Crop rotation is always a good idea, but on organic farms a sound crop rotation is essential. Options for rescuing crops from disease are limited on organic farms, making disease prevention through good crop rotation more important. Similarly, weed management requires a multiyear approach. Since nutrients for organic crop production come largely through release from organic matter in soil, manure, compost, and cover crops, a crop rotation that maintains regular organic matter inputs and large amounts of active soil organic matter is critical.
To obtain the benefits of a diverse crop rotation and take advantage of specialty markets, organic farmers usual y grow a high diversity of crops. Thus, organic field crop producers commonly grow five to ten crop species, and fresh market vegetable growers may grow thirty or more. However, because of the large variation in acreage among crops and frequent changes in the crop mix due to weather and shifting market demands, planning crop rotations on highly diversified farms is difficult.
Therefore, many organic farmers do not follow any regular rotation plan, but instead place crops on individual fields (or parts of fields) based on the cropping history of the location and its physical and biological characteristics (e.g., drainage, recent organic matter inputs, weed pressure). Skilled organic growers usual y have next year’s cash crops and any intervening cover crops in mind as they make their placement decisions but find that planning further ahead is usual y pointless because longer-term plans are so frequently derailed.
Although precise long-term rotation plans can rarely be followed on farms growing a diverse mix of crops, some experienced organic farmers follow a general repeating scheme in which particular crops are placed by the ad hoc approach described above. For example, some vegetable operations plant cash crops every other year and grow a succession of cover crops in alternate years. Many field crop producers alternate some sequence of corn, soybeans, and small grains with several years of hay on a regular basis, and some vegetable growers similarly alternate a few years in vegetables with two to three years in hay. These rest periods in hay or cover crops build soil structure, al ow time for soilborne diseases and weed seeds to die off, and provide nitrogen for subsequent heavy-feeding crops. Some vegetable growers alternate groups of plant families in a relatively regular sequence, but this general y requires growing cover crops on part of the field in years when groups that require less acreage appear in the sequence. Within all of these generalized rotation schemes, the particular crop occupying a specific location is chosen by the ad hoc process described above. Organizing the choices with a general rotation scheme greatly simplifies the decision-making process.
Dividing the farm into many small, permanently located management units also greatly facilitates effective ad hoc placement of crops onto fields each year. By this means, a precise cropping history of every part of each field is easy to maintain. Moreover, problem spots and particularly productive locations can be easily located for planting with appropriate crops.
—CHARLES MOHLER, CORNELL UNIVERSITy
are helping to increase soil organic matter. Many pro-
Vegetable farmers who grow a large selection of crops
ducers are including sunflower, a deep-rooting crop, in a
find it best to rotate in large blocks, each containing
wheat-corn-sunflower-fallow rotation. Sunflower is also
crops from the same families or having similar produc-
being evaluated in Oregon as part of a wheat cropping
tion schedules or cultural practices. Many farmers are
sequence.
now using cover crops to help “grow their own nitrogen,”
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Building SoilS for Better CropS: SuStainaBle Soil ManageMent