Each year NK Seeds Canada collects soil samples from many of our customers’ corn and soybean fields. In our soil tests, we measure Nitrogen, Phosphorus and Potassium, among other nutrients and soil parameters such as cation exchange capacity, organic matter, and pH. In this article, we will focus on the Key Plant Functions of Nitrogen, Phosphorus, Potassium, and identifying Deficiency Symptoms & Conditions Favouring them and Steps to Correct these deficiencies.

Key Plant Functions

Nitrogen

• Used in the production of amino acids and plant protein proteins, required for growth the stems, leaves and reproductive structures. Also a key component of chlorophyll production used in photosynthesis.

Phosphorus

• Important early in the plant’s lifecycle to initiate plant growth and carryout photosynthesis.

Potassium

• Known as the plant health nutrient. Important for regulating plant water usage, increasing disease tolerance, stalk quality and standability.

Deficiency Symptoms & Conditions Favouring Deficiency

Nitrogen

• Corn
  • Older leaves turn pale or yellowish-green
  • Deficiency starts with a V shape at the tip of the leaf and continues down the mid rib
• Soybeans
  • Older/lower leaves turn pale or yellowish-green
  • Deficiency develops commonly because of poor or slow nodulation, based on weather conditions and soil pH
• Conditions favouring deficiency
  • Rain-fall causing excessive leaching
  • Wet and cool soil temperatures
  • Note: Nitrogen leaches easily in most soils

  
Source: University of Minnesota (https://blog-crop-news.extension.umn.edu/2021/06/scouting-for-nutrient-deficiencies-in.html) 

Phosphorus

• Corn
  • A purple or reddish color on the lower/older leaves and stems
• Soybeans
  • Appear spindly, with smaller leaflets
  • Stunted growth habit
  • Leaves can have a dark green to almost blue appearance
• Conditions favouring deficiency
  • Cool wet conditions
  • Note: Difficult to correct in-season
  • Note: Sometimes purpling is just cold weather; some genetics show cold weather purpling more than others. If you’re unsure, we recommend speaking with your local agronomist to get more information. 

 
Source: Yara (https://www.yara.co.uk/crop-nutrition/forage-maize/nutrient-deficiencies-maize/phosphorus-deficiency-maize/)


Potassium

• Corn
  • Chlorosis on leaf margins and tips of the older leaves
• Soybeans
  • Chlorosis along the outer edge of the leaf tissue
• Conditions favouring deficiency
  • Environmental conditions that favour limited early root growth and development
  • Note: Difficult to correct in-season

 

Source: Purdue University (https://extension.entm.purdue.edu/newsletters/pestandcrop/article/low-soil-moisture-and-compaction-promote-potassium-deficiency/)

Steps to Correct

The best way to avoid any of these nutrient deficiency symptoms is a well-planned fertility program based off current soil test results. For nitrogen deficiency in corn, plan an in-season side dress application as soon as a deficiency is noted. While various forms of nitrogen are available, select a form that has a higher amount in the nitrate, or plant available form. The best method to side-dress nitrogen in corn is to inject or dribble nitrogen in close proximity to the root system for rapid uptake; if injecting or dribbling is not an option, broadcast urea granules. A pre-sidedress soil nitrate test (PSNT) can be used to estimate current soil nitrogen levels and guide application rates. For a phosphorus or potassium deficiency, in-season corrections are rarely effective. Review current soil test levels, understand the current crop’s removal rates, and plan for a fertility application after harvest. Please contact your supplier or your NK agronomist for local fertility tips.

Speak to your local NK^® Agronomist for more information, or join the conversation online – connect with @NKSeedsCanada on Twitter and Facebook.

These are general considerations. Always consider the specific situation on your field and exercise good agronomic practices. 

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