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WEIGHING THE RETURNS OF ROTATED VS. CONTINUOUS CORN Top Farmer Crop Workshop Newsletter, Purdue University, February 2005

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WEIGHING THE RETURNS OF ROTATED VS. CONTINUOUS CORN

Bruce Erickson and Jess Lowenberg-DeBoer

Many Midwest growers are considering more corn in their cropping mix, but that usually means
growing corn after corn, a situation that adds production costs, can increase risk, and most would
say compromises yield potential. But many with experience raising corn on corn see no
additional risk and a situation where they can raise some of their best yields. They have found
ways to make the continuous cropping system work, managing crop residues with fall nitrogen
and tillage, maintaining high P and K levels in the soil, adequate amounts of applied nitrogen, and
high plant populations.

Mark Dempsey of Fowler, IL seems to have perfected the recipe. A field of Dempseys that has
been in corn for four years yielded 320 bu/A in 2004, enough to place him second in the National
Corn Growers Contest, highest in Illinois. That was quite a feat with the record yield levels and
over 3,000 entrants in that contest nationwide. A modest Dempsey credits much of the success to
the weather, and insists his management practices were not that extraordinary.

We used 230 lbs N, 90 lbs potash and 60 lbs phosphate (as DAP), Dempsey said. We bumped
the population to 44,000. Our post herbicide actually went on late.

While theres a trend to reducing tillage in other systems, primary tillage seems to be a key part
of the winning recipe in continuous corn.

Its unbelievable the amount of residue from a 300+ bu/A field, Dempsey said, adding that
residue, and managing it, is a key element in success. We apply 30 lb/A N as liquid in the fall to
help break down the residue, and pull a mini-moldboard plow at a depth of about 14 inches. That
mixes the residue with the soil but still leaves the surface mostly intact, he said. Dempsey gives
a lot of credit also to the pattern tile drainage that he has installed in certain fields, which allows
soils to warm and dry, allowing more timely tillage and expediting residue decomposition.

There are several reasons why Midwest farmers seem to be happier with their corn crop as
compared to soybeans in recent years, among them:


Corn is yielding relatively better than soybeans compared to years past. Since the 1960s
U.S. soybean yields have trended upward at slightly less than 1 percent per year (about
0.4 bu/A/yr), with corn increasing at about 1.3 percent per year (1.8 bu/A/yr). Last year
both crops set records, but in the last ten years soybeans have lagged, increasing at just
0.2 bu/A/year while corn has gone up 3.4 bu/A/year. Most of that drastic difference is
due to the dismal soybean yields of 2003, but even taking that out, soybeans still lag corn.
Forty years ago soybean yields were typically 33% of corn, but now soybean yields are
about 28% of corn yields.


Soybeans have suffered from an array of pest problems, including soybean cyst
nematode, sudden death syndrome, and leaf aphids. Now, Asian soybean rust has many
wondering about the additional costs and risks of growing soybeans.


Rotation with soybeans is not solving corn rootworm problems in huge areas of the
Eastern Corn Belt where the western rootworm variant is spreading.

Comparing the dollar contributions of corn and soybeans in rotation for a typical farm, corn and
soybeans have traded off over the years, fluctuating with grain prices, weather conditions, and Top Farmer Crop Workshop Newsletter, Purdue University, February 2005

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other factors. Corn usually far exceeds soybeans for gross returns, but corn is also more
expensive to produce and harvest, with increased fertilizer, pesticide, drying, hauling, and storage
costs, evening the slate with soybeans. In contrast continuous corn has never provided a greater
contribution than either rotated corn or soybeans in the last several years of Purdue analyses, as it
has been difficult to recoup the 10% yield penalty that most agree is associated with the first year
of corn following corn, and the additional fertilizer and pesticide costs. For farms where there is
high demand for livestock feed, especially silage, the situation can be different.

University research, with few exceptions, doesnt support the idea that corn on corn yields can
match rotated. The rotation effect has been known for as long as crops have been cultivated, but
many of the reasons remain a mystery. Differences in soil fertility, crop residues, and insects,
weeds, and diseases can be partially responsible. But even when these factors are eliminated,
there often remain unexplained yield differences. In a literature review of all known published
data comparing continuous corn to a corn soybean rotation, rotated corn beat continuous corn in
all but two of the studies. Some growers contend that their second year of corn is the most
challenging and that yields recover in subsequent years, but there was no evidence of any relative
yield improvement over time in any of the long-term researcher-managed studies (see literature
review at
http://www.agecon.purdue.edu/pdf/Crop_Rotation_Lit_Review.pdf
).

Some long-time continuous corn growers and university specialists feel that a unique situation
can develop over time in high-managed continuous corn. The factors that they feel are significant
include:

1. Increases in soil organic matter. Corn produces more biomass than soybeans, and unless
harvested for silage studies have shown continuous corn production can significantly increase
soil organic matter. Increases of 2 or 3 percentage points have been documented in situations
where there have been many years of continuous corn. Conversely, a decline in soil organic
matter is well recognized in cropping systems that include soybeans. However, the high
amounts of biomass produced by corn must be managed. No-till continuous corn has not been
a successful option. Primary tillage is needed to provide soil mixing and aeration to promote
the conversion of crop residue into stable soil organic matter.

2. Increases in soil quality. Increased soil organic matter, with limits, positively influences a
number of other factors including soil structure, buffering capacity, water-holding capacity,
and microbial activity, among others.

3. Increases in available nitrogen. Nebraska studies show long-term continuous corn builds soil
N. In contrast, a corn/soybean rotation with typical fertilization rates actually results in a net
long-term loss of nitrogen in the soil. There is a limit to how much nitrogen soybeans fix
through symbiotic means, as high-yielding soybean and corn crops remove huge quantities of
nitrogen.

Continuous corn farmers Herman Warsaw, Francis Childs, and Mark Dempsey would likely
agree. The late Herman Warsaw of McClean County, Illinois was the first corn grower to break
the 300 bushel barrier in 1975. He did it with long-term continuous corn. Six-time national
NCGA non-irrigated champion Francis Childs of Iowa broke the 400 barrier in 2001 with long-
term continuous corn. The two 300+ non-irrigated yields in the 2004 NCGA yield contest were
Childs and relative contest newcomer Mark Dempsey, all corn following corn.

Some say the reason why university research has not been able to replicate the results that some
farmers are achieving with continuous corn is that university studies have been conducted at Top Farmer Crop Workshop Newsletter, Purdue University, February 2005

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normal levels of managementor that these systems may be unique to soil types or regions.
Also, the university studies were conducted in small plots, ideal for many kinds of studies, but not
ideal when testing long-term effects and varying crop rotations where there can be significant
edge effects.

To evaluate the potential of continuous corn systems, we are proposing to work with growers who
would compare a continuous corn system to a corn/soybean rotation in adjacent fields or adjacent
blocks within fields. Both cropping schemes would be at a high level of management in an
attempt to achieve exceptional yields, and to test methods distinct to continuous corn that could
lead to the development of a unique biosystem capable of out-producing a competing
corn/soybean rotation system. Data analysis will use spatial methods to compare agronomic
characteristics and the profitability of continuous corn and rotation systems.

If you are interested in participating in one of these trials, or for more information, please contact:

Jess Lowenberg-DeBoer
lowenbej@purdue.edu

(765)494-4230

Bruce Erickson
berickso@purdue.edu

(765)494-9557

Department of Agricultural Economics
Purdue University
West Lafayette, IN 47907