A factor 1

absolute humidity: Measurement of atmospheric A humidity. In a system of moist air, the ratio of the A A factor: It is the computed longtime average annual mass of water vapour present to the volume occupied soil loss carried by runoff from specific field slopes by the mixture; that is, the density of the water in specified cropping and management systems. It vapour component. Absolute humidity is normally is expressed in the RUSLE model in tons/acre/year. expressed in grams of water vapour in a cubic metre of air. A horizon: The name given to the surface (top) layer of a soil profile. This horizon has more organic matter absolute water requirement: Also called and dense microbial population hence greatest consumptive use of water. This is the quantity of biological activity than other layers or horizons, such water in ha-cm per crop season absorbed by the as B horizon and C horizon. It is also referred to as crop together with the evaporation from the crop the surface mineral horizon with decomposed organic producing land. It includes the water used by evapo- matter. This is the most important horizon from transpiration and retained in body. crop nutrition and microbial activity point of view. absolute weed: These are the , which are As the top soil, it is also the first layer to be lost undesirable regardless of time and place. during soil erosion and its protection is aimed at by absolute zero: Considered to be the point at which various soil conservation measures. theoretically no molecular activity exists or the AB-DTPA extraction reagent: An acronym for an temperature at which the volume of a perfect gas extraction reagent of 1 M ammonium bicarbonate ( vanishes. The value is 0° Kelvin, -273.15° Celsius

NH4 HCO3) in 0.005 M diethylenetriaminepenta and -459.67° Fahrenheit. acetic acid ( DTPA) that has a pH of 7.6 and is used absorption spectroscopy: This is a technique for for the extraction of phosphorus (P), potassium (K), determining the concentration and structure of a sodium (Na), iron (Fe), manganese (Mn), and zinc substance by measuring the amound of (Zn) from alkaline soils. electromagnetic radiation the sample absorbs at abiontic enzymes: Enzymes (exclusive of live cells) various wavelengths. that are (i) excreted by live cells during growth and absorption spectrum (pl. spectra): This is a plot that division; (ii) attached to cell debris and dead cells; shows how much radiation a substance absorbs at (iii) leaked into soil solution from extant or lyzed different wavelengths. Absorption spectra are unique cells but whose original functional location was on for each element and compound and they are often or within the cell. Synonymous with exoenzymes. used as chemical “fingerprints” in analytical abiotic factor: (i). Not biotic i.e., not living: Factors chemistry. The spectrum can represented by a plot like pH, temperature, moisture etc are abiotic. These of either absorbance or transmittance versus factors play a major role in plant nutrition, microbial wavelength, frequency, or wavenumber. activity and crop growth. (ii). Physical, chemical and other non-living environmental factors. They absorption, active: It is movement of ions and water are essential for living plants and animals of an into the plant root because of metabolic processes ecosystem, providing the essential elements and by the root, frequently against an electrochemical nutrients that are necessary for growth. The abiotic potential gradient. elements also include the climatic and pedologic absorption, passive: It is movement of ions and water components of the ecosystem. into the plant root from diffusion along a chemical ablation till: Loose, permeable till deposited during potential gradient. the final down-wasting of glacial ice. Lenses of absorption: It is uptake of matter or energy by a crudely sorted sand and gravel are common. substance. The process by which atoms, molecules, abrasion: Breakdown of clods, crusts, and plant or ions are taken up from the soil solution or soil material by the impact of particles moved by wind atmosphere and retained on the surfaces of solids in saltation. The impacting particles may also abrade. by chemical or physical binding. Abrasion causes soil aggregates to break down absorptivity: It is the absorbance of a solution per progressively as wind erosion continues. unit of path length and per unit concentration; a = A/ acidity, salt-replaceable 3

humus and hydrous oxides contribute to soil acidity acidic. i.e. acidification of the soil. The reduction in at low pH. Acid soils range from slightly acid (pH pH of the soil is generally brought about by removal A 6.1-6.5) to extremely acid (pH below 4.5). of cations (mainly Ca2+ and Mg2+) by leaching or Micronutrient availability, except in case of Mo is removal in the crop. usually higher in acid soils than in alkaline soils. acidity (soil): This is a chemical condition caused by Very acid soils can be amended with calcitic or acidic environment (excess of H+). Acidity has dolomitic limestone and calcium-rich industrial by adverse effect on the establishment of inoculated products such as sugar factory press mud, paper bacteria especially in very acid soils associated with mill sludge etc. the toxicity of aluminium and manganese or calcium acid sulphate soil: The acid sulphate soils, also known deficiency. Soils become acid when basic elements, as cat clays, have a soil pH as low as pH 3.0 when such as calcium, magnesium, sodium, and potassium drained. This is caused by the presence of dilute held by soil colloids are replaced by hydrogen ions. sulphuric acid resulting from sulphide oxidation. Soils formed under conditions of high annual rainfall Some soils are also salt-affected. They often contain are more acid than are soils formed under more arid toxic amounts of Fe, Al and sulphate but are generally conditions. Soils formed under low rainfall conditions poor in most major nutrients. Potentially acid tend to be generally basic with soil pH readings above sulphate soils occur in tidal swamps. Such soils often 7.0. However, over a number of produce very low yields, sometimes less than 1 years with nitrogen or manures can result

tonne/ha of grain. However, even small amounts of in soil acidification. Water (H2O) combines with lime, in combination with phosphate rock may carbon dioxide (CO2) to form a weak acid — carbonic increase the yield to 2–3 tonnes/ha. After complete acid (H2CO3). The weak acid ionizes, releasing amelioration, which is not easy, these soils can hydrogen (H+) and bicarbonate (HCO3-). The produce yields as high as normal soils. The best released hydrogen ions replace the calcium ions held way to manage such soils is amelioration with lime, by soil colloids, causing the soil to become acid. The phosphate rock and a general increase in nutrient displaced calcium (Ca2+) ions combine with the levels, which requires substantial capital input. bicarbonate ions to form calcium bicarbonate, which, However, these soils are generally used in their being soluble, is leached from the soil. The net effect natural state for growing paddy rice as flooding is increased soil acidity. increases soil reaction. Where the main problem is acidity potential: The amount of exchangeable Fe toxicity, using cultivars with high tolerance to Fe hydrogen ion in a soil that can be rendered free or can solve the problem to a certain extent. active in the soil solution by cation exchange. Usually acid-forming : A kind of fertilizer that leaves expressed in milli equivalents per unit mass of soil. behind an acidic effect in the soil (reduces soil pH). acidity, active: The activity of hydrogen ion in the Mostly such fertilizers, which lack a metallic cation, aqueous phase of a soil expressed as a pH value. are acid forming. Their continuous use makes a soil acidity, exchange: The acidity of a soil that can be acid (lowers pH) and reduces soil quality and hence neutralized by lime or a solution buffered in the productivity. The excess acidity can be neutralized range of 7 to 8. by lime application. This is generally of practical importance in case of nitrogenous fertilizers. acidity, free: The titratable acidity in the aqueous phase Example: ammonium sulphate, ammonium chloride, of a soil. anhydrous ammonia and urea. acidity, residual: Soil acidity that is neutralized by acidic cations: Cations that, on being added to water, lime or a buffered salt solution to raise the pH to a undergo hydrolysis resulting in an acidic solution. specified value (usually 7.0 or 8.0) but which cannot Hydrated acidic cations donate protons to water to be replaced by an unbuffered salt solution. It can be + calculated by subtraction of salt replaceable acidity form hydronium ions (H3O ) and thus in aqueous solutions are acids. Examples in soils include Al3+ from total acidity. and Fe3+. acidity, salt-replaceable: The aluminium and hydrogen acidification: It is a process of becoming more acid. that can be replaced from an acid soil by an unbuffered pH 7 is neutral, above this is alkaline below pH 6 is salt solution such as KCl or NaCl. 4 acidity, total

