Basics of Irrigation Water Management

In comparison to other phases of the crop growth cycle, some stages of the crop growth cycle are rendered more susceptible to soil moisture stress. “Moisture sensitive” or “Critical periods” are terms used to describe these times.

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 “Base period” refers to the number of days that irrigation water is delivered to the crop.

The Godavari delta irrigation system, built during the British time

• Consumptive use is the amount of water needed for transpiration + evaporation + used by vegetation for metabolic activities.

• Measurement of soil moisture:

•The direct approach determines the amount of water in direct contact.

• The indirect approach is used to calculate water potential.

• The gravimetric approach is a well-known technique.

• The spirit burning process is quick and easy to use in the field.

In Neutron moisture meter – There is a probe and a scaler (or) counter. The probe is made up of a rapid neutron source (mixture of Radium – Barrylium). It is ineffective for determining moisture content at the soil surface.

• In sandy soils, a tensiometer is beneficial.

• The theory employed in gypsum blocks is that resistance is impacted by changes in moisture content. Electricity flow resistance is related to the amount of moisture in the medium.

• In the laboratory, “pressure plate and pressure membrane equipment” can be used to assess soil moisture properties.

Water requirement = consumptive use + application losses + water needed for special operations.

Irrigation requirement = (W.R) – (ER + GW)
ER = Effective rainfall – Measured by ‘Randas’ method
GW = Ground water

• Net irrigation requirement =Moisture content at F.C – Moisture content before irrigation X B. density X Root zone depth/100

• Gross irrigation requirement =Net irrigation water to be applied at each irrigation/ Irrigation application efficiency

• The irrigation time does not exceed the frequency of irrigation.

Duty of water – The link between irrigation water and the area of crop that grows fully with a given amount of water is known as crop maturity.

1. In canal irrigation, the “area per unit rate of flow” is commonly used. It’s measured in ha/m3/sec.

2. Duty is also measured in terms of water depth and is referred to as “Delta.” The total depth of water necessary for the whole crop season, given in “cm,” is known as the delta.

3. Volume expressed in terms of depth per unit area – represents the entire amount of water required per unit area for a crop.

4. In the case of tank irrigation, the obligation can be represented in terms of “stored water,” which is expressed in ha/million/m3.

• Leaching of nitrogen occurs as a result of drainage in light soils.

• For maize and cotton, furrow irrigation is the most popular approach.

• Irrigation is timed to coincide with the “depletion of accessible soil moisture.” Many crops require irrigation at a moisture-sensitive stage of 20 percent DASM. Irrigation with 50% DASM during other phases.

• Tensiometer for measuring soil moisture tension, which is used to irrigate orchards, especially in “coarse texture” soils.

• The “Lysimetrer technique” can be used to measure potential evaportranspiration.

• Visual plant symptoms :

Leaf colour – Cotton, Groundnut, Bean.

Plant movement – Jowar, Bean

Exudation – Cut of stem – Cotton

Indicator plant – Sunflower.

• For Groundnut, Fingermillet, Sorghum, and Vegetables, the check basin method is employed.

• Orchards are irrigated using the basin method.

• The border strip approach is utilised for crops that grow close together, such as wheat, barley, and groundnut. The “Furrow technique” makes the most effective use of water among the surface approaches.

• Kerala uses the subsurface irrigation technology.

• Sprinkler irrigation (overhead irrigation) (Sandy Soils)

• Drip irrigation (also known as trickle irrigation) is a type of irrigation in which water is distributed through “Nozzles.”

• In drip irrigation, nozzles discharge 2 to 10 litres per hour.

Water conveyance efficiency: This refers to the losses that occur during the transport of water from the source to the place of use.

• The water application efficiency indicates how much water is held in the root zone of the soil in comparison to how much is given.

• The uniformity of water distribution in the field is measured by water distribution efficiency.

• Project efficiency is the overall efficiency of a project in terms of water usage.

• Spiles are useful for irrigation in furrows.

• Waterlogging – When the water table rises to the surface, a “parallel field drain system” is an efficient technique of surface drainage that is suitable for both irrigated and rainfed lands.

• For both surface and subterranean drainage, a “parallel field drain system” is necessary.

• Drainage coefficient: This is the depth of water in centimetres that must be evacuated from the total drainage region in a 24-hour period.

• Isolated areas are drained using the random (or natural) technique.

• The US Salinity Laboratory (USSL) classifies irrigation water based on EC and SAR (Sodium absorption ratio).

• Ragi has the highest WUE, whereas rice has the lowest.

• Punjab is the state with the highest percentage of irrigated land.

• Water application efficiency is defined as the ratio of water stored in the root zone to water given to the field multiplied by 100.

• “Seasonal Consumptive Use” refers to the total quantity of water consumed in ET by a crop during its growth season.

• The state of pure water in terms of free energy is “Zero.”

• Deep percolation is the most common kind of water loss in lowland rice farming.

• The primary goal of rice field puddling is to eliminate weeds.

• Every living creature is a combination of its biological heritage and its surroundings.

Ley farming -Fodders (or) grasses are included in the cropping system.

Cropping index -The number of crops grown/annum X 100

Sequence cropping: Each year, plant two or more crops in succession on the same land.

Relay cropping – Seeds of another crop are sown before one crop is harvested.

Catch cropping – Due to a lack of time, one additional crop is grown between two primary harvests.

Multi storeyed cropping: Due to time constraints, different crop heights are grown.

Alley cropping: Crops are mostly planted in alleyways made by trees and bushes in order to increase soil fertility.

Ideotype : It is described as a biological model that is anticipated to behave predictably in a predetermined setting.

• Dwarfness is caused by the “Dee Geo Woo Gene” in rice and the “Norin – 10” stock in wheat.

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