How the pattern of crop rotation helps in maintaing the soil fertility is explained here.

2. Introduction

3. Introduction
 Soil organic matter and clay particles hold large stores of plant nutrients.
 These reservoirs, however, are not all available to the crop.
 Crop rotation manages soil organic matter and nutrient availability by------
- incorporating different crop residues,
- cycling among crops with different nutrient needs,
- using cover crops, and
- adding soil amendments.

4. Introduction
• Most crops deplete soil nutrients during their growth cycle.
• Some of these nutrients leave the farm as harvested products, and the rest return
to the soil as crop residues.
• The nutrients in residues may or may not be available to the next crop.
• Crop roots and residues improve soil fertility by
- stimulating soil microbial communities and
- improving soil aggregation.

5. Improves soil physical properties
• This improved soil physical environment facilitates
- water infiltration,
- water holding,
- aeration, and
- ultimately, root growth and plant nutrient foraging.
• Understanding the basics of how nutrients are added to and released from soil
organic matter will help in choosing crop sequences and amendments to
optimize crop fertility.
• To effectively plan organic crop rotations to meet
crop nutrient needs, several factors should be
considered.

6. Major approaches
1. Legume crops
- capture atmospheric nitrogen and ‘fix’ it into forms available to plants
- can be used in rotations to meet the needs of nitrogen demanding crops.
2. Cover crops used after cash crop
- capture surplus plant - available nutrients and conserve these for following
crops.
3. Other amendments
- such as fertilizers and manures can supplement nutrients at targeted times
during the rotation.

7. Classical Example
An example of a successful rotation
Generate residues in the rotation
Generate cash income
Adds soil fertility

8. Crop Rotation with regard to Soil Fertility
 Crop Rotation plays a vital role in managing soil fertility in the following aspects:
1. Soil erosion
2. Soil compaction
3. Infiltration
4. Soil crusting
5. Nutrient loss or imbalance
6. Pesticide carry over
7. Soil organic matter
8. Biological activity

9. Crop Rotation and Soil Erosion
 Vegetative cover has a major effect on erosion.
 Research shows that fourth year corn, conventionally tilled at high fertility level,
had erosion rates 125 times that of highly productive grass-legume sod.
 Effective erosion control practices:
- Growing cover crops with low residue crops and
- Rotation of high residue crops with low residue crops
• Crop rotations that utilize the land more intensively such as corn, wheat and
soybeans grown in two years produce larger amounts of biomass during the
rotation and are more effective in reducing erosion than a continuous cropping
sequence (Heath et al 1976).

10. Crop Rotation and Deposition of Sediment
• Increase cover from grass and or legume rotations or high residue crops
combined with other conservation practices such as ---
- conservation tillage will reduce upland erosion which in turn,
- reduces sediment from surface runoff and wind.
Soil Aggregation at the Surface
Rotations that promote the increase of organic matter and microbial
activity will increase aggregate stability.
[Caution: If residue is incorporated, with tillage, benefits of increased biomass is
lessened.]

11. Crop Rotation and Soil Compaction
• Monoculture agriculture and tillage weaken soil structural characteristics
increasing susceptibility to compaction (Schnitzer 1991).
• Crop rotations with deep root systems can reduce compaction through the
addition of organic matter and development of channels from decayed roots;
thus improving water movement and aeration.
• Rotations that increase organic matter, microbial activity and aggregation of soil
particles, will also increase porosity and lower bulk density

12. Crop Rotation and Infiltration
• Conservation crop rotation systems that promote an increase in organic matter
and an increase of aggregate stability will maintain or improve the presence of
pores for infiltration (Schnitzer, 1991).
• Decaying roots, especially those of deep rooted crops like alfalfa and safflower,
will leave channels for improved infiltration.
• Other conservation practices may be needed in crop rotations such as crop
residue management to ensure surface protection and improve infiltration.
[Caution: Macropores can result in an increase of leaching of highly soluble
pesticides if a heavy rain occurs within a few hours after application.]

13. Crop Rotation and Soil Crusting
• If residues are left on the soil surface and crop rotations are included with high
residue crops,
- the increase in organic matter,
- improved infiltration, and
- increased aggregate stability --- will reduce soil crusting.
[Caution: Monoculture and low residue cropping systems with tillage will
increase the decay of organic matter and reduce aggregate stability which often
results in soil crusting]

14. Crop Rotation and Nutrient imbalance
 One of the principles of crop rotation is to precede a nitrogen demanding crop
with a legume crop to provide nitrogen.
 Crop rotations with deeply rooted crops can penetrate to depths of 5 to 6 feet and
‘cycle nutrients’ especially the more soluble nutrients such as nitrates.
 Crop rotations that promote increased biomass provide a slow release of
nutrients to the root zone.

15. Crop Rotation and Pesticide carry over
 Where different crops are grown each year and crop rotations reduce the chance
of pesticide build-up.
 The threat of pest tolerance to insecticides and herbicides are reduced with
rotations (Reeves, 1994).
 Rotations increasing organic matter improve the environment for biological
activity that will increase the breakdown of pesticides.

