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Soil Fertility and Nutrient Management 16 Midwest Veg Guide 2022 relevant field trials. Adjust these recommendations according to experience, soil type, cropping history, additions of organic matter, and crop culture system. For example, suppose your vegetable crop is following soybeans, alfalfa, or a grass-legume hay crop. If your soils have more than 3 percent organic matter, you may not need to add any sidedressed N. If your soils that have less than 3 percent organic matter, then half the total N can be applied preplant and the other half sidedressed early in the crop growth cycle. Now suppose your vegetable crop is following corn, rye, oats, wheat, or a previous vegetable crop. There may be no residual soil N available, so the crop may benefit from additional sidedress N. It may be useful to test the soil for nitrate-N shortly before sidedressing to assess whether the crop will benefit from the application. Phosphorus (P) P recommendations for vegetables are based on the soil test value, the type of crop, and estimates of crop removal. On mineral soils, most vegetables will benefit from P fertilization if the soil test is less than 35-40 ppm P using the Bray-Kurtz P1 extraction method. If the soil test on a mineral soil is more than 80 ppm P, then no additional P is recommended for most vegetables. P does not move readily in the soil and applied P easily reacts with soil minerals so that it is unavailable to the plant. That's why P fertilizer is applied in bands near the crop when possible, and starter solutions that are high in P are recommended for transplants. Potassium (K) K recommendations for vegetables are based on the soil test value, the soil CEC, the type of crop, and estimates of crop removal. Vegetables usually benefit from K fertilization if the soil test is: • Less than 85 ppm K in soil with low CEC (4 meq/100 g). • Less than 115 ppm K in soil with medium CEC (16 meq/100 g). The maximum annual K recommendation for most vegetables is 300 pounds of K 2 O per acre. K fertilization is not usually recommended if the soil test is more than 135 ppm K on a soil with low CEC, or more than 165 ppm K on a soil with medium CEC. Calcium (Ca), Magnesium (Mg), Sulfur (S) Calcium (Ca), Magnesium (Mg) and Sulfur (S) are considered secondary macronutrients because plants require them in smaller amounts than N, P, and K. Ca and Mg usually are deficient in acid soils. Adding the appropriate form of lime solves most Ca and Mg deficiency problems (see Soil pH and Adjustment). When Ca is deficient and there is no need to increase soil pH, you may use gypsum (calcium sulfate) as a source of Ca. Similarly, you can add Mg without affecting pH by using Epsom salts (magnesium sulfate, 10 percent Mg), sul-po-mag (11 percent Mg), or finely ground magnesium oxide (e.g., MAGOX, 58 percent Mg). If a soil test shows low Mg (less than 50 ppm in Minnesota or less than 40 ppm in other states), apply Mg at 100 pounds per acre broadcast or 20 pounds per acre in the row. If a soil test shows medium Mg (51-100 ppm in Minnesota or 40-69 ppm in other states) apply Mg at 50 pounds per acre broadcast or 10 pounds per acre in the row. If a soil test shows high Mg, no application is necessary. You can make foliar sprays of Epsom salts at the rate of 10 to 15 pounds in a least 30 gallons per acre to temporarily solve Mg deficiencies during the growing season. If a soil test indicates a need for sulfur, materials such as gypsum (calcium sulfate), Epsom salts (magnesium sulfate), ammonium sulfate, potassium sulfate, or potassium- magnesium sulfate can be used. Make sure to account for the nutrients in addition to sulfur that these materials supply. Micronutrients Micronutrients include boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn). Of these nutrients, those most likely to be lacking in Midwest soils used for vegetable production are B and Mn. Zn may also be a concern in some areas. Manganese (Mn) Mn deficiency is common in some areas. Mn deficiency occurs primarily on lakebed and fine-textured, dark- colored soils with high pH. Cool, wet conditions tend to intensify Mn deficiency. Beans, beets, onions, spinach, and tomatoes have high requirements, but deficiencies also are reported for cucumbers, peppers, and turnips. Apply manganese sulfate at 2 to 4 pounds per 100 gallons per acre to eliminate deficiency problems observed during the growing season. Fungicides containing Mn can also help correct deficiencies. Boron (B) B leaches readily, so responsive crops often need annual applications on sandy loam, loamy sand, sandy, and muck soils. Deficiency symptoms include browning on cauliflower heads, cracked stems on celery, blackheart on beet, and internal browning on turnip.