Photosynthetically Active Radiation 
The range of light with a wavelength that is from 400 to 700 nanometres which is used by green plants in the process of photosynthesis. Chlorophyll a and chlorophyll b capture light in the blue and red spectrums. Other pigments, the Carotenoids consisting of Carotene and Xanthophyll, are highly active at 450 to 500 nanometres, and typically produce the respective orange and yellow colours of autumn leaves. The main reason for this is that they do not decay as rapidly as the green colour of leaves. The term is frequently abbreviated to PAR.
Phototropism
The growth of plants towards a light source.
Continue reading about this
Phyla
Phylum
A taxonomic category that is used to group organisms. It is sometimes referred to as a Division. A Phylum is grouped from similar Classes. Similar Phyla are in turn grouped into a Kingdom.
Physical Control
The use of manual and mechanical techniques. Examples of Manual control include: Hand weeding. The hand picking of fungal fruiting bodies. Heat treatment, such as flame guns to burn off weeds. Switching or Drag brushing to remove dew or earthworm casts. Mechanical Control can include: Mowing; Scarification; Verticutting; Chain harrowing; Aeration, and the like.
Physiology
The scientific study of the functions and interactions of a living organism.
Phytochrome
A photoreceptor molecule found within plants which respond to a specific spectrum of light and are involved in the formation of chlorophyll, seed germination, flowering and leaf movement. Phytochromes will absorb either red or far-red light, allowing plants to respond to the changes which occur in the quality of light received.
Phytotoxic
A substance, which is toxic, meaning it is poisonous to plants. Depending upon the concentration and severity of the substance, the result may be an inhibition of plant growth, or death of a plant.
Plant Breeders Rights
The protection over plant varieties for plant breeders which they develop and can evidence that the variety has Distinctness, Uniformity and Stability (shortened to DUS).
Plant Breeding
There are different methods of breeding turfgrass plants, however, a general approach is:
1. Decide on the species to improve.
2. Establish the aim, i.e. what do we want to improve for this grass. For example, improved wear tolerance, disease resistance, drought resistance, finer leaf, cutting at lower height, improved sward density, etc.?
3. Is the desired goal a trait which has good variation within the species? If so, this means there is a better chance of improving it.
4. Is it fairly easy to screen (this means to identify the particular trait being looked at for improvement - this i
Continue reading about this