This document summarizes research on crop rotations in Iowa. A 2-year corn-soybean rotation is compared to 3-year and 4-year rotations that include oats, red clover, and alfalfa. The longer rotations require more labor but use 86-96% less nitrogen fertilizer and 97% less herbicide. Soil quality improves with longer rotations, which also have similar or higher yields compared to the 2-year system. Integrating livestock through manure application provides nitrogen to the crops and improves the economics and environmental sustainability of the farming system.

1. Sustainable agriculture
“Sustainable agriculture is the production of food, fiber, and
fuel using farming techniques that protect the environment,
public health, human communities, and animal welfare. This
form of agriculture enables us to produce a sufficient amount of
healthful food now without compromising the ability of future
generations to do the same.”
Evaluation of Contrasting Crop Rotation Systems
Using Multiple Performance Criteria
Matt Liebman
Iowa State University

2. Iowa, 2015:
2.5 billion bushels of corn harvested
554 million bushels of soybean harvested
2.2 million cattle, 46.6 million hogs & pigs, 12.5 billion eggs marketed
4.0 billion gallons of ethanol produced
http://www.nass.usda.gov/Statistics_by_State/Iowa/Publications/Annual_Statistical_Bulletin/2016/
http://iowarfa.org/resource-center/statistics/

3. A SIMPLIFIED, HOMOGENEOUS LANDSCAPE
Corn and soybean in Iowa: 63% of total land area, 82% of cropland
Wright County, 2014
583 sq. miles
(1,509 sq. km.)
Yellow = corn
Green = soybean
USDA-NASS Cropland Data Layer

4. Hatfield et al., 2009, JSWC
Alfalfa and other hay crops
Small grains
Large reduction in area planted to small grains,
alfalfa, and other hay crops within the Raccoon
River Basin from 1949 through 1997.

6. Challenges in Midwestern systems
related to low crop diversity and
decoupled crop and livestock production
• Soil erosion
• Water quality degradation via nutrient and
pesticide emissions
• Herbicide resistant weeds
• New crop diseases
• Reductions of wildlife populations, including
monarch butterflies, bees and other pollinators

7. Can cropping system diversification and crop-livestock integration:
• reduce reliance on synthetic fertilizers, pesticides, and fossil energy?
• maintain or increase crop productivity and profitability?
• improve important indicators of environmental performance?

8. 2-year rotation: corn-soybean (cash grain)
3-year rotation: corn-soybean-oat/red clover (green manure)
4-year rotation: corn-soybean-oat/alfalfa-alfalfa (hay)
36 plots, 18 m x 84 m each, all phases of system present every year
2001 and 2002: base-line sampling / 2003-2005: start-up period
2006-present: mature period

9. Management practices
2-year rotation 3-year and 4-year rotations
Manure None 16 Mg/ha before corn
Synthetic
N fertilizer
112 kg N/ha at
planting plus
sidedress
None at planting, but with
sidedress option
Herbicides
Broadcast in corn
and soybean phases
Banded with interrow
cultivation in corn and
soybean phases
Tillage
Chisel plow after
corn
Moldboard plow after clover
and alfalfa, chisel plow after
corn

10. Mean annual mineral N fertilizer
and herbicide use, 2006-2016
N fertilizer Herbicides
Rotation 2-year 3-year 4-year 2-year 3-year 4-year
kg N/ha kg a.i./ha
Corn 170 33 27 1.33 0.07 0.07
Soybean 2 2 2 1.63 0.12 0.12
Oat -- 2 2 -- 0 0
Alfalfa -- -- 2 -- -- 0
Rotation av. 86 12 8 1.48 0.06 0.05
Reduction -86% -91% -96% -97%

11. Mean yields, 2006-2016
Sources: Liebman et al. 2008; Davis et al. 2012;
Hunt et al. 2017
Yield, Mg/ha
Rotation Corn Soybean Oat Alfalfa
2-year 12.0 b 3.16 c --- ---
3-year 12.4 a 3.56 b 3.33 b ---
4-year 12.6 a 3.76 a 3.51 a 9.18

