Crop rotation A Lecture By Mr Allah Dad Khan Visiting Professor the University of Agriculture Peshawar KPK

3. Crop Rotation
A Lecture By
Mr. Allah Dad Khan

4. Crop rotation
 Crop rotation refers to the practice of growing different types of crops (or
none at all) in the same area over a sequence of seasons. Historians believe
farmers in the Middle East practicedcrop rotation as early as 6,000 B.C.,
although they didn’t fully understand the science behind it

5. What is Crop Rotation?
 The simplest rule of crop rotation is not to grow the same thing in the same
place two years running. In fact, the larger the gap between a crop occupying
the same piece of ground the better. Some pests may be present at high
levels initially but a gap of three or four years will see their numbers fall to
acceptable levels without a host to sustain them.
 There are many different systems for rotating crops, some fairly crude and
some quite complex, designed to ensure that following crops utilise nutrients
left by previous crops. The simplest is a three year crop rotation but a four
year crop rotation plan or. as I use, a five year crop rotation may suit you
better. I have seen eight and ten year plans but these are probably too
complex for gardeners

6. Who Invented Crop Rotation and When?
 The concept of crop rotation goes into prehistory so answering the
question of who invented crop rotation and when is not easy. Early crop
rotation methods were mentioned in Roman literature, and from the
Middle Ages to the 18th Century a three year rotation was practiced by
farmers including a fallow year

7. Principles of Crop Rotation
 The first principle of any crop rotation is to have the largest possible gap
between potatoes occupying the same piece of ground. The same applies
for brassicas, the cabbage family.
 Keep lime away from potatoes because it increases the chances of them
getting scab. Conversely, brassicas like a limey soil. So potatoes should be
planted as far away from the application of lime as possible and brassicas can
go in to soil that has been limed.
 Root crops such as carrots and parsnips do not want soil that has been
manured the previous autumn. It will cause them to fork and split.
 Where possible, keep plants of the same family together as their
requirements will be similar

8. Advantages of crop rotation
 Prevents soil depletion
 Maintains soil fertility
 Reduces soil erosion
 Controls insect/mite pests. Crop rotation as a means to control to insect pests
is most effective when the pests are present before the crop is planted have
no wide range of host crops; attack only annual/biennial crops; and do not
have the ability to fly from one field to another.
 Reduces reliance on synthetic chemicals
 Reduces the pests' build-up
 Prevents diseases
 Helps control weeds

9. Why Rotate Crops?
 Effective crop rotations are a foundation of organic cropping systems. Organic farmers recognize
that crop rotation is necessary to maintain field productivity. Expert farmers design their
rotations to (1) earn income and (2) increase soil quality or build “soil capital” (sidebar 2.1).
Crop rotation and a crop rotation plan and records are required for organic certification of a
field or farm

11. Why follow Crop Rotation?
 If you grow the same crop in the same place year after year you will get a
build up of pests and diseases specific to that crop. Different crops take
different levels of nutrients from the soil and inevitably these become
unbalanced, exhausting one nutrient but leaving a lot of another. This is
often referred to as a 'sick soil'. Even the addition of fertilizers is unlikely
to help since it is likely the trace elements and micro-nutrients are
depleted in the same way.

12. Why Rotate?
 • Soil quality Crop rotation practices such as manuring, composting, cover
cropping, green manuring and short pasturing cycles improve soil quality by
maintaining or increasing soil organic matter content. Organic matter serves
as the primary food source for soil microorganisms. These organisms provide
many benefits, including holding the soil particles together, releasing minerals
for plant uptake, enhancing the downward movement of water and air, and
providing pathways for root growth. Rotations including crops with a variety
of rooting depths make use of water and nutrients throughout the soil, aid in
loosening compacted soil and increase topsoil over time.

13. Fertility
 Fertility Well-planned rotation schedules take into account the preceding
year’s crops, ensuring that nutrients are available for crops grown the
following season.
 It is important to consider the nutrient needs of each crop to ensure they will
be met. The addition of leguminous crops in a rotation can provide nitrogen
for following crops. Including crops with a variety of rooting depths allows
crops to retrieve water and nutrients not accessed by those grown in previous
rotations. Some plants are also effective at making nutrients more available
by using less soluble forms, making them accessible for later crops.

14. Pest Management
 Pest management Pests are most easily kept in balance when different crops
are grown over a number of years. Rotate susceptible crops at intervals to
inhibit the buildup of their specific pest organisms. Rotation length should be
based on the amount of time soil-borne pathogens remain viable in the field.
A four-year rotation using crops not susceptible to the same pathogens will
generally minimize problems from soil-borne pathogens, with some
exceptions (Table 1). Two years is considered enough time to reduce the
incidence of foliar diseases.

15. Legumes
 Legumes Legumes are an important addition to a crop rotation plan because
they fix atmospheric nitrogen, which can be used as a replacement or
supplement for inorganic nitrogen fertilizer. The total N contribution varies
among species, but 50-200 lbs N/acre can be expected from a good legume
cover or cash crop stand. Unlike highly soluble nitrogen fertilizers with a
significant potential to leach, N supplied by legume

16. Cover Crops
 Cover crops and green manures Cover crops are also an important component
of a crop rotation plan and should be utilized when fields are not being used
for production. Cover crops and green manures are those crops grown
specifically for the benefits they provide. They may be incorporated into the
soil or left as a residue on the soil surface. Their benefits include increased
organic matter, improved soil structure, enhanced drought tolerance,
increased nutrient availability for plants, protection against soil erosion,
weed suppression, penetration of compacted subsoils and nutrient cycling.

