The pH scale measures the acid to base range from zero to fourteen, with 7.0 as neutral. Values below 7.0 are acidic; those above 7.0 are basic. Soil pH which is either too high or too low can present limitations. Soil with a pH of 6.4 to 7.0 makes major, secondary, and trace elements more available. It also displays less compaction, better drying, and more water absorption and retention than a soil at higher or lower pH levels.

At pH levels of 6.0 and below, potash efficiency can be reduced up to 50%. Raising pH from 6.0 to 6.4 can increase phosphorus efficiency by 48%, nitrogen by 11%, while potash remains unchanged. Inadequate soil pH may lower nutrient availabilities. But, when low pH limits productivity, applications of limestone will correct it. Most soil pH test results show two values: soil pH (or water pH, which is the same) and buffer pH. Buffer pH is related directly to soil C.E.C., and is used to calculate how much agricultural limestone to apply per acre to raise to soil (or water) pH to near neutral. On cash-rented farms or those leased from year to year, granulated or liquid lime may be used as a source of plant food or quick pH adjustment.

When pH is greater than 7.0, fertilizer placement (especially phosphorus and trace elements) is important. Stripping plow down fertilizer and trace elements can show dramatically better results than broadcasting. At high pH levels, banding fertilizer at planting is best. Needed zinc or manganese should also be banded at planting.

Nitrogen is the most essential nutrient for plant growth and development. It interacts closely with application timing, rainfall, temperature, C.E.C., organic matter levels, and specific hybrid needs. Low nitrogen levels results from extended rainfall, leaching, ponding, or insufficient application. The consequence of this deficiency may be low yields, limited growth, and reduced quality. Extended rainfall can cause nitrogen loss through denitrification from all soil types. Heavy clay soils are most vulnerable to low nitrogen rates because they are harder to drain and require more time to dry out. Low nitrogen will force nutrients needed for grain fill to translocate from the plant’s stalk structure, weakening the stalk and leading to lodged corn. Excess nitrogen can cause rot and corn lodging, especially when nitrogen levels are not balanced with other nutrients.

Phosphorus is necessary for fast, vigorous plant growth, because cell division and enlargement require this element. Phosphorus is also crucial to photosynthesis, respiration, early root formation, and energy storage and transfer. Phosphorus concentration is higher in the seed than in any other part of the plant. Therefore, it improves the seed quality of many grain crops. Only a small portion of applied and built-up phosphorus becomes available in a growing season. Organic matter is a primary source of plant-available phosphorus.

Phosphorus and potassium availability is particularly important for early plant growth in cool, damp soils. These soil conditions are likely with early planting and no-till. (Responses to row applications of starter and/or pop up fertilizer containing phosphorus and potassium are most evident in these cases. In areas with a shorter growing season, these applications speed up maturity.) Since phosphorus is most available at pH levels between 6.5 and 7.0, soil pH levels below 6.5 can affect phosphorus availability dramatically.

Phosphorus usually won’t limit yields at levels greater than 25 PPM, provided that pH levels are adjusted. At these levels, however, phosphorus can be a limiting factor because it conflicts with zinc, boron, and nitrogen. Even when ample phosphorus levels show up on a soil test, phosphorus can become unavailable to a plant when it ties up with insoluble compounds at high and low pH levels. If a soil test shows low-to-medium phosphorus levels, stripping plow down can help.

All plants require fairly high concentrations of potassium for normal growth and development. Research has shown approximately 60 enzymes become active only when surrounded by potassium. It’s essential for translocation of sugars and for starch formation, and it serves as a catalyst for chemical reactions. Potassium encourages root growth and helps plants resist disease and insects by strengthening stalks and stems, and building up natural resistance mechanism. It increases grain size and quality, making it essential for high quality forage crops. (When green vegetation, such as silage of hay, is removed, large amounts of potassium are removed, too.)

