Foliar Spray 
A light application of a liquid feed which is applied to the grass leaves and is not absorbed via the grass roots. A wetting agent might be added to the foliar spray to aid uptake into the leaf.
Frit
A finely ground glass material which contains small amounts of one or more micro-nutrients. A micronutrient source is added to sodium silicate (liquid glass) in the manufacturing process and heated to a very high temperature (about 100C, or so) to produce a molten material; this is then rapidly cooled and shatters into very fine fragments and then ground into a powder like material ready for application to plants. Also known as FTE: Fritted Trace Element/s.
Green Manure
Hidden Hunger
A term which is sometimes applied to agricultural grain crops where there is a reduction in yield but without other visible nutritional, especially potassium, deficiency symptoms. Over-application of potassium to turfgrass situations with an aim of improving drought and disease resistance may actually create a hidden excess and increase the plants susceptibility to undesirable conditions.
Hot Water Insoluble Nitrogen
The percentage of insoluble nitrogen fertiliser content (in urea formaldehyde or methylene urea products) which results from being placed in water at a temperature of 100°C for 30 minutes. (BS ISO 19670: 2017)
Hot Water Soluble Nitrogen
The percentage of soluble nitrogen fertiliser content (in urea formaldehyde or methylene urea products) which results from being placed in water at a temperature of 100°C for 30 minutes. (BS ISO 19670: 2017)
Incomplete Fertiliser
A term used to describe a fertiliser that contains just one or two of the three primary plant nutrients of Nitrogen, Phosphorus and Potassium.
Continue reading about this
Inorganic Fertiliser
A fertiliser derived from non-living natural material, also being called mineral fertiliser, artificial fertiliser, or chemical fertiliser, with an example being superphosphate. This term also includes fertilisers that contain carbon which have been manufactured, e.g. Urea, rather than produced by biological organisms. Inorganic fertilisers can dry out sward relatively quickly and will often scorch grass leaves if not adequately washed in.
Insoluble Fertiliser
A fertiliser which does not readily dissolve in water. They gradually degrade over time through primarily chemical weathering within a soil due to interaction with soil pH and micro-organism activity.
Iron
A significant micronutrient, which is represented by the chemical symbol Fe. Iron is required for the formation of chlorophyll and is a component part of many enzymes involved with plant growth and development. It is involved in the process of photosynthesis (both Photosystems I and II), being important for structural viability of thylakoid membranes.
Iron deficiency results in interveinal chlorosis, initial yellowing of the leaves, and reduced photosynthetic activity, and this can also result in photooxidative damage (due to excessive light levels penetrating into the leaves) in deficient
Continue reading about this