12. Mean weed biomass in 2006-2016 was low in the
corn and soybean phases of each system. Weed
growth was greater in oat and alfalfa phases.
Within columns, means followed by different letters are significantly different.
Weed biomass, kg/ha
Rotation Corn Soybean Oat Alfalfa
2-year 2 b 3 b --- ---
3-year 15 a 20 a 76 a ---
4-year 9 ab 8 b 72 a 58

13. Rotation effects on soybean in 2010 during SDS epidemic:
Longer rotations were healthier
3-year rotation 2-year rotation
Measurements by L. Leandro, ISU Plant Pathology & Microbiology
Photo courtesy of L. Miller

14. Longer rotations:
lower SDS incidence,
reduced SDS severity,
higher soybean yield.
Leandro et al. (in press)

15. SOIL HEALTH
Large reduction in abundance of Fusarium virguliforme
DNA per gram of soil in longer rotations
Leandro et al. (in review)
C: corn
S: soybean
2: 2-yr rotation
4: 4-yr rotation
Note log scale

16. Soil Quality Indicators in Corn
(0-20 cm)
Rotation
Particulate organic
matter carbon
Microbial
biomass
carbon
Potentially
mineralizable
nitrogen
mg POM-C cm-3 soil μg C g-1 soil mg PMN cm-3 soil
2-year 1.90 b 312.6 b 31.2 b
3-year 2.31 a 388.7 ab 40.4 a
4-year 2.19 a 472.2 a 37.3 ab
Sources: Lazicki et al., 2016; King and Hofmockel, 2017
Soil managed with longer rotations had more POM-C,
greater microbial biomass, and higher PMN.

17. Tomer & Liebman (2014)
Mean NO3-N concentrations in water samples
collected under each cropping system, 2004-2011

18. Estimated Sheet and Rill Erosion (RUSLE2)
Mg per hectare per year
2-year rotation: 2.64
3-year rotation: 2.25 (-15%)
4-year rotation: 1.75 (-34%)

19. Fossil Energy Inputs [GJ ha-1 yr-1],
2008-2014
2-Year
Rotation
3-Year
Rotation
4-Year
Rotation
Fuel for Operations 2.6 2.0 1.8
Fertilizer 5.5 0.9 0.9
Herbicide 0.4 0.3 0.2
Seed Production 0.3 0.3 0.3
Grain Drying 1.5 1.0 0.8
Total Energy Costs 10.3 4.5 3.9
About 0.6 barrels of oil equivalent = about 25 gallons diesel equivalent per acre

20. Hunt et al. 2017
Freshwater ecotoxicological potential of herbicides,
2008-2016, USEtox model

21. Input costs were taken from ISU Extension’s annual report “Costs
of Crop Production in Iowa,” and from local businesses.
Machinery operation and labor costs were based on field notes
and ISU’s “Estimating field capacity of farm machines.”
Grain and hay prices were taken from marketing year averages
provided by the Iowa office of the USDA National Agricultural
Statistics Services. Subsidy payments and insurance pay-outs
were not included in revenue figures.
Manure was assumed to be generated by on-farm or near-by
livestock and without cost for the material, but with labor and
machinery costs for spreading.
Analyses were conducted for 2008-2016 data.
Economic Analyses
Cost and Price Assumptions

22. Labor and economics, 2008-2016
Rotation
2-year 3-year 4-year
Labor inputs (hr/ha) 1.7 c 3.0 b 3.5 a
Gross returns ($/ha) 1699 a 1507 b 1576 b
Costs of production (with
labor, but not land, $/ha)
872 a 625 c 684 b
Profits (returns to land and
management, $/ha)
827 a 882 a 892 a
Diversity  greater labor requirements, lower gross
returns, lower costs, similar profits
Hunt et al. 2017 and unpublished data

