Understanding Foliar Nutrition

Foliar fertilizer applications can be a useful tool in meeting a crop’s nutrient demands during the growing season.  However, having a clear understanding of the mechanics of foliar nutrient uptake is critical to the timing and expectations of a foliar application.  Factors such as timing, weather, plant age, nutrient absorption rate and plant nutrient mobility all play important roles in making an effective foliar nutrient application.  Below are some issues to consider before you make a foliar fertilizer application:

• Nutrient Source: Weaker chelates such as LPCA are more effective in increasing nutrient absorption rates and shortening absorption time than salts (Sulfates/Oxides), large molecule complexes and chelates like EDTA.
• Timing: Early morning/evening applications in temperatures lower than 85◦F with humidity greater than 70% may improve foliar nutrient absorption efficacy.
• Plant Leaf Status: The leaf cuticle is a major limiting factor in nutrient absorption.  Younger leaves with thinner cuticles absorb nutrients more rapidly than older, hardened off leaves.  Note: Penetrating adjuvants such as Dyne-Amic® can increase the absorption rate and shorten the absorption time of a foliar nutrient application.
• Plant Growth Status: Early season when soils are colder and roots are less active are ideal times to make foliar fertilizer applications.  Newly transplanted plants with weak root systems are also prime candidates for foliar nutrition.
• Nutrient mobility: Use the above chart to guide your expectations/decisions regarding foliar nutrient selection.  Example:  If you make a foliar iron application, don’t expect to see results before a week goes by.

Remember, foliar nutrition cannot and should not replace soil fertilizer applications (especially for nitrogen, phosphorus and potassium).  However, the benefits of foliar nutrition cannot be ignored during certain situations, including:

• Supplying nutrients during periods of peak plant demand.
• Supplying nutrients when soil or root conditions are not conducive to uptake.
• Precision timing is desired.
• Providing a temporary source of nutrition until soil applications can be made.

- Paul Crout, Product Manager

References:

Western Fertilizer Handbook 8th ed, California Fertilizer Association.