What is Humectancy and Why is it Important?

June 12, 2024

A humectant is a substance that absorbs and promotes retention of moisture. Humectancy, therefore, is the absorption and retention of water. Humectants work by pulling in atmospheric moisture and resist losing moisture to evaporation. Before we can understand why humectancy can be important in crop nutrition we first must understand a critical and very basic premise of crop nutrition. Nutrients can be absorbed by plants ONLY when they are in solution. Dry pellets or particles cannot be taken into plants until they are wetted and go into solution. This premise holds true whether nutrients are applied to the soil or to plant foliage as foliar nutrient sprays.

A few factors that favor foliar nutrient uptake are:

  • Applications made during the morning and evening hours
  • Mild temperatures during application
  • High relative humidity

All three of these factors promote foliar nutrient uptake because they prolong the amount of time the spray droplets remain in the liquid phase and delay evaporation. Once the spray has dried foliar nutrient uptake ceases until leaves become moist again from dew or high relative humidity. Logically then, if we can use materials that keep foliar nutrients in the solution phase for as long as possible after being applied we should enhance the absorption of those foliar-applied nutrients.

NDemand Logo

NDemand® products contain polymer nitrogen sources that are powerful humectants. Sprays containing NDemand will remain wet on leaf surfaces longer than sprays made without NDemand. The photographs above illustrate this concept. The leaf on the left was treated with NDemand 30L, and the leaf on the right was treated with liquid urea 20-0-0. Within 5 minutes urea crystals could be seen on the urea treated leaves, and in less than 30 minutes the urea was entirely in the solid phase. At this point absorption ceases. The NDemand treated leaf remained wet and allowed for more effective uptake. This enhanced effectiveness applies not just to the NDemand itself, but also to other nutrients tank mixed with NDemand.

To prove this point a study was conducted by the University of Florida in 2005 on citrus comparing equal rates of foliar-applied nitrogen from urea or the polymer nitrogen sources contained in NDemand. Results showed a 3x increase in the rate of foliar nitrogen absorption in the first hour with the NDemand chemistry. Furthermore, leaf N levels were 23-33% greater in the polymer nitrogen treatment.

Put NDemand in your spray program for maximum effectiveness, crop safety and performance of all your foliar nutrient applications.