Irrigate wheat in a proper way

Rajeew Kumar
G.B.Pant University of Agriculture & Technology, Pantnagar-Uttrakhand

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Many factors are associated with the low yield of wheat in our country but the foremost one is the un-scientific use of available irrigation water. To harvest a bumper crop of wheat, the adequate facility for irrigation water is essential. In order to utilize the full potential, dwarf wheat needs more irrigation in comparison to local tall wheat. If irrigations are not given at required time then there is drastic reduction in yield. Under water deficit condition, the growth and development of the crop is checked. This also reduces the uptake of nutrients. Therefore, it is always necessary to give water to wheat as and when needed. Sometime farmers irrigate the crop as a routine without giving due consideration to soil type and water depth. In canal irrigated areas, the quantity of water applied is often much more than actual requirement to replenish the deficit in the root zone. It is also essential to see that excess irrigation is not given as it causes wastage of water and is harmful for the soil and the crop. It is, therefore, necessary maintain a soil water condition favorable for satisfactory growth and development of the plants. To achieve efficient and economic use of irrigation water, different aspects of water use should be considered.

Irrigation requirements

            The loss of water through evaporation and transpiration from the wheat field is known as evapotranspiration which directly influences the growth and yield of the crop. To harvest a good crop of wheat at Pantnagar, about 40 cm depth of water is used as evapotranspiration. There may be the need for 4-5 irrigations for wheat. In sandy loam soil 6-8 irrigations may be required whereas in heavy clay soil 3-4 irrigations are considered to be sufficient.

Optimum time of irrigation

Irrigating wheat crop based on the physiological stags is one of the most important recommended mtithods of scheduling irrigation. There are six stages-crown root initiation, late tillering, late jointing, flowering, milk and dough stages. At each of these irrigation should be given.

• Crown root initiation - 20-25 days after sowing. In late sown crops give first irrigation within 25-30 days after sowing.
• Late tillering -40-45 days after sowing
• Late jointing -65-70 days after sowing
• Flowering stage -90-95 days after sowing
• Milk stage - 105-110 days after sowing
• Dough stage - 120-125 days after sowing.

If the water available is adequate then irrigation should be given at all the stages. However, if water is in short supply then irrigations should be given at certain critical (crown root initiation and flowering) stages. Maximum reduction would occur if the irrigation at the critical growth stage is missed. Therefore, if the water is available for less than adequate number (5-6) of irrigations then crop should be irrigated as below :

• If water is available for only one irrigation, it should be applied at crown root initiation which comes in 20-25 days after sowing.
• If two irrigations are to be given, the first irrigation should be at crown root initiation and the second at flowering stage.
• If water is available for three irrigations, the first irrigation should be given at crown root initiation, second at late jointing and third at milk stage.
• If water is available for four irrigations, the crop should be irrigated at crown root initiation, late jointing, heading and milk stage.

Depth of irrigation

            Depth of irrigation water may be under-stood as the total thickness of the water spread over in a given area. It is desirable that the right depth of irrigation water should be applied at each irrigation. While under irrigation may bring down the yield of the wheat crop, over-irrigation would be wasteful as it causes loss of water and leaching o some nutrients from the roots zone. The depth of irrigation water should be regulated so that it makes up the soil moisture-deficit in the root zone of the crop.

            The depth of irrigation water in sandy soils is less due to lesser water holding capacity in comparison to loam and clay soils. If the crop receives irrigation at a long interval the depth of irrigation would be more. Normally, the dept of each irrigation ranges between 6-8 cm depending on the soil type and the irrigation interval. If the ground water table is close to the soil surface, irrigation depth may be small because of the contribution of the ground water.

Method of irrigation

            The most common method is to apply the water at the surface of the wheat field. There are two methods in use.

(i) Check-basin method: This method is generally adopted by farmers having small holdings. In this method, small and rectangular plots, accessible by irrigation channel, are made. The method is good provided the plot is leveled and the stream size is low.

(ii) Border of strip method: In this method, long and narrow plots are made for irrigation. This method is popular for irrigating wheat crop on large farms where the land is graded to a definite slope and stream size available is relatively large. The wheat field is divided into a number of strips preferably 8-10 meter wide and 50-200 meter long, separated by low borders. Obvisously, the length and width and depends on the slope of the field and size of the stream. The slope of the field is generally 0.1 to 0.3 per cent.

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