Tuesday, April 26, 2022

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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