17. Crop Families
 Crop families Crops within the same family are generally susceptible to the
same insect pests and diseases. A four-year rotation using crops not
susceptible to the same pathogens will generally minimize problems from soil-
borne pathogens, with some exceptions (Table 1). Two years is considered
enough time to reduce the incidence of foliar diseases and insect pests. When
planning a rotation, it is often helpful to map out where the crop families
listed below will be located and how much of each will be planted: Poaceae:
Corn Alliaceae: Onion, garlic, shallot, leeks Chenopodiaceae: Beet, chard,
spinach Cucurbitaceae: Winter and summer squash, cucumber, melon,
pumpkin Brassicaceae: Rutabaga, kale, broccoli, cauliflower, cabbage,
Brussels sprouts, radish, mustard, turnip Fabaceae: Pea, bean Apiaceae:
Carrot, parsley, celery, parsnip Solanaceae: Potato, tomato, pepper, eggplant
Asteraceae: Lettuce Convolvulaceae: Sweet potato Malvaceae: Okra*

18. Compatibility
 It is important to consider crop compatibility when planning a rotation. Some
crops may have beneficial interactions and enhance yield, while others may
have detrimental effects to subsequent crops. For example, many crops
following the cabbage family may have lower yields. Sweet corn is a good
selection to follow the cabbage family because it shows no yield decline.
Potatoes are a good crop to follow sweet corn because research has shown
sweet corn to be one of the preceding crops that most benefit the yield of
potatoes.

19. Increased Profitability
 Some forage legumes have the additional benefit of providing multiple
marketing options. Alfalfa, for example, can be fed to livestock as haylage,
sold as dry hay, or harvested for seed production. Also, the increased organic
matter and availability of nutrients that cover crops can provide create the
potential for healthier and more productive main crops under a wider range
of conditions.

20. Decreased Weed Pressure
 Field tillage, cultivation, and residue management practices all impact the
types and density density of weeds that are present present in a field. When
these practices are performed at the same time each year, certain weed
species are favored, become established, and are increasingly difficult to
control. Consider an example of a six year rotation for corn-belt organic
grains. Corn – beans – corn – small grain – hay – hay. Perennial weed pressure
can be reduced during the first three years of the rotation when annual cash
crops are being aggressively cultivated. Annual weed pressure is reduced by
competition from the hay crop and from the repeated cutting of the hay.
Adding a cereal rye cover crop following the second year of hay to this
rotation might further improve weed management through the allelopathic
qualities of the rye plowdown

21. Other Benefits
 Biodiversity of crops and wildlife
 Reduced impact of other pests such as insects and pathogens
 Distributed economic risk
 Distributed workload Improved on-farm resource utilization
 Decreased negative environmental impact

22. How long should the rotation be?
 The longer the rotation the better, but the usual length is 4 years. This means
that crops return to their original site after 4 years. If the soil is already
infected with persistent problems such as eelworm or clubroot, try to extend
the rotation of susceptible crops even further.

23. There are a few simple rules for crop
rotation:
 Don’t follow tomato, peppers or eggplant with potatoes, or each other.
 Allow 3 years before replanting the same group in any given bed.
 Onions may be planted throughout all groups.
 Beets, carrots and radishes may be planted among any group, and replanted
as early crops are removed.
 Don’t forget to interplant with companion plants to minimize pesticide use.
See the Companion Plants handout for some ideas on this practice.
 Keep good notes so you can duplicate successes.

24. Beneficial Plants to Include in Rotations
 Some plants suppress pathogens in addition to being unsuitable hosts. These
include some cover and green manure crops, as well as cash crops. Including
diseasesuppressive species in a rotation sometimes reduces the time needed
before a particular cash crop can again be produced successfully. Examples
include some legumes and crucifers. These plants suppress pathogens by
stimulating beneficial organisms in the soil and by producing toxic chemicals.
The specific mechanisms involved appear to vary with the crop and the
pathogen. Depending on the mechanism, the beneficial effect can disappear
shortly after incorporation or last for years

25. Some Diseases That Can Be Managed
with Crop Rotation
 Bacterial spot of pepper and tomato. The bacterium causing spot
(Xanthomonas campestris pv. vesicatoria) can be effectively controlled with
rotation because this pathogen cannot survive in the soil once diseased plant
debris decomposes. A minimum of two years without a host crop is
recommended.
 Bacterial speck of tomato. This disease is more difficult to control with
rotation than bacterial spot because the pathogen (Pseudomonas syringae pv.
tomato) can survive on roots and leaves of taxonomically diverse weeds.
Therefore, success requires good control of weeds and volunteer tomatoes
during the rotation period. A study on survival of this bacterium showed that
it lived up to 30 weeks on crop debris but less than 30 days just in soil.