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 Pests with 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 Pests with 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 Rotation Disease and nematode factors: ●Non-host alternate crops ●Rotation duration ●Soil micro-organism dynamics

Nematodes influenced 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.

Diseases influenced by crop rotation ●Verticillium wilt ●Rhizoctonia ●Common scab ●Silver scurf ●Pink rot ●White mold

Minimize Weeds with 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 Nutrients with 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 Health with 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 Management with 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 & Quality with Crop Rotation Consider current crop will influence the next crop Examples –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 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

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 ●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