Glossary (trial version)

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Particle density

dry mass per unit volume of soil particles.

Participatory management

(environmental) management undertaken by local people, making use of local resources, indigenous environmental knowledge and management practices. Usually established and organised using participatory appraisal techniques.

Peak runoff

The maximum rate of runoff at a given point or from a given area during a specified period, in reaction to rainfall.

Peat

An organic soil, which contains at least 65% organic matter (less than 35% mineral material), and is at least 0.5 m in depth and 1.0 ha in areal extent.

Permanent wilting point

volumetric soil moisture content at the time when plants will suffer from water strees, caused by deficiency in soil moisture.

Permeability

(1) Qualitatively, the quality or state of a porous medium relating to the readiness with which such a medium conducts or transmits fluids. (2) Quantitatively, the specific property governing the rate or readiness with which a porous medium transmits fluids under standard conditions. See also Hydraulic conductivity.

pF

The numerical measure of energy with which water is held in the soil, expressed as the common logarithm of the absolute value of the matric head in centimetres of water.

Pg

1 Petagram = 10¹⁵ grams = 10⁹ metric tons = 1 gigatonne (Gt)

pH

A measure of the hydrogen ion concentration in a solution, expressed as the common logarithm of the reciprocal of the hydrogen ion concentration in gram mol per litre.

Piezometer

an instrument used to measure the elevation of the water table.

Plant-available water

The difference of water retained at field capacity (pF 2.2 or a suction of 0.33 bar) and water retained at wilting point (pF 4.2 or a suction of 15 bar).

Pleistocene

geological epoch dated 1.8-1.6 million to 10,000 BP. During the Pleistocene, the climate fluctuated between cold (glacial) and warm (interglacial) periods, causing a rise and drop of the sea level, due to melting of the glaciers and ice formation.

Pneumatophores

roots rising above the level of water or soil and acting as respiratory organ in some peat swamp forest trees

Podzolization

the leaching of soluble complexes (formed by chelation) of aluminium and iron from the A-horizon of a soil, and the subsequent deposition of these metals, together with organic matter, in the B-horizon. This process leads to the formation of a soil called a podzol.

Pores

See voids.

Porosity

The volume of voids as a fraction of the volume of soil.

Poverty trap

Expression to indicate a situation where decreasing farm income due to continuous lower nominal prices for agricultural products causes that farmers are trapped in (developing) regions where no other employment is available

ppm, ppmv

for liquids and solids ppm = parts per million = µg/g or mg/kg, for mixtures of gases ppmv = µl/l; the volume mixing ratio ppmv is the ratio of the number of moles of water vapour to the number of moles of dry air contained in the volume V occupied by the mixture.

Precipitation

The total amount of water received from the sky (rain, drizzle, snow, hail, fog, condensation, hoar frost, and rime).

Pressure head

the water pressure in relation to the atmospheric pressure. In the unsaturated zone, the pressure head is negative

This glossary is based up on the published glossary taken from the following publication:

Rieley, J. O. and S. E. Page, (2005), Wise Use of Tropical Peatlands: Focus on Southeast Asia, ALTERRA - Wageningen University and Research Centre and the EU INCO - STRAPEAT and RESTORPEAT Partnerships, Wageningen, The Netherlands.

Click here to download a PDF copy of the publication - http://www.restorpeat.alterra.wur.nl/download/WUG.pdf (Filesize: 23.3 Mbytes)