What Do We Know About Crop Rotations?
May 30, 2002 9(11):84-85
Joe Lauer, Corn Agronomist
To begin to answer this question, let me first state that agronomists do not know
the mechanism of the rotation effect. It remains a mystery. Farmers have long observed
it and used it for managing crops, but we do not know what causes it. The purpose
of this article is to provide a timeline regarding changes in thinking about the
crop rotation effect.
Simply stated the rotation effect is the additional benefit of rotating crops when
all production variables appear to be optimum, or when problems associated with
monoculture are not apparent. The rotation effect was originally defined as the
effect of all contributions, other than N, supplied by legumes in a rotation (Baldock
et al., 1981). However, it is also recognized that other non-legume crops can provide
benefits as well (Robinson, 1966; Crookston and Kurle, 1988).
Varro in the first century B.C. recognized that the rotation effect improved crop
production (as cited by Baldock et al., 1981). Prior to the 1950s, farmers recognized
the importance of rotation because there were few options for fertility and pest
management. Between the 1950s and 1960s, the practice of corn and soybean monoculture
became popular. Chemical fertilizers and pesticides were thought to be able to substitute
for rotation. The attitude seemed to be "Continuous corn yields just as well,
if not better than rotated corn" (Benson, 1985). The rotation effect was thought
to be primarily N related.
In the 1970s, it became apparent that all rotation effects could not be overcome.
Allelopathic effects from weed species were found to influence corn and soybean
growth (Bhowmik and Doll, 1984). Research attempts were made to separate N effects
and non-N effects (Baldock et al., 1981).
During the 1980s, the main question was: "What does crop rotation do in the
system?" Researchers reported improvement of soil moisture (Roder et al., 1989),
improvement of soil structure (Dick and Van Doren, 1985; Griffith et al., 1988),
increases of beneficial soil microbes (Cook, 1984), decreases of pests (Cook, 1984;
Dabney et al., 1988; Edwards et al., 1988), and decreases of phytotoxic compounds
or growth promoting substances originating from crop residues (Yakle and Cruse,
During the 1990s, many experiments were designed to eliminate factors. Above-ground
residue was found to have no rotation effect (Crookston and Kurle, 1989). Host-specific
pathogens could not account for the rotation effect (Whiting and Crookston, 1993).
Some root development differences were observed (Nickel et al., 1995). Grain nutrient
composition was found to be unaffected by rotation (Copeland and Crookston, 1992).
Many studies provided management recommendations and the rotation effect was better
quantified (Meese et al., 1991; Porter et al., 1997; Porter et al., 1998; Adee et
al., 1994; Porter et al., 1997; Lund et al., 1993).
Which brings us to the current state of knowledge regarding rotation effects. Probably
the biggest change in thinking is recognition that the crop rotation effect on yield
partially involves soil microbes and is specific to a location (Porter et
al., 2001). The rotation effect may not be due to one mechanism; rather numerous
factors acting alone or in combination chip away at yield and vary in importance
from site to site within and between fields.
Many rotation studies begun in the 1980s are maturing and currently have the ability
to generate long-term, longitudinal cropping sequence results. Next week some specific
examples of new insights gained from these long-term rotation experiments.
Adee, E. A., E. S. Oplinger, and C. R. Grau. 1994. Tillage, rotation sequence, and
cultivar influences on brown stem rot and soybean yield. Journal of Production Agriculture
Baldock, J. O., R. L. Higgs, W. H. Paulson, J. A. Jackobs, and W. D. Shrader. 1981.
Legume and mineral N effects on crop yields in several crop sequences in the upper
Mississippi valley. Agronomy Journal 73:885-890.
Benson, G. O. 1985. Why the reduced yields when corn follows corn and possible management
responses? p. 161-174. Proceedings of the 40th Annual Corn and Sorghum Research
Bhowmik, P. C. and J. D. Doll. 1984. Allelopathic effects of annual weed residues
on growth and nutrient uptake of corn and soybeans. Agronomy Journal 76:383-388.
