1. Introduction
1.1 Crop rotations – A historical perspective
Crop rotation is the production of different economically important plant species in
recurrent succession on a particular field or group of fields. It is an agricultural practice that
has been followed at least since the Middle Ages. During the rule of Charlemagne crop
rotation was vital to much of Europe which at that time followed a two-field rotation of
seeding one field one year with a crop and leaving another fallow. The following year the
fields were reversed (Butt, 2002). Sometime during the Carolingian period the three-field
rotation system was introduced. It consisted of planting one field, usually with a winter
cereal, a second with a summer annual legume, and leaving a third field fallow. The
following year a switch would occur. Sometime during the 17th and /or 18th centuries it was
discovered that planting a legume in the field coming out of fallow of the three-field rotation
would increase fodder for livestock and improve land quality, which was later found to be
due to increased levels of available soil nitrogen (N). During the 16th century Charles
Townshend 2nd Viscount Townshend (aka Turnip Townshend) introduced the four-field
concept of crop rotation to the Waasland region of England (Ashton, 1948). This system,
which consisted of a root crop (turnips (Brassica rapa var. rapa)), wheat (Triticum aestivum
L.), barley (Hordeum vulgare L.), and clover (Trifolium spp.) followed by fallow. Every third
year introduced a fodder crop and grazing crop into the system, allowing livestock
production the year-round and thus increased overall agriculture production. Our present
day systems of crop rotation have their beginnings traceable to the Norfolk four-year
system, developed in Norfolk County England around 1730 (Martin, et al., 1976). This
system was similar to that developed by Townshend except barley followed turnips, clover
was seeded for the third year and finally wheat on the fourth year. The field would then be
seeded to turnips again with no fallow year being part of the rotation.
In the new world, prior to the arrival of European settlers, the indigenous people in what is
now the Northeastern United States, practiced slash-and-burn agriculture combined with
fishing, hunting, and gathering (Lyng, 2011). Fields were moved often as the soil would
become depleted and despite the tale of Native Americans teaching the European settlers to
put a fish into the corn hills at planting, there is little or no evidence of the aboriginal people
fertilizing their crops. Maize would be planted in hills using crude wooden hoes with
gourds and beans (Phaseolus spp. L.) being planting alongside and allowed to climb the
maize stalks. When an area would become depleted of plant nutrients, it would be
abandoned and over time, would recover its natural fertility. Lyng (2011), describes the
Native Americans of the northeast as not so much conscience ecologist but rather people
with a strong sense of dependences on nature minus the pressure to provide for consumer
demands. Plains Indians on the other hand are classified as being of two cultures. There
were the nomadic nations that followed the herds of bison that roamed the region and lived
mainly on a diet of bison meat and what they might gather in the way of wild berries, fruits,
and nuts with very little farming except for some maize and tobacco (Nicotiana tabacum L.).
There were then the nations that lived on a combination of meat and crops they would raise.
These peoples tended to live in established villages and would fish, hunt, and gather wild
fruit and berries. The crop farming they practiced again, were maize, beans, and squash
(Cucubina spp. L.), sometimes referred to as “The Three Sisters” in Native American society
(Vivian, 2001). As with the nations in what would become the northeastern United States,
the Plains Indians that practiced crop farming would usually clear their garden areas by
slash and burn, grow their crops, and then allow a two-year fallow before planting again.
Just prior to planting, some villages would carry in brush and other plant debris to burn
along with the refuge that grew in the field during fallow to “enrich” the soil for the crops
about to be planted.
The early European settlers attempted to raise those crops (wheat, and rye (Secale cereal L.))
which they were accustom to, using cultivation methods they had used in the old country.
They also, introduced livestock, (cattle, swine, and sheep) which were not found in the New
World but that had been a major source of food for them in their native homeland. They
soon discovered that clearing fields for planting and pasturing was an arduous task and in
order to survive adopted some of the crop production techniques practiced by the
indigenous peoples and allowed their livestock to forage open-range (Lyng, 2011). As
colonization expanded and available labor increased along with the demand for food, the
permanent clearing of arable land increased along with the introduction of more Old World
crops and, unfortunately, their pests that continue to demand time and financial resources
to contain today.
