The many elements utilized by plants have a complex and interwoven relationship with each other in the soil, in the water in the soil, and in the plant. Soil biology mediates these relationships and adds another layer of complexity.
It is important to understand how minerals move in the plant in order to understand when they are most needed and what they do. Minerals that move up through the xylem can move from roots to the growing points above ground. Minerals that can move both up through the xylem and down through the phloem can be stored and redistributed in the plant as needed. The ability or inability of minerals to move in the plant influences where deficiency symptoms are first seen.
Excesses can be more difficult to understand and deal with than deficiencies. Excess minerals can block the uptake of otherwise adequate minerals, causing deficiency symptoms. They can also substitute for other minerals inside the plant, blocking functions.
We have put together this table to summarize the main interactions that enhance deficiencies and excesses so that we may see more easily how to move our crops toward balance and health. This table is mainly based on the information generously provided by William McKibben in his book, A Grower’s Guide for Balancing Soils and Jerry Brunetti in his book, The Farm As Ecosystem.
| Mobile in the plant? | Moves up (xylem) or down (phloem)? | Role in the plant | Site of initial deficiency | These situations can cause or create deficiencies {or excesses}. | An excess in the soil impacts these minerals | These minerals or situations can increase availability. | |
|---|---|---|---|---|---|---|---|
| Nitrogen | Yes | Both | Used throughout plant growth, more when plants are bigger. Major component of plant proteins and amino acids. Necessary for vitamins and cell division | Older leaves | In soil: High C:N ratio > 10:1, losses from leaching. In legumes, a sulfur deficiency. In plant: Deficient copper, excess chloride. | Insects and disease. May cause iron deficiency. Reduces soil organic matter if C:N < 10. Excesses may be reduced with calcium, sulfur or potassium. | Microbial activity brings C:N ratio toward 10:1. Excess C robs N. Excess N reduces soil organic matter. |
| Sulfur | Minimally | Mainly up | Needed to balance nitrogen. Necessary for amino acids, enzymes and vitamins. Impacts seed development, disease tolerance, nitrate levels in the plant and chlorophyll | New growth | In soil: Leaching by rain or irrigation. | Anaerobic conditions / poor drainage. Microbial activity. | |
| Phosphorus | Yes | Both | Needed most by small rapidly growing plants. Constantly taken up, including after flowering. Regulates energy and growth | Overall size of plant, especially early in the season. | In soil: Cool weather. Dry soil. Poor microbial life. Easily tied up by calcium or magnesium at pH > 7 or by iron or aluminum at pH < 5.5. No-till creates stratification since P does not move in the soil. In plant: anything reducing root mass. | Mainly iron and zinc, but also calcium, manganese and boron | Microbial action. Silica ion in the soil solution. Soil pH 6.0 - 6.5. |
| Calcium | No | Up | Used in new growth only, including roots. Must be at the point of root growth. Critical for roots, cell wall integrity, nitrogen use, pollination and fruit set. | New leaves | In soil: Excess soil nitrogen increases plant demand. High magnesium or potassium on clay soils. In plant: High humidity or excessive rain keeps Ca from being drawn up. First fruit set (blossom end rot) b/c Ca is going to vegetative growth. | Inhibits magnesium, potassium uptake. | Adequate and balanced boron levels in the soil. |
| Magnesium | Yes | Both | Needed all the time for chlorophyll production. Also used for phosphorus movement in the plant, enzyme function. | Older leaves moving to new growth | In soil: high calcium or potassium can reduce uptake. Lime applications can temporarily block uptake. | Interferes with the uptake of calcium, potassium. Tightens clay soils | Sufficient manganese and boron levels in the soil. Nitrate nitrogen. |