Cook, R. J. 1984. Root health: Importance and relationship to farming practices.
p. 111-127. In D.F. Bezdicek (editor). Amercian Society of Agronomy, Madison,
Copeland, P. J. and R. K. Crookston. 1992. Crop sequence affects nutrient composition
of corn and soybean grown under high fertility. Agronomy Journal 84:503-509.
Crookston, R. K. and J. E. Kurle. 1988. Using the kernel milkline to determine when
to harvest corn for silage. Journal of Production Agriculture 1:293-295.
Crookston, R. K. and J. E. Kurle. 1989. Corn residue effect on the yield of corn
and soybean grown in rotation. Agronomy Journal 82:229-232.
Dabney, S. M., E. C. McGawley, D. J. Boethel, and D. A. Berger. 1988. Short-term
crop rotation systems for soybean production. Agronomy Journal 80:197-204.
Dick, W. A. and D. M. Van Doren. 1985. Continuous tillage and rotation combinations
effects on corn, soybean, and oat yields. Agronomy Journal 77:459-465.
Edwards, J. H., D. L. Thurlow, and J. T. Eason. 1988. Influence of tillage and crop
rotation on yields of corn , soybean, and wheat. Agronomy Journal 80:76-80.
Griffith, D. R., E. J. Kladivko, J. V. Mannering, T. D. West, and S. D. Parsons.
1988. Long-term tillage and rotation effects on corn growth and yield on high and
low organic matter, poorly drained soils. Agronomy Journal 80:599-605.
Lund, M. G., P. R. Carter, and E. S. Oplinger. 1993. Tillage and crop rotation affect
corn, soybean, and winter wheat yields. Journal of Production Agriculture 6:143-144,
Meese, B. G., P. R. Carter, E. S. Oplinger, and J. W. Pendleton. 1991. Corn/soybean
rotation effect as influenced by tillage, nitrogen, and hybrid/cultivar. Journal
of Production Agriculture 4:74-80.
Nickel, S. E., R. K. Crookston, and M. P. Russelle. 1995. Root growth and distribution
are affected by corn-soybean sequence. Agronomy Journal 87:895-902.
Porter, P. M., S. Y. Chen, C. D. Reese, and L. D. Klossner. 2001. Population response
of soybean cyst nematode to long teerm corn-soybean cropping sequences in Minnesota.
Agronomy Journal 93:619-626.
Porter, P. M., R. K. Crookston, J. H. Ford, D. R. Huggins, and W. E. Lueschen. 1997.
Interrupting yield depression in monoculture corn: Comparative effectiveness of
grasses and dicots. Agronomy Journal 89:247-250.
Porter, P. M., J. G. Lauer, D. R. Huggins, E. S. Oplinger, and R. K. Crookston.
1998. Assessing spatial and temporal variability of corn and soybean yields. Journal
of Production Agriculture 11:359-363.
Porter, P. M., J. G. Lauer, W. E. Lueschen, J. H. Ford, T. R. Hoverstad, E. S. Oplinger,
and R. K. Crookston. 1997. Environment affects the corn and soybean rotation effect.
Agronomy Journal 89:441-448.
Robinson, R. G. 1966. Sunflower-soybean and grain sorghum-corn rotations versus
monoculture. Agronomy Journal 58:475-477.
Roder, W., S. C. Mason, M. D. Clegg, and K. R. Kniep. 1989. Yield-soil water relationships
in sorghum-soybean cropping systems with different fertilizer regimes. Agronomy
Whiting, K. R. and R. K. Crookston. 1993. Host-specific pathogens do not account
for the corn-soybean rotation effect. Crop Science 33:539-543.
Yakle, G. A. and R. M. Cruse. 1984. Effects of fresh and decomposing corn plant
residue extracts on corn seedling development. Soil Science Society of America Journal