The first export from the American colonies to England was tobacco. Though not a food
crop, tobacco played a pivotal role in helping sustain the Jamestown colony and gave the
settlers something to exchange for necessary items to survive. Tobacco is a high cash value,
very labor intensive crop. Even as of 2002, with only about 57,000 total farms in the United
States being classed as tobacco farms producing an average of 3 hectares of the crop per
farm, the average cash value of those 3 hectares was nearly $42,000 (Capehart, 2004).
Though tobacco preserved the Virginia colony, within seven years of its cultivation and
export, its continued production in the New World would usher in the African slave trade,
the darkest part of America’s past, and would culminate 200 years later into the American
Civil War.
Prior to colonization, a species of cotton, Gossypium barbadense, was being grown by the
indigenous people of the New World (West, 2004). Columbus received gifts from the
Arawaks of balls of cotton thread upon making landfall in 1492. Egyptian cotton (G.
hirsutum L.) was introduced to the colonies as early as 1607 by the Virginia Company in an
attempt to encourage its production and help satisfy the European appetite for the fiber that
was currently being exported from India . However, tobacco production and the lucrative
prices being paid for it along with the belief that cotton depleted the soil and required too
much hand labor, dissuaded the colonist from planting the crop. Even encouragement from
the colonial Governors, William Berkley and Edmund Andors could not convince the
settlers to switch to cotton. Small hectarages of G. hirsutum L. though were grown along the
Mid Atlantic colonies for individual household use. The Revolutionary War halted imports
of large quantities of cotton to the former colonies from Britain and forced the Americans to
grow their own supply. By the mid 1780’s production had expanded and the newly formed
United States became a net exporter of cotton to Britain.
After the development of the cotton gin by Eli Whitney in 1793 the key to financial success
in the southern states was acquiring large hectares of land for cotton production and large
numbers of slaves to tend to the crop. Maize, small grains, forages, and food crops were
grown only in sufficient quantities to sustain the plantations that had developed. These
crops were not grown for the purpose of commerce and were often relegated to some of the
marginal lands on the plantation or near the homestead for convenient harvest. The bulk of
all cleared fields were devoted to production of tobacco or “King Cotton” as it would
become known. From 1800 to 1830 cotton went from making up 7% ($5 million) of exports
from the United States to 41% ($30 million) (West, 2004). Tobacco production went from
45.4 million kg at the outbreak of the Revolutionary War to 175.8 million kg prior to the
Civil War (Jacobstein, 1907). Crop rotation was not even considered an option with respect
to these crops due to the cash value paid for them. By 1835 the top soil of eastern Georgia
had eroded away with the remaining clay unsuitable for cotton production. As soils became
depleted of nutrients necessary for the crops’ production, more wilderness, particularly
further west would be cleared and farmed. This resulted in conflicts with the native peoples
that resulted in their forced resettlement onto reservations and the spread of slavery
westward into newly chartered states in the south. This further deepened political and
economic conflicts that would explode into the American Civil War.
1.2 Advent of agricultural education and research
The Morrill Act of 1862 and again 1892 established the American Land-Grant colleges in
each state and charged them with the responsibility of teaching the agricultural and
mechanical disciplines, along with other responsibilities necessary to an advanced
education. The Hatch Act of 1887 then established the Agriculture Experiment Station
system which, in most states, is administered by the Land-Grant Universities and was to
provide further enhancement of agricultural teaching through experimentation. In 1914 the
Smith-Lever Act established the State Cooperative Extension Service which disseminates
information to the public of advances in agriculture production discovered by the state
agricultural experiment stations. All three of these legislative acts came about because of a
need to better understand sound farm management practices, including crop rotations, to
improve the nation’s farm economy.
The concept of agriculture research stations was not an American idea. The Rothamsted
Experiment Station in the United Kingdom is said to be the world’s oldest, being established
in 1843, while Möcken station in Germany, established in 1850, is said to be the world’s
oldest state supported agricultural research station. Agricultural research stations can now
be found in most all developed countries and even many less developed nations. Research
on crop rotations has been and continues to be conducted at virtually all of these stations,
with specialization towards the environment and crop species indigenous to their location.
Some of these studies have been in existence since the late 19th century (Rothamsted, 2011).