23. The cost of manure
• Our primary analyses assumed that there were
labor and machinery costs for spreading manure,
but that there was no cost for the material itself.
• How much could a crop farmer using the 3-year
or 4-year rotations pay for manure and still match
the profitability of the 2-year rotation, which
didn’t receive manure?
• 3-year rotation: $8.55/Mg (fresh weight)
• 4-year rotation: $13.48/Mg (fresh weight)

24. Increasing cropping system diversity and reintegrating
crop and livestock production can balance productivity,
profitability, and environmental health
Hunt et al. 2017. Env. Sci. & Tech., doi:10.1021/acs.est.6b04086
Davis et al. 2012. PLoS ONE, doi:10.1371/journal.pone.0047149

25. Special thanks to:
• C. Chase
• A. Davis
• M. Fiscus
• J. Hill
• N. Hunt
• D. James
• A. Johanns
• A. King
• P. Lazicki
• L. Leandro
• D. Sundberg
• M. Tomer
• M. Wander
• M. Woods

27. 2011 Wright County, Iowa
0 1.42 2.84 4.26
miles
LandOCoverOCategories
DbyOdecreasingOacreage-O
AGRICULTURE
Corn
Soybeans
GrasslandOHerbaceous
Alfalfa
OtherOHay/NonOAlfalfa
Oats
WinterOWheat
SweetOCorn
Sod/GrassOSeed
Fallow/IdleOCropland
DblOCropOWinWht/Soybeans
Rye
Clover/Wildflowers
Switchgrass
NON-AGRICULTURE*
Developed/OpenOSpace
WoodyOWetlands
DeciduousOForest
Developed/LowOIntensity
HerbaceousOWetlands
OpenOWater
Produced by CropScape - http://nassgeodata.gmu.edu/CropScape * Only top 6 non-agriculturecategroies are listed.
A SIMPLIFIED, HOMOGENEOUS LANDSCAPE
Corn and soybean in Iowa: 63% of total land area, 82% of cropland
Wright County, 2011
583 sq. miles
(1,509 sq. km.)
Yellow = corn
Green = soybean
USDA-NASS Cropland Data Layer

28. How are agricultural systems
affected by low crop diversity and
decoupled crop and livestock
production?

30. Yield reduction for major crops grown in
shortened rotations or monoculture
Crop Yield decline
Barley (Hordeum vulgare) 11-19%
Corn (Zea mays) 7-36%
Oilseed rape (Brassica napus) 3-25%
Potato (Solanum tuberosum) 10-30%
Rice (aerobic) (Oryza sativa) 19-54%
Soybean (Glycine max) 8-20%
Sugarcane (Saccharum spp.) 3-50%
Sweet potato (Ipomoea batatas) 21-57%
Wheat (Triticum aestivum) 9-20%
Bennett et al. (2012) Biological Reviews 87: 52-71

31. Why do reductions in
crop diversity lead to
lower yields?
(1) Build-up of plant
pathogens, nematodes,
insect pests, & weeds
(2) “Deleterious rhizosphere
microorganisms”
(3) Autotoxicity (allelopathy)
(4) Degradation of soil
physical and chemical
properties
Bennett et al. (2012) Biological
Reviews 87: 52-71

32. Source: Janssen (1984), Plant & Soil 76:297-304, as cited in Magdoff & Weil (2004)
Effects of 25 years of cropping practices and
fertilizer and manure applications
on soil properties
MinN: mineral N fertilizer; GM: green manure; AnMan: animal manure and pasture ley
Soil property Management/amendments
MinN MinN +
GM
MinN +
GM +
AnMan
BD (g cm3) 1.50 1.45 1.35
Total SOM (Mg/ha) 78.4 81.9 86.9
Young SOM (Mg/ha) 6.2 11.0 15.2
Old SOM (Mg/ha) 72.2 70.9 71.7
Total N (Mg/ha) 4.0 4.4 4.6
Mineralized N from young SOM (Mg/ha) 34 74 108
Mineralized N from old SOM (Mg/ha) 26 26 26

