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Autotrophic Cells - Cells able to synthesize macromolecules from simple nutrient molecules like carbon dioxide, ammonia and water.
Autotrophic Plants - The plants getting their foods exclusively from inorganic materials occurring in soil, air and water.
Autumn fly - A non biting fly which irritates cattle in large numbers and feeds on nose and eye secretions and open wounds. They cause cattle to huddle together and cease feeding.
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Auxins - A group of plant growth regulating substances or hormones, which are produced by growing tips of stems are roots. Artificial or synthetic auxins are also produced which are important in agriculture and horticulture, e.g., inhibiting sprouting of potato tubers and thus lengthening the storage period, and preventing fruit drop in orchards. Some synthetic auxins exhibit differential toxicity, 2, 4-D is toxic to dicotyledons, but not to monocotyledons, and is used successfully to control weeds in cereal crops and lawns.
Auxotroph - Strain of a microorganism which needs some nutrient not needed by the original strain from which it was derived. An auxotroph may be produced by the occurrence of one or more mutations in a prototroph'
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Available Nutrients - Chemical elements or compounds in the soil that can be readily absorbed and assimilated by growing plants ('available' should not be confused with 'exchangeable').
Available Phosphoric Acid - Refers to the sum of the water soluble phosphoric acid (monocalcium phosphate) and citrate soluble phosphoric acid (dicalcium phosphate) in the soil.
Available Water - The portion of water in the soil that can be readily absorbed by plant roots. Most soil scientists consider it to be the water held in the soil against a pressure of up to about 15 bars.
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Available Water Supply - Refers to that amount of water which may be expressed either in terms of a rate of flow or as a volumetric quantity, and exists in a source of water supply like a stream, or reservoir, over and above the quantity necessary to supply valid and prior rights and demands.
Average Infiltration Rate - Obtained by dividing the mass infiltration that takes place during the time rainfall intensity exceeds the infiltration capacity, by the time during which infiltration takes place at capacity rate.
Avain Tubercle Bacillus - Micro-organism causing tuberculosis in swine and polutry but rarely in sheep or cattle.
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Avian Tuberculin - Used for diagnosing the avian type of tuberculosis in farm animals, particularly swin and poultry.
Avidin - Protein material which can undergo combination with biotine making the vitamin to be unavailable to the body. Cooking renders avidin inactive.
Avitaminosis - Refers to vitamin deficiency.
Awn - Refers to a small bristle at the tip of a flower or fruit, especially
in the grasses, or of a leaf. the wan gets attached to the husk and encloses the grains.
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Awner - The part of a threshing machine which cuts off the awns, consisting of knives rotating on a fast moving spindle.
Axenic Culture - Refers to the growing of an organism of a single species of strain e.g., bacterium in a medium free of other living organisms i.e., a pure culture.
Axial Gradient - Refers to the gradation of the rate of metabolism along the length of a principle axis of an animal.
Axil - Refers to the angle between the upper side of a leaf and the stem on which it is borne; the normal position for lateral buds.
Axillary - Growing from an axil. Thus an axillary bud grows from the axil between stem and leaf.
Axillary Bud - Bud greating in the axil of a leaf.
Axle-tree - The beam on a cart or wagon connecting two opposite wheels.
Azoic - Means without life applicable to precambrian era or rocks.
Azonal Soils - Refers to broad soil order in genetic classification of soils. It includes soils that have poorly developed profiles. Examples of azonal soils include sand dunes, loess, recent deposits of alluvium, and partially weathered bedrock.
Azotobacter - Azotobacter chroocoaum. It is a non-symbiotic nitrogen fixing bacterium occurring in the soil. It is utilizing soluble carbohydrates; strongly aerobic, susceptible to phosphate deficiency.
Azoturia - Specific disease of horse, which is caused due to excessive lactic acid, one of the byproducts resulting from the metabolism of glycogen.
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