Scheduling of Irrigation

Scheduling of Irrigation

1. SCHEDULING OF IRRIGATION Water management is the planned use of water for better utilization in agriculture. It includes irrigation (the application of water to soil or crop or crop plants to assist crop production) and drainage (removal of excess surface or ground water from land) by means of surface or sub- surface drains. The soil needs the application of water to remove stress conditions, release nutrients in the soil solution for absorption by plants, leach or wash out injurious salts from the soil, prepare land for raising crops and maintain the temperature and humidity of the soil, maintain micro – climate and the activity of soil microbes at the optimum level. On the other hand excess water needs removal for the normal aeration and functioning of roots and shoots of the plants except of aquatic or semi aquatic crops.

2. IRRIGATION For successful crop production, plants must be supplied with water as required by them. The water requirement of crops is that quantity of water required by the crops is that quantity of water required by the crops with in a given period of time for their maturity and it included losses due to evaporation plus the unavoidable losses during the application of water and water required foe special operations such as land preparation, puddling and leaching. This water requirement of crops is partially met by rain or ground water which are very often not in conformity with the requirement of the crops at different stages of their life span. Rains do not occur throughout the year in all cultivable fields and their intensity, duration and distribution also differ. A very high ground water table is not always desirable. In such areas, sub surface drainage is needed for various reasons.

3. C ont…… The application of water is found to be essential for maintaining the optimum soil moisture balance suitable for the crop variety, its cultural practices and for other operations such as application of fertilizers and pesticides, for grain maturity and for case of harvesting. The entire volume of water used for irrigation does not meet the purpose of irrigation as a considerable part is lost in conveyance and by deep percolation and seepage. Only a percentage serves the purpose in practice. This is termed irrigation efficiency (the ratio expresses in percentage of water stored in the root zone depth of the soil to the water delivered in the field from the farm supply source.) effective irrigation is the controlled and uniform application of water to crop land in the required amount at the required time, with minimum cost to produce optimum yields without wastage of water and any adverse effect on the soil the form of soil salinity and water logging problems .

4. SCHEDULING IRRIGATION For scheduling irrigation due consideration should be given to the soil condition, crop variety, type of culture, growth stage of the crop and atmospheric condition. The moisture content in the root zone of soil is determine by using tensiometers , gypsum block etc. They are not always applicable for practical use in the farms. The use of indicator plants which shows system of wilting earlier than the plants growing in the field, tissue testing, crop logging and soil moisture determination are also difficult from farmer plant of view. All these need standardization with respect to soil, season, crop variety and cultural practices.

5. Cont….. Practical experience is essential for scheduling irrigation. For example wetland rice needs irrigation when the soil surface shows hair like cracks or even before. Once the crack deepens the objective of puddling is defeated as the cracks make the impervious layers more porous. Well fertilized soils, light soils dense leafy, shallow rooted crops and crop with underground storage tissues require light but frequent irrigation. Deep rooted crop in heavy soils require heavy irrigation with wide intervals. Heavy soils with shallow rooted crops require light but frequent irrigation.

6. Cont….. Further, light but frequent irrigation helps to establish seedlings, endure moderate vagaries of weather including light showers or high wind velocity that prevails immediately after irrigation. The depth of irrigation may be increased with progress of crop growth up to a certain limit. Light irrigation at wider intervals helps in uniform and early ripening of crops. Shallow but repeated irrigation reduces the injurious effects of salts.

7. Time Irrigation should be scheduled when the soil temperature is moderate. There is greater loss of water through evaporation if irrigation is applied on hot soil. The activities of roots make collapse when a sudden drop in soil temperature or the presence of warm water that receives heat from the soil. Irrigation on cold soil may injure some crops. Moreover, during cold period the evaporation rate is less and water use efficiency is reduced. Therefore, in hotter season it is better to irrigate the field late afternoon or at night so that plant and the soil get sufficient time to absorb water before dry weather prevails the next day.

8. C ont…… If irrigation is extremely necessary during very cold season, then it should apply during morning hours when the soil starts warming up. First irrigation to a grown up crop should not be given when it is too windy as it may result in lodging particularly when the flood method of irrigation is adopted. For the furrow method, the first irrigation should be as little water as possible to stabilize the soil in the ridge. Frequent irrigation increases application loss and cost but it helps to increase use efficiency of fertilizer and other inputs. However, how much water should be applied in each irrigation depends on the need on the crop for water, the availability of water for irrigation, the capacity of the root zone soil to store water, the season of raising the crop, the cultural practices and anticipated rainfall.

9. Cont…. Growing crops use water continuously but the rate of use varies with the crop grown, the age of the crop, the temperature, atmospheric condition, special treatment to the crop (use of anti- transpirents and growth modifiers) and the moisture status of the soil. It is not desirable or possible to supply water uniformly throughout the life span of the crop. There are certain critical periods of water requirement for each crop. If the crop experiences stress condition during these periods there is drastic reduction in yield. These periods are mostly specific. Therefore irrigation should be applied/ schedule around such critical stages of water requirement of the crop provided there is no other source to recharge the root zone with the moisture.

10. CROP CRITICAL STAGES Rice Tillering initiation, flower premordia and flowering Wheat Crown root initiation (CRI), milk Maize Silking, cob developing Sorghum Seedling, flowering Red gram Flower initiation, pod filling Peas Start of flowering, pod formation Linseed Pre flowering, capsule development Sunflower Flowering, grain filling Different growth stages of different crops have been recognized as critical stages of water requirement are as follows

11. At each irrigation a volume of water sufficient to supply the seeds of the crop for a period varying from a few days to several weeks is stored in the unsaturated soil in the form of available soil water. Irrigation practices, comprise of three interlinked components: The quantity of water at each irrigation ( normally 5-10 cm) The interval between to irrigations (normally 10-20 days) Total number of irrigations in the life span of a crop (1 to 50 or more)