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P, phosphorus

P2O5 P x 2.29 = P2O5

Parent material

Mineral or rock material on and/or from which soils are formed during pedogenesis (soil formation process); parent material is one of the five major soil forming factors.

Partial productivity

Productivity as a result of a single input factor.

Pasture

Grassland used for grazing of mainly domestic herbivores.

Peat

Organic soil material with more than 50% of organic matter derived from plant residues with not fully destroyed structure. Peat forms in a wet soil environment or below the water table where mineralisation of organic matter comes close to zero; a peat horizon or layer is normally more than 30cm thick.

Peatland

A generic term for any wetland where partially decayed plant matter accumulates; mire, moor and muskeg are terms used for peatlands in Europe and Canada; see also bog and fen.

Ped

An individual natural soil aggregate, in contrast to a clod caused by disturbance, or a concretion caused by cementation. Described as a range of shapes: platy (laminated), prismatic (vertical axis of aggregates longer than horizontal), columnar (prisms with rounded tops), blocky (angular or subangular) and granular.

Pedo-climatic zone

Zones that are relatively homogeneous concerning climate and soil (e.g., Metzger et al., 2005).

Pedogenesis

Process of soil formation and development by soil forming factors: climate (mainly temperature and precipitation), parent material, living organisms (plants and biota), topography, time, water and Man.

Pedon

The smallest volume that can be called "a soil.'' A pedon is three dimensional and large enough to permit study of all horizons. Its area ranges from about 1 to 10 m2, depending on the variability of the soil.
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