Absorption-Movement of ions and water into the plant root.

Acid Soil- Soil with a pH higher than 7.0.

Adsorption- The process by which atoms, or ions are taken up and retained on the surfaces of solids by chemcial or physical binding.

Aerate- To allow or promote exchange of soil gases with atmospheric gases.

Aerobic- Growing only in the presence of molecular oxygen, as aerobic organisms.

Aggregate- A unit of soil structure formed by natural processes as oppesed to artificial processes, and generally greater than 10 mm in diameter.

Alkali Soil- A soil containing sufficient exchangeable sodium as to interfere with the growth of most crops, and with or without significant quantities of soluble salts.

Alkaline Soil- Any soil with a pH greater than 7.0.

Ammonification- The biochemcial process whereby ammoniacal nitrogen is released from nitorgen containing organic compounds.

Anaerobic- Growing in the absence of molecular oxygen, as anaerobic bacteria.

Anion- Acid-forming elements, which are negatively charged.

Available Nutrients- Nutrient ions or compounds in forms which plants can absorp and utilize in growth.

Base Saturation Percentage- The extent to which the absorption complex of a soil is saturated with alkali or aklaline earth cations, expressed as a percentage of the cation exchange capacity.

Bulk Density- The mass of dry soil per unit bulk volume. In general expressed in grams per cubic centimeter.

Cation Exchange Capacity- The sum of exchangeable cations that a soil, soil constitutent, or other material can adsorb. The value is expressed in milliequivalents per 100 grams of soil.

Denitrification- Reduction of nitrate or nitrite to gaseous forms of N by microbial activity or chemical reductants producing molecular N or oxides of N.

Electrical Conductivity- The measure of salt concentration in a soil, water, or other solid or liquid material. It is expressed in mmhos/cm or decisiemens/m.

Equivalent- The weight in grams of an ion or compound that combines with or replaces 1 gram of hydrogen. The atomic weight or formula weight divided by the valence of the element or compound.

Exchangeable- An ion which can replace or be replaced by another ion ot ions having the same total electrical charge, generally an adsorbed cation.

Fertigation- Application of plant nutrients in irrigation water to accomplich fertilization.

Fertilizer Requirement- The quantity of certain plant nutrient elements needed, in addition to the amount supplied by the soil, to increase plant growth to a designated level.

Gypsum Requirement- The quantity of gypsum or its equivalent required to reduce the exchangeable sodium content of a given amount of soil to an acceptable level.

Humus- The relatively resistant, usually dark brown to black, fraction of soil o.m., peats, or sompost, which is formed during the biological decomposition of organic residues. It contains many times the major fraction of the organic matter in the soil.

Ion- Atom, group of atoms, which is electrically charged as the result of the loss of electrons (cations) or the gain of electrons (anions).

Lime Requirement- The amount of liming material required to change the soil to a specified state with respect to pH or soluble Al content.

Milliequivalent- One thousandth part of an equivalent.

Nitrification- Biological oxidation of ammonium to nitrite and nitrate, or a biological induced increase in the oxidation state of nitrogen.

Organic Matter- The residue remaining in soil from plant and animal life processes, especially after initial decompostion. It is expressed in percent of soil weight.

pH- The negative logarithm of the hydrogen ion activity of a soil. The measurement of the degree of acidity or alkalinity of a soil

Saline Soil- A nonsodic soil containing sufficient soluble salts to cause a negative affect to the growth of most crop plants.

Sodic Soil- A nonsaline soil containing sufficient exchangeable sodium to adversely affect crop production and soil structure under most conditions of soil and plant type.

Soil Salinity- The amount of soluble salts ina soil. Measurement is expressed in mmhos/cm or deciSiemen/m.

Valence- The number of atoms of hydrogen which one atom of element will combine with or displace.