Potassium is necessary for guard cells’ stomata in the leaf to open and close. This cellular process enables the plant to slow or stop water loss in hot, dry weather. If these guard cells are not formed, leaves roll up, causing the plant’s manufacturing processes to slow—and even stop. A potassium deficiency will most likely occur in sandy, strong weathered, organic or compact soils. Preceding crops, like alfalfa or corn silage, may also remove potassium. Symptoms of a potassium deficiency include yellowing and dying leaf margins (beginning at the tips of the lower leaves). But, since potassium is very mobile within the plant and moves from old to new leaves, the top leaves may appear normal. If the deficiency is extreme, however, the entire plant becomes yellowish. If C.E.C is 15 or higher and base saturation of potassium is 3% or greater, potassium will not limit yields. (Percent of base saturation expresses how much of the soil’s ability to hold exchange nutrients is being utilized by potassium). If C.E.C. is lower than 15, the base saturation should be 5% or higher. If the potash base saturation is less in the preceding two cases, potassium can, in fact, limit yields and stand ability.

Even high potassium levels cannot overcome the effects of a severe drought. Under extremely dry growing conditions, plants cannot extract enough potassium for optimal growth and yield, even if potassium levels are adequate. Conversely, poorly drained, waterlogged soils can fix potassium on minerals within the particles, making it unavailable to the plant. To make potassium more plant available in soils with low-to-medium levels, strip plow down potash. A nitrogen to potash ratio of 1:1 ensures health and stand ability of high yield corn. Potash levels should never exceed magnesium levels, because high potassium levels can restrict a plant’s ability to take up sufficient magnesium.

Following potassium, calcium is the number two health aid to corn and other grain crops. It stimulates root and leaf development, forms cell wall compounds (which lends to stand ability), helps reduce plant nitrates, activates several enzyme activities, and neutralizes organic acids. Calcium reduces soil acidity, which in turn lowers solubility and toxicity of manganese, copper, and aluminum. What’s more, calcium improves the root growth condition, microbial activity and stimulates other nutrient uptake. Calcium also acts as a neutralizing agent to control soil pH. Most crops prefer a near-neutral pH level, where the base saturation of calcium falls between 65% and 75%. (Percent of base saturation expresses how much of the soil’s ability to hold exchange nutrients is being utilized by calcium. Calcium seldom limits yields when pH is 5.5 or higher on mineral soils and at least 4.8 on organic soils.

When pH levels are extremely low, a calcium deficiency may result. Calcium deficiencies also happen when pH is very low and magnesium and/or potassium levels cause symptoms similar to those of amide herbicide injury, where newly emerging corn leaves fail to unfold because leaf tips stick together (in a ladder like configuration). Affected plants may also have a slight yellow green tint and may be severely stunted. However, the side effects of low calcium (low pH; too much manganese, iron, and aluminum) will usually affect corn growth adversely before levels drop low enough for ladder like leaf symptoms to develop. But calcium can also limit yields if the concentration is too high, because it can inhibit magnesium, potassium, ammonium, and sodium uptake. The best way to both avoid and treat a calcium deficiency is to maintain an adequate pH level, which may be done with the application of Ag lime.

Sulfur helps plants use nitrogen and form protein. While a high level of sulfur will not limit yields, a sulfur deficiency (levels below 12 PPM) will. Symptoms are similar to those of nitrogen deficiency (pale yellow or light green leaves.) Sulfur is highly soluble and subject to leaching in the sulfate form used by plants, so for proper protein formation, add sulfur to each corn crop. Corn grows adequately at sulfur levels between 15 and 20 PPM, but grows best at levels of 20 PPM or higher. Grass plants, like corn, require approximately one pound of sulfur for each 14 pounds of nitrogen. Legume crops (such as soybeans and alfalfa) require one pound of sulfur for each ten pounds of nitrogen.

Boron is essential for growth and development of pollen, for seed and cell wall formation and for sugar translocation within corn plants (because it forms sugar/borate complexes). Correct boron levels promote increased flowering, better pollination, improved quality and higher yields. Boron leaches easily from the root zone, especially in sandy soil and in soils with low organic matter levels.

