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Field preparation, crop r otations , and green manures Mark Pavek - WSU. Pre-cropping practices Crop rotation Green manures Field selection Field preparation. Crop Rotation – What and Why?. Same field – different crop each year Common duration: 3-5 years, then repeat

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Field preparation, crop r otations , and green manures Mark Pavek - WSU

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Field preparation, crop rotations, and green manuresMark Pavek - WSU

Pre-cropping practices

  • Crop rotation

  • Green manures

  • Field selection

  • Field preparation

Crop Rotation – What and Why?

  • Same field – different crop each year

    • Common duration: 3-5 years, then repeat

  • To build/maintain healthy soils and productive, profitable crops sustainably for the long-term

Crop Rotation Concept

  • Minimize Pests

    • Insects, nematodes, weeds, mites

  • Minimize Disease

    • Bacteria, viruses, fungi

  • Optimize Available Nutrients

    • Nitrogen, phosphorous, potassium, micros

  • Optimize Soil Health

    • Aeration, tilth, organic matter

  • Facilitate Tillage, Planting, Harvest and Post-harvest Activities and Quality

Minimize Insect & Mite Pestswith Crop Rotation

  • How rotation can help:

    • Remove host crop of insect

    • Proximity to other insect hosts

    • Disrupt insect overwintering in soil via tillage from different cropping practices

Minimize Insect & Mite Pestswith Crop Rotation

Insects/mites influenced by rotation & location:

Colorado potato beetle (overwinters in soil)

Wireworms (flourishes in small grains, clover)

Mites (likes corn, alfalfa, mint, dusty roads)

Leafhopper (specific weeds, proximity to)

Grasshoppers (overwinters in soil)

Seedcorn maggot (corn is its favorite)

Leather jackets (spring incorporated alfalfa)

White grubs

Minimize Nematodes & Diseasewith Crop Rotation

Disease and nematode factors:

  • Non-host alternate crops

  • Rotation duration

  • Soil micro-organism dynamics

Nematodesinfluenced by crop rotation

Crop rotation can be useful in reducing nematode populations

  • Root-knot

    • Alfalfa is not a host

  • Lesion

  • Stubby-root

    Research in the Pacific Northwest has shown that cover crops of rapeseed, mustard, oilseed radish, or sudangrass reduce populations of root knot nematodes when incorporated as green manure.

Diseasesinfluenced by crop rotation

  • Verticillium wilt

  • Rhizoctonia

  • Common scab

  • Silver scurf

  • Pink rot

  • White mold

Minimize Weedswith Crop Rotation

  • Follow “easy to weed” crops with “hard to weed” and visa versa

  • Alternating herbicides each year

    • To prevent herbicide-resistant weeds

    • Certain weeds not controlled by all herbicides

  • Consider volunteer-crop-weeds

  • Consider herbicide carryover

Herbicide Carryover

Optimize Available Nutrientswith Crop Rotation

  • Follow legume forage crops, such as alfalfa, with high nitrogen-demanding crop, like potatoes or corn

  • Grow less nitrogen-demanding crops following crops like potatoes or corn

Optimize Soil Healthwith Crop Rotation

Healthy Soils

  • Good Soil tilth/condition

  • Accumulate Organic Matter

  • Beneficial organisms

  • Lack of erosion

  • Nutrient availability

  • Aeration, lack of compaction

  • pH balanced, not influenced by additives

Soil Health Managementwith Crop Rotation

Soil Tilth, Aeration, Water Availability, Minimal Erosion, Nutrients

Important factors:

  • Accumulation of O.M.

  • Management of residues

  • Choice of crops

  • Tillage traffic

Facilitate Tillage, Planting, Harvest and Post-harvest Activities & Qualitywith Crop Rotation

  • Consider current crop will influence the next crop


    • Corn ears in harvested potatoes

    • Alfalfa roots complicating planting or early season tillage

    • Residue complicating bed or row formation

Corn Residue – cobs can be an issue at a processing plant

A solution might be to chop the stubble into a fine residue prior to tillage

Crop Rotation

Typical Rotations: Eastern Idaho

Grain  Potatoes

Grain  Grain  Potatoes

Grain  Sugar beets  Grain Potatoes

Grain  Alfalfa (2+ yrs)  Grain Potatoes

Crop Rotation

Typical Rotations: Central and Western Idaho, Central Washington

Combinations of grain, beans, peas, sugar beets, onions, and corn in a 5-6 year cycle with potatoes

Beans avoided just prior to potatoes

(white mold/sclerotinia)

Green Manures


  • Same as rotation: tilth, nutrition, water availability, aeration, pest control

  • Plus:

    • Improved erosion control

Radish green manure

Grain rotation

Green Manures


  • Rotation crop green manures (full-season)

  • Interval green manures (between crops)

Green Manures

Potential Disadvantages

  • Reduced income

  • Additional management costs

  • Hosting of pests

  • Additional weed (volunteer) problems

Green Manures

Potential Advantages

  • Improved yield and quality

  • Reduced fertilizer costs

  • Reduced soil-borne pest control costs

Green Manures

Crops for Green Manures:

  • Radish and mustard (interval, fall)

  • Rapeseed (interval, fall)

  • Legumes (full-season or interval)

  • Cereals (full-season or interval, regrowth)

  • Corn (full-season)

  • Sudangrass (full-season)

Oilseed Radish



From Davis et al., 1991

From Davis et al., 1991

Field Selection

Important Factors:

  • Physical properties

  • Irrigation/water availability

  • Chemical properties

  • Topography

  • Cropping history

  • Pest history

Field Selection

Physical properties

  • Course to moderate texture

  • High water infiltration rate

  • Lack of compaction layers

  • Adequate organic matter

Field Selection

Chemical properties

  • pH 6.5-7.5

  • Adequate CEC

  • Low salinity (<1.7 ds/m)

  • Low sodium (sodicity, SAR < 6)

  • Lack of nutrient toxicity

Field Selection


  • Slope <5%

  • Lack of drainage problems

Field Selection

Cropping History

  • Adequate rotation

  • Avoidance of long grass rotations

  • Avoidance of heavy-traffic crops

Field Selection

Pest History

  • Avoid fields with known problems:

    • Nematodes

    • Wireworms

    • Verticillium wilt

    • Volunteer potatoes

    • Nutsedge

Field Preparation

Practices dependent on:

  • Soil type

  • Erosion potential

  • Residue management

  • Energy costs

Field Preparation


  • Incorporate residues

  • Reduce compaction

  • Improve permeability

  • Incorporate fertilizers and pesticides

  • Prepare bed for planting

Field Preparation

  • Prior to freezing temps (fall)

    • Plant green manure, incorp

    • Cross Rip ~ 18 in deep

    • Fumigate if necessary

  • Spring

    • Soil sample, fertilize, incorp

    • Plant

Field Preparation


  • Moldboard plow

  • Chisel plow

  • Disk harrow

  • Roller packer

  • Bedding tools

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