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Glossary for agroforestry

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


    A conceptual model of a plant type that will be best suited to a particular set of circumstances. Ideotypes can be defined in terms of both form and function. There can be 'isolation', 'competition' and 'crop' ideotypes.

illuvial horizon

    1. A soil layer in which material from above has been deposited; the layer of accumulation.

    2. A soil horizon that receives material in solution or suspension from some other part of the soil. See also eluviation


    The process of seeds absorbing water from their surroundings or the stage at which they do it, for example, after a dry seed has been planted in moist soil.


    The conversion of an element from the inorganic to the organic form in microbial tissues, thus rendering the element not readily available to other microorganisms or to plants.

impeded drainage

    Restriction of the downward gravitational movement of water. May result in the development of anaerobic conditions because of waterlogging.

impervious soil

    1. Soil through which water, air or roots cannot penetrate. No soil is ever completely impervious.

    2. A soil resistant to penetration by water and, usually, by air and roots.

inbred line

    A line produced by continued inbreeding.


    1. The breeding of closely related individuals; if carried through enough generations the families can become homozygous, that is, have the same genotypes within their chromosomes.

    2. The mating of individuals that are closely related genetically. Mating in a population consisting of a few individuals.

    3. The mating of individuals more closely related than individuals mating at random.

income-equivalent ratio

    The ratio of the area of sole crops that will give the same gross income as one hectare of intercrop at the same management level. See also land-equivalent ratio


    In breeding systems, strictly the inability of gametes to unite and form a zygote. Frequently restricted to the inability of pollen to fertilize through pollen tube growth, being arrested in the style. Inability of embryos to develop.


    The increase in girth, height, volume, weight or value of individual trees or crops over a stated period. See also harvest increment

independent variable

    See variable


    1. Of a stem, when it continues to grow from the apex. Of an inflorescence, when the terminal flowers open last and therefore the growth or elongation of the main axis is not arrested by the opening of the first flowers (for example, as in a panicle).

    2. Having the axis or axes of plants not ending in a flower or bud; resulting in elongation.

indeterminate flowering

    A plant in which flowering is more or less continuous until climatic conditions become unfavourable.

indeterminate growth

    A pattern of development in which the apical meristem remains vegetative, that is, does not produce flowers, so that new leaves and stems continue to be produced while flowers are also forming. See also determinate growth


    Native to a specified area, not introduced. An indigenous tree is one that grows naturally within a specific environment or within certain predetermined boundaries. See also exotic


    The adducing of a number of separate facts, particulars, and similar items, especially to prove a general situation. The opposite of deductive.

indurated soil

    Soil that is cemented into a hard mass that will not soften on wetting. See also hardpan


    Of soil, compacted or hard layers in the soil profile that offer resistance to root growth.

industrial forestry

    Large-scale, commercial tree planting for timber and other wood products (for example, wood chips).


    Containing great numbers of insects, mites, nematodes and so on, as applied to an area or field. Also applied to a plant surface or soil contaminated with bacteria, fungi, and so on.


    See beating up


    1. The downward entry of water into soil or other material.

    2. The flow of a liquid into a substance through pores or other openings; connoting flow into a soil as opposed to percolation, which strictly means flow through a porous substance.

infiltration capacity

    The maximum rate at which water can be absorbed by a given soil per unit surface under given conditions.

infiltration rate

    Rate at which a particular soil absorbs water.


    A device for measuring the rate of entry of fluid into a porous body; for example of water into soil.


    1. A group of flowers, usually set apart from the foliage leaves. The inflorescence is classified according to its mode of branching, which may be racemose (indefinite and not terminating in a flower) or cymose (definite, terminating in a flower).

    2. The system in which flowers are arranged about a plant axis. The term includes the branch stems, flower stalks and bracts as well as the actual flowers.

informal survey

    Field study in which interviews with farmers, direct observations and existing information are used to develop an understanding of the farming system's constraints and potential. See also diagnosis and design


    An individual who is respondent in an interview. Observed individuals are not informants. A key informant is a well-informed person from the region or village who can provide accurate background information; not necessarily a person of authority.


    The inflorescence converted into fruits.


    Of rhizobia or mycorrhizae. The deliberate introduction of material containing microorganisms into soils, nursery composts or living plants.


    A preparation containing live microorganisms (rhizobia, mycorrhizal fungi) that can be used to add to the soil, or directly to the seeds, so as to inoculate suitable plant species with these favourable organisms. Commercial preparations can be as a liquid suspension, or a gel, or they may be peat based.

in situ

    'On the site'. When applied to tree plantations, refers to seed planted in the same area as it was collected. See also ex situ

integrated pest management

    1. An approach that attempts to use all available methods of control of a disease, or of all the diseases and pests of a crop plant, for best control results but with the least cost and the least damage to the environment.

