Wheat Irrigation Requirements and Methods
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Water requirements of wheat
When does wheat need irrigation?
Depending on the species/cultivar of wheat, both the time of the year that is cultivated as well as the length of the cultivation period can significantly vary. There is a great variety of spring- and winter-type wheat varieties. More specifically, Durum species and hard wheat are usually cultivated mainly during winter, while bread wheat species (soft wheat) can be cultivated either as a winter or as a spring crop. The time period in which wheat is grown, is very important since it will define the need for irrigation or not.
Winter wheat is generally sown at the start of autumn and harvested at the end of spring, while spring wheat is sown during spring and harvested in late summer or early autumn. Many farmers prefer to cultivate winter-type wheats because they can have up to 30% higher yield potential compared to spring types, while the need for irrigation is more limited (1). Generally, wheat is cultivated as a dryland crop but plants perform better under irrigation and give greater yields. At the same time, the droughts and heatwaves that become more and more frequent at the end of spring (or early autumn) – and in some cases coincide with the highest water use stages of the plants – force farmers to irrigate.
How to irrigate wheat?
In wheat crops, farmers often apply irrigation through sprinklers (artificial rain) since the very close plant distances do not allow the application of furrow irrigation. According to University of California Davis, drip and sprinkler irrigation systems can apply smaller amounts of water than surface flood systems, and therefore, less applied water moves past the root zone of wheat. Frequent irrigation with sprinkler systems can result in rapid disease development in wheat crop. Surface flood systems are more efficient at leaching salts, which is important if salts are a problem for the wheat crop. Flood irrigation in wheat farming is most common in the Central Valley and Low Desert regions of California, whereas, sprinklers are more common in the Intermountain Region. Research has proven that with the optimum irrigation amount, increasing drip irrigation frequency can increase wheat root length and root weight and aboveground biomass accumulation, thereby improving yield and water use efficiency.
Attention: If you use sprinklers, they should be adjusted so that the water will not cause plant lodging. Additionally, when the temperature is in favorable levels for fungal disease dispersal, farmers should inspect their plants frequently in order to apply disease control measures when needed.
The need and the number of water applications through irrigation will be determined from:
- The number of rainfalls
- The variety
- The soil type (sandy soils demand more frequent irrigations with less water amount)
- The temperature
- The water availability in the irrigation system and the soil
The availability or scarcity of water can affect the quantity and the quality of final grain yield. An easy way to calculate it is by applying the following mathematical formula suggested by the Montana State University (2).
Estimated yield (in bushels/acre) = 5.8 (SM + R/I – 4.1) bushels/acre where:
SM = soil moisture (inches)
R = rainfall (inches)
I = irrigation (inches)
1 Bushels of wheat = 60lbs =27.216kg
1 acre = 0.405 hectares
Water needs in different growth stages of wheat
In order for wheat to reach physiological maturity and its potential yield, it needs on average around 350 – 600 mm of water. In many areas, the rainfalls during the winter season cover those needs. However, despite the importance of meeting the total quantity of water needed, its distribution is equally important for high yields. Water stress or water surplus, in sensitive stages, will inevitably lead to yield losses. Moderate water stress occurs when the soil depletion level is over 70%. To avoid this, farmers can irrigate in the appropriate moment and with the appropriate water amounts. It goes without saying that wheat crops cultivated for grain production are more water demanding, followed by forage crops harvested at soft dough (28% less water needs), or at boot (60% less water needs) (3).
In areas where rainfalls are not sufficient, it is suggested to irrigate 4-6 times during the cultivation period especially when farmers use high yielding winter wheat varieties. These irrigations mean to cover plants’ needs during critical growth stages: crown root initiation, tillering, jointing, flowering, milk and dough (4). In dry lands, where there is water availability through irrigation systems, applications can take place every 12-18 days until the stage of soft dough (3).
At Sowing-Emergence stage
Lack of water during the emergence period of the crop can lead to crop failure.