33. Diversification includes the integration of crops and livestock:
Composted manure is applied to red clover and alfalfa, before corn,
in the 3-year and 4-year rotations.
N added by clover and alfalfa through biological nitrogen fixation
N, P, K, and other nutrients recycled through manure application

34. Managing weeds in longer rotations with diverse tactics
Asynchronous harvests
Banded
Stubble clipping &
hay removal
CultivationBand spraying

35. Nitrogen Fertility Management
in Contrasting Rotation Systems
Rotation Corn
2-year
112 kg N/ha applied at planting with
additional N side-dressed according to
soil test results
3-year and
4-year
(Legume residues + manure)
No fertilizer N applied at planting
N side-dressed according to test results

36. Tillage:
In the 3-year and 4-year rotations, red clover and alfalfa
are incorporated with a moldboard plow in the fall
preceding corn production. Moldboard plowing is not used
in the 2-year rotation.

37. Oat production

38. Management practices for oat
• Soybean residue disked or field cultivated.
• Ground is then cultipacked.
• Oat (IN09201) sown with JD 1520 drill @ 80 lbs/acre
with red clover @ 12 lbs/acre or alfalfa @ 15 lbs/acre.
• Row spacing: 7.5”.
• Average oat density: 22 plants per square foot.
• Direct harvest of grain with a JD 9450 combine.
• Straw raked, baled, and removed.
• Grain stubble mowed 5 to 6 weeks later for weed
control.
• September alfalfa hay harvest possible when moisture
is sufficient.

39. Mean oat yield, 2006-2016
Rotation system
Yield, bu/acre
@ 14% moisture
3-year, oat with red clover 93 ± 3.2
4-year, oat with alfalfa 98 ± 3.3
p = 0.0011
Average test weight: 35 lb/bu
Range: 33 to 38 lb/bu

40. Red clover growing in oat stubble

41. Sustainable agriculture
“Sustainable agriculture is the production of food, fiber, and
fuel using farming techniques that protect the environment,
public health, human communities, and animal welfare. This
form of agriculture enables us to produce a sufficient amount of
healthful food now without compromising the ability of future
generations to do the same.”
Seeding-year red clover

42. Second-year alfalfa yield
4.1 ± 0.14 tons/acre, mean ± SE

43. Average Nitrogen Content of Legumes
in October, 2006-2013
Shoots Roots (to 12”) Total
lb N/acre
Red clover (1st year) 112 43 155
Alfalfa (2nd year) 47 74 121
Average N content of composted manure
applied at 7 tons/acre: 101 lbs N/acre

44. Mean annual mineral N fertilizer
and herbicide use, 2006-2016
N fertilizer Herbicides
Rotation 2-year 3-year 4-year 2-year 3-year 4-year
lb N/acre lb a.i./acre
Corn 152 29 24 1.18 0.06 0.06
Soybean 2 2 2 1.45 0.10 0.10
Oat -- 2 2 -- 0 0
Alfalfa -- -- 2 -- -- 0
Rotation av. 77 11 7 1.32 0.05 0.04
Reduction -86% -91% -96% -97%

45. Mean yields, 2006-2016
Crop 2-year 3-year 4-year
Corn (bu/acre) 192 b 198 a 201 a
Soybean (bu/acre) 47 c 53 b 56 a
Oat (bu/acre) --- 93 b 98 a
Alfalfa (tons/acre) --- --- 4.1
Sources: Liebman et al. 2008; Davis et al. 2012;
Hunt et al. 2017

46. Mean weed biomass in 2006-2016 was low in the
corn and soybean phases of each system. Weed
growth was greater in oat and alfalfa phases.
Crop phase
2-year:
Corn-Soybean
3-year:
Corn-Soybean-
Oat/Red Clover
4-year:
Corn-Soybean-
Oat/Alfalfa-
Alfalfa
lb/acre
Corn 2 b 13 a 8 ab
Soybean 3 b 18 a 7 b
Oat/legume --- 68 a 64 a
Alfalfa --- --- 52
Within rows, means followed by different letters are significantly different.