acidity, total: The total acidity including residual and been improved for use on land. On the average, A exchangeable acidity. Often it is calculated by nutrient content of activated sewage sludge is 5.8%

subtraction of exchangeable bases from the cation N, 3.2% P2O5 and 0.6% K2O. It also contains lesser exchange capacity determined by ammonium and variable amounts of secondary and exchange at pH 7.0. It can be determined directly micronutrients and toxic heavy metals. Care has therefore to be taken while deciding the optimum using pH buffer-salt mixtures (e.g. BaCl2 plus triethanolamine, pH 8.0 or 8.2) and titrating the application rates considering its composition. A basicity neutralized after reaction with a soil. potential organic fertilizer. acidophile: Term referring to acid loving. An organism activator: A substance that can accelerate (speed up) a that grows well under acidic conditions. Example: process, usually of decomposition. Trichurus Acetobacter diazotrophicus. spiralis, Paeciliomyces fusisporus, and Trichoderma viride are used as compost activators (accelerators) acidulant: It is a substance added to food or beverages as the inoculation of compost piles with such to lower pH and to impart a tart, acid taste. organisms speeds up the process and cuts down the Phosphoric acid is an acidulant added to cola drinks. compost preparation time. acidulation: It is a process of treating a fertilizer source active ingredient (a.i.): The potent portion of a with an acid. The most common process is treatment compound (such as fertilizer, insecticide, fungicide of phosphate rock with an acid (or mixture of acids) or herbicide applied on the soil or plant) used as such as sulphuric, nitric, or phosphoric acid. basis to estimate the chemical effect. Useful for acre-foot (acre-ft): The volume of water required to comparing the strength or toxicity of chemicals. cover 1 acre of land (43,560 square feet) to a depth of activity index (Al): Activity index is used by the 1 foot. Equal to 325,851 gallons or 1,233 cubic metres. Association of Official Analytical Chemists (AOAC) actinomycetes: A group of microorganisms, intermediate to evaluate the solubility of urea formaldehyde between bacteria and true fungi, that usually produces compounds: a characteristic branched mycelium. These organisms %CWIN− %HWIN are responsible for the earthy smell of compost. AI= X100 %CWIN actinorhizal plants: Plants, which are nodulated by Frankia - a nitrogen-fixing actinomycete. The Where CWIN, nitrogen insoluble in cold water (25° C); resulting nitrogen-fixation is similar to that by and HWIN, nitrogen insoluble in hot water (100°C). Rhizobium in symbiosis with legumes. Example: actual evapotranspiration: It is an average value, Alnus, Casuarina etc. which represents the actual rate of water uptake by activated charcoal: Charcoal, which has been treated the plant. It is determined by the level of available to remove impurities. Activation carried out by water in the soil. Evapotranspiration comprises the heating charcoal under partial aeration. Used in simultaneous movement of water from the soil and chemical analysis. vegetation into atmosphere through evaporation (E) activated coal: This is the most commonly used and transpiration (T). adsorption medium, produced by heating carbonaceous ad libitum feeding: Where animals are permitted to substances or cellulose bases in the absence of air. It eat daily as much as they desire. has a very porous structure and is commonly used to adaptive research: Research conducted to validate, remove organic matter and dissolved gases from water. modify and/or calibrate a new technology to specific Its appearance is similar to coal or peat. Available in soil, climate, socioeconomic, or environmental granular, powder or block form; in powder form it characteristics of a given area. has the highest adsorption capacity. additive (fertilizer): Material incorporated in a activated sewage sludge: It is biologically active fertilizer- (i) to improve its physical performance/ sewage sludge which has been obtained by repeated condition, e.g. in storage or spreading characteristics, exposure of sewage to atmospheric oxygen, thus (ii) to provide a minor nutrient, e.g. boron, (c) to facilitating the growth of aerobic bacteria and other provide a non-nutrient biological action, e.g. unicellular micro-organisms and in the process has pesticides or growth regulators. 6 aerial deposition

atmosphere above the soil. Poorly aerated soils planting of a forest crop on land that has not

A usually contain a much higher content of CO2 and a previously, or not recently, carried a forest crop. lower content of O2 than the atmosphere above the aflatoxin: Aflatoxin is a naturally occurring mycotoxin soil. The rate of aeration depends largely on the produced by two types of mold: Aspergillus flavus volume and continuity of air-filled pores within the and Aspergillus parasiticus. Both species are soil. common and widespread in nature, but A. flavus is aerial deposition: Some nutrients are supplied in small more likely to infect grain, cotton seed, and peanuts quantities to the soil surface through aerial deposition. grown under stressful conditions such as drought. These include nitrates in rainwater, ammonia as a Favourable conditions for mold growth include high gas or dissolved in rainwater, sulphur in acid rain, moisture content and high temperature. At least 13 salts and chlorine in marine spray and calcium in the different types of aflatoxin are produced in nature

form of dust. with aflatoxin B1 considered as the most toxic. aerial spraying: Application of pesticide or fertilizer after-cultivation: Harrowing, rolling, tilling and other in the form of spray by using aero plane or cultivations carried out in a field after the crop has helicopter, with the objective of covering vast area emerged. in a short time. agar agar: A dried gelatin like mucilaginous substance aerobic composting: The process of composting used as solidifying agent to form the base for solid organic wastes of plant and animal origin such as and semi solid culture media for bacteria. It is animal shed bedding, sweeping, urine, plant waste, extracted from Ceylon moss (Gelidium corneum), dung etc in the presence of air. red alga (Rhodophyceae). Chemically it is a kind of aerobic digestion: The partial biological polysaccharide. It solidifies at about 38°C and melts decomposition of suspended organic matter in at about 100ºC. Also known as ‘agar’. wastewater or sewage in aerated conditions. agenda 2000: It is a Common Agricultural Policy (CAP) aerobic: (i). Having molecular oxygen as a part of the reform package proposed by the European environment. (ii). Growing only in the presence of Commission in 1998. After a number of molecular oxygen, such as aerobic organisms. (iii). modifications, the European Union Heads of State Occurring only in the presence of molecular oxygen agreed to a package of reforms in March 1999. (said of chemical or biochemical processes such as agenda 21: Agenda 21 is the plan of action to achieve aerobic decomposition). sustainable development that was adopted by the aeroponics: A technique in growing plants wherein world leaders at the United Nations Conference on the plants derive their nutrients and water from a Environment and Development held in Rio de mist of air and aqueous solution that comes in contact Janeiro, Brazil, in June 1992. with the roots. aggregate demand analysis: This type of economic aerosol: Particulate matter, solid or liquid, larger than analysis takes place at the level of a region or a a molecule but small enough to remain suspended in country. It gives useful information and data of total the atmosphere. Natural sources include salt particles demand for that area and of the important from sea spray, dust and clay particles as a result of components that create that demand. It can be weathering of rocks, both of which are carried upward extremely useful for studying government policies. by the wind. Aerosols can also originate as a result However, it does not consider differences among of human activities and are often considered different groups within a society and generally pollutants. Aerosols are important in the atmosphere presents an incomplete picture of the welfare of the as nuclei for the condensation of water droplets and population. ice crystals, as participants in various chemical aggregate stability: It is a measure of the stability of cycles, and as absorbers and scatters of solar radiation, soil structure and soil tilth. Aggregate stability refers thereby influencing the radiation budget of the to the ability of soil aggregates to resist disruption Earth’s climate system. when outside forces (usually associated with water) afforestation: (i). Conversion of bare land into are applied. Aggregates are conglomerates of clay, forestland by planting of forest trees. (ii). The silt, and sand particles that are held together by agricultural economics 7

