effective rain fall

Effective Rainfall
Factors influencing Effective Rainfall
Scientific irrigation scheduling
Advantages of Irrigation Scheduling

1. 1 d.in Email: [email protected] Bhanu dangi

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.

4. 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 .

5. 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 .

6. 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