A boron deficiency is most likely to occur in drought conditions since boron availability lessens with decreasing soil moisture. Yields may suffer if levels fall below 1.5 PPM or during excessive rainfall or drought. Boron availability also decreases in soils with pH levels above 7.0 and after recent heavy liming. Since boron interacts with other nutrients, more boron may be required when nitrogen levels are high or phosphate levels are low. If boron levels are already low, high levels of potassium application may induce boron deficiency. A constant supply of boron must be available throughout the growing season, since boron does not translocate within the plant. Boron should be applied in a broadcast or plow down program—never in starter fertilizer. It may, however be applied with herbicides in a broadcast herbicide program.

Magnesium aids in phosphate metabolism, plant respiration, and activation of several enzyme systems. But it’s most important role is as a building block of plant chlorophyll. Chlorophyll is crucial to photosynthesis and ultimately, carbohydrate build up. Since chlorophyll contains green pigments, a magnesium deficiency causes the interveinal leaf area to turn pale green or yellow. (This deficiency is likely when calcium and magnesium are imbalanced, which happens after a high-calcium lime has been used for several years on soils with low magnesium levels). Magnesium deficiency can also occur when high rates of potassium or anhydrous ammonia are applied.

The wrong combination of magnesium, potassium, and C.E.C. can cause a high or low magnesium level to limit yields. So can potash; if pounds of potash are greater than that of magnesium, magnesium availability may be limited. When potash saturation is greater than 4% and C.E.C. is below 10%, levels of magnesium below 10% of base saturation may be limiting. (Percent of base saturation expresses how much of a soils ability to hold exchange nutrients is being utilized by magnesium). Low magnesium is more likely to occur in soils with C.E.C. s below 7 (sandy soils), than is soils with C.E.C. above 7. Highly calcitic-derived soils can also show magnesium deficiencies. For adequate growth, a minimum of 10% magnesium base saturation is generally best. High magnesium levels will not limit yields if calcium is equal to or greater than 50% of the total base saturation. If magnesium is less than 10% base saturation and pH is above 6.5, consider applying magnesium as a nutrient. If soil pH is below 6.5, magnesium (in the form of dolimitic lime) may be applied to correct the pH and supply additional magnesium.

Manganese works in enzyme systems, which aid in chlorophyll production, and carbohydrate and nitrogen metabolism. Plants require a small amount of manganese because it is recycled. Therefore, manganese deficiency is rare. If manganese shortages do occur, however, lower yields can result. Deficiency symptoms—olive colored streaking between veins—resemble iron or zinc deficiency symptoms. As with most micronutrients, soil pH appears to be the most important factor governing manganese availability. Manganese is more available in soils with pH levels of 6.5 or less. But, as soil pH rises, manganese solubility and availability decreases. Manganese is limited when pH is 7.0 or greater—or organic matter levels are high. Low nitrogen or iron levels, poor drainage and excessively wet, cool spring conditions also cause manganese deficiencies.

Low sulfur levels limit available manganese, while acid forming nitrogen fertilizers (like ammonium nitrate and ammonium sulfate) increase manganese availability on alkaline soils. Phosphorus can also increase manganese availability. Calcium regulates manganese absorption. Band application of manganese with acid-forming fertilizers is recommended, because this placement keeps plant available manganese from oxidizing into forms which are plant unavailable. Foliar sprays may also be effective.

Zinc is crucial to growth regulation because it forms part of the plant’s enzyme system. It’s also essential to chlorophyll production, carbohydrate formation and silk development. It contributes to corn test weight and feed quality. Like iron, zinc is not translocated; deficiencies first appear on younger leaves. Since zinc can affect maturity rates, zinc deficient plants usually mature later than normal plants. A zinc level below 5 PPM with a soil pH above 6.5 can limit yields. Zinc can also be limiting when levels are below 3.5 PPM and soil pH is below 6.5. In either case, zinc should be added in starter fertilizer. Since zinc can tie up with phosphorus, it can become unavailable and limit yields when phosphorus levels are above 50 pounds per acre.

Iron is essential for chlorophyll formation and acts as an oxygen carrier in corn plants. Since iron is not translocated, deficiency symptoms first appear on younger leaves at the tops of plants. Early correction is crucial. Cold, wet soils, acid soils, calcareous soils, and alkaline soils with high pH levels can trigger iron deficiencies. So can micronutrient imbalances, excessive phosphorus, high pH, and prolonged applications of copper, manganese, and zinc.