Some of the more famous experiments in the United States that continue to be performed at
some of the Land-Grant Universities, and are now designated on the National Register of
Historic Places, include The Old Rotation experiment on the Auburn University campus in
Alabama, The Morrow Plots on the campus of the University of Illinois, and Sanborn Field at
the University of Missouri. Mitchell et al., (2008) published that the Old Rotation experiment in
Alabama has shown over the long-term, seeding winter legumes were as effective as fertilizer N
in producing high cotton lint yields and increasing soil organic C levels. Rotation schemes with
corn or with corn-winter wheat- and soybean (Glycine max L. Merr.) produced no yield
advantage beyond that associated with soil organic C (Table 1). However, winter legumes and
crop rotations contributed to increased soil organic matter and did result in higher lint yields.
†Values followed by the same letter are not significantly different at P<0.05
‡Recent data show the effect of increasing soil organic matter on cotton productivity.
Table 1. Long-term effects of crop rotations, winter legumes and nitrogen fertilizer on cotton lint
yields at the “Old Rotation Experiment” of Auburn University in Alabama. (Mitchell, 2004).
Data from the Morrow Plots in Illinois have shown that yields from continuous corn have
always been much less than corn yields from a of corn-oats (Avena sativa L.) rotation or a or
corn-oats-and hay (clover (Trifolium spp.) or alfalfa (Medicago sativa L.)) rotation (Aref and
Wander, 1998). After the introduction of hybrid corn varieties in 1937, the first plots to
show an increase in corn yields due to these varieties were the corn-oats-hay rotation. Yield
increases due to hybrids were not noticed in the corn-oat plots until the late 1940’s and in
the continuous corn plots until the early 1950’s. These lower corn yields of the continuous
corn and the slower response to corn hybridization in the corn-oat rotation appear to
coincide with long-term average levels of soil organic matter and nitrogen observed in the
various plots (Table 2).
Table 2. Soil carbon C, nitrogen N, and C-N ration from a crop rotation experiment on the
Morrow Plots of the University of Illinois.
Means of samples taken in 1904, 1911, 1913, 1923, 1933, 1943, 1953, 1961, 1973, 1974, 1980,
1986, and 1992. (Aref and Wander, 1998). Values within a column followed different letters
are significantly different P0.05.
Corn and wheat yields at Sanborn Field at the University of Missouri have been consistently
higher when grown in rotation with each other along with red clover (Trifolium pratense L.)
inter-seeded into the wheat in late winter for forage the following year (Miles, 1999). Plots
of both corn and wheat have been grown continuously since the site’s establishment in 1888,
some receiving animal manure, some commercial fertilizer, and some no fertility treatment.
All have had reduced grain yields compared to those grown in rotation, even with the
added manure and/or fertilizer.
Thirty years after Sanborn Field’s establishment, its focus began to shift to the study of
cropping systems as related to soil erosion and the resulting loss of productivity. An
experiment conducted in 1917 by F.L. Duley and M.F. Miller on the campus of the
University of Missouri used seven test plots to measure soil erosion resulting from rainfall
(Duley and Miller, 1923). This research led to creation of the Soil Conservation Service of
the USDA, which in now a component of NRCS-USDA. It led to the establishment of
experiment stations throughout the United States dedicated to the study of crop rotations on
soil erosion and developing cropping systems to minimize erosion’s impact (Weaver and
Noll, 1935). Experiments at these stations in Iowa, Missouri, Ohio, Oklahoma, and Texas all
showed plots planted to a continuous cropping system had higher surface soil losses and
losses of rainfall than plots planted to a forage or in a three or four year rotation (Uhland,
1948).
2. Crop rotations vs. continuous cropping
Crop rotation schemes are, by and large, regional in nature and a specific rotation in one
environment may not be applicable in another. Continuous cropping schemes or
monocultures for the most part, have fallen out of favor in many farming regions. Roth
(1996) published mean corn yields from a 20 year crop rotation experiment in Pennsylvania
that included rotation with both soybean and alfalfa showing higher yields with all rotation
schemes than continuous corn (Table 3). The extensive use of commercial fertilizers and
pesticides has helped mask most of the beneficial effects of crop rotation. But Karlen et al.
(1994) has stated” no amount of chemical fertilizer or pesticide can be fully compensated for
crop rotation effects”. However, economics continues to be the large determining factor into
how a field is managed.
