Figure 1. Heavy residue cover in continuous corn field that can reduce stand establishment, decrease nitrogen availability, and increase pest pressure.Placing continuous corn on more productive fields has been found to help minimize yield penalty.
Growing continuous corn comes with agronomic challenges that can significantly decrease yield if left unmanaged.
Managing residue, fertility, and pest pressure is critical to maximizing yield potential in continuous corn.
Challenges of Growing Continuous Corn
The number of continuous corn acres in the U.S. fluctuates each year depending on variables such as grain prices, input costs, and the previous growing season. Yield penalties associated with lack of crop rotation (continuous corn) are a common concern and can be caused by multiple related issues:
Increased residue
Reduced stand establishment
Decrease soil nitrogen (N) availability
Elevated disease pressure
Increased insect pressure
With proper management, growers can reduce the continuous corn yield penalty and increase profit potential.
Managing Residue
Corn residue from previous years can create multiple issues such as reduced nutrient availability and soil temperature as well as increased soil moisture and pest pressure. The high carbon to nitrogen ratio of corn residue can immobilize soil nitrogen making it less available that season. Colder and wetter soils can slow emergence and increase risk of seedling disease and stand loss. Cooler spring soils can also delay mineralization and availability of other nutrients such as sulfur (S). Residue can also harbor pathogens from previous years that can develop into diseases. Corn residue has even been believed to have an allelopathic effect that can slow early season growth of the following corn crop. At planting, heavy levels of residue creates a physical barrier for seedlings to grow through (Figure 1).
As corn yields continue to increase, so does the amount of stover accumulation. A 180 bu/A corn crop accumulates 4.3 tons of stover per acre. As yields increase to 300 bu/A, the amount of stover accumulation can be over 7 tons/acre.1
There are different ways to manage residue such as removing it by baling corn stalks. However, removing residue can also remove nutrients such as N and potassium (K) that must eventually be replaced. Another option is to incorporate residue into the soil with tillage to speed up residue breakdown. Sizing residue into smaller pieces increases the surface area for microbes to breakdown biomass faster. Vertical tillage or chopping stalks with a mower can size residue but also requires an extra pass in the field. Attachments for corn heads can size the residue while harvesting. Chopping corn heads, residue managing stalk rolls, and aggressive stalk stompers are all combine attachments that can create more surface area for microbes to enter. There are also biological products on the market that either contain physical microbes or catalysts to increase the activity of microbes already present in the soil to accelerate the decomposition process.
Figure 2. Difference in remaining residue and plant health during the following growing season after harvesting with OEM stalk roll on left compared to residue sizing stalk roll on right (Vogel and Below 2019).A study conducted at the University of Illinois showed a 7% increase in residue decomposition overwinter when using a sizing stalk roll compared to the original equipment manufacturer (OEM) stalk roll (Figure 2). The 7% increase in residue degradation resulted in a 10 bu/A increase in yield suggesting that reducing the amount of residue from the previous crop can mitigate continuous corn yield penalty.2
Fertility Management
Corn stover contains a much higher amount of carbon than nitrogen (60:1) relative to other crop residues like soybeans (25:1) which break down much faster. Soil microorganisms need a C:N ratio diet of 24:1 to be able to survive and stay active. In cases where residue C:N ratios are greater than 24:1, such as with corn, soil microorganisms will seek out additional nitrogen to consume the extra carbon. This results in soil nitrogen being immobilized and unavailable until those microbes die. Due to this, continuous corn requires between 40-50 lbs/A more nitrogen than rotated corn. Broadcasting N directly on corn residue further increases risk of N immobilization. Delaying N applications closer to time of planting and applying in a band near the row can help reduce immobilization and increase plant availability.
Corn residue also slows soil warming in the spring which reduces root growth, slows the rate of diffusion, and slows soil mineralization. Nutrients that are taken up by the plant through diffusion, such as P and K, may become deficient early in the season. Using a starter fertilizer and placing nutrients near the root zone provides immediately available nutrients to the plant. As soils warm, organic matter mineralizes to supply the bulk of plant S needs. However, with cooler soils mineralization is slowed and can cause early season sulfur deficiency in continuous corn. Apply at least 15 lbs/A of S around planting time to avoid S deficiency problems.
Graph 1. Effect of crop rotation on corn yield averaged across 41 site-years between 2005-2011.Pest Control
Insect pests such as wireworms, seedcorn maggots, and white grubs can become more problematic with heavy residue situations. Using a premium seed treatment will help protect seed and seedlings against insect pests.
Many crop diseases overwinter in corn residue. In addition, many diseases prefer a cool and wet environment to survive and infect the plant. Using a premium seed treatment can protect seedlings from root and shoot infections. Foliar fungicides are even more important in continuous corn due to the more conducive environment for disease. Prolonging plant and stalk health is critical for late season standability.
In continuous corn, corn rootworm (CRW) population can become elevated. Using a soil applied insecticide or transgenic hybrid with two below ground modes of action against CRW can help protect the roots against feeding. Foliar insecticide applications properly timed to control female CRW beetles has also been found to help reduce future year CRW populations.
Graph 2. Effect of crop rotation on corn yield at 41 sites between 2005 and 2011.Golden Harvest Crop Rotation Trials
Golden Harvest conducted crop rotation studies across the Midwest from 2005-2011 for a total of 41 site-years. On average, corn grown in a rotation with soybean yielded 19 bu/A greater than corn grown continuously (Graph 1).
The magnitude of yield penalty varied between sites. The effect of crop rotation was drastically different from year to year even at the same location suggesting that growing conditions play a large role in the severity of yield loss. For example, corn grown continuously at Elk City, NE experienced a loss of 3 bu/acre in 2005, 21 bu/acre in 2007, 42 bu/acre in 2010, and 14 bu/acre in 2011 compared to rotated corn (Graph 2). Adequate precipitation and mild temperatures mitigate the detrimental effect continuous corn can have on yield.
Consider placing continuous corn rotations in more productive fields to help reduce yield penalty. Previous rotation trials have seen an overall lower percent yield loss at locations with higher overall yield potential (Graph 3). Pre-existing environmental stress which creates lower yield environments likely exasperates the negative responses of continuous corn itself, causing larger penalties.
Graph 3. Influence of yield environment on continuous corn yield penalty at 41 sites between 2005 and 2011.Hybrids differ in their suitability for continuous corn. When selecting hybrids, choose locally-adapted hybrids with desired traits, relative maturity, and proven yield. Focus on hybrids with solid agronomics such as strong disease package, excellent seedling vigor, and good root and stalk strength.
Overcoming the Continuous Corn Yield Penalty
Despite the challenges when growing continuous corn compared to rotated corn, high yields are still achievable with proper management. Placing a strong agronomic hybrid in a high yielding environment while focusing on residue management, fertility, and pest control is key to overcoming the continuous corn yield penalty.
References
1Graham, R.L., R. Nelson, J. Sheehan, R.D. Perlack, and L.L. Wright. 2007. Current and potential U.S. corn stover supplies. Agron. J., 99: 1-11. https://doi.org/10.2134/agronj2005.0222
2Vogel, A.M. and F.E. Below. 2019. Residue and agronomic management to reduce the continuous corn yield penalty. Agronomy, 9(10): 567. https://doi.org/10.3390/agronomy9100567
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