Daily Water Requirements for Barley by Growth Stage
Barley's water needs are not constant throughout its life. They fluctuate depending on the plant's physiological demands at each stage of its life cycle, a metric often measured in millimeters (mm) per day.
Early Vegetative Stages (Germination, Tillering)
In the initial weeks after germination, the barley plant's water needs are relatively low but consistent. The focus is on establishing a healthy root system. Cereal crops during the tillering stage, where the plant produces side shoots, require approximately 2 to 3 mm of water per day under optimal conditions. During this period, light and frequent irrigation is recommended, especially in dry seedbeds, to encourage rapid root development. Maintaining available soil moisture above 60% in the upper 50cm of the soil profile is a good target.
Peak Water Use (Stem Elongation, Heading, Flowering)
This is the most critical period for barley's water consumption. As the plant enters the reproductive phase, its water use increases dramatically. During the stem elongation stage, daily water use can be around 3 to 5 mm per day. The highest water use occurs during the heading, flowering, and grain filling stages, often reaching 7 to 8 mm per day under ideal conditions. This peak period, typically from mid-June to late July, is when moisture deficits can cause the most significant yield reductions, affecting the number of heads and grains per head. Avoiding water stress during this phase is paramount for maximizing potential yield.
Late Growth (Soft Dough, Hard Dough, Maturation)
As the barley grain fills and matures, its daily water requirement begins to decline sharply. By the soft dough stage, the need for water is much lower, though still necessary for proper grain size. For most soil types, the final irrigation can be applied at the soft dough stage. On loamy sands with lower water retention, a final irrigation may be needed closer to the hard dough stage. No further irrigation is needed once the heads have changed color from green to brown, as the crop is physiologically mature.
Factors Influencing Barley's Daily Water Needs
The exact amount of water a barley crop needs is not a single number and is influenced by several variables. Farmers and gardeners must consider these factors to optimize their watering schedule.
Climatic Conditions
- Temperature: Warmer, drier days increase the rate of evapotranspiration (ET), the combined water loss from the soil (evaporation) and the plant (transpiration). This means more water is needed to compensate. Conversely, cooler conditions mean less water is needed for the plant's cooling processes.
- Relative Humidity and Wind: High humidity and low wind speed reduce evapotranspiration, while dry air and strong winds increase it.
- Rainfall: The amount and timing of natural rainfall greatly affect irrigation decisions. In regions with reliable rainfall, irrigation may only be needed as a supplement during dry spells.
Soil-Plant Relationships
- Soil Texture and Type: Sandy soils drain quickly and require more frequent, smaller irrigation events. Clay-loam soils retain water better and need less frequent, but larger, applications.
- Rooting Depth: A deep, well-developed root system allows the plant to draw water from deeper soil layers, making it more resilient to short-term dry spells.
- Variety: Some barley varieties are bred for greater drought tolerance and naturally require less water.
Crop Management
- Seeding Rate and Density: A higher density of plants leads to more competition for water and higher overall water demand per area. Adjusting seeding rates can help manage water use.
- Fertilization: Proper nutrition enhances plant health and water use efficiency. A well-fertilized plant uses water more effectively.
Comparison of Barley Water Needs by Growth Stage
| Growth Stage | Typical Daily Water Use (mm) | Description of Water Needs |
|---|---|---|
| Early Vegetative | 2-3 mm | Low, consistent water is needed for germination and root development. Avoid moisture stress to ensure vigorous initial growth. |
| Stem Elongation | 3-5 mm | Water use steadily increases as the plant grows and canopy density increases. Maintain sufficient moisture levels. |
| Heading & Flowering | 7-8 mm (Peak) | The most sensitive stage to water stress. High daily water use is essential for reproductive growth and maximum yield potential. |
| Grain Filling | 7-8 mm (Peak) | High water use continues to ensure proper grain development and weight. Water stress still reduces yield and grain size. |
| Maturation (Soft Dough) | Decreasing | Water needs decline. Final irrigation can be applied, after which the plant draws from remaining soil moisture. |
Strategies for Efficient Irrigation
To achieve optimal yield and water use efficiency, a strategic approach to irrigation is necessary.
- Monitor Soil Moisture: Don't rely solely on a fixed schedule. Use soil probes or monitoring tools to track the moisture level in the root zone. Ensure soil moisture stays above 60% of available capacity during critical stages.
- Use Weather Data: Incorporate local weather forecasts for rainfall and evapotranspiration rates. For example, the FAO's CROPWAT program uses historical and real-time climate data to help determine irrigation needs.
- Optimize Application Timing: In many regions, scheduling larger irrigation applications during the late boot stage can help recharge the root zone before the sensitive flowering period, reducing the risk of disease like Fusarium Head Blight associated with a wet canopy during flowering.
- Consider Drought Tolerance: Choose barley varieties that are more suited to your specific climate. While barley has natural drought resilience, selecting specifically adapted landraces or cultivars can further improve yield stability in low-rainfall areas.
To see how water use can vary regionally, a study on irrigated barley in southern Alberta noted that under optimal conditions, the crop requires 380 to 430 mm of water over the entire growing season. Contrast this with data for drier areas, where higher seasonal requirements may be needed to achieve maximum yields. Farmers in water-scarce regions might also adopt deficit irrigation strategies to maximize water productivity, irrigating with only 85% or 70% of the crop's full evapotranspiration (ETc) requirements.
Conclusion
While a single daily figure is impossible to determine without specific data, the water needs of barley are highly predictable once you understand its growth cycle and environmental factors. Daily water use peaks significantly during the reproductive stages (heading and flowering) at around 7-8 mm per day, making this the most sensitive time for water stress. By monitoring soil moisture, considering climate and soil type, and tailoring irrigation to match the crop's specific growth stage, growers can effectively manage their water resources to produce a healthy, high-yielding barley crop. Relying on good irrigation scheduling based on sound data, rather than guesswork, is the most effective approach for success.