47. SDS incidence SDS severity
Large reduction in soybean
sudden death syndrome in longer rotations
Leandro et al. (in press)

48. Estimated Sheet and Rill Erosion (RUSLE2)
Tons per acre per year
2-year rotation: 1.18
3-year rotation: 1.00 (-15%)
4-year rotation: 0.78 (-34%)

49. Labor and economics, 2008-2016
Rotation
2-year 3-year 4-year
Labor inputs (hr/acre) 0.7 c 1.2 b 1.4 a
Gross returns ($/acre) 688 a 610 b 638 b
Costs of production (with
labor, but not land, $/acre)
353 a 253 c 277 b
Profits (returns to land and
management, $/acre)
335 a 357 a 361 a
Diversity  greater labor requirements, lower gross
returns, lower costs, similar profits
Hunt et al. 2017 and unpublished data

50. Crop 2-year 3-year 4-year
Corn (bu/acre) 192 b 198 a 201 a
Soybean (bu/acre) 47 c 53 b 56 a
Oat (bu/acre) --- 93 b 98 a
Alfalfa (tons/acre) --- --- 4.1
Mean Yields, 2006-2016
Sources: Liebman et al. 2008; Davis et al. 2012; Hunt et al. 2017.

51. Mean annual mineral N fertilizer use,
2006-2016
Rotation 2-year 3-year 4-year
lb N/acre
Corn 152 29 24
Soybean 2 2 2
Oat -- 2 2
Alfalfa -- -- 2
Rotation average 77 11 7
Reduction -86% -91%

53. Diversified rotations had higher corn yields

54. 2-yr vs. 3-yr and 4-yr: p=0.0069; average increase of 4%
3-yr vs. 4-yr: p=0.6871
191
198 199
Hunt et al. (2017)

55. • Caused by a soilborne fungus - Fusarium
virguliforme
• Root infection causes root rot and poor
root vigor
• Leaf symptoms caused by fungal toxins
moved from roots to leaves
• Disease favored by cool, wet weather
• Yield losses can be severe
Sudden Death Syndrome

56. Diversified rotations had higher soybean yields

57. 2-yr vs. 3-yr and 4-yr: p<0.0001; average increase of 19%
3-yr vs. 4-yr: p=0.1408
47
55
57
Hunt et al. (2017)

58. Environmental indicators

59. Estimated Sheet and Rill Erosion (RUSLE2)
Tons per acre per year
2-year rotation: 1.18
3-year rotation: 0.92 (-22%)
4-year rotation: 0.71 (-40%)

60. Hunt et al. (2017)
Freshwater ecotoxicological potential of
herbicides, 2008-2016, USEtox model

61. Input costs were taken from ISU Extension’s annual report “Costs
of Crop Production in Iowa,” and from local businesses.
Machinery operation and labor costs were based on field notes
and ISU’s “Estimating field capacity of farm machines.”
Grain and hay prices were taken from marketing year averages
provided by the Iowa office of the USDA National Agricultural
Statistics Services. Subsidy payments and insurance pay-outs
were not included in revenue figures.
Manure was assumed to be generated by on-farm or near-by
livestock and without cost for the material, but with labor and
machinery costs for spreading.
Analyses were conducted for 2008-2016 data.
Economic Analyses
Cost and Price Assumptions

62. Economic performance, 2008-2016
Rotation system
2-year 3-year 4-year
Gross returns ($/acre) 688 a 618 b 642 ab
Costs of production (including
labor, but not land, $/acre)
353 a 269 b 289 b
Profits (returns to land and
management, $/acre)
335 a 349 a 353 a
Diversity  lower gross returns, lower costs,
similar profits
Hunt et al. (2017) and
A. Johanns, unpublished data