Drought is defined as a situation when annual rainfall is less than 75% of the normal rainfall of that area.

In the troposphere, temperature decreases at an average lapse rate of about 6°C per km. This layer influences earth’s climate and extends up to 8–18 km from the surface.

The lower part of the thermosphere is called the ionosphere. Due to ionized particles, it reflects radio waves and supports long-distance communication.

An anemometer measures wind speed. Wind direction is measured by a wind vane, while pressure is measured by a barometer.

Dry land farming refers to cultivation in areas where annual rainfall is more than 750 mm but less than 1150 mm. It is mainly practiced in semi-arid regions.

Agro-forestry is a sustainable land management system that combines production of crops, fruits, forest plants, and/or animals. It is also known as tree-crop planning system.

As per NBSS&LUP, India was earlier divided into 21 agro-ecological zones, which are now revised to 20 zones.

Drizzle consists of very small water droplets with diameter less than 0.5 mm. Larger drops (0.5–6 mm) are classified as rain.

Windbreaks protect crops from desiccating winds up to 5–10 times the height of tall trees on the windward side and up to 30 times on the leeward side.

A pyrheliometer measures the amount of direct solar radiation received from the sun. Total incoming radiation is measured by a pyranometer.

PE index = P/E × 100, where P is annual precipitation and E is annual evaporation. It is used in climate classification.

De Candolle (1900 AD) was the first to classify climate based on vegetation, linking plant distribution with climatic conditions.

Source is the part where photosynthesis occurs, generally leaves. It produces assimilates that are later transported to sink organs.

In soil air, nitrogen percentage is more or less the same as atmosphere, but oxygen content slightly decreases due to respiration of roots and microorganisms.

Evapo-transpiration is the combined loss of water through evaporation from soil surface and transpiration from plant surfaces.

LAI = Total leaf area (m²) / Ground area (m²). It was developed by Watson in 1948 and indicates crop canopy development and photosynthetic capacity.

CRI = (Number of crops in crop rotation / Number of years in crop rotation) × 100. For example, Rice–Pea in 1 year gives 200% intensity.

Dry farming refers to cultivation in areas receiving less than 750 mm annual rainfall. It is common in arid regions and relies on moisture conservation practices.

Contour cultivation means sowing crops across the slope. This reduces runoff speed and helps in conserving soil, soil fertility, and water.

In the Celsius scale, water freezes at 0°C and boils at 100°C under standard atmospheric pressure.

Albedo is the percentage of incident solar radiation reflected by a surface. Fresh snow has very high reflectivity, around 75–95%.

PAR or photons are measured using a Quantum sensor. It specifically measures radiation in the 400–700 nm range important for photosynthesis.

Graded bunding is recommended in high rainfall areas receiving more than 800 mm annually. It safely disposes excess runoff water and prevents erosion.

A piezometer is used to measure the depth of the water table or groundwater level below the surface.

In dryland farming, Potential Evapotranspiration (PET) is greater than precipitation (P), leading to moisture shortage for crops.

A tensiometer measures soil moisture tension, which indicates the availability of water to plants in the soil.

Reflecting type chemicals (e.g., kaolin, silicone, oils, waxes) reflect solar radiation, reduce leaf temperature, and thereby reduce transpiration loss.

In crop rotation, the same land is used while different crops are grown in sequence each year. It improves soil fertility and reduces pest and disease incidence.

PAR includes radiation between 0.4–0.7 µm (400–700 nm). This is the most effective range used by green plants for photosynthesis.

A cyclone is a low-pressure system where pressure is always lowest at the center and increases rapidly outward. Winds move towards the center.

Rainfed farming (rainfall > 800 mm) usually supports double cropping or intercropping, while dryland farming generally follows single or mixed cropping.

The mesosphere lies above the stratosphere and extends from about 50 km to 80 km from the earth’s surface. It is a cold region with rapid temperature decrease.

Bench terracing is practiced on steep and undulating lands with slope between 16–33%. It converts steep slopes into step-like terraces to control erosion.

MAI = Rainfall at 50% probability ÷ Potential Evapotranspiration (PET). It indicates moisture adequacy during a given period.

Agronomic measures are suitable for gentle slopes (<2%) where erosion problems are not severe. They are preventive practices like contour cultivation and mulching.

Khus (Vetiveria zizanioides) is most suitable for vegetative barriers. It is planted along contours to reduce runoff velocity and soil erosion.

Agro-climatic regional planning was initiated in 1988 by the Planning Commission during the Seventh Five Year Plan.

To compensate for nitrogen immobilization, 25% more nitrogen is applied at the time of the first fertilizer dose of the succeeding crop.

As per MDI classification, semi-arid regions have MDI values between –33.3 to –66.6. This system is adopted by AICRP on dry land (ICAR).

The normal lapse rate (vertical temperature decrease with altitude) is about 6.5°C per km in the atmosphere.

Zing terracing is adopted on lands with 3–10% slope and is constructed in medium to deep soils under moderate to high rainfall areas.

Cropping Intensity (C.I.) = (Total cropping area / Net cultivated area) × 100. In India, it is nearly 135%, indicating multiple cropping practices.

Relative humidity is the ratio of actual water vapour present to that required for saturation × 100. Hence, it is expressed in percentage (%).

As per the Planning Commission, India has been divided into 15 agro-climatic zones for balanced regional development.

Anti-transpirants are applied on plant surfaces to reduce transpiration. They also reduce photosynthesis; hence, their use is limited to conditions of severe moisture stress, especially in nurseries and horticultural crops.

Harvest Index = (Economic yield (grain) / Biological yield (grain + straw)) × 100. It indicates the efficiency of partitioning of assimilates toward economic produce.

Nitrogen constitutes about 78.08% of the atmospheric volume, making it the most abundant gas in the atmosphere.

Stomata-closing type anti-transpirants reduce water loss by closing stomata. Atrazine (and CO₂) are mentioned as effective examples in this category.

Irrigation projects with Culturable Command Area (CCA) greater than 10,000 hectares are classified as major projects.

BBF system is used in deep black soils where surface drainage becomes a problem during the monsoon. It helps in effective rainwater management.

Mulching involves covering the soil surface to check evaporation. It conserves soil moisture and reduces erosion, especially in dry regions.

Koppen divided world climate into 5 major groups based on weather elements like temperature and precipitation.

Agri-silviculture refers to growing agricultural crops along with forest trees on the same land, integrating agriculture and forestry practices.

When LER > 1, intercropping is beneficial. LER = 1.10 means the mixture produces 10% more yield compared to sole cropping on the same land area.

Absolute humidity represents the mass of water vapour per unit volume of air. Its unit is grams per cubic meter (g/m³).

The ozone layer is present in the stratosphere, where most ozone concentration is found around 25 km height. It absorbs harmful UV rays, hence also called ozonosphere.

Contour bunding is suitable up to 6% slope. It is mainly used in arid and semi-arid areas with high infiltration and permeability.

Kelvin is the absolute temperature scale. Conversion formula is K = °C + 273. For example, 0°C equals 273 K.

Solar constant is the energy received per minute on 1 cm² area at the outer boundary of the atmosphere. Its value is about 1.94 Cal/cm²/min or 1353 W/m².

Sorghum stubbles have a wide C:N ratio, leading to temporary nitrogen immobilization during decomposition. This causes early nitrogen deficiency in the succeeding crop.