Plant Nutrition Basics

As we often go through our daily routines, we can sometimes take for granted the finer scientific reasons behind our ability as producers to grow the best crop possible.  Our previous article discussed fall as an ideal time for soil sampling.  As you get your soil test results back this fall, this article will provide some of the basics of the chemical side of plant growth and development and why it is important for you to prioritize meeting the nutrient needs of your plants. 

There are 17 essential nutrients for plant growth and development.  While plant growth is a product of those chemical elements, 96% of the dry weight is due to carbon, hydrogen and oxygen.  These non-mineral elements are supplied through water and carbon dioxide exchanges. By utilizing photosynthesis, the plant converts these elements into sugar which develop further into starch, proteins and fats.  The remaining 4% of the plant dry weight is supplied from the nutrients in the soil.

Nitrogen, phosphorous, and potassium (N, P and K, respectively) are required in relatively large amounts and are considered our primary macronutrients.  These major nutrients are most likely to become deficient in a highly productive system where plant material is harvested and removed from the field.  

Nitrogen is the main component of chlorophyll which is needed to utilize sunlight energy to produce sugars from water and carbon dioxide. Thus, N deficiencies are visible as pale yellowing and stunted plants.  Phosphorus is also known for capturing and converting the sun’s energy but is vital to genetics and likely more commonly understood as a root growth stimulator.  Deficiencies in P typically show up in early growth as the roots have not expanded enough to find adequate amounts.  Potassium is essential for sustaining plant growth.  Deficiencies of K result in less resistance to drought, temperature variations, pests, disease and nematodes.

The remainder of the nutrients supplied by the soil are required in much smaller amounts and less likely to become deficient unless you have a pH imbalance, excessive nutrients competing for plant uptake or other “poor” soil conditions such as a textural class imbalance of sand or clay.  The results of a soil test can help to differentiate the condition of individual fields.

One of the most critical soil measurements is pH.  The soil pH is a relative measure of soil acidity.  That relative acidity affects plant growth by limiting the availability of nutrients to be taken up by plant roots.  Acidity can also affect the activity of microorganisms in the soil.  The microorganisms are responsible for the breakdown of organic matter to release nutrients into a more readily useable form for root absorption.  In general, the majority of plants produce most effectively in a soil pH range of 6.0-7.0.

The imbalance of soil acidity is likely the most hidden deficiency in production agriculture.  While the macronutrients are affected by pH differently, overall fertilizer use efficiency can be greatly diminished by even a slight decrease in pH. The following table shows that a pH of 5.5 will ultimately result in 33% loss in fertilizer applied.  In a relative scale scenario, for every $100 spent on fertilizer, you are only getting $67 worth of good or $33 loss in applied fertilizer.  So, as the old advertisement indicated, “Liming Pays” is quite true when your soils are acidic.  Your soil test report will resolve that question for you.

When considering environmental stewardship, soil health parameters, feeding an ever growing world population and your economic bottom line, understanding plant nutrition basics can provide you the clues to enhance your production capabilities.  So, as you get your soil test results back this fall, reflect on going back to the basics of plant growth and development and why it is important for you to cultivate a plan for your crops’ nutritional needs in 2017.

Source: Todd Lorenz, MU Extension Agronomy Specialist

 

Fertilizer Use Efficiency In Relation To Acidity

pH

Nitrogen

Phosphorus

Potassium

Lost Fertilizer

(salt)

%

%

%

%

4.0

30

23

33

71

4.5

53

34

52

54

5.0

77

48

77

33

5.5

89

52

100

20

6.5

100

100

100

0