Glossary of Agronomic Terms (Martin et al. 1976) A Horizon The surface and subsurface soil that contains most of the organic matter and is subject to leaching. Abscission The natural separation of leaves, flowers, and fruits from the stems or other plant parts by the formation of a special layer of thin-walled cells. Acid soil A soil with a pH reaction of less than 7 (usually less than 6.6). An acid soil has a preponderance of hydrogen ions over hydroxyl ions. Litmus paper turns red in contact with most acid soils. Adventitious Arising from an unusual position on a stem or at the crown of a grass plant. Aerial roots Roots that arise from the stem above the ground. Aftermath The second or shorter growth of meadow plants in the same season after a hay or seed crop has been cut. Agrobiology A phase of the study of agronomy dealing with the relation of yield to the quantity of an added fertilizer element. Agronomy The science of crop production and soil management. The name is derived from the Greek words agros (field) and nomos (to manage). Aleurone The outer layer of cells of the endosperm of the seed. Alkali soil A soil, usually above pH 8.5, containing alkali salts in quantities that usually are deleterious to crop production. Alkaline soil A soil with a pH above 7, usually above pH 7.3. Ammonification The formation of ammonia or ammonium compounds in soils. Amylose The straight-chain fraction of normal starch. 106 Glossary of Agronomic terms Angiosperms The higher seed plants. Annual A plant that completes its life cycle from seed in one year. Anther The part of the stamen that contains the pollen. Anthesis The period during which the flower is open and, in grasses, the period when the anthers are extended from the glumes. Apomixis A type of asexual production of seeds, as in Kentucky bluegrass. Aquatic plant A plant that lives in the water. Arid climate A dry climate with an annual precipitation usually less than 10 in. and not suitable for crop production without irrigation. Asexual Reproduction without involving the germ or sexual reproduction cells. Ash The nonvolatile residue resulting from the complete burning of organic matter. Auxins Organic substances that cause stem elongation. Awn The beard or bristle extending from the tip or back of the lemma of a grass flower. B Horizon The subsoil layer in which certain leached substances are deposited. Backcross The cross of a hybrid with one of the parental types. Beard The awn of grasses. Bed A narrow flat-topped ridge on which crops are grown with a furrow on each side for drainage of excess water. Biennial Of 2 years' duration; a plant germinating one season and producing seed the next. Binder A machine for cutting a crop and tying it into bundles with twine. Blade The part of the leaf above the sheath. Boll The subspherical or ovoid fruit of flax or cotton. Boot The upper leaf sheath of a grass. Glossary of Agronomic terms 107 Branch A lateral stem. Broadcast To sow or scatter seed on the surface of the land by hand or by machinery. C Horizon The layer of weathered parent rock material below the B horizon of the soil but above the unweathered rock. Calcareous soil An alkaline soil containing sufficient calcium and magnesium carbonate to cause visible effervescence when treated with hydrochloric acid. Caliche A cemented deposit of calcium carbonate often mixed with magnesium carbonate at various depths, charac­ teristic of many of the semiarid and arid soils of the world. Cambium The growing layer of the stem. Carbohydrates The main constituents of plants, including sugars, starches, and cellulose, in which the ratio of hydrogen molecules to oxygen molecules is 2: 1. Carotene A yellow pigment in green leaves and other plant parts, which is the forerunner of vitamin A. Caryopsis The grain or fruit of grasses. Cell The unit of structure in plants. A living cell contains protoplasm, which includes a nucleus and cytoplasm within the cell wall. Cereal A grass cultivated for its edible seeds or grains. Chernozem soil A dark to nearly black grassland soil high in organic matter developed in a subhumid climate. Chestnut soil A soil having a dark brown surface developed under mixed tall and short grasses in a subhumid to semiarid climate. Chlorophyll The green coloring matter in plants that takes part in the process of photosynthesis. Chlorosis The yellowing of leaves and other chlorophyll-bearing plant parts. Clay Small mineral soil particles less than O.OO2mm in diameter. Climate The total long-time characteristic weather of any region. 