Crop Rotations on Organic Farms

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