Module 6:

6.3 Soil science

6.3.1 Plant nutrition

1   How are fertilisers supplied?

The manner in which a fertiliser is supplied for use or how it is formulated can vary significantly. Sometimes this fertiliser formulation is just called fertiliser products. This can be in the form of a solid material which includes powder, crystals, granular, mini-granular, crumbs, prills; and also as a liquid material.

• Granular: The most common fertiliser sold by suppliers, and being classified according to granule size, for example, fine (micro-granular / mini-granular, for example, 1.5-2mm diameter), medium (2-4mm), and coarse (4mm+).
• Crumb: A granular shape, often created by crumbled organic pellets, but without or with reduced dust, or by grinding of organic material into finer particles, such as from bonemeal. it may also be used as just another name for a mini-granular fertiliser.
• Crystals: Some fertilisers manufactured from inorganic materials, with water being driven off in the manufacturing process, such as sulphate of iron or ammonium sulphate. The latter might be in smaller crystal of <1mm diameter, or larger granular crystals of 2-3mm in diameter.
• Liquid: This is often a nutrient concentrate which needs to be diluted and may be dissolved or water dispersed, for example, ICL Greenmaster Spring & Summer Liquid Fertilizer. Liquid fertilisers will usually provide for rapid leaf uptake, as well as requiring more regular feeds for a plant.
• Powder: This is very dusty and not commonly applied, although can be mixed with a carrier to other fertilisers to aid spreading, especially for fine turfgrass surfaces, with dried blood being an example.
• Prill: A manufactured uniform sphere, primarily for agriculture but mini-prills might be suited for longer turfgrass situations. Ammonium nitrate is a common fertiliser, but this wouldn’t be applied to turf as it is too high in nitrogen, although dissolving in water and applying as a liquid spray would be more appropriate.
• Homogenous granule: A fertiliser has been manufactured with a consistent quantity of nutrients contained within each uniform granule.

2   What are the different types of fertiliser?

This could refer to various interpretations for a fertiliser, for example, organic / inorganic; rate of nutrient release – slow, fast, controlled; straight, mixture or compound; as well as how it might be formulated, for example granular etc.

For this course Fertiliser Type will be defined as those fertilisers which can be classed as follows:

• Straight: Single (often primary) nutrient, for example, sulphate of ammonia supplying nitrogen.
• Mixture: This is a fertiliser product which is made by physical mixing of straight fertilisers and may be two or more different nutrient fertilisers but can also be a fertiliser with the same nutrient. For example, this could be sulphate of ammonia mixed with superphosphate; or sulphate of ammonia mixed with hoof and horn meal.
• Compound: Usually referring to a chemically combined product (meaning they cannot be separated out and each granule has a consistent amount of the nutrients within it) due to a manufacturing process, with two or more of the primary nutrients (N, P and K). This is the most common fertiliser used. It may sometimes also mean a blend with two or more of the primary nutrients, especially when reviewing older literature from the 20th Century.
• Blend: The physical mixing, in a dry condition, of two or more fertilisers. This will be either one or more straight fertilisers with one or more compound fertilisers, or two or more compound fertiliser mixed together. It is possible that there may only be one nutrient supplied in a blend, although this would be an uncommon situation.
• Complex: Chemically combined fertiliser with two or more macro-nutrients (primary and secondary).

A sub-category can also be recognised as follows:

• Complete fertiliser: One which contains all three primary macronutrients N:P:K.
• Incomplete fertiliser: One which contains all only one or two of the three primary macronutrients, e.g. 8:0:4 (therefore missing phosphorus).
• Balanced fertiliser: One which contains the same proportions of each primary macro-nutrient, e.g. 7:7:7. A plant will not require nutrients in this same ratio, so if a balanced fertiliser is to be applied it is not about making an even amount available within a soil, but rather about topping up soil levels to ensure adequate amounts are available during the year, especially where additional nitrogen only (or dominant) fertilisers are to be applied, as P and K will be withdrawn from the soil due to increased growth produced by the applied nitrogen fertiliser and where the clippings are boxed off and removed from a pitch.