†First year corn yield
‡Second year corn yield
Table 3. Mean corn grain yields as influence by crop rotation from 1969 to1989 at Rock
Springs, PA. (Roth, 1996).
One primary benefit to crop rotation is the breaking of crop pest cycles. Roth (1996) states
that in Pennsylvania, crop rotations help control several of the crop-disease problems
common to the area such as gray leaf spot in corn (Cercospora zeae-maydis) take-all in wheat
(Gaeumannomyces graminis var. tritici), and sclerotina in soybean (Sclerotinia sclerotiorum). In
corn, corn rootworms (Diabrotica virgifera spp.) can be a devastating pest and crop rotation
was considered to be the most effect method of control. However, beginning in the late
1980’s there was a variant of the Western corn root worm (D. virgifera virgifera LeConte) that
began egg laying in soybean fields, making larvae present to feed upon first year corn in a
soybean-corn rotation (Hammond et al., 2009). Prior to this time the standard method to
avoiding rootworm damage was to rotate. However, during the mid-1960’s in the Cornbelt
there was a movement to engage in growing corn continuously on highly productive soils.
Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] was being readily adopted
for weed control in corn and a number of insecticides were becoming available for of control
corn rootworm and other corn insects. Also sources of nitrogen fertilizer were readily
available and relatively inexpensive. Competitive profits for other crops, particularly
soybean, and continued research showing tangible benefits to rotations though returned
most fields to some sort of rotation scheme. However, there are some producers today who
are profitable at growing continuous corn. But, such a system appears to require strict
adherence to sound management practices.
Cotton is probably the principle crop that has been grown continuously on many fields,
some for over 100 years. The crop was profitable and well suited for production in areas
prone to hot summer temperatures and limited rainfall. There was also an infrastructure
available in these production regions for processing the lint and seed as well as a social
bond that connected the crop to the people who grew it. Corn, hay, and small grains were
the “step children” of agronomic crops for generations of southern planters. Corn and
winter oats were grown in the Cottonbelt solely as feed grains for the draft animals used to
grow cotton and the meat and dairy animals grown for home consumption. There were
basically no markets available or facilities to handle some of these crops for commercial
trade. Despite being introduced in the 1930’s, it wasn’t until the early 1950’s that soybean
became an important crop in the lower Mississippi River Valley (Bowman, 1986). Rice
(Oryza sativa L.) was introduced to the Mississippi River Delta in 1948 and together these
crops provided alternative sources of agronomic income to cotton but did little to encourage
crop rotation. Both rice and soybean were relegated to the heavier clay soils of the
Mississippi Delta with the sandy loams, silts, and silty clays remaining in cotton. It wasn’t
until changes in government support programs in the mid-1990’s that planters in the Mid
South became interested in alternatives to continuous cotton and began to produce corn for
commercial sale and rotate it with cotton. Corn hectareage in the states of Arkansas,
Louisiana, and Mississippi increased from 161,000 ha in 1990, to 382,000 ha in 2000, to
630,000 ha in 2010 (USDA-NASS, 2011).
Until 2007 research information about corn-cotton rotations were limited. An extensive
study on various corn-cotton rotation schemes yielded data on the effects of rotation on
yields and reniform nematode (Rotylenchulus reniformis) a serious pest to cotton. Bruns, et al.
(2007), reported corn grain yields were greater following cotton than in plots of continuous
corn. Pettigrew, et al. (2007), noted that cotton plant height increased 10% in plots following
one year of corn and 13% following two years of corn when compared to continuous cotton
(Table 4). Lint yields increased 13% following two years of corn primarily due to a 13% in
bolls per m2. No other increases were noted however. Stetina, et al., (2007) found that
following two years of corn production, reniform nematode populations remained below
damaging levels to the cotton plants. However, cotton following just one year of corn
would have reniform nematode populations rebound to damaging levels towards the end of
the growing season.
†Lint yield for cotton; grain yield at 155 g kg-1 seed moisture; all values are means of eight reps
averaged across four genotypes.
‡Within each crop and year, means followed by the same letter are not significantly different by lsd (P0.05)
Table 4. Effect of crop rotation sequence on crop yield of corn and cotton from 2000 to 2003
in Stoneville, MS. (Stetina et al., 2007).
to be continued
