Crop Rotations on Organic Farms

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Table 1. Effective root zone depth of key crops calculated in inchesField <strong>Crop</strong>sBarley, 24Corn (Field), 24Cotton, 24Flax, 24Oats, 24Peanuts, 24Rye, 24Sorghum, 24Soybeans, 24Sunflower, 24Tobacco, 18Wheat, 24Forage <strong>Crop</strong>sAlfalfa, 24Bluegrass, 18Bromegrass, 24Ladino Clover, 18Orchardgrass, 24Red & Sweet Clovers,24Sudan Grass, 24Ryegrass, 24Bermuda Grass, 18Tall Fescue, 18Vegetable <strong>Crop</strong>sAsparagus, 24Beets, 12Broccoli, 12Cabbage, 12Cantaloupes, 18Carrots, 12Cauliflower, 12Celery, 12Corn (sweet), 24Cucumbers, 18Kale, 18Lettuce, 6Lima Beans, 18Onions (bunch), 6Onions (dry),12Peas, 18Peppers, 18Potatoes, 18Radish, 6Snap Beans, 18Spinach, 6Squash, 18Tomatoes, 18Watermelons, 24Fruit <strong>Crop</strong>sApples, 24Blueberries, 18Cane Fruits & Grapes,18Peaches, 18Pears, 18Strawberries, 6TurfAthletic Fields (in activeuse), 6Athletic Field (not inactive use), 12Golf Greens/Fairways, 6Grass Sod (beingestablished or preparedfor immediate sale), 6Grass Sod (lawn andsod being heldfor sale), 12FlowersAnnual Flowers, 6Ericaceous OrnamentalPlants (Azalea, etc.), 12Gladioli/Peonies/Irises,12Other Bulb or CormPlants, 12Nursery PlantsBedded Plants (afterpropagation). 6Finished LandscapePlants,(ready for sale),18 to 24Ground Cover Plants(vinca, ivy, etc.), 6Lining-out Plants, 12Perennial Ornamentals,24Trees, Shrubs (conifersand flowering shrubs),24Root depth was based on these factors:1. The depth of soil to which most of the total root system has developed when the marketable part ofthe crop is being produced or when the loss of water from turf and ornamental plants is greatest.2. Research and experience regarding the overall water needs of each crop for maximum quality as wellas yield or growth.3. The kind of soil in which some crops are grown. The depth of irrigation while the crop is developing itsroot system should be determined by the actual root depth at the time of irrigation.Data adapted from: Soil Moisture Sensors for Irrigation Management, Bulletin 312, University of MarylandCooperative Extension Service, 1984; Evapotranspiration and Irrigation Water Requirements, ASCE Manualon Engineering Practice, No. 70. Disclaimer: Commercial products are named in this publication forinformational purposes only. The authors, Virginia Cooperative Extension, and Virginia PolytechnicInstitute and State University do not endorse these products specifically and do not intend discriminationagainst other products that are not mentioned but which might also be suitable.Organic Production—<strong>Crop</strong> <strong>Rotations</strong> on Organic Farms 8
Versatility is a Plus for Organic Farmers• Organic vegetable farmers have ampleopportunities to change their rotationplans even in mid-season, for example,as a response to insufficient nitrogenfrom green manures. They can choosefrom a diversity of vegetable crops thathave widely ranging nutrientrequirements. So, rotations can bequickly altered to fit the situation.• Many vegetable crops, such as lettuce,remain in the field for a relatively shortperiod, thus allowing for multiplecroppings.• Producing two or three crops in oneseason may offset the costs associatedwith leaving a field out of productionevery third or fourth year for“rebuilding.”• The patchwork nature of many small- tomedium-sized market vegetable farms,containing many small fields, allowsfarmers to give individual attention tothe particular fertility or physical needsof each field.Source: Sarrantonio, 1992CROP ROTATIONS AND PESTMANAGEMENTConsider the sheer abundance of insects,pathogens, weeds, and plant diseases, andyou will realize the critical role of croprotations in reducing damage by these pestson organic farms. Farmers who implementa good crop sequence must consider twothings at once:• How one crop can benefit from the cropthat precedes it.• How any pest problems these cropsshare can be addressed.Because organic farmers cannot useconventional agricultural chemicals tomanage crop pests and must rely largely oncultural strategies, they must have a betterunderstanding than most farmers abouthow crop pests live and function. Basically,they must outwit these pests as theyemploy many kinds of strategies tocomplement crop rotations.Learning Pest HistoriesUnderstanding the natural history of a pestis extremely important for determining thesequence of crops in a rotation. Manyinsects and diseases attack more than onefamily of plants, and rotating into adifferent family may do little to reducepathogen potential or insect pressure if thesubsequent crop is also a host plant. Forexample, southern blight, Sclerotium rolfsii,is a pathogen that attacks most vegetablecrops, regardless of family, genus, orspecies. If a field has a history of problemswith this pathogen, managers may have toinclude a row crop in the rotation—forexample, corn or some other grass, hay, ora pasture crop for two or three years.Controlling Soilborne DiseasesOrganic farmers also must know about thesoilborne pathogens that build up when asoil is sown with the same crop or family ofcrops every year.<strong>Crop</strong> Families. Generally, crops in thesame family should not follow one anotherin the field. For instance, cantaloupesshould not follow cucumbers. A cucumbermelon-squashrotation obviously invitesdisease problems. At a minimum, cropsfrom a particular family should beseparated by at least two years of crops fromother families. For example, a rotation ofOrganic Production—<strong>Crop</strong> <strong>Rotations</strong> on Organic Farms 9
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Crop Rotations on Organic Farms

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