What’s in Your Soil: Making Sense Out of Macronutrients

After sampling your soil and sending it to the lab for analysis, you’ll receive a report outlining the amount of macronutrients and micronutrients present in the soil to help guide one of your most important agronomic decisions: fertility.

Interpreting a soil analysis report is critical to making an efficient nutrient plan, so it is important to understand how the nutrients that show up on the report can impact crop growth.

Essential Elements in Plants

Plants rely on 16 essential elements for proper growth. These elements can be divided into non-mineral elements, including hydrogen, oxygen, and carbon, and mineral elements.

Non-Mineral Elements

The three non-mineral elements for successful plant growth can be found in the Earth’s atmosphere and from rainfall. During photosynthesis, plants convert carbon dioxide (CO2) and water (H2O) using energy from the sun to produce starches and sugars, which provides them with food.

Mineral Elements

The remaining 13 elements for successful plant growth are mineral elements, which are divided into macronutrients and micronutrients.

What Are Macronutrients?

By definition, macronutrients are the mineral elements used in large quantities for healthy plant growth and seed production. They include nitrogen, phosphorus, potassium, calcium, magnesium and sulfur.

Here’s how macronutrients functions to support plant growth:

1. Nitrogen (N)

Nitrogen plays a key role in photosynthesis and protein production; too little nitrogen can limit plant productivity.

In general, soils are typically deficient in the total nitrogen needs for most crops. Symptoms of nitrogen deficiency can include stunted plants, yellow and aborted leaves, poor grain quality and lower yields. Because nitrogen is mobile in the soil and within plants, this can lead to leaching of nitrogen beyond the root zone, making it unusable to the plant.

This element demands a sound fertility management plan in order to prevent nitrogen loss and water contamination. Many farmers use nitrogen stabilizers and split N applications to manage nitrogen levels in their crops.

2. Phosphorus (P)

Phosphorus is a primary component of cell membranes and enzymes of plants; it also plays a crucial role in photosynthesis.

Plants utilize large quantities of phosphorus and require annual monitoring to ensure adequate levels. Phosphorus deficiency appears as purple to red leaves accompanied by stunted plant and root growth. When phosphorus levels are too low, it can lead to lower yields and late plant maturation.

Phosphorus is considered immobile in the soil; it is added annually to the soil to retain soil fertility levels.

3. Potassium (K)

Potassium is the third most common mineral element to be deficient in soils, after nitrogen and phosphorus. Essential for the translocation of sugars within the plant, potassium moves easily within the plant and is slightly mobile in the soil. This element plays an vital role in stomata formation, which regulates plant moisture loss and stress from heat and cold temperatures.

Unfortunately, symptoms of potassium deficiency are difficult to see until after yield loss has occurred.

4. Calcium (Ca)

Most soils typically have adequate calcium to maintain plant growth. Immobile within plants and demonstrating low mobility in soil, calcium plays an important role in nutrient transport and plant membrane strength. Calcium applications can also help to increase soil pH. Deficiency symptoms include stunted roots and poor plant standability.

5. Magnesium (Mg)

Magnesium levels are typically sufficient in most soils. However, soils low in magnesium could see noticeable yield bumps with a magnesium application. Significant for enzyme production, chlorophyll structure and photosynthesis, magnesium is considered immobile in soil. Magnesium deficiency typically manifests as chlorosis in the oldest leaves.

6. Sulfur (S)

A mobile nutrient in the plant and the soil, sulfur helps plants take up other nutrients. Sulfur is also essential to amino acid and protein synthesis. Symptoms of sulfur deficiency include young leaves demonstrating severe necrosis and premature leaf loss.

What Are Micronutrients?

Micronutrients include zinc, iron, manganese, boron, chlorine, copper and molybdenum, and are normally reported on standard soil tests. Cobalt, vanadium, sodium and silicon are also micronutrients but are rarely found to be deficient.

1. Zinc (Zn)

Zinc is considered immobile in both plants and soil, and is the most commonly applied micronutrient in corn and soybean production. It is important for protein, enzyme formation and cell wall integrity of plants.

There can be problems from zinc tie-ups with high calcium levels in the soil, rendering the zinc unable to be absorbed by plants. Also, high phosphorus levels can cause zinc to not be absorbed as plant growth requires, leading to zinc deficiency symptoms. These symptoms include white banding or striping on corn leaves and shortened internodes in soybeans.

Yields can be impacted from a lack of adequate zinc in the soil.

