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eturn to table of contents CORN MANAGEMENT IN HIGH pH SOILS by Nanticha Lutt, Agronomy Sciences Intern, Sandy Endicott, Senior Agronomy Manager, and Dan Berning, Technical Services Manager SUMMARY • Management of high soil pH is necessary to grow healthy corn as soil pH affects many processes necessary for crop growth and yield. • All micronutrients, with the exception of molybdenum, decrease in availability as the pH increases above 7.5 in the soil. • High pH soil conditions can restrict corn’s use of iron, resulting in iron chlorosis. • Corn is highly sensitive to zinc. There is a high probability that the crop will respond positively to applied zinc in the case of low soil zinc availability or if the soil has a pH greater than 7.3. • At soil pH levels from 7.2 to 8.5, phosphorus becomes unavailable to plants because it fixes as insoluble calcium phosphates. 76

eturn to table of contents INTRODUCTION Soil pH is a measure of the relative acidity or alkalinity of the soil solution and is expressed on a 14-point scale. Soil acidity increases as pH drops below seven (neutral pH), and soil alkalinity increases as pH increases above seven. Alkaline soils may be naturally occurring or can be caused by over-liming or by using high pH irrigation water in arid areas. Management of high soil pH is necessary to grow healthy corn as soil pH affects many physical, chemical, and biological reactions necessary for crop survival, growth, and yield. MICRONUTRIENT RELATIONSHIP TO SOIL PH Plants require 16 essential elements for growth and development. Seven are classified as micronutrients because they are used in very small amounts. For most, corn crop uptake is less than one pound per acre (1.1 kilogram/hectare) per year (Table 1). Natural inputs of chlorine come mainly from weather and other physical processes. Micronutrient availability can be severely limited by soil pH and result in poor corn growth. Table 1. Estimates of micronutrient uptake in corn. Micronutrient 200 bu Corn (lbs/acre) 12.5 mt/ha (kg/ha) Iron 2.4 2.7 Manganese 0.4 0.4 Zinc 0.4 0.4 Boron 0.2 0.2 Copper 0.1 0.1 Iron Manganese Boron Nitrogen Copper and Zinc Phosphorus 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 pH Potassium Sulfur Calcium Magnesium Molybdenum Figure 1. Relative availability of plant nutrients by soil pH (Truog, 1946). DIAGNOSIS OF MICRONUTRIENT PROBLEMS Micronutrient deficiencies generally have an uneven distribution in fields due to management history and natural variation in soils, and visual symptoms of micronutrient deficiencies often occur too late for effective corrective action. Soil tests for pH level can be useful for accurately monitoring problems and are recommended in seeking management solutions. Application of micronutrient fertilizers can also be restricted to deficient areas in order to minimize the risk of exposing plants to an excess of nutrients, which could lead to plant damage (Wortmann et al., 2013). Molybdenum 0.01 0.01 Adapted from: Role of Micronutrients in Efficient Crop Production, D.B. Mengel, Purdue University AY-239. All micronutrients, with the exception of molybdenum, decrease in availability as the pH increases above 7.5 in the soil (Figure 1). Higher pH can limit the solubility of many nutrients and, as a result, these micronutrients are precipitated as solid materials that the plant cannot use. For example, the solubility of iron, a limiting micronutrient for growth, is high at low pH but drops drastically at pH values above 7.5, creating an iron-deficient environment unable to support optimum plant growth. These conditions occur often in calcareous soils, which are highly alkaline (pH > 7) due to the presence of excess calcium carbonate. Sulphuric Acid Battery Acid Stomach Acid Coca Cola Coffee Milk Figure 2. Corn plants exhibiting yellow striped leaves from micronutrient deficiency next to corn plants with no symptoms. Hard Milk of Washing Lye Water Magnesia Soda Solution Very Strong Strong Moderate Slight Slight Moderate Strong Very Strong 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acid Neutral Base/Alkaline Figure 3. Normal soil pH for plant growth ranges from 4 - 10.5. Normal Soil pH for Plant Growth 77