Cultivation, preplanting soil preparation, and other tillage practices are extremely variable and usually specific for each producing region, soil type, crop rotation scheme, erosion control problem, energy cost, and other factors. Since potato tubers are susceptible to bacterial rots which may be enhanced by anaerobic conditions, any practice which renders the soil anaerobic for any period of time should be avoided. Probably the largest factor causing anaerobiosis is overirrigation. The potato requires large amounts of potassium and nitrogen for adequate growth. Phosphorus and other minor elements are generally required in smaller amounts. There is some variation in quantity of nutrients required in various growing regions because of the difference in production potential due to climate, soil types, and disease factors. The molecular form in which the fertilizer nutrients such as nitrogen, phosphorus, or potassium are applied can influence crop growth. Some fertilizer formulations, such as ammonium sulfate, tend to acidify the soil in root zone, thus indirectly affecting plant growth.