physical and chemical forces. The bonds that hold Yba = Mixture yield of species b in combination these particles together can be broken by applying with a A energy to the soil, for example, by shaking aggregates Ybb = Pure stand yield of species b in water. A common method of determining aggregate Zab = Sown proportion of species a in mixture stability is to place aggregates on a sieve with uniform with b openings and move the sieve up and down in a water Zba = Sown proportion of species b in mixture bath. If a lot of soil passes through the sieve, the with a aggregate stability is low, while it is high if most soil agrarian policy: A policy concerned with the land or remains on top of the sieve. Tillage destroys landed properties. aggregates. Increasing soil organic matter content is agrarian system: A historically constituted and the best method to increase aggregate stability. Crop durable mode of exploitation of the environment; a rotations and crop mixtures can help to improve the technical system adapted to the bioclimatic aggregation of soils. Crops with extensive, fine root conditions of a given area and which complies with systems such as grasses and cereals stimulate its social conditions and needs at that moment. aggregate stability in the long term. Crops with easily decomposed residue stimulate aggregate stability in : (i). Agriculturally related businesses that the short term, because bacteria that feast on the supply inputs (such as fertilizer or equipment) residue produce polysaccharides that act as glue or are involved in the marketing of farm products holding aggregates together. Amendments (such as (such as warehouses, processors, wholesalers, manure or sewage sludge) that stimulate biological transporters, and retailers). (ii). The combination of the activity will help improve aggregate stability. producing operations of a farm, the manufacture and distribution of farm equipment and supplies and the aggregate: A group of primary soil particles that cohere processing, storage, and distribution of farm commodities. to each other more strongly than to other surrounding particles. Soil aggregates are groups of soil particles agric horizon: A mineral soil horizon in which clay, that bind to each other more strongly than to adjacent silt and humus derived from an overlying cultivated particles. The space between the aggregates provides and fertilized layer have accumulated. The pore space for retention and exchange of air and wormholes and illuvial clay, silt and humus, occupy water. at least 5% of the horizon by volume. The illuvial clay and humus occur as horizontal lamellae or fibres, aggregation: The process whereby primary soil or as coatings on ped surfaces or in wormholes. particles (sand, silt, clay) are bound together, usually by natural forces and substances derived from root agricultural area: Land used primarily for the exudates and microbial activity. Soil aggregates are production or collection of farm commodities. According arranged to form soil peds, units of soil structure, to the land uses a distinction is made between arable classified by size, shape (platy, prismatic, columnar, land, land under protective cover, land under angular, subangular, blocky, granular…) and grade permanent crops in open air, land under permanent (single-grain, massive, weak, moderate, strong). meadows and pastures both naturally grown or From an agronomical point of view, the most cultivated. important soil aggregates are in range 3 – 1 mm. agricultural climatology: Climatology as applied to aggressivity: It gives a simple measure of how much the effect of climate on crops. It includes especially the relative yield increase in species ‘a’ is greater the length of the growing period, the relation of than that for species ‘b’ in an intercropping system growth rate and crop yields to the various climatic and can be expressed as Aab: factors and the optimum and limiting climates for any given crop, the value of irrigation, and the effect Yab Yba Aab = − of climatic and weather conditions on the Yaa Zab Ybb Zba development and spread of crop diseases . Where, agricultural economics: An applied social science Yaa = Pure stand yield of species a that deals with the production, distribution, and Yab = Mixture yield of species a in combination consumption of agricultural or farming goods and with b services. agronomic efficiency 9 agro-chemical: General term for any chemical used in factors into the analysis of food production systems /horticulture for enhancing crop and to use this knowledge to improve these systems, A production. It includes mineral fertilizers, pesticides, taking into account the needs of both the ecosystem herbicides, fungicides, plant growth regulators, as a whole and the people within it. hormones, etc. In practice however, the term is agro-economic zones: Zones which are defined in generally used for materials other than mineral terms of common features from an agricultural point fertilizers and soil amendments. of view. For different purposes these features will agroclimatic regions: The grouping of different differ but may involve such dimensions as climate, physical areas within the country into broadly soil resources, land use, ethnic groupings and market homogeneous zones based on climatic and edaphic access . factors. agroeconomics: The economics of agriculture. agroclimatic zone: A land unit defined in terms of agroecosystem (=agricultural ecosystem): (i). The major climate and growing period, which is collection of physical, environmental, economic and climatically the homogeneous response of a crop or social factors that affect a cropping enterprise. (ii). a farming system. It is composed of the total complex of the crops or agroclimatic: Relating to the relationship between animals in an area together with overall environment crop adaptation and climate. and as modified by management practices. agroclimatology: Study of those aspects of climate, : Agroforestry is a collective name for which are relevant to the problems of agriculture. land-use systems and technologies where woody perennials (trees, shrubs, palms, bamboos, etc.) are agro-ecological cell (AEC): An area or point with a deliberately used on the same land management unit unique combination of land, soil and climate as agricultural crops and/or animals, in some form of characteristics. The agroecological cell is the basic spatial arrangement or temporal sequence. In processing unit for physical analysis in an AEZ (agro- agroforestry systems there are both ecological and ecological zoning) study. economic interactions between the different agroecological zone: (i). A land resource mapping components. unit, defined in terms of climate, landform and soils, agrohydrology: The science dealing with the distribution and/or land cover, and having a specific range of and movement of rainfall and/or irrigation water and potentials and constraints for land use. Essential soil solution to and from the root zone in agricultural elements in defining an agro-ecological zone are the land, and with the distribution and movement of growing period, the temperature regime and the soil irrigation and surface water in conveyance systems units. (ii). A major area of land that is broadly on agricultural land. homogeneous in climatic and edaphic factors, but not necessarily contiguous, where a specific crop agroindustry: Industry dealing with the supply, exhibits roughly the same biological expression. (iii). processing and distribution of farm products. Zones of similar agricultural performance as defined agrology: The study of applied phases of soil science by soil and climate. and soil management. agro-ecological zoning (AEZ): The division of an agronomic characters: Plant characters related to crop area of land into smaller units, which have similar production usually observed during plant growth; characteristics related to land suitability, potential e.g., height, maturity, tiller number, panicle size, yield production and environmental impact. and quality factors. : (i). The study of the interrelationships agronomic efficiency: Denotes the units of additional of living organisms with each other and with their crop produced per unit of input (nutrient) added environment in an agricultural system. (ii). The use externally. Example: kg grain/kg of a nutrient (macro of ecological concepts and principles to study, design, or micro) added. Agronomic efficiency has a direct and manage agricultural systems. Agroecology seeks bearing on better utilization of applied nutrients, to evaluate the full effect of system inputs and the profitability of their usage and minimization of outputs by integrating cultural and environmental nutrient losses. 10 agronomic rate

