Soil Science and Agricultural Chemistry constitute important branch of Agriculture, which have implicit greater magnitudes due to their diverse fields of specialization. Considering enormous scope and diversity of the subject, a variety of books have been contributed by many authors encompassing numerous aspects of soil science.

1. The unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants. - Soil Science Society of America

ABIOTIC FACTORS: Environmental influences produced other than by living organisms for example, temperature, humidity, pH and other physical and chemical influences. Contrast it with ‘biotic factors’ - meaning effects due to biological components.

ACTIVATION ENERGY: The energy required before the reaction of concern will proceed. Often, heating will supply the needed energy. Enzymes or other catalysts lower the activation energy of a reaction.

AGRICULTURAL WASTE: The characteristics of the agricultural waste materials make them important in respect of their use and economic value. Agricultural wastes can he put to use because (1) Farm development (improvement of soil health, soil fertility, soil physical conditions and plant protection), it is the source of energy and power, (3) it acts as animal feed and fodder, (4) it is the human food

ACID-FORMING FERTILIZER: A term applied to commercial fertilizers which leave an acid residue in the soil. The amount of calcium carbonate required to neutralize the acid residue is referred to its equivalent acidity.

ALLIC: soil family class term used in Oxisols as a calcareous and reaction class category. Soils placed in the allic class are acid and have low CEC with high amounts of KCl-extractable aluminum in a layer at least 30 cm thick within the control section. If used for agriculture, these Oxisols require large inputs of lime to displace the aluminum and raise pH.

ABSORPTION ACTIVE: Movement of ions and water into the plant root as a result of metabolic processes by the root, frequently against an electrochemical potential gradient.

ACID SOILS: Acid soils with pH below 6.5 are widespread. Main limitations of these acid soils are low pH, low CEC, low status of bases, especially Ca, Mg, and K along with toxicity of Al and Mn. Use of acidifying fertilizers aggravates this situation.

AERATION, SOIL: The exchange of air in soil with air from the atmosphere. The air in a well aerated soil is similar to that in the atmosphere; the air in a poorly aerated soil is considerably higher in carbon dioxide and lower in oxygen.

ACCELERATED EROSION: Erosion in excess of natural rates, usually as a result of anthropogenic activities.

AIRBORNE SENSING: Remote sensing from an airplane. (Related words: airphoto, aerial)

ABSORPTION (of light): A process by which light is taken-up by another material. Examples include soot consisting of tiny black particles, which absorb all visible light; and nitrogen dioxide, a pollutant mostly from diesel and gasoline engines, that absorbs blue light resulting in air with a brown tint.

Three kinds of symbols are used in combination to designate horizons and layers. These are capital letters, lower case letters, and arabic numbers; capital letters are used to designate master horizons and layers; lower case letters are used as suffixes to indicate specific characteristics of the master horizon and layer; arabic numerals are used both as suffixes to indicate vertical subdivisions within a horizon or layer and as prefixes to indicate discontinuities (Soil Taxomony available online atftp:// ftp-fc.sc.egov.usda.gov/NSSC/Soil_Taxonomy/tax.pdf. 1999.