Field preparation, crop rotations, 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
• 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 & Disease
with Crop RotationDisease 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 cropExamples– 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 PotatoesGrain Grain PotatoesGrain Sugar beets Grain PotatoesGrain 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
Purposes
●Same as rotation: tilth, nutrition, water availability, aeration, pest control
●Plus:●Improved erosion control
Radish green manure Grain rotation
Green Manures
Types
●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
Alfalfa
Sudangrass
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
Topography
●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
Purposes
●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
Tools
●Moldboard plow●Chisel plow●Disk harrow●Roller packer●Bedding tools