| Potassium | Yes | Both | Very mobile and not incorporated into the plant structure. Needed for cell expansion. Inhibits freezing. Converts sugar to starch. Reduces sucking insects. | Older leaves | In soil: Low CEC soils. Compaction in high magnesium clay soils. Dry soil. Overliming. Excess ammonium. | Interferes with the uptake of calcium, magnesium, ammonium, boron, manganese, zinc. | Adequate and balanced boron levels in the soil. |
| Sodium | Yes | Both | Not usually deficient. Helps maintain Turgor pressure | In most plants, none. Sugar beets show thinning leaves | May interfere with the uptake of calcium, magnesium, potassium. Destroys the soil structure of clay, causing drainage and aeration problems. | ||
| Chloride | Yes | Both | Not usually deficient. Affects plasma (exchange between cells) and water efficiency. | Wilting at the margins of young leaves. {More commonly, excess results in tip burn.} | {Excess in soil: Salt damage, poor irrigation water. Can be reversed by leaching.} | ||
| Boron | No | Up | Needed during flowering. Cell wall formation, seed production, Sugar translocation | New growth. | In soil: excess potassium makes deficiency worse, high pH due to calcium applications. Sandy soils or calcarous soils. Low soil phosphorus increases plant demand. In plant: high humidity limits uptake. | Needs to be balanced with calcium. A soil excess can easily cause boron toxicity, which may be reduced by leaching. | |
| Iron | No | Up | Continuously absorbed. Chlorophyll formation, oxygen carrier, cell division and growth | New growth | In soil: Carbonates, bicarbonates, excessive nitrogen or phosphorus. Extreme wet or dry. Tight, saturated soils. High organic matter soils. High soil pH. Glyphosate in soil. In plant: crop removal of iron containing fruit the previous year, esp. in high pH soil. | Phosphorus tie-up | |
| Manganese | Semi-mobile. Improved by good levels of silicon and molybdenum. | Both | Needed during vegetative growth when transitioning to reproductive growth. Chlorophyll synthesis, enzymes, improves calcium and phosphorus uptake, disease resistance | Midway up the plant at new growth | In soil: Over-liming and tillage. Muck soils. Loose dry soils. Bicarbonates in irrigation water. High soil pH. Glyphosate in soil. Excesses of calcium, magnesium, iron, zinc and ammonia compete w/ Mn for uptake. A soil excess of Mn can occur when pH < 5.5. | Low pH. Good levels of silicon and molybdenum in the plant. | |
| Copper | No | Up | Needed during early growth. Metabolic catalyst, photosynthesis, reproduction | Structural parts of the plant such as stems and stocks | In soil: Excess nitrogen. High soil pH. Glyphosate in soil. In plant: anything that reduces the root mass, including calcium deficiency compaction, tillage, insects. | Blocks the uptake of the other metals, manganese, iron, zinc. | |
| Zinc | No | Up | Needed during auxin production - vegetative growth prior to reproduction. Chlorophyll production, flowering and seed production, enzymes, cell division | New growth and shoot tips | In soil: Carbonates, bicarbonates. Cool soil. Dry soil. Tied up by excess phosphorus, high pH, high organic matter or montmorillonite clays. Glyphosate in soil. | Needs to be balanced with phosphorus. Impacts uptake of iron, manganese, copper. | The addition of K-mag and magnesium sulfate. Lowing soil pH. |
| Molybdenum | Poorly | Both | Prevents nitrate accumulation. Aids nodulation. Amino acid and protein. Transfer of ADP to ATP. | New leaves | In soil: Dry soil. pH < 7.2. High levels of sulfate, chloride, manganese, copper and zinc. | ||
| Cobalt | Poorly | Both | B12 production. Nodulation. | In legumes, looks like a nitrogen deficiency. | In soil: High pH, calcareous soils. Overlimed, sandy soils. | Iron deficiency. | |
| Silicon | Poorly | Up | Improves structural integrity | Poor structural integrity, poor disease and insect resistance. Susceptiblity to powdery mildew. | In soil: Sandy soils, high organic matter soils. |
