corn Production can be found in a previous Crop Insights article (Butzen, 2012).

Field Selection
University research and grower experience both indicate that CC yield losses are minimized in highly productive and low stress environments (Porter et al. 1997). This understanding is consistent with Gentry et al.'s (2013) findings that soil N supply capacity was the most important factor explaining the CC yield penalty, and that CC was more negatively affected by adverse weather conditions than CS. The ability of soil to serve as a source of N for crop growth is directly related to its organic matter content. Soils with high organic matter, in turn, generally have high water-holding capacity. Therefore, positioning CC on soils with high organic matter content and high water-holding capacity (or access to irrigation) is critical for consistently maximizing yields in this system.

Residue Management
Interference from past years' corn residues was a key factor identified by Gentry et al. (2013) as contributing to the CC yield penalty. Growers can take several actions to manage residues for improved CC performance.

Hybrid selection is a critical decision in any production system, but is particularly important for CC where high residue levels often cause additional management challenges. To assist in selecting hybrids for CC production, Pioneer sales professionals can provide hybrid ratings for high-residue suitability, disease resistance, and stalk and root strength. They can also recommend products with appropriate insect resistance traits and refuge options, as well as the best seed treatments.
Partial residue removal can be a very effective way to manage excessive residue levels in high-yield CC environments. On-farm research conducted by Pioneer in Iowa in 2012 and 2013 indicated that removing approximately half of the previous year's corn stover improved CC yield by an average of 5 bu/acre. Removing excess residue was found to improve CC stand establishment and yields (Heggenstaller 2013). Removing excess corn residues can provide many of the benefits associated with rotation with soybean. Residue removal is particularly advantageous in no-till CC systems, where residues are not incorporated into the soil (Heggenstaller 2012).
Tillage is a key residue management practice in most CC systems. Sizing and incorporating residues into the soil are the first steps in getting them to begin to break down in advance of establishing the next crop. Full-width chisel plowing and strip-tillage in the fall are generally the best-suited tillage practices for CC systems.
Fall nitrogen applications can help to accelerate the rate at which residues break down in environments where temperature and moisture are not limiting.

Removing corn stover. — Removing a portion of corn stover from fields can provide many of the advantages of rotation with soybean.

Limited Rotation with soybean can be an effective way to maintain high yields in systems where corn is frequently grown consecutively for 2 or more years. Research conducted by Pioneer and the University of Illinois found that the yield penalty for second-year corn in a corn-corn-soybean rotation was only 5% compared to corn grown following soybean, compared to 17% for corn grown continuously (Doerge 2007).

References

Butzen, S. 2012. Best Management Practices for Corn-After-Corn Production Crop Insights. Vol. 22, no. 6. Pioneer, Johnston, IA.

Doerge, T., 2007. A New Look at Corn and Soybean Rotation Options. Crop Insights Vol. 17, No. 2. Pioneer, Johnston, IA.

Erickson, B. 2008. Corn-soybean rotation literature summary. Department of Agricultural Economics. Purdue University. West Lafayette, IN.

Heggenstaller, A. 2013. Corn Establishment and Yield Following Partial Stover Harvest. Research Update. Pioneer Agronomy Sciences, Johnston, IA.

Gentry, F., M.L. Ruffo, and F.E. Below. 2013. Identifying factors controlling the continuous corn yield penalty. Agronomy Journal 105:295-303.

Porter, P.M., J.G. Lauer, W.E. Lueschen, J.H. Ford, T.R. Hoverstad, E.S.Oplinger, and R.K. Crookston. 1997. Environment affects the corn and soybean rotation effect. Agronomy Journal. 89:441-448.