Corn grain yield response to crop rotation during odd growing seasons

Earlier this week we looked at corn grain yield response to crop rotation in extreme growing seasons when both Growing Degree Unit (GDU) accumulation AND precipitation were abnormal (click here). In extreme growing seasons, crop rotation was the best treatment while continuous corn was impacted more than during average growing seasons. I was asked a follow-up question about the crop rotation effect on grain yield when growing seasons were "off" for GDU accumulation OR precipitation. Again, data from the 35-yr corn-soybean rotation experiment conducted during 1987 to 2021 at Arlington, WI was used for the analysis.

Odd GDU accumulation years were selected when a growing season was + one standard deviation from the average (Figure 1). Cooler seasons included: 1992, 1993, 1997, 2004, 2008, 2009, 2013 and 2014. Warmer growing seasons included: 1987, 1988, 1991, 1995, 2005, and 2021. Grain yield during an average GDU growing season was 195 bu/A. Warm seasons averaged 170 bu/A, and cool seasons averaged 171 bu/A.

Figure 1. Corn grain yield response to growing season Growing Degree Unit (GDU) accumulation during 1987 to 2021 at Arlington, WI. Years were selected and grouped when GDU accumulation was + one standard deviation from the average. Click to enlarge.

Likewise,  odd precipitation years were identified  when a growing season was + one standard deviation from the average (Figure 2). Drier growing seasons included: 1988, 1989, 2003, 2005, 2011, 2012, and 2021. Wetter growing seasons included: 1993, 2006, 2008, 2010, 2018, and 2019. Grain yield during an average precipitation growing season was 188 bu/A. Grain yield during dry seasons averaged 166 bu/A, and during wet seasons averaged 178 bu/A.
 

 

Figure 2. Corn grain yield response to growing season precipitation during 1987 to 2021 at Arlington, WI. Years were selected and grouped when precipitation was + one standard deviation from the average. Click to enlarge.

The key point is that crop rotation maximizes corn grain yield consistently regardless of the kind of growing season. As a cropping sequence becomes more continuous, corn grain yield is more affected by odd growing seasons compared to an "average" growing season whether cool/warm or dry/wet. Grain yield in the second corn year following five years of soybean (2C) is more affected in a warm growing seasons than 2C in cool or dry/wet growing seasons. By 3C, the rotation effect is gone and grain yield are similar to 35+ years of continuous corn.

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Farmers continue to increase corn plant density

As technologies improve over time, management decisions need to be adjusted to keep up with the changing times. Better equipment, improved bio-engineered hybrids, better seed treatments, irrigation technologies, new pesticides, etc. have all contributed to corn grain yield progress. One management decision that continues to evolve is plant population. For some recent articles on this topic click here and here. For the latest USDA-NASS data collected in farmer fields during August, see Figure 1. Field plant populations are increasing at the rate of 270 to 300 plants/A*yr. Usually about 5 to 10% of the seed planted does not emerge, so seeding rates are 31,000 to 35,000 seeds/A.

Figure 1. Corn plant density changes over time for selected U.S. states. The rate of change (slope) in plants/A*yr since 1982 is reported for each state. Data derived from USDA-NASS (1982-2021). Click to enlarge.

It is clear from our research data that maximum yield plant densities (MYPD) and economic optimum plant densities (EOPD) are increasing. Recent research has shown that each hybrid has a MYPD and EOPD. There is gathering evidence that even each field within a farm may have a corn MYPD and EOPD. In many years (not 2022), seed cost can be as big of an input cost as nitrogen cost (Figure 2). Input adjustments can mean significant cost savings when corn grain prices are low (again not 2022).

Figure 2. USDA-ERS cost of production estimates for corn (last updated October 1, 2021). The Northern Crescent includes the northern tier of U.S. states along the Great Lakes. The Heartland includes Midwest Corn Belt states. Click to enlarge.

Adjusting plant density for your fields is one of the key production decisions for producing high yielding corn. Clearly farmers are adjusting plant densities higher. One approach to adjusting this decision is to plant the majority of your field to a target plant density based upon your experience. Then for one round (or pass) in a couple parts of the field, increase plant density 10%. Measure yield at the end of the season and during the season watch for "runt" plants, tillering, prolificacy, ear bareness. big versus small ears, ear tip "nose-back" and plant lodging. Adjust the field accordingly the following year.

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Corn grain yield response to crop rotation during extreme weather

 

The 2022 growing season started out with drought concerns and now wet, cool weather conditions make many wonder when we will ever get into the field. I have been curious about how well some of our agronomic recommendations hold up in extreme weather conditions. Let's review what happens with the crop rotation recommendation where we encourage farmers to rotate crops when possible. I will use data from a corn-soybean rotation experiment that was initiated in 1983 at Arlington, WI.

The first four years of this experiment were "set-up" years for the crop rotations and were discarded from the analysis below. So that leaves data collected during the 35-yr period from 1987 to 2021. Extreme growing degree unit (GDU) accumulation years were selected when a growing season was + one standard deviation from the average. Cooler seasons included: 1992, 1993, 1997, 2004, 2008, 2009, 2013 and 2014. Warmer growing seasons included: 1987, 1988, 1991, 1995, 2005, and 2021. Likewise,  extreme precipitation years were identified  when a growing season was + one standard deviation from the average. Drier growing seasons included: 1988, 1989, 2003, 2005, 2011, 2012, and 2021. Wetter growing seasons included: 1993, 2006, 2008, 2010, 2018, and 2019. The growing seasons that were most extreme for both GDU accumulation AND precipitation were: Cool/Wet= 1993 and 2008; and Warm/Dry= 1988, 2005, and 2021. All other growing seasons were lumped into average years for producing Figure 1.

Figure 1. Relative corn grain yield (percent of maximum) of various cropping sequences following soybean during 1987 to 2021 at Arlington, WI. Cool/Wet and Warm/Dry growing seasons were determined by selecting years + one standard deviation from the average for both growing degree unit accumulation AND precipitation. Click to enlarge.

For a previous report on grain yield response in this experiment, click here. Corn grain yield during an "average" growing season over this 35-yr time period was189 bu/A. Corn grain yield during "cool/wet" seasons was 179 bu/A and during "warm/dry" seasons was 155 bu/A; both lower than the yield of an average season.

Regardless of the kind of growing season, the best grain yielding treatment was corn following 5-yrs of soybean (1C). Corn in a corn-soybean annual rotation (CS) was the next best rotation treatment and usually not statistically different than corn following 5-yrs of soybean, except in a cool/wet year. Continuous corn (CC) yielded 17% less in an average season than 1C. However, during cool/wet and warm/dry season grain yield was 27 to 28% less than 1C. 

Relative grain yield of second year corn (2C), 3C, 4C, and 5C was lower in cool/wet and warm/dry growing seasons than an average year. In an average year, we typically see a yield response for 2C while 3C, 4C and 5C yield similarly to CC. In a warm/dry season there was no rotation response for 2C compared to 3C, 4C and 5C, while cool/wet seasons still had a yield response in 2C. For all growing seasons, 3C, 4C and 5C do not yield differently than CC.

Although the corn-soybean rotation is the dominant cropping sequence in the Midwest U.S., many Wisconsin farmers add other crops like wheat and alfalfa when possible. I would expect a similar response as above, especially in the second year of the continuous crop. At least two break years from the continuous crop will produce a rotation response in the second year, unless the growing season is warm/dry (i.e. drought). The rotation response disappears by the third continuous crop regardless of the type of growing season.

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