|  | Public Health Safety | Public Health

Physical Properties of Fertilizers

Fertilizers release nutrients into the soil, but the physical characteristics of a fertilizer are almost as important as the nutrient content. It determines how easily and uniformly the fertilizer spreads during application. Fertilizers with poor physical properties form lumps or dust, flow badly, accumulate too much water or become segregated.

  1. Particle Size

    • Particle diameter is the usual measurement of particle size. Particles in a particular fertilizer have a range of different diameters. This range is called the particle size distribution. In a fertilizer, smaller particles dissolve in water faster. This quickly releases nutrients. Particle size also affects application and storage of the fertilizer.

    Density

    • Density compares the weight of fertilizer to the volume. It depends on how closely packed the particles are. A low-density fertilizer will take up more space than the same weight of a high-density one. This has implications for storage and is important when calibrating machinery.

    Granule Hardness

    • Fertilizer particles need to be hard enough to withstand the pressures of handling and storing them. Granule hardness will depend on the chemical composition of the fertilizer as well as its other physical properties such as the shape of the particles and how much moisture they contain. Granules need to be strong enough to cope with crushing forces, abrasion and impacts (such as hitting a hard surface during spreading). Hard particles also make fertilizers less dusty.

    Moisture Content

    • Most fertilizers absorb water to a certain extent. If they take in too much water, however, it can be problematic. Moisture absorption depends on the chemical composition of the fertilizer, environmental conditions and the shape and size of the particles. Granules with larger surface areas absorb relatively more water. Critical relative humidity (CRH) is the level of humidity required for the fertilizer to absorb water. Fertilizers with high CRH values can be handled and stored in wetter environments. If the CRH is too low, the fertilizer can clump together and be difficult to spread, and will need to be stored more carefully to prevent it from getting wet. The results of moisture absorption vary between fertilizers. Some can take in more water than others before they are adversely affected.

    Liquid Fertilizers

    • The important physical properties of fluid fertilizers are density, viscosity and pH. The strength of the gelling agent is also important. It should be strong enough to keep the solids in suspension, but not so strong that the liquid is too thick to be pumped and poured.

Public Health - Related Articles