Crop Rotations

Acknowledgment: Thanks to Mathew Struthers, former Crop Extension Specialist, Saskatchewan Ministry of Agriculture, Moose Jaw.
Institution: SASKATCHEWAN POLYTECHNIC

Definition: The act of growing different crop types on the same area of land.
Factors: The types of crops chosen for rotation are heavily influenced by: - Economic constraints - Management constraints
Example Crops Used in Rotation: - Wheat - Canola - Winter Wheat - Peas

Diversity Importance: The best agronomic situation is characterized by the greatest diversity of crop life histories.
Life Cycles Available for Cropping on Prairies: - Summer Annual Grain Crops: - Normal crops are planted in spring and harvested in fall (e.g., Canola, Wheat, Pea). - Winter Annual Grain Crops: - Planted in early fall (late August or early September), overwintering in vegetative state to be harvested in late summer or early fall (e.g., Winter Wheat, Fall Rye). - Biennial Green Manure or Forage Crops: - Plant in spring (often with companion crops), grows and overwinters, flowering next spring/summer (e.g., Sweet Clover, Red Clover – grown with Oat in first year). - Perennial Forage Crops: - Planted in spring (often with companion crops), lives for several years, with productivity highest in mid-life (e.g., Alfalfa, Brome Grass).

Assessment Factors: - Rooting depth: Shallow vs. deep - Moisture use efficiency - Soil texture: Heavy vs. fine

Guidance: Length of active growing season is the best overall guide to the relative amount of soil water depletion.
Indicators: - Rooting depth of crops also impacts depletion.
Table of Water Depletion:
  - Sunflower: Heavy department, Long, Deep   - Corn: Heavy, Long, Moderate Deep   - Soybean: Moderate Heavy, Moderate Long, Moderate Shallow
  - Spring Wheat: Medium to Moderate Light, Medium Heavy to Moderate Light, Short   - Canola: Medium, Moderate, Medium but Variable, Short   - Dry Pea: Moderate, Heavy, Medium, Shallow
  - Wheat: Data derived from a Phase II crop sequence experiment.
Source: Diversifying Cropping Systems Enhances Productivity, Stability and Nitrogen Use Efficiency.

Leguminous Crops: - Nitrogen fixation by legumes available for subsequent crops increases yield and protein while decreasing fertilizer requirements. - Forage legumes and green manure provide the most fixed nitrogen. - More crop residue input into the soil (green manure): Alfalfa and sweet clover produce the most biomass.

Differential nitrogen uptake abilities of crops depend on rooting depth and structure.
Deep-rooting crops can recover leached $ext{NO}_3$ , while horizontal root growth captures immobile nutrients.

Plant N Consumption (lb/ac): - Data indicating % of total nitrogen requirements fixed from various legumes including Alfalfa, Faba bean, Sweet clover, Field Pea, Lentil, Chickpea, Dry Bean (measured biochemically).

Table 6: Nitrogen and Phosphorus uptake ( ext{P}_2 ext{O}_5)
- Details various Saskatchewan crops based on yield and corresponding nitrogen/phosphorus uptake. - Variables include: - Crop Yield/A - Grain and Straw Yield - Total Nitrogen and Phosphorus uptake per acre.
Source: Nutrient Uptake and Removal by Field Crops - Western Canada; Canadian Fertilizer Institute.

Importance of Crop Rotation: Primary reason for implementing crop rotation is to reduce severity of soil or residue-borne diseases. - Diseases sources include; - Wind and water-borne (e.g., rusts) - Seed-borne (e.g., smuts) - Insect-borne (e.g., aster yellows)
Mechanism: Infected crop residue serves as a substantial source of inoculum, thereby breaking disease life cycles (such as black leg in canola).
Suggested Practices: - Utilize both susceptible and non-susceptible crops. - Extend intervals between planting susceptible crops for multiple years to aid in residue decomposition. - Assess risks based on severity of infestation and consider growing resistant varieties.

Table 1: Overview of Important Diseases of Saskatchewan Crops.
- A list of diseases impacting crops such as Field peas, Pulses, Cereals, and Oilseeds with specific implications for economic importance based on color coding in the chart.

Weed Control Challenges: Crop rotation alone may not effectively eliminate weeds. - Certain crops with similar life histories favor weeds with parallel life cycles.
Weed Management Strategy: Rotation of crops with different life cycles can help mitigate weed proliferation. - Example rotation combination: Alfalfa (3 years), Spring Wheat, Canola, Winter Wheat, Peas. - Different weed types adapt based on their lifecycle, e.g., perennial weeds flourish alongside perennial crops.
Herbicide Selection: Different herbicide groups are linked with specific crop types.
- This allows for a rotation of applications through changes in crop types.

Recommendations: - Employ crops sown at different times of the year. - Consider potentially allelopathic crops which chemically suppress weed growth (examples include barley, oat, fall rye, buckwheat). - Alternate planting of grass and broadleaf crops. - Avoid planting 2 non-competitive crops in a row, such as lentil and chickpea. - Regularly rotate herbicide groups to prevent resistance. - Be cautious of sensitive crops following application of residual herbicides.

Insect Control Limitations: Difficult to manage with crop rotation due to insect mobility and generalists.
Some insects show limited mobility and respond positively to cropping changes (e.g., sunflower beetle, cutworms).

Narrow rotations contribute to herbicide resistance, often resulting from the overuse of one mode of action.
Breakdown Requirements: - Time - Heat - Moisture
Herbicides need to decompose effectively to reduce residual impact.

Includes specified numbers of cropping seasons before re-planting following herbicide application.
Listing indicates which crops can be planted after application, with exceptions noted for time in days (indicated with “d”) or months (“mths”).

Economics: The selected crop must be financially viable or profitable.
Risk: Different crops present varying degrees of yield variability and nutrient demand.
Labor Availability: Some cropping systems may require more labor than others.
Farm Equipment: Availability or capability of farmers’ equipment for specific crops.

Cultivar Impact: Each crop has a set of recommended previous crops based on potential issues such as Fusarium Head Blight (FHB), admixtures, and residual herbicide considerations.
Crop Recommendations: Include various options with suggested indicators for nitrogen benefits and potential crop health considerations (e.g., clubroot, sclerotinia).

Soil Fertility and Crop Rotation Planning | Crop Guides and Publications | Government of Saskatchewan.