Authors: Rajeev Ranjan1*, Adarsh Bahuguna1, Ankita Jha2 and Raj Pal Meena2
1Department of Agrometeorology, GBPUA&T, Pantnagar
2Resource Management Division, ICAR-IIWBR, Karnal
*Email: rajeevranjanagri@gmail.com
Summary:
Improved irrigation methods help farmers to schedule irrigation and reduce the amount of water without compromising with crop yield. Proper irrigation scheduling methods help farmers determine the time and amount of irrigation water to be applied. As both deficit and excess irrigations have equally damaging effects on crop production therefore, adoption of appropriate irrigation scheduling method is essential to produce consistently high yields with minimum costs/inputs. As far as wheat is concerned, it requires cool climate with moderate quantity of water (24-48 cm/year). The crop requires 4 to 6 irrigations depending on the soil type and the amount of rainfall. The amount of water in soil is determined by soil moisture measurements which forms an important aspect in determining plant moisture status and evapotranspiration loss.
Wheat (Triticum aestivum) is the second most important food crop in India and covers the largest area in the country. As wheat is a rabi crop, it is sown with the onset of winters and is harvested during initial summer season. The time of sowing and harvesting differs in different regions due to varied climatic conditions. The sowing of wheat normally begins in the month of October in Karnataka, Maharashtra, Andhra Pradesh, Madhya Pradesh and West Bengal; October-November in Bihar, Uttar Pradesh, Punjab, Haryana Rajasthan, plains of Uttarakhand and December-January in Himachal Pradesh, hilly regions of Uttarakhand and Jammu & Kashmir. The harvesting starts in February in Karnataka and Andhra Pradesh extending till April in Punjab, Haryana, U.P. Rajasthan to May in Himachal Pradesh and J&K. The growing period of wheat which varies from one agro climatic zone to another; influence the vegetative and reproductive period ultimately leading to differences in the potential yield.
The ideal climatic conditions for wheat crop at the time of sowing ranges between 10 to 15°C. The cool and sunny winters are very conducive for the growth of wheat. It can be grown on all kinds of soils, except the highly deteriorated alkaline and water logged soils. Well-drained loams and clayey loams are best suited to wheat. Wheat grows well in areas receiving an annual rainfall about 25 to 175 cm; regions with 62.54 to 87 cm rainfall are most suitable for wheat cultivation (Jaiswal, 2009). If annual rainfall is less than 500 mm, sufficient irrigation is necessary for good growth & development of the crop. The crop requires 4 to 8 irrigations depending on the soil type and the amount of rainfall. The sole aim of irrigating soil is to supply sufficient moisture to the plant for its normal growth. However for optimum yield of wheat; irrigation at proper time and at appropriate physiological stages is a must.
Water requirements for wheat
Water is essential for plant growth and it serves many functions in plants. It is a medium for supplying nutrients to plants. For crop production, the effective management of water is important and essential so as to evade the damaging effects of water shortage. Major loss of water is due to poor farm management practices such as surface runoff, downward drainage, siltation of channels, percolation, leaching and evaporation of water through soil surface and transpiration from plants. Proper irrigation scheduling is essential to conserve water and improve irrigation efficiency. The boost in wheat production depends upon changes in management practices including high yielding varieties, field preparation, timely planting, better crop stand, effective control of weeds, pests and disease, efficient use of fertilizers and irrigation water management. Wheat yield may strongly correlate with winter rainfall especially January-March. The adequate water supply in March is critical for the wheat crop.
Concept of Irrigation Scheduling
Irrigation scheduling is the process of determining the right time and the right amount of water to be applied per irrigation. Proper irrigation scheduling is necessary for efficient use of water, and all other necessary inputs. Benefits of proper irrigation scheduling include; improved crop yield, water conservation and low production costs. Several methods are used to determine the time of irrigation keeping in mind the plant conditions, soil conditions and water budget technique. Generally, over irrigation is done by farmers because of lack of awareness about crop water requirements under the fixed interval system of water distribution; however, both excess and deficit irrigation directly reduce crop yield. Excess irrigation causes leaching of essential nutrients creating anaerobic conditions for a short interval of time. In this perspective, improved irrigation scheduling and irrigation practices shall result in increased crop yield and at the same time reduce seasonal irrigation water requirements.
Irrigation provides water to soil; which in turn is used as moisture for plant growth. Yields are influenced by both amount of water used and the frequency of irrigation. For normal growth of wheat under optimum growing conditions, 4-8 irrigations are sufficient out of which first irrigation is applied 3-4 weeks after sowing and subsequent irrigations are applied at 21 days intervals depending upon the crop and soil conditions. As for example, in sandy loam soil 6-8 irrigations may be required whereas in heavy clay soil 3-4 irrigations are considered to be sufficient for the crop growth (Kumar, 2009).
