Bio Stimulants for Nitrogen Management – What to Know

 By Bob Gunzenhauser, Director of Agronomy

Bio stimulants have been gaining more attention in production agriculture in recent years.  The potential promise of stimulating the plants to extract more nutrients from the soil, protect itself from biotic and abiotic stresses, or grow faster and with more biomass has gained the attention of many farmers and researchers, not to mention many manufacturers and retailers. 

Plant hormones are generated by the plant

Bio Stimulant Application Using a Spray Drone

through a myriad number of processes to

regulate itself.  Exogenous applications of plant hormones, either with the seed or as a foliar application, are ways to add extra levels of hormones believed to be useful to the plant.  However, a deeper understanding of what these hormones are and what they do to the plant should be considered.  In addition, knowing which will improve nitrogen use efficiency will provide guidance in the quest to produce the best return on nitrogen fertilizer investment. 

Here is a list of common plant hormones and bio stimulants, their role and example products. 

Cytokinin (CKs) 

• Role:

  • These hormones delay leaf senescence (stay green), enhance N mobilization from vegetative tissues to grain, and stimulate root nitrate uptake via upregulation of nitrate transporters.  They also improve heat stress tolerance and reduced “tip back” in ear development.

• Products:

  • Foliar application of kinetin or seaweed extracts 

Gibberellins (GAs) 

• Role:

  • GAs promote stem elongation and sink strength (kernel demand), which indirectly affects N partitioning.  Gibberellic acid can enhance assimilation enzymes under ample nitrogen environments.

• Products:

  • Gibberellic acid can be applied from early vegetative stages to early reproductive stages, depending on the desired outcome.  Early applications promote rapid growth with stem elongation and overcome stress from cool conditions.  Later applications can improve ear length, tip fill and kernel count. 

    
    

Auxins (AXs) 

• Role:

  • Stimulate lateral root growth and increase N uptake capacity.  They are typically focused on roots but can be applied in a foliar manner. 

    
    

• Products:

  • Indole-3-acetic acid (IAA) or indole-3-butryic acid (IBA) are found in some bio stimulants or humic substances. 

    
    

Brassinosteroids (BRs) 

• Role:

  • These enhance photosynthesis and N assimilation under abiotic stress, particularly in low N environments.  This is an emerging space.   

    
    

• Products:

  • 24-Epibrassinolide (EBL)  

    
    

Abscisic Acid (ABA) 

• Role:

  • Closes stomata under N stress, but exogeneous ABA can maintain N uptake by sustaining root hydraulic conductivity. 

    
    

• Products:

  • Abscisic acid, but may be too expensive for typical corn production 

These are examples of hormones and bio stimulants that have been found to improve nitrogen use efficiency in one way or another.  While it may seem advantageous to apply any (or all) of these products to growing corn, it must be considered that there may be undesirable outcomes from these treatments; plants will naturally develop these hormones based on the environment, and over-application and thus plant concentration may cause imbalances that cause more issues to the plant than intended. 

Hormones and bio stimulants also do not replace a solid fertility plan to ensure proper and balanced levels of nutrients are available to the plant.  These products won’t stimulate nitrogen out of thin air; they may, however, make it easier for the plant to ward off stresses that would disrupt nitrogen uptake and translocation. 

Proper testing of these products in your own environment is prudent; utilizing commercialized products and following their labels will help create potential success.  It must be understood that the stresses that these products could alleviate may not be present at the time of application; applying a stress-reducing hormone may not be useful if the plant is not currently dealing with the targeted stress. 

We should approach the use of bio stimulants and hormones with caution and a sense of experimentation, especially for the purpose of improving nitrogen use efficiency.  As more is learned of these products and their benefits, better positioning of applications will be possible.