108 Glossary of Agronomic terms Coleoptile The sheath covering the first leaf of a grass seedling as it emerges from the soil. Combine A machine for harvesting and threshing in one operation. Companion crop A crop grown with another crop, such as a small grain crop grown with a forage crop. Consumptive use The use of water in growing a crop, including water used in transpiration and evaporation. Cover crop A crop grown between orchard trees or on fields be­ tween cropping seasons to protect the land from leaching and erosion. Crown The base of the stem where the roots arise. Culm The jointed stem of grasses. Cultivar (variety) A group of individuals within a species that differ from the rest of the species. Cytoplasm The contents of a cell outside of the nucleus. Deciduous Plants or trees that shed their leaves at a particular season or stage. Drill A machine for sowing seeds in furrows. Ecology The study of the mutual relations between organisms and their environment. Embryo The rudimentary plantlet within a seed. The germ. Endosperm The starchy interior of a grain or seed. Ensilage Silage. Epidermis The external layer of cells. Erosion The wearing away of the land surface by water or wind. Fallow Cropland left idle, usually for one growing season, while the soil is being cultivated to control weeds and conserve moisture. Fertilization (plant) The union of the male (pollen) nucleus with the female (egg) cell. Fertilization (soil) The application to the soil of elements or compounds that aid in the nutrition of plants. Glossary of Agronomic terms 109 Fibrous root A slender thread-like root, such as the roots in grasses. Fodder Maize, sorghum, or other coarse grasses harvested whole and cured in an erect position. Forage Vegetable matter, fresh or preserved, gathered and fed to animals. Gene The unit of inheritance, which is transmitted in the germ cells. Genetics The science of heredity, variation, and sex determination. Gluten The protein in wheat flour that enables the dough to rise. Grain (1) A caryopsis, (2) a collective term for the cereals, (3) cereal seeds in bulk. Grass A plant of the family Gramineae. Green manure Any crop or plant grown and plowed under to improve the soil, especially by the addition of organic matter. Hardpan A hardened or cemented soil horizon. Hay The herbage of grasses or fine-stemmed plants cut and cured for forage. Humus The well-decomposed and stable part of the organic matter in the soil. Husk The coarse outer envelope of a fruit, such as the glumes of an ear of maize. Hybrid The offspring of two parents unlike in one or more heritable characters. Inflorescence The flowering part of a plant. Leaf The lateral organ of a stem. Legume Any plant of the family Leguminoseae. Lister An implement for furrowing land, often having a planting attachment. Loam A soil composed of a mixture of clay, silt, and less than 52% sand. 110 Glossary of Agronomic terms Meadow An area covered with fine-stemmed forage plants, wholly or mainly perennial, and used to produce hay. Middlebuster A double-shovel plow or lister. Mulch A layer of plant residues on the surface of the soil. Neutral soil A soil neither acid nor alkaline, with a pH of about 7. Nutrient A chemical element taken into a plant that is essential for growth, development, and reproduction of the plant. Organic farming Growing crops without applying pesticides and mineral fertilizers in an inorganic form. Panicle An inflorescence with a main axis and subdivided branches, as in oats and sorghum. Pasture An area of land covered with grass or other herbaceous forage plants, used for grazing animals. Perennial Living more than 1 year but, in some cases, producing seed the first year. Plant Any organism belonging to the plant or vegetable kingdom. Planter A machine fOT opening the soil and dropping tubers, cuttings, seedlings, or seeds at intervals. Pollen The male germ cells produced in the anthers of a flower. Pollination The transfer of pollen from the anther to the stigma of a flower. Productivity The capability of a soil to produce a specified plant (of soil) or sequence of plants under a specified system of management. Profile (of soil) A vertical section of the soil through all its horizons and extending into the parental material. Protoplasm The contents of a living cell. Pubescent Covered with fine, soft, short, hairs. Pure line A strain of organisms that is genetically pure because of continued inbreeding. Rachis The axis of a spike in grasses. Radicle That part of the seed which upon growing becomes the root. Glossary of Agronomic terms 111 Reaction (of soil) The degree of acidity or alkalinity of the soil expressed as pH. Replication Multiple repetition of an experiment. Respiration The process of absorption of oxygen and giving out of carbon dioxide. Root The part of the plant (usually subterranean) which lacks nodes. Runner A creeping branch or stolon.