Glossary - Agroecology: The Ecology of Sustainable Food Systems - page 372

hybrid vigor The production of an exceptionally vigor-
ous and/or productive hybrid progeny from a directed
cross between two pure-breeding plant lines. A synonym
for heterosis .
hydration The addition of water molecules to a min-
eral's chemical structure.
hydrological cycle The process encompassing the evap-
oration of water from the earth's surface, its condensa-
tion in the atmosphere, and its return to the surface
through precipitation.
hydrolysis Replacement of cations in the structure of a
silicate mineral with hydrogen ions, resulting in the
decomposition of the mineral.
hydroxide clay A mineral component of the soil without
definite crystalline structure composed of hydrated iron
and aluminum oxides.
hygroscopic water The moisture that is held the most
tightly to soil particles, usually with more than 31 bars
of suction; it can remain in soil after oven drying.
importance value A measure of a species' presence in
an ecosystem or community—such as number of indi-
viduals, biomass, or productivity—that can be used to
determine the species' contribution to the diversity of
the system.
insolation Expsosure to sunlight, or, more technically,
the rate of solar radiation received per unit area.
integrated farm A farm on which livestock animals and
crop plants are combined to take advantage of the
synergisms that arise from this combination.
integrated pest management The use of a variety of
methods and approaches to manage pests and diseases,
with a goal of eliminating pesticide use.
intermediate disturbance hypothesis The theory that
diversity and productivity in natural ecosystems are
highest when moderate disturbance occurs periodically
but not too frequently.
interspecific competition Competition for resources
among individuals of different species.
intraspecific competition Competition for resources
among individuals of the same species.
inversion The sandwiching of a layer of warm air
between two layers of cold air in a valley.
K -strategist A species that lives in conditions where
mortality is density-dependent; a typical K -strategist
has a relatively long lifespan and invests a relatively
large amount of energy in each of the few offspring it
produces.
landrace A locally adapted strain of a species bred
through traditional methods of directed selection.
landscape ecology The study of environmental factors
and interactions at a scale that encompasses more than
one ecosystem at a time.
leaf-area index A measure of leaf cover above a certain
area of ground, given by the ratio of total leaf surface
area to ground surface area.

light compensation point The level of light intensity
needed for a plant to produce an amount of photosyn-
thate equal to the amount it uses for respiration.
light reactions The components of photosynthesis in
which light energy is converted into chemical energy
in the form of ATP and NADPH.
limiting nutrient A nutrient not present in the soil in
sufficient quantity to support optimal plant growth.
living mulch A cover crop that is interplanted with the
primary crop(s) during the growing season.
lodging The flattening of a crop plant or crop stand by
strong wind, usually involving uprooting or stem breakage.
macronutrient A nutrient plants need in large quanti-
ties; the macronutrients include carbon, nitrogen, oxy-
gen, phosphorus, sulfur, and water.
maritime influence The moderating effect of a nearby
large body of water, such as an ocean, on the weather
and climate of an area.
mass selection The traditional method of directed selec-
tion, in which seed is collected from those individuals
in a population that show one or more desirable traits
and then used for planting the next crop.
microclimate The environmental conditions in the
immediate vicinity of an organism.
micronutrient A nutrient necessary for plant survival
but needed in relatively small quantities.
mineralization The process by which organic residues
in the soil are broken down to release mineral nutrients
that can be utilized by plants.
mountain wind The downslope movement of air at
night that occurs as the upper slopes of a mountain cool
more rapidly than those below.
multifunctionality The ability of agroecosystems to
perform a variety of functions in addition to food and
fiber production, including land conservation, mainte-
nance of landscape structure, biodiversity conservation,
environmental services, economic viability, and social
good.
mutualism An interaction in which two organisms
impact each other positively; neither is as successful in
the absence of the interaction.
mycorrhizae Symbiotic fungal connections with plant
roots through which a fungal organism provides water
and nutrients to a plant and the plant provides sugars to
the fungi.
natural selection The process by which adaptive traits
increase in frequency in a population due to the differ-
ential reproductive success of the individuals that
possess the traits.
net primary productivity The difference between the
rate of conversion of solar energy into biomass in an
ecosystem and the rate at which energy is used to main-
tain the producers of the system.
niche amplitude The size or range of one or more of the
dimensions of the multidimensional space encompassed