agronomic rate: The rate at which fertilizers, organic ahu rice: An early rice similar to “Aus”; grown in A wastes or other amendments can be added to soils Assam, India. for optimum plant growth. air (=aerial) photographs: Photographs of the land : (i). Science of agriculture that deals with surface taken from aircraft, usually at a vertical angle, all aspects of field crop production and soil normally at scales of from 1:50000 to 1:5000. For management. (ii). A branch of agriculture dealing with interpretation, air photographs are viewed all aspects of tillage, crop production and soil stereoscopically to give a three-dimensional management including nutrient management. Derived impression. Landforms, vegetation, land use and from the Greek word “agros” meaning fields and some infrastructure (especially roads and tracks) can “nomos” meaning management. be directly seen on air photographs, while soil agropastoral system: A land-use system in which properties, geology and other land properties require crops and (but not trees) are the only indirect interpretation and administrative boundaries components. cannot be seen. Air photographs can also be used as base maps for presentation of a land-use plan. Air agrosilvicultural system: An agroforestry system for photographs may be panchromatic (black and white), the concurrent production of agricultural crops colour (true colour) or false colour. (including woody perennial crops) and forest crops. The forest crops serve in either a productive or a air (-filled) porosity: The fraction of the bulk volume service role. Woody perennial and agricultural crops of soil that is filled with air at any given time or are chosen first for their productive capacity. under a given condition, such as a specified soil- water content or soil-water matric potential. agrosilvipastoral system: Any agroforestry system that includes trees or shrubs and herbaceous food air dry: (i). The state of dryness at equilibrium with the crops and pastures and animals. water content in the surrounding atmosphere. The actual water content will depend upon the relative agrostology: A branch of science which deals with the humidity and temperature of the surrounding study of grasses, their classification, management atmosphere. (ii). To allow to reach equilibrium in water and utilization. content with the surrounding atmosphere. agrotain: Agrotain (NBPT) is a product that inhibits air entry value: The value of water content or potential conversion of urea to ammonium carbonate, thereby at which air first enters a porous media. reducing the potential for ammonia volatilization from urea materials, including UAN solutions. Like air mass: Large body of air, often hundreds or thousands N-Serve , it might be viewed as an insurance policy of miles across, containing air of a similar temperature that will reduce potential nitrogen losses in seasons and humidity. Sometimes the differences between when cultivation or rain does not incorporate the air masses are hardly noticeable, but if colliding air urea into the soil soon after application. It is most masses have very different temperatures and useful when urea or UAN are applied without humidity values, storms can erupt. incorporation to the surface of fields with high levels air pollution: One or more chemicals or substances in of crop residue, such as in no-till situations, or fields high enough concentrations in the air to harm humans, with high pH levels at the surface. other animals, vegetation, or materials. Such agroterrorism: The deliberate introduction of an chemicals or physical conditions (such as excess heat animal or plant disease with the goal of generating or noise) are called air pollutants. fear, causing economic losses, and/or undermining akiochi soil: Soil with an imbalance of nutrients stability. Agroterrorism is a subset of the more associated with hydrogen sulphide toxicity. These general issue of bioterrorism. An agroterrorism event are flooded soils where hydrogen sulphide is formed would affect the production agriculture sector due to sulphate reduction and anaerobic economically in terms of plant and animal health, decomposition of organic matter. and affect supply and demand. Humans could be at albedo: The fraction of the total solar radiation incident risk in terms of food safety or public health, on a body that is reflected by it. Albedo can be especially if the chosen disease is transmissible to expressed as either a percentage or a fraction of 1. humans (zoonotic). Snow covered areas have a high albedo (up to about 12 alkaline (or basic) fertilizer

reaction). Gelatinization temperature of starch is (iii). This is an advanced form of agroforestry in A estimated based on spreading value: low (6-7); which food crops are planted in the alleys (inter- intermediate (4-5); intermediate-high (3); and high row area) between lines of trees, shrubs or (1-2). leguminous crops. Alley crops, such as maize, millet, alkaline (or basic) fertilizer: A fertilizer, which leaves cassava or grasses are grown between rows of behind an alkaline reaction in the soil (raises soil perennial trees, such as Azadirachta indica, pH). Example: calcium nitrate, sodium nitrate. L. leucocephala or Gliricidia sepium, from which leaf material can be taken for mulching, or shrubs alkaline: Having a pH higher than 7. such as C. cajan, that form hedges. The deep-rooting alkalinity: The quality, state, or degree of being alkaline. system of such perennial trees or shrubs can bring alkalinophile: Alkali-loving. An organism that grows nutrients from deeper layers of the soil up to those well at an alkaline pH (above 7). Example: layers where they can be taken up by the roots of Agrobacterium. agricultural crops, i.e. a form of nutrient cycling. alkalization: Alkalization is a next step to salinization. alley crops: When arable crops are grown in alleys It takes place due to preponderance of Na ions in formed by trees or shrubs, established mainly to the exchange complex. When Na from the soluble hasten soil fertility restoration, enhance soil salts enters into clay complex (due to base exchange productivity and reduce soil erosion they are known reactions) and its proportion increases, the soils as alley crops. Such crops should have slight shade become alkaline. tolerance and should be non-trailing, for instance allelochemicals: Non-nutritional substances sweet potato, blackgram, turmeric and ginger in produced by a plant that affect the behaviour, growth, between the rows of Eucalyptus, subabool and health, or physiology of another plant or insect. Cassia. Certain crop residues produce allelochemicals during allochthonous flora: Organisms that are not indigenous decomposition, if sufficient time is allowed to lapse to the soil but that enter soil by precipitation, diseased between the harvests and sowing of the subsequent tissues, manure, and sewage. They may persist for crop, the allelochemicals produced disappear. some time but do not contribute in a significant allelo-inhibition: Allelochemicals inhibit more the way to ecologically significant transformations or growth of plants of species other than producer interactions. species. allometric relationships: The changes in the ratio allelopathy: (i). An interaction between different plants between two dimensions of an organism, such as or between plants and microorganisms in which root weight:shoot weight or total dry weight: stem substances (allelochemicals) produced by one diameter. It can be expressed over time or, better, organism affect the growth of another (usually with reference to changes in a particular growth factor adversely). (ii). The suppression of germination or (for example, specific root or shoot activity). Important growth or the limiting of the occurrence of plants, as in defining partitioning of dry matter in plants. a result of the release of chemical inhibitors by some allophane: An aluminosilicate with primarily short- plants. range structural order. Occurs as exceedingly small alley cropping: (i). An agroforestry intercropping spherical particles especially in soils formed from system in which species of shrubs or trees are volcanic ash. planted at spacing relatively close within row and allowable soil-water depletion: Depth of soil water wide between row, to leave room for herbaceous in the root zone readily available to the crop for cropping between, that is, in the ‘alleys’ (syn: given soil and climate allowing unrestricted evapo- hedgerow intercropping). (ii). A conservation- transpiration as the fraction of total available soil oriented farming system in which arable (field) crops water between field capacity and wilting point. are grown in alleys formed by trees or shrubs, mainly Expressed as mm/m. to hasten soil fertility restoration, enhancing soil alluvial fan: A fan or cone-shaped mass of sand and productivity and conserving the soil. Commonly gravel deposited by a stream where it emerges from a practiced in tropical and subtropical rainfed areas. narrow valley and spreads on to a plain or wide valley. aluminium fertilizers 13 alluvial soil: (i) A soil developing from recently alternative crops: Non-traditional crops that can be deposited alluvium and exhibiting essentially no grown in an area to diversify rotations and increase A horizon development or modification of the recently income. deposited materials. (ii) When capitalized the term alternative energy: Energy produced from sources refers to a great soil group of the azonal order other than fossil fuels (solar, wind, hydroelectric, consisting of soils with little or no modification of geothermal, and biomass). the recent sediment in which they are forming. This altimeter: An instrument used to measure the altitude is by far the largest and most important soil group of an object above a fixed level. For example, a laser of India contributing the largest share to the altimeter can measure height from a spacecraft to an agricultural wealth. In this immense tract though a ice-sheet. That measurement, coupled with radial great deal of variation exists, the main features of the orbit knowledge, will enable determination of the soil are derived from the deposition laid by the topography. numerous tributaries of the Indus, the Ganges, and altitude: Vertical distance above sea-level. the Brahmaputra systems. These streams , draining altocumulus cloud: Middle altitude cloud that is the Himalayas, bring with them the products of coloured from white to gray. This cloud is composed weathering of rocks constituting the mountains in of a mixture of water droplets and ice crystals. It various degrees of fineness and deposit them on appears in the atmosphere as layers or patches that the plains. are well rounded and commonly wavelike. Found in alluvial terraces: Flat elevated benches composed of an altitude range from 2,000 to 8,000 metres. unconsolidated alluvium found either side of a stream altostratus cloud: Gray-looking middle altitude cloud channel. Formed when a stream down cuts into its that is composed of water droplets and ice crystals. floodplain. Appears in the atmosphere as dense sheet like layer. alluvial: Pertaining to alluvium; a clayey, silty, sandy, Can be recognized from stratus clouds by the fact or gravely material deposited by a stream or other that you can see the sun through it. Found in an bodies of running water. altitude range from 2,000 to 8,000 metres. alluvium: Sediments deposited by running water of aluminium and hydrogen toxicity: It is caused by streams and rivers. It may occur on terraces well excess water-soluble and exchangeable aluminium, above present streams, on the present flood plains usually on acid sulphate soils and strongly acidic or deltas, or as a fan at the base of a slope. soils. Symptoms are white or yellow interveinal blotches on the leaves. The leaves dry out and die. alternate drying and wetting (rice): Frequent Roots are short and scanty and plants are stunted. draining and reflooding (aerobic and anaerobic cycle) Root injury is observed at pH 5.0 and lower. At in rice fields, especially to save water. these low levels, lateral root development is alternate set irrigation: A method of managing suppressed and in some cases root tips are killed. irrigation whereby, at every other irrigation, alternate The roots become discoloured brown or a dull gray furrows are irrigated, or sprinklers are placed midway (similar to nematode damage). At low pH and low between their locations during the previous irrigation. Ca concentrations, damage to root membranes is alternate side irrigation: The practice of furrow accentuated. At pH 5.0 and below, high Al irrigating one side of a crop row (for row crops or concentrations suppress the uptake of cations such ) and then, at about half the irrigation time, as Ca and Mg and results in deficiencies of these irrigating the other side. elements, particularly in soils with a very low cation alternative agriculture/ farming: A concept of exchange capacity (CEC). At pH 5.5 and above, farming based on the exclusion of mineral fertilizers however, there is little if any suppression of cation and synthetic pesticides but including mainly organic uptake. manures, waste recycling and biological agents, as in aluminium fertilizers: Aluminium appears to be , in contrast to modern agriculture in beneficial to only to a few plants, e.g. tea. Tea leaves which optimum use of mineral fertilizers and contain 0.2–0.3 percent Al, which appears to pesticides is sought to be made. promote growth. Where Al is considered to be 14 aman rice

deficient, aluminium sulphate [Al2(SO4)3] can be alanine, valine, leucine, isoleucine, proline, A added. However, aluminium sulphate acts mainly as phenylalanine, tryptophane and cysteine); acidic a soil-acidifying agent and its favourable effect on (aspartic acid and glutamic acid) and basic (lysine, some “acid-loving” plants such as blueberries may arginine, hystidine). The sequence of amino acids not be due to an improved Al supply but to the determines the shape, properties and the biological mobilization of some micronutrients as a result of role of a protein. Plants and many microorganisms acidification. For most crops, even small amounts can synthesize amino acids from simple inorganic of soluble Al ions are toxic. compounds. Aspartic acid and glutamic acid play a aman rice: A term used in Bangladesh and East India significant role in BNF. for lowland rice grown in the wet season during June ammonia volatilization: It refers to the gaseous loss to November. Water depth does not exceed 0.5 m. of nitrogen as ammonia from the soil. Ammonium N + ambient air: Air that reflects surrounding environmental (NH4 -N) in the soil is either formed by conditions. mineralization of soil organic N and applied inorganic N or after hydrolysis of urea. This NH + can undergo ameliorant: A substance added to a soil for the 4 several processes such as adsorption on soil colloids, improvement of its physical and chemical properties fixation by clay minerals, nitrification, fixation by so as to help in improving its tilth for realizing higher microorganisms or volatilization. Ammonium in the crop yields. Term not used for mineral fertilizers soil is in equilibrium with atmospheric ammonia but sometimes for bulky organic manures. Example: (NH ) through different equilibria. Volatilization lime to acid soils, gypsum and pyrites to alkali soils. 3 usually occurs from surface applied fertilizer, Similar to soil amendment. especially urea, and can be severe in alkaline sandy amensalism: An interaction between two organisms soils during hot and dry periods. in which one organism is suppressed by toxins ammonia: It is a gas at normal temperature and produced by the other. pressure. It is a gas containing about 80 percent of amide-N: It is form of nitrogen in urea is transformed nitrogen. Under suitable conditions of temperatures (hydrolyzed) relatively rapidly through the activity and pressure, it becomes liquid (anhydrous of the enzyme urease, which is ubiquitous in surface ammonia). Another form, ‘aqueous ammonia’, results soils, to ammonia, CO2 and H2O: from the absorption of ammonia gas into water, in + →Urease + which it is soluble. Ammonia is used as a fertilizer in CO(NH)222 HO 2NH 32 CO Even at relatively low temperatures the transformation both these forms. Anhydrous ammonia can be applied of amide-N to ammonium-N is completed within by introducing it into irrigation water, or directly one to three days, under tropical and subtropical into the soil from special containers, which makes conditions within few hours. Where urea is not its use rather expensive. It gets converted to + incorporated into the soil, but left on the soil surface, ammonium ions (NH4 ) in water which is one of the substantial evaporation losses of ammonia will occur, main forms in which plants absorb N from soil. particularly on alkaline soils (soils with a high pH ammoniated superphosphate: A product obtained value). Where it is incorporated - and a superficial from superphosphate treated with ammonia or incorporation is sufficient - the ammonia is attracted solutions containing free ammonia. The end product + (adsorbed) as NH4 on the clay and organic matter provides extra nitrogen but in the process its total particles of the soil and thus protected against phosphorus content as also the water solubility of evaporation losses. this phosphorus is decreased. amino acid: A group of acids containing the amino ammoniation: It is the process of introducing various

group (NH2). In particular, any of 20 basic building ammonium sources into other fertilizer sources blocks of proteins with a free amino (NH2) and a forming ammoniated compounds. Ammonium free carboxyl (COOH) group, and having the basic polyphosphates and ammoniated superphosphate

formula NH2-CH(-R)-COOH. According to the side are ammoniated compounds. group R, they are subdivided into: polar or ammonification: A process describing the hydrophilic (serine, threonine, tyrosine, asparagine transformation of organic nitrogen (as in protein) and glutamine); non-polar or hydrophobic (glycine, into ammonia with the help of ammonifying 16 ammonium sulphate (AS)

ammonium sulphate (AS): It contains 21 per cent N amplitude: The magnitude of the displacement of a A and 24 percent sulphur (S). This fertilizer is non- wave from a mean value. For a simple harmonic hygroscopic, with good handling and storage wave, it is the maximum displacement from the mean. characteristics. It is especially suitable for use in the For more complex wave motion, amplitude is usually humid tropics and subtropics. After application, part taken as one-half of the mean distance (or difference) + - of the NH4 is normally transformed to NO3 and between maxima and minima. available for plant uptake or denitrification and loss. anabaena azollae: A species of Anabaena, which only Ammonium can also be fixed on clay minerals and grows with its host Azolla (a fern) where it lives in retained by soil colloids preventing it from leaching. the cavity of Azolla’s dorsal leaf lobe. It fixes nitrogen Most ammonium sulphate results as a by-product of symbiotically with Azolla. industrial processes. It is not a widely used material, anabaena: A genus of blue green algae. It has 15 species due to its relatively low nitrogen content, but may e.g. Anabaena ambigna, Anabaena doliolum etc. become more popular as sulphur deficiencies become One of the BGAs which is used as biofertilizer for more widespread. It is not as prone to nitrogen flooded rice. volatilization as urea, but is slightly more so than ammonium nitrate, particularly on alkaline soils. anaerobe: An organism, which lives and grows in the absence of free oxygen. Example: Clostridium tetani. ammonium sulphate nitrate (ASN): A fertilizer containing 26 percent N and 15 percent S, both in anaerobic composting: One of the methods of soluble and plant available form. It is a double salt of composting in which the decomposable wastes are kept ammonium sulphate and ammonium nitrate in which under insufficient air/oxygen supply. Decomposable 75 percent of total N is present as ammoniacal-N raw material is filled in pits to a height of 40-50 cm. and 25 percent as nitrate-N. Agronomically, it is The decomposition of organic matter is caused by comparable to ammonium sulphate, except for the microorganisms in an anaerobic (absence of air/ more mobile nitrate-N component in ASN. oxygen) environment. The compost is ready within 4-5 months and contains 0.8-1.0% N. See compost. ammonium thiosulphate: A liquid fertilizer containing 12 percent N and 26 percent S (thio refers anaerobic respiration: The metabolic process to S). Fifty percent of the S is in the sulphate form whereby electrons are transferred from a reduced and the rest is in elemental form. It can be used compound (usually organic) to an inorganic acceptor directly or mixed with neutral to slightly acid P- molecule other than oxygen. The most common containing solutions or aqueous ammonia or N acceptors are carbonate, sulphate, and nitrate. solutions to prepare a variety of NPK + S and NPKS anaerobic: (i). The absence of molecular oxygen. (ii). + micronutrient formulations. It can also be applied Growing in the absence of molecular oxygen (such through irrigation, particularly through drip and as anaerobic bacteria). (iii). Occurring in the absence sprinkler irrigation. of molecular oxygen (as a biochemical process). + ammonium-N (NH4 -N): It is the most common form andosols: Andosols (derived from Jap. ando=black) of mineral N in manure/fertilizers and other organic [Andisols in the US system] make up about 1% of soil amendments. It is also subject to loss (through tropical soils, originating from young, volcanic glassy volatilization) into the air if manure/fertilizer is left ashes. Grey to black in colour, they weather rapidly laying on the surface of the soil. Ammonium N will to allophanes with a large pH dependent variable bind to soil particles so does not normally leach. charge. They are very fertile soils. They have a large amoozemeter: A tool that uses a constant head of waterholding capacity, good porosity, allowing rapid water to measure the rate of water movement in a water infiltration, and up to 20% SOM. The strong saturated soil, and thus estimates saturated hydraulic anion fixing capacity, mainly for P, increases with conductivity. decreasing pH. However, this nutritional constraint can be partly compensated for by mulching. amphoteric: A substance that can act as either an acid or a base in a reaction. For example, aluminium anemometer: Mechanical instrument used to measure wind speed. These instruments commonly employ hydroxide can neutralize mineral acids ( Al(OH)3 + three methods to measure this phenomenon: (i). A 3 HCl = AlCl3 + 3 H2O ) or strong bases ( Al(OH)3 device with three or four open cups attached to a + 3 NaOH = Na3AlO3 + 3 H2O). 18 anion

anion: A negatively charged ion. Example: nitrate (NO3), therefore important in petroleum exploration and 2– – A sulphate (SO4 ), borate [B(OH)4 ], molybdate extraction. The opposite of a syncline. 2 – (MoO4 ), chloride (Cl ). During electrolysis, it anticyclone: An atmospheric pressure system travels to the anode (positive electrode). consisting of an area of high pressure and outward annual crops: Crop plants that complete their life circular surface wind flow. In the Northern cycles within a season or year such as rice, wheat, Hemisphere winds from an anticyclone blow maize, mustard and tobacco. They produce a crop clockwise, while in Southern Hemisphere systems of seed and die. Some of these crop plants may blow counterclockwise or anticlockwise. produce tillers. If such rooted tillers are separated anti-quality constituents (forages): The toxic from the main shoot and planted, each tiller will substances present in forage plants which may either survive that season as a new plant, but will not live cause direct metabolic damage to the animal or until another season. interfere with some phase of digestive utilization annual plants: Plant species that complete their life- are referred to as anti-quality constituents. The anti- cycle within 12 months from the date of germination. quality constituents of some forage species are as antagonism: In plant nutrition, the interference of follows: Castrogens (Subterranean clover, red clover, one element with the absorption or utilization of white clover), Coumarins (Sweet clover-Melilotus other nutrient by plants. spp.), Saponins (Lucerne/alfalfa, ladino clover, bur clover, strawberry clover, trefoil), Alkaloids antagonism: It is the phenomenon in which one (Phalaris, Lupins, Desmodium, Lespedeza, element or substance inhibits or reduces the uptake, Crotalaria), Hydrocyanic acid/HCN/ prussic acid / assimilation or performance of the other. It is not cyanigenetic glucosides (Sorghum spp., Trifolium mutually beneficial or performance-enhancing. repens, Lotus spp., Poa acquatica, Zieria laevigata, Common in soil-plant systems and largely a fall-out Phyllanthus qastroemmii, Cynodon plectostachyus, of nutrient imbalance. Example: P-Zn antagonism. Pteridium acqullinum), Nitrate (Oat, paragrass), Nutrients exhibiting antagonism are referred to as Oxalic acid (Napier grass, pearlmillet), Mimosine antagonistic. (subabool- Leucaena leucocephala), Bloat-producing antagonistic symbiosis: A symbiotic association constituents-plant cytoplasmic protein (Trifolium which is destructive to one of the symbionts or spp., white clover), and Tannins (Shrub and tree partners involved in the association. spp.). anthropogenic: Human made. In the context of apatite: Common name of the major P-bearing greenhouse gases, emissions that are produced as a compound in rock phosphates (used as raw material result of human activities. in the manufacture of phosphate fertilizers). General

antibiosis: The antagonistic association between two formula: Ca10(PO4, CO3)6 (F, OH, Cl)2. Depending organisms producing detrimental effects on one of upon the dominance of F, Cl or OH in the apatite them. It could also mean an association between one crystal structure, it is known as fluorapatite, organism and a metabolic product of another. chlorapatite or hydroxyapatite. anti-caking agent: A Substance used as surface apedal soil material: Soil materials without peds, i.e. treatment for granular fertilizers to prevent caking structureless. or lump formation on storage particularly under apparent nutrient recovery (ANR): A conventional humid conditions or on prolonged storage. Used measure of the proportion of applied nutrient mostly for fertilizers containing major nutrients. recovered in the crop biomass. If a crop absorbs 10 Example: talc, chalk, kaolin, oil, clay. kg P/ha without P application and 16 kg P/ha when anticline: Layers of rock folded into the shape of an 30 kg P/ha is applied, then the apparent recovery of arch. The youngest rock layers are on the outer layer P is 20% {(16-10)x100/30}. of the arch, and the oldest layers are at the core of application rate: (i). (irrigation) Rate at which water the fold. Anticlines with reservoir-quality rocks in is applied per unit area; usually in mm per hour, (ii). their core and impermeable rocks in the outer layers Weight or volume of a fertilizer, soil amendment, or of the fold are excellent traps for oil and gas and are pesticide applied per unit area. aquox 19 application rate: The amount of fertilizer, insecticide, aqueous ammonia: A solution containing water and or herbicide applied per unit area or volume in ammonia in any proportion, usually qualified by a A experiments or commercial production. reference to ammonia vapour pressure. Aqua applied research: Research in which results can be ammonia for example has a pressure of less than 0.7 2 2 used immediately by the farmer and can be applied kg/cm (10 lb/in ). Commercial grades commonly to the peculiar problems of a country or a region. contain 20-25% nitrogen. It is used either for direct application to the soil or for preparation of appropriate technology: It is a technology that may ammoniated superphosphate. be suitable or proper in the context of a particular community, region, or country. It must be aquerts: Vertisols that are saturated with water for economically viable, technologically feasible and periods long enough to limit their use for most crops should fit in the socio-economic fabric of the local other than pasture and woodland unless they are communities. artificially drained. Aquerts have in one or more horizons between 40 and 50 cm from the surface, approved fertilizer/fertilizer grade: A fertilizer/ aquic conditions for some time in most years and fertilizer grade, which is recognized through fertilizer chromas of two or less in 50 percent of the pedon or legislation and listed in the fertilizer legislation evidence of active ferrous iron. documents of a country. Example: fertilizers, which are listed in the Fertilizer Control Order (FCO) and aquic conditions: Continuous or periodic saturation approved for production or sale in India. and reduction. The presence of aquic conditions is indicated by redoximorphic features and can be aqua regia: A mixture of nitric and hydrochloric acids, verified by measurement of saturation and reduction. usually 1:3 or 1:4 parts HNO3 to HCl, used to dissolve gold. aquic moisture regime: A reducing moisture regime in a soil that is virtually free of dissolved oxygen : Aquaculture is the farming of aquatic because it is saturated by ground water or by water organisms including fish, molluscs, crustaceans and of the capillary fringe. aquatic plants. Farming implies some sort of intervention in the rearing process to enhance aquic: A mostly reducing soil moisture regime nearly production, such as regular stocking, feeding, free of dissolved oxygen due to saturation by protection from predators. groundwater or its capillary fringe and occurring at periods when the soil temperature at 50 cm below aqualfs: Alfisols that are saturated with water for the surface is >5°C. periods long enough to limit their use for most crops other than pasture or woodland unless they are aquiclude: A sediment body, rock layer, or soil horizon artificially drained. Aqualfs have mottles, iron- that is incapable of transmitting significant quantities manganese concretions or gray colours immediately of water under ordinary hydraulic gradients. below the A1 or Ap horizons and gray colours in the aquifer: Rock formations that store groundwater. A argillic horizon. (A suborder in the U.S. system of saturated, permeable geologic unit of sediment or soil taxonomy.) rock that can transmit significant quantities of water aquasilvicultural system: An agroforestry system under hydraulic gradients. that combines trees with the raising of aquatic aquitard: A body of rock or sediment that retards but animals. does not prevent the flow of water to or from an aquatic plant: A plant that grows and develops in adjacent aquifer. It does not readily yield water to standing water and provides sufficient aeration to wells or springs but may serve as a storage unit for the parts under water. groundwater. aquents: Entisols that are saturated with water for aquorizem: Soil characterized by a distinct accumulation periods long enough to limit their use for most crops horizon of iron oxide and manganese oxide below other than pasture unless they are artificially drained. the traffic pan, formed as result of wetland rice Aquents have low chromas or distinct mottles within cultivation. 50 cm of the surface, or are saturated with water at aquox: Oxisols that have continuous plinthite near all times. the surface, or that are saturated with water sometime 20

