How to identify macronutrient deficiencies in your crop

Depending on the soil in your region, your plants could face deficiencies in primary, secondary and micronutrients. We previously discussed how to spot micronutrient deficiencies in your crops, and now we’ll take a closer look at the unique role of macronutrients, and how to tell when your crops are deficient.

When it comes to macronutrients in your crops, there are six key essentials. Nitrogen, phosphorous and potassium are regarded as the three primary macronutrients, while calcium, magnesium and sulfur are considered secondary macronutrients.

  • Nitrogen, which affects a variety of factors including resistances, root growth and color
  • Phosphorus and Calcium, which affect maturation and root growth
  • Magnesium and Sulfur, which affect chlorophyll production
  • Potassium, which affects hardiness, drought tolerance and disease resistance

We’ve compiled a summary of the role of several key macronutrients in crop growth and deficiency symptoms to help you identify what your crops may be missing.


Role in plant

Nitrogen is a necessary component in ALL proteins. It’s needed to make chlorophyll molecules that carry out photosynthesis in the plant.

Deficiency symptoms

  • General chlorosis of older leaves
  • Stunted growth
  • Low protein content of foliage or seeds


Role in plant

Phosphorus is often referred to as “the root and fruit nutrient” because it helps with root development, tillering and seed production. It is needed in virtually all plant parts because it helps drive chemical reactions in the plant. Phosphorus also helps drive maturity.

Deficiency symptoms

It is important to note that it is difficult to diagnose phosphorus deficiency because abnormalities don’t show up until the deficiency is severe.

  • Severe deficiency can result in purple leaf color, while mild cases may actually darken the green leaf color due to a surplus of nitrogen
  • Slow growth and delayed maturity
  • Poor tillering
  • Low seed yields


Role in plant

Potassium acts as a regulator of osmotic water flow from one part of the plant to another. It works as an enzyme activator in many cell reactions and is especially important in activating enzymes responsible for forming carbohydrates in tubers and seeds.

Deficiency symptoms

  • Appear on old growth first, since potassium is very mobile in the plant
  • General chlorosis intensifying to scorched edges and interveinal areas of the older leaves
  • Poor stem strength which may lead to lodging and low bushel weight of cereals due to shriveled seeds


Role in plant

Sulfur is a component of the two amino acids that make up plant proteins. Legumes have high levels of sulfur-containing proteins. Sulfur is needed to produce oils in canola and other oilseed crops.

Deficiency symptoms

  • Deficiency symptoms usually begin in new growth because sulfur is not easily translocated in the plant
  • General chlorosis of leaves
  • Stunted growth and low seed yields
  • In canola, sulfur deficiency may also cause low oil content in seeds and produce deformed cup-shaped leaves that take on a reddish-bronze coloring

The Rainbow Plant Food advantage

Rainbow Plant Food is a homogenous, granular fertilizer. Precise amounts of each nutrient – primary and secondary, as well as micronutrients – are chemically compounded to form a homogenous mixture. As a result, each granule contains nearly identical amounts of all the ingredients. Granules are uniform in size, shape and weight, so the fertilizer spreads evenly. Whether you broadcast or apply it in-row, every plant across the field will have the necessary nutrients available when it’s needed most.

See how Rainbow Plant Food is made here.

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