Dryland Agriculture-2 Point Wise Notes For Competitive exam

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• Moisture stress delays maturity.

• If stress occurs before flowering, duration of the crop increases.

• If stress occurs after flowering, duration of the crop decreases.

• During ripening, which involves dehydration and certain biochemical processes, moisture regime has very little effect on yield components.

• In cereals, moisture stress at panicle initiation is critical.

• Pod abortion takes place due to drought in several legumes including in soybean.

• Drought decreases leaf sucrose and starch concentrations.

• Drought increases hexose (glucose + fructose) concentrations.

• When the yield is fibre or chemicals where economic product is a small fraction of total dry matter, moderate stress on growth does not have adverse effect on yields.

• Ability of crop to grow satisfactorily under water stress is called drought adaptation.

• Evading the period of drought is the simplest means of adaptation of plants to dry conditions.

• Many desert plants, the so called ephemerals, germinate at the beginning of the rainy season and have an extremely short life period (5 to 6 weeks) confined to the rainy season.

• Ephemerals have no mechanism for overcoming moisture stress, therefore not drought resistant.

• Certain varieties of pearl millet mature within 60 days after sowing.

• Short duration pulses like cowpea, greengram, blackgram included under ephemerals.

• The disadvantage of breeding early varieties is that yield is reduced with reduction in duration.

• Stress avoidance is the ability to maintain water balance, and turgidity even when exposed to drought conditions.

• Favourable water balance under drought conditions achieved by

1. Conserving water by reducing transpiration

2. Accelerating water uptake

• Photosynthetic efficiency is higher in C4 plants than C3 plants.

• In C4 plants, the carboxylating enzyme PEP carboxylase has very high affinity for CO2.

• C4 plants are said to be drought resistant as they are able to grow better even under moisture stress.

• CAM plants are highly drought resistant.

• CAM plants open stomata only during night when they take CO2 into the leaves and store it as organic acid.

• Examples of CAM plants are Pineapple and Agave.

• Soybean, sorghum etc., reduce water loss by depositing lipids on leaves and plant surface.

• In grasses, leaves roll or curl due to moisture stress and reduce the area exposed to solar radiation resulting in low transpiration.

• Leguminous plants show prahelionastic movements i.e., the leaves are oriented parallel to sun rays thus avoiding the load of solar radiation.

• Moisture stressed groundnut plants reduce radiation load during midday by about 60 to 70% due to folding of leaves.

• Pubescence (hairiness) increases leaf reflectance and reduces solar radiation incidence.

• Awned varieties give more yield drought conditions compared to awnless varieties.

• Awns contribute 12% of photosynthates to grain.

• Compared to transpiring area of awns, its contribution of photosynthates to grain is more.

• Water uptake is improved by well developed deep root system.

• Drought increases root growth and root-shoot ratio which is an important mechanism of drought resistance.

• By improving water uptake, high water potential is maintained in leaves and the rate of photosynthesis is not reduced.

• Lowering of resistance to water can be achieved by increasing either diameter of xylem vessels or their number.

• Abscisic acid produced in leaves at lower turgor reduces seed set through its effect on pollen viability.

• By osmotic adjustment, production of abscisic acid is reduced.

• At low osmotic potential, photosynthetic activity and rate of hypocotyl extension are reduced due to inhibition of enzymatic activity.

• Osmotic adjustment allows turgor to be maintained as the leaf water potential and water content decreases.

• Turgor pressure is the pressure exerted on the cell wall by the cell contents inside it when the cell contents are fully turgid.

• In drought tolerance, water potential of plant is reduced and its adverse effects are felt.

• Drought tolerance can be defined as tolerance of the plants to a level of stress at which 50 % of cells die.

• Simplest way of mitigating stress is by resisting dehydration and by maintenance of higher osmotic pressure by accumulating higher amounts of solutes.

• Leaves with thick cuticle resist cell collapse.

• Plastic strain indicates irrevocable loss of plant tissues due to moisture stress.

• Crops with C4 and CAM type of photosynthesis are preferred in dry regions.

• Under normal conditions, contribution of pre anthesis assimilates to grain is less than 20% in most plants except in rice where it ranges from 20 to 40%.

• Under moisture stress conditions pre anthesis assimilates contribution may be up to 50 to 75%.

• Collecting and storing water for subsequent use is known as water harvesting.

• Water harvesting is a method to induce, collect, store and conserve local surface runoff for agriculture in arid and semiarid regions.

• Catchment area is the part of the land that contributes the rain water.

• Command area is where water is used.

• In arid regions, collecting area or catchment area is substantially in higher proportion compared to command area.

In arid lands, runoff is induced in catchment area.

• In semi arid regions, runoff is not induced in catchment area, only excess rainfall is collected and stored.

• Treating soils with chemicals like sodium salts of silicon, latexes, asphalt and wax fill soil pores or make soil repellent to water.

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