Effective rainfall refers to the portion of total rainfall that is useful for crop production. It is influenced by factors like rainfall amount and intensity, land characteristics like slope and soil type, soil water holding capacity, groundwater levels, and crop water needs. Management practices like bunding and mulching can increase effective rainfall by reducing runoff and improving infiltration. Proper irrigation scheduling allows farmers to apply optimal amounts of water at the right times, maximizing yields while minimizing costs, water use, and damage to soil properties. Common irrigation methods include border, furrow, basin, flood, sprinkler, subsurface, and drip irrigation.

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2. The extent of the rainfall received and its utility in crop production in a given location
determines its effectiveness. In simplest terms, effective rainfall means useful or
utilizable rainfall. Dastane (1974) has defined
“that portion of the total annual or seasonal rainfall which is useful directly and/or
indirectly for meeting the crop water needs in crop production at the site where it falls
but without pumping”.
Factors influencing Effective Rainfall
a) Rainfall characteristics: Amount, intensity and distribution of rainfall influence surface
runoff and hence its effectiveness. Greater amount of rainfall at high intensities reduce
the effective fraction of the rainfall. Similarly, uneven distribution decreases the extent of
effective rainfall
b) Land characteristics: The time interval between receipt of rain water and its recession
by soaking into soil is known as opportunity time.
Water stays longer on flat and leveled land and this has longer opportunity time than on
slopping land, leading to higher fraction of effective rain than on undulating lands.
Effective Rainfall

3. c) Soil characteristics: Higher infiltration and permeability rates increase effectiveness of
rainfall. Fraction of the effective rainfall increases with increasing water holding capacity of
the soil.
• effective rainfall is lower in irrigated than the unirrigated areas where there is often
greater deficiency of soil moisture
d) Ground water characteristics: The amount of effective rainfall is greater when the water
table is deep than when it is shallow.
Upward capillary movement of water decreases the deficit of moisture and hence
the amount of effective rainfall.
e) Management practices: Any management practice influencing runoff, infiltration,
permeability or evapotranspiration also influences the degree of effective rainfall.
Bunding, terracing, ploughing, ridging and mulching reduce runoff and increase effective
rainfall.
f) Crop characteristics: Higher crop ET rates create greater depletion of soil moisture. Hence,
effective rainfall is directly proportional to the rate of water uptake by the crop.

5. • Scientific irrigation scheduling is a technique
providing knowledge on correct time and
optimum quantity of water application at each
irrigation to optimize crop yields with maximum
water use efficiency and at the same time
ensuring minimum damage to the soil
properties.

6. Advantages of Irrigation Scheduling
a) It enables the farmer to schedule water rotation among the various fields to
minimize crop water stress and maximize yields.
b) It reduces the farmer’s cost of water and labor through fewer irrigations,
thereby making maximum use of soil moisture storage.
c) It lowers fertilizer costs by holding surface runoff and deep percolation
(leaching) to a minimum.
d) It increases net returns by increasing crop yields and crop quality.
e) It minimizes water-logging problems by reducing the drainage requirements.
f) It results in additional returns by using the “saved” water to irrigate non-cash
crops that otherwise would not be irrigated during water-short periods.

7. Method of Irrigations
Irrigation water may be applied by flooding on the field surface, by
applying it beneath the soil surface, by spraying it under pressure or by
applying it in drops. The water supply, the type of soil, the topography of
the land and the crop to be irrigated determine the method of irrigation to
be used. Commonly, following methods are followed for irrigating
different crops.
1. Border irrigation
2.Furrow irrigation
3. Check basin irrigation
4. Ring or Basin irrigation
5. Flood irrigation
6. Sprinkler irrigation
7. Sub-surface irrigation
8.Drip irrigation