As growth stages of wheat are much sensitive to drought hence in this case, two approaches are used to irrigate wheat crop. The first approach is to irrigate crop at definite crop growth stages and secondly irrigating when the soil moisture in field is depleted; irrespective of growth stage. The stages like crown root initiation; tillering, booting, heading, milking and dough are the critical ones. Such growth stages may appear as tillering (21-25 days after sowing), heading (55-60 days after sowing), milking (80 days after sowing) and dough (100-105 days after sowing). The highest wheat yields may be obtained from following four irrigations: crown root initiation, booting, flowering and milking stages. Out of all stages, crown root initiation is the most important stage for irrigation as far as root development is concerned. Maximum yield of wheat may be obtained when supplemental irrigation was applied at the crown root initiation stage (21-25 days after sowing). Irrigations at CRI, maximum tillering, booting and grain filling may produce better yields. However, the maximum yield loss is associated with reduced number of grains per spike observed due to water stress at tillering stage.
Importance of Irrigation Scheduling
Fraction of irrigation water stored in the soil is removed by crop’s roots and other part is lost through evaporation, runoff, or seepage/leaching. The amount of water lost through these processes is affected by design of the irrigation system and its management. Judicious scheduling minimizes runoff, leaching and percolation losses, which in turn maximizes irrigation efficiency by saving energy and water use. It curtails fertilizer costs by holding surface runoff and deep percolation (leaching) losses to a minimum rate. Over irrigation can reduce yields because the excess soil moisture often results in enhanced plant disease, nutrient leaching and reduced pesticide effect. Proper irrigation scheduling using water balance methods can save upto 15 to 35% of the water normally pumped without slashing yield. Therefore, an optimum irrigation schedule helps maximize profit and optimize water and energy use.
Irrigation scheduling strategy
The crop water need or evapotranspiration (ET) for wheat depends on its variety, growth stage, canopy density, climatic conditions, irrigation and crop management etc. Effective irrigation scheduling uses soil water levels in the root zone as a measure for starting and stopping irrigations. Before seeding, a light irrigation of 6 cm should be applied in a dry seedbed. During the vegetative growth stages, water should not deplete to less than 50% in the upper 50 cm of the root zone. Irrigation is given during this stage when the available soil water is close to 60%. At the beginning of the heading and flowering stages, irrigations should be scheduled so as to fill the entire root zone at 100% or field capacity. During this stage, the root zone should be increased from 50 cm to 100 cm and soil moisture must not go below 60% of available water. Once the crop has reached maturity and the colour has turned to brown from green, the crop no longer needs irrigation.
Irrigation management
The main aim of irrigation management is to optimally utilise available irrigation water and managing the soil moisture environment of crops. The total water requirement of wheat crop is 24-48 cm, which has to be provided uniformly over the first 100 days of crop growth. The water lost through evaporation and transpiration from the field, directly influences the growth and yield of the crop. The optimum time of irrigation based on the physiological stages is one of the most important recommended methods of scheduling irrigation in wheat crop. Irrigations should be done at the right time to minimize evaporation losses. The irrigation requirements of wheat at different growth stages have been mentioned in table 1. The table depicts the stages out of which three of them are very critical; Crown root initiation, boot stage, milk and dough stages.
Table 1: Irrigation requirements of wheat at different growth stages
| Irrigation Frequency | Days after sowing | Critical Crop Development Stage |
| First irrigation | 20-25 days | CRI (Crown Root Initiation) |
| Second irrigation | 40-45 days | Tillering stage |
| Third irrigation | 60-65 days | Node formation/late jointing or booting stage |
| Fourth irrigation | 80-85 days | Heading/flowering stage |
| Fifth irrigation | 100-105 days | Milking stage |
| Sixth irrigation | 115-120 days | Grain filling/dough stage |
Conclusion
Irrigation scheduling requires knowledge of the soil characteristics and soil-water status. Farmers must be encouraged to properly manage irrigation by regularly monitoring soil water and crop water use (evapotranspiration) to ensure that the availability of water does not become a limiting factor in producing high-yielding wheat crop. Irrigation should be applied before the depletion of available soil water up to 50 per cent during the pre-flowering stage and 60 per cent between early heading and physiologic maturity. As shortage of water in soil during critical growth stages of crop significantly affects the crop yield; hence, irrigation should be scheduled by taking into account the amount of rainfall received, quantity of water lost through and a good knowledge of crop water needs at each stage of development starting from seedling to maturity of the crop.
References
Jaiswal, J.P. (2009). Rainfall-Climatic requirement for wheat, agropedia (available online at http://agropedia.iitk.ac.in/content/rainfall-climatic-requirement-wheat ).
Kumar, R. (2009). Irrigate wheat in a proper way, agropedia (available online at ( http://agropedia.iitk.ac.in/content/irrigate-wheat-proper-way).
http://www.apnikheti.com/en/pn/agriculture/crops/cereals/wheat-kanak-gehu
About Author/ Additional Info .
Dr. Rajeev Ranjan: Asst. Prof (Agrometeorology) at GBPUA&T, Pantnagar
Mr. Adarsh Bahuguna: Student at GBPUA&T, Pantnagar
Dr. Ankita Jha- Scientist (Agri. Meteorology), ICAR-IIWBR, Karnal and
Dr. Raj Pal Meena- Sr. Scientist (Agronomy), ICAR-IIWBR, Karnal
About Author / Additional Info: