Tamil Nadu HSE Second Year Agricultural Science key terms

The number of crops raised on the same field in one agricultural year, expressed as a percentage of the net sown area; growing two crops gives 200 per cent and indicates how intensively land is used.

Growing a planned sequence of different crops on the same land over successive seasons so that soil fertility is maintained and pest and disease cycles in the soil are broken.

Practice of raising two or more crops on the same field in a single year, either in sequence or together, to increase total output and spread the risk of crop failure.

Growing two or more crops simultaneously in the same field in definite row proportions, chosen so that the crops compete minimally and together yield more than either alone.

Index comparing the land area needed in sole cropping with the area needed in intercropping to produce the same yield; a value above one shows an intercropping advantage.

Total quantity of exchangeable cations a soil can hold on its clay and humus surfaces, measured in centimoles of charge per kilogram; it indicates the soil's ability to retain plant nutrients.

Proportion of the soil's cation exchange capacity occupied by basic cations such as calcium, magnesium, potassium and sodium rather than by hydrogen and aluminium; high values indicate a less acidic soil.

Degree of acidity or alkalinity of the soil expressed as pH measured in a soil-water suspension; it governs nutrient availability, microbial activity and choice of crop and amendment.

Quantity of agricultural lime needed to raise the pH of an acidic soil to a target level suited to the crop, determined from the soil's exchangeable acidity and buffer capacity.

A quick-growing legume or other crop raised and ploughed into the soil while still tender, so that its biomass adds organic matter and biologically fixed nitrogen to the field.

Material of plant or animal origin such as farmyard manure, compost or vermicompost applied to supply nutrients slowly, improve soil structure and support soil microbial life.

The stage in a crop's life when weeds must be removed to prevent the largest yield loss; it usually falls early in the season, when the crop is small and growth is slow.

Chemical used to kill or suppress weeds; selective types injure weeds without harming the crop, while non-selective types kill all vegetation and are used before planting or between rows.

Portion of sunlight, roughly 400 to 700 nanometres in wavelength, that chlorophyll can absorb and use in photosynthesis; it sets the upper limit on dry matter production by a crop.

Total leaf area of a crop canopy divided by the ground area it occupies; values near three to four usually give maximum light interception and crop growth.

Ratio of economic yield, such as grain or fibre, to total biological yield of the crop, expressed as a percentage; it shows how efficiently dry matter is partitioned to the harvested part.

Weight of water transpired by a crop divided by the weight of dry matter produced; a lower ratio means the crop uses water more efficiently.

Amount of crop yield or dry matter produced per unit of water used, whether supplied by rain or irrigation; it guides scheduling of irrigation and choice of methods.

Moisture content remaining in a soil two to three days after thorough wetting, once free water has drained away; it is the upper limit of readily available soil water.

Soil moisture content at which a plant wilts and cannot recover even in a humid atmosphere, because the remaining water is held too tightly for roots to absorb.

Water held in the soil between field capacity and permanent wilting point, which roots can take up; it is the useful reservoir an irrigator manages.

Method of applying water drop by drop through emitters near the root zone, saving water and reducing weed growth and leaf wetness compared with flooding the whole field.

Application of soluble fertiliser through an irrigation system, usually drip, so that nutrients reach the root zone in small doses matched to crop demand.

Approach combining resistant varieties, cultural methods, biological control and monitored, need-based pesticide use so that pests are kept below economic injury levels with least harm to the environment.

Pest population density at which control measures must be started to prevent the pest from rising to the level where the crop loss equals the cost of control.

Four steps used to prove that a microorganism causes a disease: it must be found in diseased plants, isolated in pure culture, re-inoculated to produce the same symptoms, and recovered again.

Suppression of a pest or pathogen by its natural enemies such as predators, parasitoids or antagonistic microbes, released or conserved in the field as part of integrated pest management.

Production of seed without fertilisation, so that seedlings are genetically identical to the mother plant; it interests horticulturists because it fixes hybrid vigour in fruit crops.

Raising a new plant from a detached stem, leaf or root piece that forms roots and shoots; it keeps the variety true to type, unlike seed propagation.

Heating animal fat or bone to melt and separate the fat from protein and moisture; the clarified fat is used in feed and industrial products.

Fodder crop preserved by controlled anaerobic fermentation in a pit or silo, where acids lower the pH and keep the green feed usable for livestock over dry periods.

Gross income from an enterprise minus its variable costs, leaving the return available to cover fixed costs and profit; it is used to compare competing farm enterprises.

Total discounted benefits of a project divided by its total discounted costs; a value greater than one means the investment returns more than it consumes.

Written plan estimating the costs, returns and resource needs of a farm or enterprise for a season or year, used to guide decisions and to borrow or apply for credit.

Pull exerted by a tillage implement on the tractor or animal drawing it; it depends on soil condition, depth and width of cut and implement design.

Mechanical working of the soil by ploughs, harrows and cultivators to prepare a seedbed, control weeds and loosen compaction before sowing.

Weight of water in a produce sample divided by the total weight of the wet sample, expressed as a percentage; it is the figure used in drying and safe storage decisions.

Storage of grain in airtight bags or bins so that respiration of insects and grain depletes oxygen and raises carbon dioxide, killing pests without chemicals.

Care of silkworms during their early larval stages in a separate, hygienic rearing house with tender mulberry leaves, before they are transferred to the main rearing bed.

Transfer of mature silkworm larvae to a spinning mount or chandrika, where each larva spins its cocoon; timing and mount design affect cocoon quality and reelability.

Rearing of several fish species with different feeding habits together in one pond, so that food available at different levels is used and pond yield rises.

Adding organic or inorganic fertiliser to a fish pond to encourage plankton growth, which forms the natural food base for carp and other cultured fish.

Deliberate growing of trees or shrubs together with crops or livestock on the same land, providing fuel, fodder and timber while protecting soil and microclimate.

Row of trees or shrubs planted across the direction of prevailing wind to reduce wind speed, check soil erosion and protect crops and orchards from wind damage.