Certain stages in the crop growth period are made sensitive to soil moisture stress compared
with others. These are known as “Moisture sensitive” or “Critical periods”.
Crop Moisture sensitive period
Rice, Finger millet – Primordia development, heading, flowering
Sorghum – Booting, Blooming
Maize – Tasseling, Silking
Wheat – Crown-root initiation
Groundnut – Peg penetration, flowering
Sunflower – Two weeks before flowering to 2 WAF
Safflower – From rosette to flowering
Cotton – Flowering, boll development
Tobacco – Tapping stage
Potato – Tuber initiation to tuber maturity
Onion – Bulb formation
The periods in days during which irrigation water is supplied to the crop is termed as “Base period”.
• Irrigation project constructed during British period Godavari delta system
• Consumptive use is the amount of water needed for transpiration + evaporation + used by vegetation for metabolic activities.
• Measurement of soil moisture:
Direct method measures direct water content.
Indirect method measures water potential.
• Gravimetric method is a standard method.
• Spirit burning method is rapid and suitable for field.
• In Neutron moisture meter – A probe and a scaler (or) counter are present. The probe consists of a source of fast neutron (mixture of Radium – Barrylium). It is not suitable for measuring moisture content very near to the soil surface.
• Tensiometer is useful in sandy soils.
• Resistance affected by a change in moisture content is the principle used in the gypsum blocks. Resistance to flow of electricity is proportional to moisture content in the medium.
• Soil moisture characteristics in the laboratory can be determined by using “Pressure plate and pressure membrane apparatus”.
• Water requirement = consumptive use + application losses + water needed for special
• Irrigation requirement = (W.R) – (ER + GW)
ER = Effective rainfall – Measured by ‘Randas’ method
GW = Ground water
Moisture content at F.C – Moisture content before
Net irrigation requirement =______________________________ X B. density X Root zone depth
Net irrigation water to be applied at each irrigation
Gross irrigation requirement =____________________________
Irrigation application efficiency
Irrigation period is not greater than the irrigation frequency.
• Duty of water – It is the relationship between the irrigation water and the area of crop that
matures fully with the given amount of water.
1. In canal irrigation duty is usually expressed as the “area per unit rate of flow”. It is expressed
2. Duty is also expressed interms of depth of water and is referred to “Delta”. Delta is the total
depth of water required for the entire crop period and expressed in “cm”.
3. Volume interms of depth over unit area – ha.cm. represent the total quantity of water needed
for a crop per unit area.
4. In case of tank irrigation, duty may be expressed as the interms of “Stored water” expressed
• Drainage in light soils leads to leaching loss of Nitrogen.
• Furrow irrigation is the most common method for maize and cotton.
• Irrigations are scheduled based on “depletion of available soil moisture”. For many crops
irrigation at 20% DASM at moisture sensitive stage. At other stages irrigations at 50% DASM.
• Soil moisture tension (Tensiometer) used for irrigating orchards especially in “Coarse
• Potential evaportranspiration can be estimated by “Lysimetrer method”.
• Visual plant symptoms :
Leaf colour – Cotton, Groundnut, Bean.
Plant movement – Jowar, Bean; Exudation – Cut of stem – Cotton
Indicator plant – Sunflower.
• Check basin method is used for Groundnut, Fingermillet, Sorghum and Vegetables.
• Basin method is used for irrigating orchards.
• Border strip method is used for close growing crops like Wheat, Barley and Groundnut. In
the surface methods, most efficient use of water is seen in “Furrow method”.
• In Kerala subsurface irrigation method is practiced
• Over head irrigation – Sprinkler irrigation (Sandy Soils)
• Drip irrigation – Trickle irrigation – water is released from “Nozzles”.
• In drip irrigation the discharge from nozzles is 2 to 10 liters per hour.
• Water conveyance efficiency: It indicates the losses that occur while water is conveyed from
the source to the point of utilization.
· The Water application efficiency gives an indication of the quantity of water that is stored in
the root zone of soil out of the quantity that is delivered.
• Water distribution efficiency is a measure of the uniformity of water distribution with in the
• Overall efficiency of a particular project in terms of water use is Project efficiency.
• Spiles are convenient in furrow irrigation
• Waterlogging – When the water table comes near the surface “Parallel field drain system” is
the effective method of surface drainage and is well suited both for irrigated and rainfed
• “Parallel field drain system” is required for both surface and subsurface drainage.
• Drainage coefficient : It is defined as the depth of water in cm. to be removed in 24 hours
period from the entire drainage area.
• The random (or) natural system is used for draining isolated patches.
• Classification of irrigation water by US Salinity laboratory (USSL) based on EC and SAR
(Sodium absorption ratio).
• Highest WUE crops – Ragi, Lowest – Rice.
• The State having maximum per cent of irrigated area is Punjab.
Water stored in the root zone
Water application efficiency = X 100
Water delivered to the field
· The total amount of water used in ET by a crop in its growing season is known as “Seasonal
• Free energy status of pure water is “Zero”.
• The major type of water loss in lowland rice cultivation is in the form of Deep percolation.
• The main objective of puddling in rice field is to reduce the weeds.
· Every living organism is a product of its biological heridity and its environment.
• Ley farming – Inclusion of fodders (or) grasses in cropping system. Cropping index -The
number of crops grown/annum X 100
• Sequence cropping: growing two or more crops in sequence on the same field per year.
• Relay cropping – Before harvesting one crop the seeds of other crop are sown.
• Catch cropping – growing one extra crop between two main crops due to availability of time.
• Multi storeyed cropping: Growing different heights of crops due to availability of time.
• Alley cropping: Crops are grown in alleys formed by trees and shrubs mainly to hasten the
• Ideotype : It is defined as a biological model which is expected to perform in a predictable
manner with in a defined environment.
• Incase of Rice “Dee Geo Woo Gene” and in Wheat “Norin – 10” stocks are responsible for