20 MIN READ
Corn Nutrition 101
December 2, 2019
It is imperative to understand the principles of soil fertility to efficiently manage corn nutrients, and corn production, and environmental stewardship. There are 17 chemical elements that are known to be essential for plant growth, 14 of these elements come from the soil. Each essential plant nutrients needed in different amounts by the plant, each varies in mobility within the plant and varies in concentration in the harvested mature corn plant components. Knowing the relative amount of each nutrient by crop and the amounts removed with harvest is useful for calculating the amount of fertility that will need to be added to the soil to maintain optimum harvest levels).
Table 1. Essential plant elements, source, roles and relative quantities in the plant
To be classified as “essential”, the element needs to meet the following criteria:
The plant cannot complete its life cycle (seed to new seed) without it.
The elements’ function cannot be replaced by another element.
The element is directly involved in the plant’s growth and reproduction.
Non-mineral nutrients:
Three elements, carbon (C), hydrogen (H), and oxygen (O), are non-mineral nutrients because they are derived from the air and water. Although they represent approximately 95% of plant biomass, they are generally given little attention in plant nutrition because they are almost always in sufficient supply. However, other factors such as soil management and the environmental conditions can influence the availability and crop growth response.
The 14 mineral nutrients are classified as either macronutrients or micronutrients based upon plant requirements and relative fertilization need. There are 6 macronutrients: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). The macronutrients, N, P, K, are often classified as primary macronutrients, because deficiencies of N, P, K are more common than the secondary macronutrients, Ca, Mg, and S. The micronutrients include boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn). Most of the macronutrients represent 0.1 -5% or 100-5000 parts per million (ppm), of dry plant tissue, whereas the micronutrients generally comprise less than .025% or 250ppm, of dry plant tissue (Table1).
How plants uptake nutrients:
Each of the nutrients cannot be taken up by plants in its elemental form, they must instead be taken up in an ‘ionic’ or charged form, with the exception of boron (B) as boric acid which is uncharged (Table 2). Most fertilizers are made up of combinations of these available nutrient forms, so when fertilizer dissolves, the nutrient(s) can be immediately available for uptake. Knowing what form of a nutrient the plant absorbs helps inform what controls the cycling and movement of the nutrient in the soil. Additionally, understanding how nutrients function within the plant is useful in diagnosing nutrient deficiencies.
Table 2. Nutrient Forms Taken up by Plants
Nutrient uptake by roots is dependent on the activity of the root (corn root number, root dry matter, and root length), ability to absorb nutrients, and the nutrient concentration at the surface of the root. Roots come directly in contact with some nutrients (interception) as they grow; however, this only accounts for a very low percentage of the total amount of nutrients taken up by plants. Therefore, other mechanisms must cause the movement of nutrients to the plant.
Water moves toward and into the root as the plant use water or transpires. This process is referred to as ‘mass flow’, accounts for a substantial amount of nutrient movement toward the plant root, especially for the mobile nutrients such as NO3-. Specifically, mass flow has been found to account for about 80% of N movement into the root system of a plant, yet only 5% of the more immobile P. It has been found that ‘diffusion’ accounts for the remainder of the nutrient movement.
Diffusion is the process where chemicals move from an area of high concentration to any area of low concentration. Fertilizing near the plant root, the plant is less dependent on exchange processes and diffusion to uptake nutrients, especially P. The nutrients that are most dependent diffusion to move them toward a plant root are relatively immobile, have relatively low solution concentrations, and yet are needed in large amounts by the plant, such as P and K. The secondary macronutrients (Ca, Mg, S) often do not depend of diffusion because their solution concentrations are fairly high in soil, relative to plant requirements.
How nutrients move within the plant
All nutrients move relatively easily from the root to the growing portions of the plant. Some nutrients can also move from older tissue to newer tissue if there is a deficiency of that nutrient. Knowing which nutrients are ‘mobile’ is very useful in diagnosing plant nutrient deficiencies because if only the lower leaves are affected, then a mobile nutrient is most likely the cause. Conversely, if only the upper leaves show the deficiency, then the plant is likely deficient with an immobile nutrient because that nutrient cannot move from older to newer leaves. Table 3 list the six mobile and eight immobile mineral nutrients. Sulfur is one element that lies between mobile and immobile elements depending on the degree of deficiency.
Table 3. Mobile and Immobile Nutrients
Nutrient Deficiencies of Corn Symptoms
The following pictures represent some of the more common nutrient deficiency symptoms in corn. When visual symptoms of nutrient deficiency particularly N and K, yield loss has occurred.
Developing Fertilizer Recommendations, understanding Nutrient Uptake and Partitioning
Biotechnology, breeding, and agronomic advancements have increased corn yields to new highs. Current fertilization practices developed decades ago, may not match the requirements of newer hybrids which are now grown at population densities higher than ever before. A re-evaluation of nutrient uptake and partitioning can provide the foundation for fine-tuning our practices as we strive to achieve corn’s maximum yield potential.
When developing fertilizer recommendations, two major aspects of plant nutrition are important to understand and manage high yield corn production:
- Total Nutrient Uptake: The amount of a given mineral nutrient acquired during the growing season.
- Partitioning: The amount of that nutrient contained in the grain or removed withthegrain.
Further improving fertility practices require matching in-season nutrient uptake with the availability of nutrients. For some nutrients (e.g., N, P, K, Mg, Mn, and Fe), as much as two-thirds of total uptake occurs during vegetative growth. Of critical importance is supplying N to meet corn’s peak needs of 7.8 lb N/day from V10-V14. Uptake of N does not cease at VT/R1 since as much of 50 lb N/acre is accumulated and petitioned directly into the developing seeds during grain fill.
Contrary to nutrients like N and K, nutrient accumulation of P, S, Zn, and Cu is equally distributed between vegetative growth and during reproductive growth (ear development and grain-fill). Season-long supply of P, S, Zn, and Cu is imperative to maximize corn yields. Relative to total uptake, P is removed to a greater extent than any other nutrient. Agronomic practices which do not adequately replace removed P may eventually lead to a depletion in soil fertility levels.
Even though nutrient management is a complex process, improving understanding of uptake timing and rates, partitioning, and remobilization of nutrient by corn provides opportunities to optimize fertilizer rates and application timing.