Agroforestry Planting trees and crops together.

alley cropping Planting of crops in strips with rows of trees or shrubs on each side.

animal manure Dung and urine of animals used as a form of organic fertilizer. Compare green manure.

Commercial  inorganic fertilizer Commercially prepared mixture of plant nutrients such as nitrates, phosphates, and potassium applied to the soil to restore fertility and increase crop yields.Compare organic fertilizer. 

compost Partially decomposed organic plant and animal matter used as a soil conditioner or fertilizer. 

Conservationtillage farming Crop cultivation in which the soil is disturbed little (minimum-tillage farming) or not at all (no-till farming) to reduce soil erosion, lower labor costs, and save energy. Compare conventional-tillage farming. 

contour farming Plowing and planting across the changing slope of land, rather than in straight lines, to help retain water and reduce soil erosion.

Conventionaltillage farming Crop cultivation method in which a planting surface is made by plowing land, breaking up the exposed soil, and then smoothing the surface. Compare conservation-tillage farming. 

convergent plate boundary Area where earth's lithospheric plates are pushed together. See subduction zone. Compare divergent plate boundary, transform fault. 

core Inner zone of the earth. It consists of a solid inner core and a liquid outer core. Compare crust, mantle.

crop rotation Planting a field, or an area of a field, with different crops from year to year to reduce soil nutrient depletion. A plant such as corn, tobacco, or cotton, which removes large amounts of nitrogen from the soil, is planted one year. The next year a legume such as soybeans, which adds nitrogen to the soil, is planted. 

crust Solid outer zone of the earth. It consists of oceanic crust and continental crust. Compare core, mantle. 

desertification Conversion of rangeland, rain-fed cropland, or irrigated cropland to desertlike land, with a drop in agricultural productivity of 10% or more. It usually is caused by a combination of overgrazing, soil erosion, prolonged drought, and climate change. 

divergent plate boundary Area where earth's lithospheric plates move apart in opposite directions. Compare convergent plate boundary, transform fault.

earthquake Shaking of the ground resulting from the fracturing and displacement of rock, which produces a fault, or from subsequent movement along the fault.

erosion Process or group of processes by which loose or consolidated earth materials are dissolved, loosened, or worn away and removed from one place and deposited in another. See weathering.

geology Study of the earth's dynamic history. Geologists study and analyze rocks and the features and processes of the earth's interior and surface. 

green manure Freshly cut or still-growing green vegetation that is plowed into the soil to increase the organic matter and humus available to support crop growth. Compare animal manure. 

gully reclamation Restoring land suffering from gully erosion by seeding gullies with quick-growing plants, building small dams to collect silt and gradually fill in the channels, and building channels to divert water away from the gully.

humus Slightly soluble residue of undigested or partially decomposed organic material in topsoil. This material helps retain water and water-soluble nutrients, which can be taken up by plant roots.

igneous rock Rock formed when molten rock material (magma) wells up from the earth's interior, cools, and solidifies into rock masses. See rock cycle. Compare metamorphic rock, sedimentary rock.

infiltration Downward movement of water through soil. 

Inorganic fertilizer See commercial inorganic fertilizer.

Land classification Method for reducing soil erosion that identifies easily erodible land that should not be planted in crops or cleared of vegetation. 

leaching Process in which various chemicals in upper layers of soil are dissolved and carried to lower layers and, in some cases, to groundwater. 

lithosphere Outer shell of the earth, composed of the crust and the rigid, outermost part of the mantle outside the asthenosphere; material found in earth's plates. See crust, mantle. 

loams Soils containing a mixture of clay, sand, silt, and humus. Good for growing most crops. 

mantle Zone of the earth's interior between its core and its crust. See lithosphere. Compare core, crust . 

manure See animal manure, green manure. 

Metamorphic rock Rock produced when a preexisting rock is subjected to high temperatures (which may cause it to melt partially), high pressures, chemically active fluids, or a combination of these agents. See rock cycle. Compare igneous rock, sedimentary rock. 

mineral Any naturally occurring inorganic substance found in the earth's crust as a crystalline solid. See mineral resource. 

Minimum-tillage farming See conservation-tillage farming.

no-till farming See conservation-tillage farming.

organic fertilizer Organic material such as animal manure, green manure, and compost, applied to cropland as a source of plant nutrients. Compare commercial inorganic fertilizer.

permeability Degree to which underground rock and soil pores are interconnected and thus a measure of the degree to which water can flow freely from one pore to another. Compare porosity.

plate tectonics Theory of geophysical processes that explains the movements of lithospheric plates and the processes that occur at their boundaries. See lithosphere, tectonic plates.

plates See tectonic plates.

porosity Percentage of space in rock or soil occupied by voids, whether the voids are isolated or connected. Compare permeability. 

rock Any material that makes up a large, natural, continuous part of earth's crust. See igneous rock, metamorphic rock, mineral, sedimentary rock. 

rock cycle Largest and slowest of the earth's cycles, consisting of geologic, physical, and chemical processes that form and modify rocks and soil in the earth's crust over millions of years. 

salinization Accumulation of salts in soil that can eventually make the soil unable to support plant growth.

sedimentary rock Rock that forms from the accumulated products of erosion and in some cases from the compacted shells, skeletons, and other remains of dead organisms. See rock cycle. Compare igneous rock, metamorphic rock. 

shelterbelt See windbreak.

soil Complex mixture of inorganic minerals (clay, silt, pebbles, and sand), decaying organic matter, water, air, and living organisms. 

soil conservation Methods used to reduce soil erosion, prevent depletion of soil nutrients, and restore nutrients already lost by erosion, leaching, and excessive crop harvesting. 

soil erosion Movement of soil components, especially topsoil, from one place to another, usually by wind, flowing water, or both. This natural process can be greatly accelerated by human activities that remove vegetation from soil. 

soil horizons Horizontal zones that make up a particular mature soil. Each horizon has a distinct texture and composition that vary with different types of soils. See soil profile. 

soil permeability Rate at which water and air move from upper to lower soil layers. Compare porosity. 

soil porosity See porosity. 

soil profile Cross-sectional view of the horizons in a soil. See soil horizon. 

soil structure How the particles that make up a soil are organized and clumped together. See also soil permeability, soil texture.

soil texture Relative amounts of the different types and sizes of mineral particles in a sample of soil.

strip cropping Planting regular crops and close-growing plants, such as hay or nitrogen-fixing legumes, in alternating rows or bands to help reduce depletion of soil nutrients. 

subduction zone Area in which oceanic lithosphere is carried downward (subducted) under the island arc or continent at a convergent plate boundary. A trench ordinarily forms at the boundary between the two converging plates. See convergent plate boundary.

tectonic plates Various-sized areas of the earth's lithosphere that move slowly around the mantle's flowing asthenosphere. Most earthquakes and volcanoes occur around the boundaries of these plates. See lithosphere, plate tectonics. 

transform fault Area where the earth's lithospheric plates move in opposite but parallel directions along a fracture (fault) in the lithosphere. Compare convergent plate boundary, divergent plate boundary.

volcano Vent or fissure in the earth's surface through which magma, liquid lava, and gases are released into the environment.

waterlogging Saturation of soil with irrigation water or excessive precipitation so the water table rises close to the surface.

weathering Physical and chemical processes in which solid rock exposed at earth's surface is changed to separate solid particles and dissolved material, which can then be moved to another place as sediment. See erosion. 

windbreak Row of trees or hedges planted to partially block wind flow and reduce soil erosion on cultivated land.