For winter wheat, early irrigation (or rainfalls) will help in the quick and uniform emergence of the plants, the good establishment of the crop, and increase the head number per m2. An application of 150 mm of water could be beneficial. However, in some cases, deep sowing may be needed to avoid false sprouting. The plants should start sprouting when the upper 10 cm of the soil is sufficiently wet. Generally, both for winter and spring wheat, root development is significantly favored when the root zone is in field capacity, during emergence. The root of wheat plants can grow up to 1.2-2m (47.2-78.7 in) deep, however, 70 to 80% of the total water uptake occurs in the first 0.6m of soil, where it is grown more than 80% of the plant’s root (Cutforth et al., 2013, 5). As a result, the added amount of water through irrigation should be enough to keep this soil layer sufficiently wet.
During the Vegetative growth stage (emergence to double ridge)
As plants grow and produce more active leaf area, the water demand increases. To keep plants photosynthetically active, farmers can irrigate accordingly in order to always keep the stomata open (leaf water potentials higher than -1.5 MPa) (Palta et al., 1994).
The critical stage from Double ridge to Anthesis
This is considered to be the most critical and water-demanding growth stage of wheat. Even mild-moderate water stress during these stages will result in a reduction in the final yield of the plants (kernel number m-2), due to limited photosynthesis, and decreased cell and leaf growth. Up to 70% of the total plant’s needs in water are from the end of tillering until the flowering stage. In many regions, this amount is covered by rainfalls. However, complementary irrigation of 90-150 mm of water may be needed in the flowering stage, even in these areas. On the other hand, in the Mediterranean, the south-central states of the U.S, or in Northern India (for spring wheat) more than one irrigation may be needed during that period. Water deficit close to anthesis can decrease dramatically the number and quality of wheat grains produced.
Yield loss due to a surplus of water
This period is described as water sensitive not only in regard to water scarcity but also to waterlogging. Based on scientific evidence, yield losses of up to 92% occurred as a result of water surplus from the expansion of the 7 leaves to the anthesis stage (de San Celedonio et al., 2014).
Except for waterlogging, which is easily observed, the farmer should take measures to avoid the rise of groundwater level-table. Prolonged anaerobic conditions in the root system (rise of groundwater table to 0.5 m or 19.7 in) and lodging of the plants can lead to a 20-40% yield decrease. (5, 2). Lodging risk is higher in the tall and spring wheat varieties.
Until Crop Maturation-Harvest
The water deficit remains a problem even shortly after the stage of flowering, decreasing the duration of grain-filling, grain number, and weight (6). After flowering, the grain-filling stage is considered to be one of the 3 most sensitive stages to water stress resulting in significant crop yield loss. However, experimental results have proven that water deficit is possible to increase grain proteins (glutenin strength) and breadmaking quality of the produced wheat flour (Zhou et al., 2018). However, more scientific evidence points out that water scarcity during milking and dough stages decreases Nitrogen uptake, and the accumulation of grain proteins negatively affected the quality of the final product (Ali and Akmal, 2022).
All farmers, regardless of the region or period they cultivate wheat should know that plants become more productive based on water availability in the soil compared to seasonal irrigations. For that reason, it is very important to take actions that improve soil fertility and water holding capacity.
Ali, N., & Akmal, M. (2022). Wheat Growth, Yield, and Quality Under Water Deficit and Reduced Nitrogen Supply. A Review. Gesunde Pflanzen, 1-13.
Cutforth, H. W., Angadi, S. V., McConkey, B. G., Miller, P. R., Ulrich, D., Gulden, R., … & Brandt, S. A. (2013). Comparing rooting characteristics and soil water withdrawal patterns of wheat with alternative oilseed and pulse crops grown in the semiarid Canadian prairie. Canadian Journal of Soil Science, 93(2), 147-160.
de San Celedonio, R. P., Abeledo, L. G., & Miralles, D. J. (2014). Identifying the critical period for waterlogging on yield and its components in wheat and barley. Plant and Soil, 378(1), 265-277.
Palta, J.A., Kobata, T., Turner, N.C. & Fillery, I.R. 1994. Remobilization of carbon and nitrogen in wheat as influenced by post-anthesis water deficits. Crop Sci., 34: 118-124.
Zhou, J., Liu, D., Deng, X., Zhen, S., Wang, Z., & Yan, Y. (2018). Effects of water deficit on breadmaking quality and storage protein compositions in bread wheat (Triticum aestivum L.). Journal of the Science of Food and Agriculture, 98(11), 4357-4368.
Wheat Irrigation Requirements and Methods