    2. The use, in a closely coordinated way, of biological, chemical and (if appropriate) mechanical methods of controlling pests (plant pathogens, insect  pests or weeds).

    3. The control of one or more pests by a broad spectrum of techniques ranging from biological means to pesticides. The goal is to keep damage below economic levels without trying to eliminate the pest completely.

integrated resource management

    A form of forest or woodlot management in which a number of resources or roles (e.g. hydrological functions), are obtained or fulfilled at the same time over the whole area. See also multiple-use management


    Tendency for the effect of varying one factor to depend on the level of another factor. Measured as the difference between two differences. See also non-additivity

intercepted rainfall

    The proportion of the gross precipitation that is held up in the canopy and that does not reach the ground either through stemflow or as throughfall. Also termed interception loss.


    Process by which precipitation is caught and held by vegetation (or structures), then lost by evaporation without reaching the ground.

interception loss

    The fraction of precipitation that does not reach the ground but that is intercepted by vegetation and then evaporates back into the atmosphere.


    1. The cultivation of two or more crops simultaneously on the same field, with or without a row arrangement (row intercropping or 'mixed intercropping').

    2. The growing of two or more crops on the same field with the planting of the second crop after the first one has already completed development. Also called relay cropping. See also mixed cropping, multiple cropping


    A form of multiple cropping where perennial (usually tree) crops are grown in association with other species to form a multilayered system.


    Hardships (stress) caused by the proximity of neighbouring plants. A blanket term to describe different kinds of competition or sometimes to describe competition only between genotypically identical or similar plants.

intermittent growth

    Non-continuous growth without the predictable regularity of rhythmic growth; hence intermittent branching.

intermittent succession

    See crop succession

internal rate of return

    The discount rate that, when applied to the streams of costs and revenues generated by a project, will reduce the net present value to zero.


    A region of the stem between two succesive nodes. See also node

interpolated cropping

    A cropping sequence where two or more species are grown on the same unit of land but at least one species has a later sowing (planting) time and an earlier harvest than the other(s). Refers to situations where the crop duration of species is very different.

intertropical convergence zone

    The axis, or a portion thereof, of the broad trade wind current of the tropics. The dividing line between the northeast and southeast trade winds.


    In intercropping, the degree to which different plant component species are spaced so as to be close to one another. See also tree–crop interface


    Long, continued hydridization leading to the spread of genes from one race or species to another.

in vitro

    In a laboratory (strictly 'in glass', that is, a test tube). For example, the digestibility of animal feeds may be estimated by appropriate chemical methods 'in vitro' in a laboratory; 'in vivo' (in the animal itself) using a fistula (narrow tube) to extract material ingested after it has been through the rumen (first stomach), or later, to see what has been absorbed; or, ultimately, by liveweight gain per amount of intake. See also in vivo

in vivo

    'In the living body'. See also in vitro

iron pan

    A soil in which iron compounds have been washed from the upper layers and deposited as a hard layer lower down. The layer prevents free drainage and root penetration but may possibly be broken mechanically by subsoiling. See also indurated soil

irrigated lowland

    In tropical regions, an area where, invariably, a rice crop is grown with irrigation. Availability of irrigation water may be year-round or seasonal. Other, non-rice crops, particularly high-value crops, may be grown with irrigation.


    'Equal slope'. A line on a map or chart joining locations having equal values.

isoenzyme analysis

    Analysis of plant proteins by substituting known enzymes in a plant substrate to determine whether a reaction will occur. It is done so as to determine the presence of various enzymes within plant tissue. See also isozyme

isogenic lines

    Two or more lines differing from each other genetically at one locus (place on a chromosome) only. Distinguished from clones, homozygous lines, identical twins, and so on, which are identical at all loci.


    A line on a chart or diagram drawn through places or points having the same rainfall or precipitation over a stated period.


    The prevention of crossing among populations because of distance or geographic barriers (geographic isolation), growth on different sites (ecological isolation), difference in flowering time (phenological isolation) or genic or chromosomal differences preventing normal seed set (genetic isolation).


    Any line on a chart or diagram drawn through places or points having the same value of a meteorological element.


    A line on a graph representing a particular (stated) value of output as the result of interaction of two variables represented on the x and y axes.


    Curve passing through points of equal temperature.


    Different molecular forms of the same enzyme.


    Related to or being a computational procedure in which replication of a cycle of operations produces results that approximate the desired result more and more closely. In the context of social science tools, this describes the need to apply tools repeatedly to obtain validity and reliability, and to update solutions.

University of Georgia The Bugwood Network Forestry Images   The Bugwood Network - The University of Georgia
College of Agricultural and Environmental Sciences and Warnell School of Forest Resources
Copyright 2004. All rights reserved.       Page last modified: Wednesday, August 8, 2001
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