2. Iron (Fe)

Iron is an immobile nutrient. It plays a vital role in photosynthesis and plant respiration, and is also needed for nitrogen fixation in soybeans.

Iron deficiency symptoms include interveinal chlorosis of the soybean leaves, referred to as iron chlorosis, and is usually found on high pH soils of 7.5 to 8.3. Severe cases of iron chlorosis can lead to plant death.

To correct the shortage, apply iron fertilizer to the soil prior to planting. A foliar application of iron to growing plants can help to resolve the discoloration, but may be only a temporary fix requiring repeated applications.

3. Manganese (Mn)

Manganese is mobile in the soil but immobile within plant tissue. The primary function of manganese is to serve as an activator of plant growth enzymes. It also helps in chlorophyll formation.

Manganese deficiency symptoms can often be confused with iron chlorosis, which is another reason why soil testing is so critical. Soil pH is generally higher in the areas where the yellowing leaf symptoms develop.

Adding manganese to areas that have low soil levels of it should see a yield response — cut areas of soil and eroding soil sidehills often respond well to manganese applications.

4. Boron (B)

Boron helps with cell wall formation and regulates plant metabolism. It is a mobile element and can be leached from the soil with rainfall, making it unavailable to plants. However, boron is also immobile once introduced into plants — plant availability of boron decreases in dry environments and when soil pH is high.

Boron deficiencies can be identified by malformed and discolored young leaves and stunted plants.

5. Chlorine (Cl)

Chlorine, a very mobile element, regulates osmosis and charges compensation (the movement of cations, atoms and small molecules in and out of plant cells as part of normal cell activity).

While maintaining proper plant growth requires small amounts of chlorine, concentrations inside plants are high, similar to macronutrient concentrations. Many agronomists speculate that most of the chlorine used by plants comes from rain, soil and air pollution.

Overall, you may find that you have more problems of toxicity from too much chlorine rather than a deficiency — symptoms include bronzing leaves followed by wilting and chlorosis.

6. Copper (Cu)

Copper is immobile in both soil and plants. It assists plants in protein and enzyme production and is rarely in short supply. Like chlorine, be careful to avoid the possibility of copper toxicity when adding copper to a fertility program.

Copper deficiency symptoms include dark, blue-green leaves and stunted plant growth followed by young seedling death.

7. Molybdenum (Mo)

Molybdenum is required by plants in the smallest quantity of any micronutrient in order to help control the metal component of enzyme formation. It also enables plants to use nitrogen efficiently. Molybdenum is immobile in plants and a bit mobile in the soil.

Molybdenum deficiency symptoms tend to mimic those of nitrogen shortage, including yellowing, stunted plants that lack vigor.

Cobalt (Co) and Nickel (Ni) are two more micronutrient elements found in plant tissues, but it’s quite rare that they need to be supplemented through a fertilizer application.

Testing for Micronutrient Deficiencies

Plant tissue tests should accompany the diagnosis to verify the deficiency. Of course, a reliable soil test can also confirm that there is indeed a micronutrient deficiency requiring the addition of fertilizer to correct the shortage.

If you and your agronomist determine that your fields have a confirmed micronutrient deficiency, depending on when the symptoms are discovered, you can most likely correct micronutrient element shortages with a soil-applied fertilizer. It is usually the most efficient method and is often less expensive than a foliar-applied fertilizer application. Always be sure to read and follow label use instructions.

Why Is Soil pH Important?

Soil pH, a measure of how acidic or alkaline the soil is, is the most important soil characteristic that controls nutrient availability, plant growth and microbial health.

A pH of 7.0 in neutral on the pH scale of 0 to 14. Most row crops prefer the pH between 6.3 and 7.2 for maximum yield potential. These pH levels are where the mineral elements are most available to the plants.

Micronutrients tend to be more available when the pH is 7 to 7.5, which is slightly alkaline, while macronutrients prefer a pH between 6.2 to 7.0, which is slightly acidic.

Understanding each micronutrient mineral element’s function in plant growth will help you to determine the right nutrient applications and diagnose any potential crop production problems.

Develop a Soil Nutrition Plan with Products from FBN Direct®

Once you understand the nutrient levels in your soil, you can make strategic adjustments using specific nutritional products to adjust particular elements.

FBN Direct offers a diverse range of crop nutrition products, including high uptake nutrients, soil prebiotics, soil probiotics and carbon sources. With streamlined online ordering, fast shipping, and convenient delivery options, FBN Direct helps you get the nutrition products you need for a successful growing season.

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