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Glossary for agroforestry

Compiled and edited by Peter Huxley and Helen van Houten, International Centre for Research in Agroforestry - 1997

water balance

    1. The distribution of water in space, and over time, within a system. Where plants are growing on land this means considering rainfall (and also interception loss, stemflow and throughfall), drainage, evapotranspiration, runoff and soil water storage.

    2. Balance of input and output of water within a given defined hydrological area such as a basin or a lake, taking into account net changes of storage. Also used for smaller areas, for example, a field or a plot.

water catchment

    See catchment area, micro water catchment, water spreading

water harvesting

    A general term for any means of collecting and re-distributing runoff water. See also micro water catchment, water spreading

water-holding capacity

    Of a soil, the amount of water that it is capable of holding, between field capacity and permanent wilting point.

waterlogged

    1. A condition of land where the groundwater stands at a level that is detrimental to plants. It may result from over irrigation, seepage or inadequate drainage.

    2. Saturated with water. A soil condition with a high or a perched water table; detrimental to plant growth.

water potential

    The free-energy status of water. A concept of general applicability to the measurement of water in soils, plants and the atmosphere. See also soil water potential

watershed

    1. A physiographic unit in the landscape defined by the drainage dividers around the area drained by a particular body of water. If a lake, there is often one watershed with subunits for contributing streams. If a river, it may be defined for any point or all.

    2. The whole surface drainage area that contributes water to a lake. The total area above a given point on a stream that contributes water to the flow at that point (syn: 'drainage basin', 'catchment basin', 'river basin').

    3. The total area, regardless of size, above a given point on a waterway that contributes runoff water to the flow at that point. A major drain-area subdivision of a drainage basin on the basis of this concept.

water shoot

    See coppice shoot, epicormic shoot

water spreading

    1. The application of water to lands to increase the growth of natural vegetation or to store it in the ground for subsequent withdrawal by pumps for irrigation. Part of water harvesting.

    2. Methods of controlling the flow of water locally so as to distribute it better over a farmer's fields. A way of avoiding damage ('gullying') where there is a likelihood of large inflows from any land above a farm or plot.

water-stable aggregate

    A soil aggregate stable to the action of water such as falling drops or agitation as in wet-sieving analysis.

water table

    1. The upper edge of free water in the soil. When a hole is dug, water will fill the hole to the level of the water table.

    2. The level below gound at which free water persists. See also phreatophyte

water-use efficiency

    The above-ground dry matter or harvested portion of a crop produced per unit of rainfall received on the same area of ground i.e. including water lost from the soil surface or by runoff and drainage as well as that used in transpiration.

water-use ratio

    The ratio of the weight of water actually transpired by a crop during its growing season to the weight of dry matter produced (usually exclusive of roots). Also called the 'transpiration ratio'. See also dry matter to transpiration ratio

weathering

    All physical and chemical changes produced in rocks at or near the earth's surface by atmospheric agents.

weather side

    See windward side

weed

    A plant growing where it is not wanted.

weeding

    The elimination of competing vegetation around young trees, for example, by cultivation, by the use of herbicides, or by cutting or slashing. When the trees are big enough to overcome weed competition, a tree plantation is said to be 'established'.

weedkiller

    See herbicide

wettable powder

    A type of formulation for pesticides or herbicides for spray application in which the active materials are mixed with an inert carrier, finely ground, and with a surface-acting agent added, so that it will form a suspension when agitated with water. See also emulsifier

wetting agent

    A surface-active agent that, when added to a liquid, increases its wetting properties.

whorl

    A ring or circle of plant organs arising close together, for example, leaves from a node, or a spiral of conifer branches from a main stem.

wildfire

    See fire

wilding

    A young seedling that develops in the wild without the help of humans. This type of seedling is the best source of stock for some species.

wilting point

    The point in a soil at which the tension of the water it holds causes a plant to start to wilt; when the amount of water held in the fine pores of the soil is insufficient to maintain the turgidity of the plant. See also permanent wilting point

windbreak

    A group of trees or shrubs in any arrangement that will afford protection from high winds to animals or crops or both. When the arrangement is in a long line the group is called a shelterbelt. If an associated reason is also to harvest timber at some future date it is sometimes called a 'timberbelt'. See also windstrip

windstrip

    A narrow plot of low vegetation (shrubs, bushes, herbs and grasses) that is left when natural vegetation is cleared so as to provide shelter to adjacent crops and to prevent wind erosion on sandy soils. See also windbreak

windward side

    The upwind side of, for example, a shelterbelt. Sometimes called the 'weather side'. See also lee side

wood

    1. Lignified secondarily thickened plant tissue. The structural parts of woody perennials. See also timber

    2. A small grove of trees of mixed species complete with undergrowth. The size is variable but it does not cover a large area.

wooded grassland

    Land covered with grasses and other herbaceous species, and with woody species that cover between approximately 10 to 40% of the ground.

woodland

    An open stand of trees > 8 metres high and with a canopy cover of 40% or more, usually among grasses. Woodland is often described by its dominant species, for example, 'Acacia woodland','Acacia-Themeda woodland', 'Combretum woodland'.

woodlot

    A small plot of trees grown for fuelwood, which can also provide small timber and poles. See also coppice, wood

woody clump

    The aggregate of stems arising from woody organs at or below ground level; initiated from a single individual but sometimes separating to form a group of individual plants of the same genotype. See also clumpwood

woody perennial

    A plant with lignified stems that continues to grow from year to year.

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