potato 5-9-12 CLEAN - Vegetableipmasia.org

ORGANIC POTATO PRODUCTION 4.2 Crop Rotation PlanA careful crop rotation plan is the cornerstone of organiccrop production because it allows the grower to improvesoil quality and proactively manage pests. Althoughgrowing a wide range of crops complicates the crop rotationplanning process, it ensures diversity in crop residues in thesoil, and greater variety of beneficial soil organisms.Individual organic farms vary widely in the crops grown andtheir ultimate goals, but some general rules apply to allorganic farms regarding crop rotation. Rotating individualfields away from crops within the same family is critical andcan help minimize crop-specific disease and non-mobileinsect pests that persist in the soil or overwinter in the fieldor field borders. Pests that are persistent in the soil, have awide host range, or are wind-borne will be difficult tocontrol through crop rotation. Conversely, the more hostspecific, non-mobile, and short-lived a pest is, the greaterthe ability to control it through crop rotation. The amount oftime required for a crop rotation is based on the particularpest and its severity. Some particularly difficult pests mayrequire a period of fallow. See specific recommendations inthe disease and insect sections of this guide (Sections 12, 13,15). Partitioning the farm into management units will helpto organize crop rotations and ensure that all parts of thefarm have sufficient breaks from each type of crop.A well-planned crop rotation is key to weed management.Short season crops such as lettuce and spinach areharvested before many weeds go to seed, whereas viningcucurbits, with their limited cultivation time and longgrowing season, allow weeds to go to seed before harvest.Including short season crops in the rotation will help reduceweed populations provided the field is cleaned up promptlyafter harvest. Other weed reducing rotation strategiesinclude growing mulched crops, competitive cash crops,short-lived cover crops, or crops that are intensivelycultivated. Individual weed species emerge and mature atdifferent times of the year, therefore alternating betweenspring, summer, and fall planted crops helps to interruptweed life cycles.Cash and cover crop sequences should also take intoaccount the nutrient needs of different crops and theresponse of weeds to high nutrient levels. High soilphosphorus and potassium levels can exacerbate problemweed species. A cropping sequence that alternates cropswith high and low nutrient requirements can help keepnutrients in balance. The crop with low nutrientrequirements can help use up nutrients from a previousheavy feeder. A fall planting of a non-legume cover cropwill help hold nitrogen not used by the previous crop. Thisnitrogen is then released when the cover crop isincorporated in the spring. See Section 3: Cover Crops andSection 5: Weeds for more information.Rotating crops that produce abundant organic matter, suchas hay and grain-legume cover crops, with ones thatproduce less, such as vegetables, will help to sustain organicmatter levels and promote good soil tilth (see Section 2: SoilHealth and Section 8: Crop and Soil Nutrient Management).Potatoes generally have a high nutrient requirement (Table4.2.1). Growing a cover crop, preferably one that includes alegume, prior to or after potatoes will help to renew soilnitrogen, improve soil structure, and diversify soil organisms.Including short season crops in the rotation will help toreduce the overall weed population in the field.Table 4.2.1 Crop Nutrient Requirements Nutrient Needs Lower Medium Higher Crop Bean Beet Carrot Herbs Pea Radish Cucumber Eggplant Brassica greens Pepper Pumpkin Spinach Chard Squash Winter squash Broccoli Cabbage Cauliflower Corn Lettuce Potato Tomato From NRAES publication Crop Rotation on Organic Farms: A Planning Manual. Charles L. Mohler and Sue Ellen Johnson, editors (Reference 21). Crop information specific to potatoes Plan at least 2 years between potato crops and relatedcrops, such as tomato and eggplant. See Cornell’sminimum years to avoid specific diseases (Reference 54).Phosphorous and potassium: Many fields with a long historyof potato production have accumulated large amounts ofthese nutrients. Excessive levels of potash can depressspecific gravity, an important factor in harvest quality.Moreover, high phosphorus and potassium levels canexacerbate problem weed species. For example, highphosphorus promotes common purslane and highpotassium promotes dandelion. Removing alfalfa hay fromthe field for several years can reduce phosphorus andpotassium levels.Stem canker and black scurf (Rhizoctonia solani): Reducecanker and black scurf incidence by planting grass andcereal crops in rotation with potato or as green manurecrops before potatoes. Tomato, strawberry, cabbage andBrussels sprout host canker and black scurf and willincrease soil inoculum levels.Common scab (Streptomyces scabies): Use winter grain orforage grass as a green manure before potato or rotate withsoybeans to reduce common scab. Avoid sweet clover as agreen manure before potatoes. Rotate away from commonscab hosts: beets, carrots, parsnip, radish, rutabaga and turnip.White mold (Sclerotinia sclerotiorum): Beans, cabbage andBrussels sprouts host white mold and will increase soilinoculum levels.Wireworms: Plant grains or grasses that are only in the field forpart of the season because wireworm populations can build upin the soil if grasses are grown for an entire season or longer.62012