during the year if not artificially drained. Aquox have aridisols: Mineral soils that have an aridic moisture A either a histic epipedon, or mottles or colours regime, an ochric epipedon, and other pedogenic indicative of poor drainage within the oxic horizon horizons but no oxic horizon. Soil order representing or both. desert ands semi-desert (arid and semi-arid) mineral arable land: Land which is ploughed, and on which soils (USA system). Example: Soils of western crops are cultivated; agriculture based on the Rajasthan. Such soils can be (but not always) deficient production of field crops, such as sorghum, millet, in sulphur, zinc and iron. Boron toxicity is possible maize and vegetables. Arable land includes all land in these soils. used in most years for growing temporary crops aridity index (AI): According to Thornthwaite, the and which is lying fallow or has not been sown due degree of water deficiency below water need at any to unforeseen circumstances. Arable land does not given station. It is a measure of dryness of a region include land under permanent crops or land under and is expressed as: protective cover. No. of rainy days × Mean precipitation / day AI = arboretum: A collection of specimen trees, preferably Mean temperature + 10 growing close to a nursery, from which seeds and cuttings can easily be gathered. aroma: The distinctive smell imparted by the volatile arboriculture: A general term for the cultivation of trees. constituents present in the planting material, its distilled essential oil and oleoresin extract. archaebacteria: (i). Prokaryotes with cell walls that lack murein, having ether bonds in their membrane aromatic compound: Carboxylic compound containing phospholipids, that are characterized by growth in a certain amount of unsaturation in the ring. extreme environments. (ii). A primary biological aromatic: Applied to a group of hydrocarbons and kingdom distinct from both eubacteria and their derivatives characterized by the presence of eukaryotes. the benzene ring. area-time equivalency ratio: It is the ratio of number arrowing: The flowering in sugarcane is referred as of hectare-days required in to the arrowing. number of hectare-days used in intercropping to arsenic: Arsenic is a highly poisonous semi-metallic produce identical quantities of each of the component element. It can cause bladder, lung, and skin cancer crop. and may cause kidney and liver cancer. Arsenic harms argillic horizon: A mineral soil horizon that is the central and peripheral nervous systems, as well characterized by the illuvial accumulation of as heart and blood vessels, and causes serious skin phyllosilicate clays. The argillic horizon has a certain problems. It also may cause birth defects and minimum thickness depending on the thickness of reproductive problems. These health impacts are caused the solum, a minimum quantity of clay in comparison when arsenic contaminates drinking water supplies. It with an overlying eluvial horizon depending on the enters water supplies either from natural deposits in clay content of the eluvial horizon, and usually has the earth or from industrial and agricultural pollution. coatings of oriented clay on the surface of pores or artesian water: Groundwater confined under peds or bridging sand grains. hydrostatic pressure. arid climate: Generally extremely dry climate. W. artesian well: A well where the water rises and flows Koeppen and others have applied the name desert out to the surface because of hydrostatic pressure. climate for similar conditions of extreme aridity. artificial water bodies: Areas which are covered by Annual precipitation usually less than 10 inches. It water due to the construction of artifacts such as is not suitable for crop production without irrigation. reservoirs, canals and artificial lakes. Without these aridic: A soil moisture regime that has no water structures the area would not be covered by water . available for plants for more than half the cumulative arviculture: Crop science. time that the soil temperature at 50 cm below the surface is >5°C, and has no period as long as 90 ash: The mineral residue remaining after the destruction consecutive days when there is water for plants while of organic material by burning. Ash of plant residues the soil temperature at 50 cm is continuously >8°C. or wood is usually a rich source of potassium. 22 atomic weight

presented by the electrons, for example, atomic chamber for the steam and that is used for sterilizing, A number of hydrogen is 1. cooking or other purposes requiring moist temperatures o atomic weight: The average weight of the neutral atoms above 212 F or 100°C. Used for sterilization. of an element existing as a mixture of isotopes in the autotroph: An organism that produces food molecules same ratio as found in nature. inorganically by using a light or chemical based auger (soil): A tool for boring holes into the soil. A sources of external energy. This organism does not soil auger is used to withdraw a small soil sample for require outside sources of organic food energy for observation. survival. augmentation cropping: When subcrops are sown to autotrophic nitrification: Oxidation of ammonium supplement the yield of the main crops, the subcrops to nitrate through the combined action of two are known as augmenting crops, for instance chemoautotrophic bacteria, one forming nitrite from Japanese mustard with berseem, chinese cabbage ammonium and the other oxidizing nitrite to nitrate. with mustard. Here the mustard or cabbage helps in autotrophic: Self-nourishing organisms capable of getting a higher yield of fodder in spite of the fact utilizing carbon dioxide or carbonates as the sole that berseem gives a poor yield in the first cutting. source of carbon and obtaining energy for life auricle: (i). A pair of small ear-like appendages borne processes from radiant energy or from the oxidation at the base of the leaf blade and usually arising at of inorganic elements or compounds such as iron, the sides where the ligule and the base of the collar sulphur, hydrogen, ammonium and nitrate. Example: are joined. (ii). An ear-shaped appendage, usually green plants, crops, some algae, and nitrifying occurring at the junction of the leaf sheath and the bacteria. blade that may not be present in older leaves. availability (fertilizer): The extent to which the aus rice: A photoperiod-insensitive, rainfed, drought- nutrients in a fertilizer can be taken up by crops, prone, lowland, or upland rice, broadcast and often measured approximately (in the absence of a transplanted during the early part of the wet season good biological criterion) by solubility in water or from March to September in Bangladesh and from dilute acids; also used of soil nutrients to describe April to August in east India. the fraction that can be taken up by plants. autecology: (i) The of an individual organism available nutrient: Form(s) of a plant nutrient in the or taxonomic group. (ii). The study of environmental soil or fertilizer that is immediately or potentially organisms and their effects on plants. available for being taken up by growing plants during their growth span. This is usually a small fraction of autochthonous flora: (i). That portion of the the total nutrient content of the soil. Usually microflora presumed to subsist on the more measured in soil testing laboratories for making resistant soil organic matter and little affected by

the addition of fresh organic materials. (ii). fertilizer recommendations. Example: sodium bicarbonate-extractable P, CaCl -extractable S, Microorganisms indigenous to a given ecosystem; 2 the true inhabitants of an ecosystem; referring to DTPA-extractable Zn. In soils, available nutrient the common microbiota of the body of soil status if measured correctly describes the state of microorganisms that tend to remain constant despite soil fertility at that particular time and provides a constant fluctuations in the quantity of fermentable guideline for external nutrient application. organic matter. Contrast with zymogenous flora. available soil water: The available water capacity of Also called as oligotrophs. a soil refers to the maximum quantity of water that autochthonous: Microorganisms and/or substances can be extracted from the soil profile by plants. It is indigenous to a given ecosystem; the true inhabitants generally defined as the difference in the amounts of of an ecosystem; referring to the common microbiota water held by a soil when at field capacity and when of the body of soil microorganisms that tend to remain at its permanent wilting point (-1.5 MPa matric potential). In fact, the soil water content at which constant despite fluctuations in the quantity of non-recoverable wilting occurs is crop dependent. fermentable organic matter. Because of the shape of the water retention curve at autoclave: An airtight chamber that can be filled with low water potentials, precise definition of steam under pressure or surrounded by another permanent wilting point is less critical than that of