Current Category » Rainfed Agriculture
Drought Resistance And Characteristics Of Drought Resistant Crops And Their Varieties
Drought is a hazard to successful production. It occurs due to various combinations of the physical factor of the environment. Internal water stress in crop lands reduces their productivity. This reduction in productivity is brought by
1. Adely or prevention of crop establishment
2. Weakening or distraction of established crops
3. Predisposition of crops to insects & diseases.
4. Predisposition of crops to insects & diseases.
5. Alteration of physiological & bio - logical metabolism in plants & alternation of quality of grain forages fiber etc.
i) "Deficiency of available soil moisture which produces water deficits in the plant sufficient to cause a reduction in plant growth. Or
ii) "Drought is a period of inadequate or no rainfall over extended time creating soil moisture deficit and hydrological imbalances."
Classification of Drought:
A) On the basis of source of
B) On the basis of
C) On the basis of
1) Meteorological drought
2) Agril. Drought
3) Hydrological drought
4) Socio - economic drought
1) Permanent drought
2) Seasonal drought
3) Contingent drought
1) Soil through
2) Atmospheric a drought
A) On the basis of water availability:-
1) Meteorological drought: - Ramdas (1960) defined this as actual rainfall is deficient by more than twice the mean deviation.
Indian Metrological Department (IMD) has defined meteorological drought as the situation when actual rainfall is less than 75% of the normal rainfall over an area. This is accepted principally because of its simplicity. The IMD uses two measures to define drought conditions.
i) Rainfall conditions
ii) Drought severity.
i) Excess - 20% more than average of 70 - 100 yrs.
ii) Deficient - 20% less than average of 70 - 100 yrs.
iii) Deficient - 20 to 59% less than average of 70 - 100 yrs.
iv) Scanty 60% less than average of 70 - 100 yrs.
The IMD classifies droughts as follows from rainfall departures.
i) Slight drought when rainfall departure is 11 to 25% from normal rainfall.
ii) Moderate drought when rainfall departure is 26 to 50% from normal rainfall.
iii) Severe drought when rainfall departure is 50% and more from normal rainfall.
Drought years the year is considered drought when less than 75% of the normal rainfall is received.
2) Hydrological drought: - Definition of hydrological drought is concentrated with the effects of dry speels on surface & sub surfaces hydrology rather than with the meteorological explanation of the event. Linsley et al. (1975) considered hydrological drought as "a period during which stream flows are inadequate to supply established used under given water management system". The frequency and severity of hydrological droughts often defined on the basis of water depletion or shortage in reserve basins, reservoirs lakes wells etc. This drought affects industry and power generation.
3) Agricultural drought:-
Heathcoat (1974) defined agricultural drought as the shortage of water harmful to man's agril. Activities.
This is a situation resulted from inadequate rainfall when soil moisture falls short to meet the water demands of the crop during the growing period. This affects the crop growth or crop may wilt due to moisture stress resulting in yield reduction.
4) Socio - Economic drought:-
The socio - economic effects of drought can also incorporate features of meteorological hydrological and agricultural droughts. They are usually associated with the supply & demand of some economic goods. This drought should be linked hot only to precipitation but also trends of fluctuations in demand.
B) On the basis of time of occurrence:-
Droughts differ in time and period of their occurrence. As per thornithwaite the various droughts are:
1. Permanent drought:-
This is the drought area of permanent dry arid or desert regions. Crop production due to inadequate rainfall is not possible without irrigation in these areas. Vegetation like cactus thorny shrubs, xerophytes etc are generally observed.
2. Seasonal drought:-
In the regions with clearly defined rainy (wet) and dry climates seasonal droughts may result due to large scale seasonal circulation. This happens in monsoon area.
3. Contingent drought:-
This results due to irregular & variability in rainfall especially in humid & sub humid regions. The occurrence of drought may coincide with critical crop growth stages resulting in severe yield reduction.
C) On the basis of medium: - Maximov (1929) has defined into 2 types.
1. Soil drought: - It is the condition when soil moisture depletes & falls short to meet the potential Evapotranspiration (PET) of crop.
2. Atmospheric drought: - This results from low humidity dry and hot winds & causes desiccations of plants. This may happen even when rainfall & moisture supply is adequate.
Current Category » Rainfed Agriculture