16. Crop Rotation and Soil Organic Matter
 The amount and type of organic matter is indicative of soil productivity
(Mitchell et al 1996).
 The types of crops grown, the amounts of roots, biomass yield, and efficiency of
harvest, and the management of residues affect soil organic matter (Magdoff,
1993).
 High residue crops in rotation with cover crops and conservation tillage
increase amounts of organic matter compared to conventional tillage and
monoculture.
 It is practically impossible to increase organic matter where mouldboard
ploughing is taking place. (Reicosky et al, 1995).
 Vegetables and other low residue crop rotations will need other practices such as,
cover crops to increase biomass yield.

17. Crop Rotation and Biological Activity
 There is a direct relationship to the amount of residue and the population of soil
microorganisms.
 Research in Oregon showed wheat-fallow systems had only 25% of the
microorganisms found under pasture.
 When rotations are more complex and include rotational crops soil biological
diversity will increase (Magdoff, 1993).
 Soil organisms that are active in the soil, include bacteria, fungi, actinomycetes,
protozoa, yeast, algae, earthworms and insects.
 Numbers of soil organisms in general are proportional to organic matter
concentrations in the upper 15 inches (Schnitzer, 1991).

18. Crop Rotation and Soil Salinity
 Conservation practices along with crop rotations that help control soil salinity
include ---
- reducing summer fallow,
- increasing organic matter,
- use deeply rooted perennial forage crops,
- conservation tillage, and
- plant salt tolerant crops (Eilers et al 1995).
 Effective crop rotations are important for sustaining productivity and conserving
our natural resources.

19. Vegetables – nutrient availability
Ranking of annual vegetables based on nutrient requirements
Low Medium High
Beans, all Brassica greens Broccoli
Beet Cucumber Cabbage
Carrot Eggplant Cauliflower
Herbs Pepper Corn
Peas Pumpkin Lettuce
Radish Spinach, chard Potato
Squash Tomato
Sweet Potato
Watermelon
Winter squash
Note: Vegetables are classified as having low, medium, or high
nutrient requirements. These categories do not account for
differences among varieties.

20. Rooting pattern
Rooting depth and lateral spread of roots for several crops
Crop Estimated rooting depth
(inches)
Lateral rooting
spread (inches)
Oat 60 10
Turnip 60 30
Soybean 80 20
Barley 55 10
Alfalfa 120 5
Pea 35 25
Rye 60 10
Potato 35 15
Sorghum 70 25
Wheat 60 5
Field corn 70 40
Source: Adapted from reference 42: A. A. Hanson, Practical
Handbook of Agricultural Science (Boca Raton, FL: Taylor & Francis
Group, LLC 1990).

21. Cost benefits
How much does it cost:
There is little to no cost to implement this practice.
Financial benefits:
 Reduced fertilizer inputs
 Reduced pesticide inputs

22. Crop Rotation planning considerations
Identify soil erosion, nutrient, and soil health concerns
Soil test (every 1-3 years) for pH, organic matter and
nutrients. Use soil test recommendations to adjust pH
and nutrient levels for optimum crop yields and
quality
Determine nutrient (fertilizer manure or composts)
needs

23. Crop Rotation planning considerations
Choose the crops/varieties to meet the erosion, soil
health, nutrient concerns
Evaluate and modify the crop sequence based on the
identified concerns.
Evaluate cover crop needs
Clean field equipment when moving from one field to
another. Wash with water and/or physically remove
the soil and plant residue from the equipment

24. Practical applications
 Using a map, lay out a rotation for
the crops by year for the length of the
rotation.
 Plan the rotation for the operation to
establish a nearly equal acreage of
each crop each year.
Example 4 year crop rotation:
Corn – Oats – Hay – Hay

25. Crop Rotation maintenance
1. Periodic soil testing (initially every 1-3 years, then later at 3-5 years).
2. Crop and pest scouting.
3. Annually, evaluate cropping sequence for income needs and soil concerns.
4. Calibrate sprayers, planters and fertilizer applicators to:
 Apply the recommended rates.
 Establish uniform distributions
 Provide uniform seeding depths

26. Some tips on Crop Rotation

27. Some tips on Crop Rotation

28. Some tips on Crop Rotation

29. Some tips on Crop Rotation

30. References
Websites :
1. http://www.sare.org/Learning-Center/Books/Crop-Rotation-on-Organic-
Farms/Text-Version/Physical-and-Biological-Processes-In-Crop-
Production/Crop-Rotation-Effects-on-Soil-Fertility-and-Plant-Nutrition
2. http://people.oregonstate.edu/~muirp/sustfert.htm
3. http://soilquality.org/practices/row_crop_rotations.html
Books
1. John L. Havlin, Samuel L. Tisdale, Werner L. Nelson, James D. Beaton, Soil
Fertility and Fertilizers an introduction to nutrient management.