A
agroforestry growing both tree and food crops on the same piece of land.

B
biodiversity the maintenance of many different interrelated species in an ecological community.

biophysical cycles the circular flow of organic and inorganic materials in ecosystems.

C
carrying capacity the level of population and consumption sustainable by the available natural resource base.

common property resource(s) a resource not subject to private ownership and available to all, such as a public park or the oceans.

crop rotation and fallowing an agricultural system involving growing different crops on the same piece of land at different times and regularly taking part of the land out of production.

crop value index an index indicating the relative value of production of different crops on a given quantity of land.

D
depletable resource a renewable resource that can be exploited and depleted, such as soil or clean air.

discount rate the annual rate at which future benefits or costs are discounted relative to current benefits or costs.

E
elasticity of supply the sensitivity of quantity supplied to prices; an elastic supply means that a proportional increase in price results in a larger proportional change in quantity supplied; an inelastic supply means that a proportional increase in price results in a smaller proportional change in quantity supplied.

environmental sustainability the continued existence of an ecosystem in a healthy state; ecosystems may change over time but do not significantly degrade.

external cost(s) a cost, not necessarily monetary, not reflected in a market transaction.

externalities an effect of a market transaction on individuals or firms other than those involved in the transaction.

I
induced innovation innovation in a particular industry resulting from changes in the relative prices of inputs.

information asymmetry a situation where different agents in a market have different knowledge or access to information.

information-intensive techniques production techniques that require specialized knowledge; usually these techniques substitute knowledge for energy, produced capital, or material inputs, often reducing environmental impact.

integrated pest management the use of methods such as natural predators, crop rotations, and pest removal to reduce pesticide application rates.

intercropping an agricultural system involving growing more than one crop on a piece of land at the same time.

L
labor-intensive techniques production techniques that rely heavily on labor input.

M
marginal physical product the additional quantity of output produced by increasing an input level by one unit.

marginal revenue product the additional revenue obtained by increasing input by one unit; equal to marginal physical product multiplied by marginal revenue.

micronutrients nutrients present in low concentrations in soil, required for plant growth or health.

monoculture an agricultural system involving the growing of the same crop exclusively on a piece of land year after year.

multiple cropping an agricultural system involving growing more than one crop on a piece of land.

N
nitrogen cycle the conversion of nitrogen into different forms in the ecosystem, including the fixation of nitrogen by symbiotic bacteria in certain plants such as legumes.

nutrient recycling the ability of ecological systems to transform nutrients such as carbon, nitrogen, and phosphorus into different chemical forms.

nutritional deficit failure to meet human demands for basic levels of nutrition.

P
present value the current value of a stream of future costs and/or benefits, calculated through the use of a discount rate.

proxy variable a variable used to represent a broader concept, such as the use of fertilizer application rates to represent the input-intensity of agricultural production.

R
renewable resource(s) resources supplied on a continuing basis by ecosystems; renewable resources such as forests and fisheries can be depleted through exploitation.

resistant pest species pest species that evolve resistance to pesticides, requiring either higher pesticide application rates or new pesticides to control the species.

S
salinization and alkalinization of soils the buildup of salt or alkali concentrations in soil with the effect of reducing soil productivity.

sustainable agriculture systems of agricultural production that do not deplete the productivity of the land or environmental quality, including such techniques as integrated pest management, organic techniques, and multiple cropping.

U
user cost(s) opportunity costs associated with the loss of future potential uses of a resource, resulting from consumption of the resource in the present.