Last reviewed: January 2026
A
- Ammonium (NH₄⁺)
- A positively charged ion form of nitrogen that plants can absorb. It binds to soil particles and must be converted to nitrate by soil bacteria (nitrification) for many plants to use efficiently.
- Anion
- A negatively charged ion. Nitrate (NO₃⁻) is an anion, which means it does not bind to negatively charged soil particles and remains mobile in soil solution.
- Application rate
- The amount of fertiliser applied per unit area, typically expressed in kg/ha or lb/acre.
C
- Cation
- A positively charged ion. Potassium (K⁺) and ammonium (NH₄⁺) are cations that can be held on soil exchange sites.
- Cation exchange capacity (CEC)
- A measure of the soil's ability to hold positively charged ions. Higher CEC soils retain more nutrients.
- Chloride (Cl⁻)
- An essential micronutrient for plants, but can be toxic at high concentrations. Some crops are particularly sensitive to chloride.
- Chloride sensitivity
- The susceptibility of certain crops to chloride toxicity. Chloride-sensitive crops include tobacco, potatoes, stone fruits, and some vegetables.
D
- Deficiency
- A condition where a plant lacks sufficient quantity of a nutrient for normal growth and development.
- Drip irrigation
- A method of irrigation that delivers water slowly and directly to the plant root zone through emitters.
E
- Electrical conductivity (EC)
- A measure of the salt content of a solution or soil extract, expressed in mS/cm or dS/m. Higher EC indicates more dissolved salts.
F
- Fertigation
- The application of fertilisers through an irrigation system, allowing precise nutrient delivery to the root zone.
- Foliar application
- The application of nutrients directly to plant leaves as a spray, allowing rapid uptake of nutrients.
K
- K₂O
- Potassium oxide, the standard unit for expressing potassium content in fertilisers. To convert to elemental K, multiply by 0.83.
L
- Leaching
- The downward movement of dissolved nutrients through the soil profile with percolating water, potentially moving nutrients out of the root zone.
M
- Macronutrient
- A nutrient required by plants in relatively large amounts. The primary macronutrients are nitrogen (N), phosphorus (P), and potassium (K).
- Micronutrient
- A nutrient required by plants in small amounts, including iron, manganese, zinc, copper, boron, molybdenum, and chloride.
- MOP (Muriate of Potash)
- Potassium chloride (KCl), the most common potassium fertiliser. Contains approximately 60% K₂O and 47% chloride.
N
- Nitrate (NO₃⁻)
- A negatively charged ion form of nitrogen that is immediately available to plants. It is highly mobile in soil and the dominant form of nitrogen absorbed by most crops.
- Nitrification
- The biological oxidation of ammonium to nitrate by soil bacteria. This process is temperature and pH dependent.
- Nitrogen (N)
- An essential macronutrient required for plant growth, a component of proteins, chlorophyll, and nucleic acids.
P
- pH
- A measure of acidity or alkalinity on a scale of 0-14, with 7 being neutral. Most crops grow best in slightly acidic to neutral soils (pH 6.0-7.0).
- Potassium (K)
- An essential macronutrient involved in water regulation, enzyme activation, and transport of sugars within the plant.
- Potassium nitrate (KNO₃)
- A water-soluble fertiliser containing approximately 13% nitrogen (as nitrate) and 46% potassium (as K₂O). Free of chloride and sodium.
S
- Salt index
- A measure of a fertiliser's tendency to increase the osmotic pressure of the soil solution, relative to sodium nitrate (index = 100). Lower salt index indicates less risk of salt damage.
- Solubility
- The amount of a substance that can dissolve in water at a given temperature, typically expressed in g/L. Potassium nitrate has solubility of 316 g/L at 20°C.
- SOP (Sulphate of Potash)
- Potassium sulphate (K₂SO₄), a chloride-free potassium fertiliser containing approximately 50% K₂O and 18% sulphur.
U
- Uptake
- The absorption of water and nutrients by plant roots or leaves.