Water Deficits in Arable Farming: Understanding and Adapting to Drought Stress

Understanding Water Deficits in Agriculture

When we talk about “drought” in everyday language, we’re often picturing hot, dry weather and dusty fields. But in agricultural science, the more accurate term is water deficit. Unlike drought, which implies heat, a water deficit simply refers to the lack of available water for plants, and it can occur even in winter.

Water deficits are among the most critical challenges in arable farming, directly affecting plant health, crop yields, and soil function. They are responsible for more global crop losses than all other abiotic stresses combined.

The Science Behind Water Deficits

Plants need water for:

• Photosynthesis
• Nutrient transport
• Turgor pressure (cell structure)
• Growth and thermal regulation
• Absorbing carbon dioxide (via stomata)

Even drought-tolerant plants lose water during growth. The majority of water lost through a plant is due to evaporation from leaves, driven by the need to regulate temperature and absorb CO2.

A key physiological player in water deficit response is abscisic acid (ABA). This hormone helps regulate stomatal closure to conserve water and maintains root growth so plants can access deeper moisture.

Field Challenges: Irrigation Limitations and Soil Variability

In many parts of the UK, irrigation is only commonly used on crops like potatoes. For most arable and field vegetables, it’s not feasible. This means farmers rely heavily on soil health and weather conditions.

Organic matter plays a crucial role in soil water retention. Soils with high organic matter and reduced tillage (as seen in regenerative farming) are far more resilient during dry periods. In contrast, heavily tilled, high pH soils lose moisture faster and become hydrophobic.

Detecting and Measuring Water Deficits

Unlike measuring heat stress, identifying water deficits is challenging:

• Dielectric sensors measure soil conductivity to indicate moisture.
• Tensiometers simulate plant root stress.
• Thermal imaging can highlight temperature differences between well-watered and stressed plants.
• Perometers and sap flow gauges measure water loss from leaves, though they can be costly.
• Leaf curling, chlorosis, and growth slowdown are visible signs of stress.

Recent advances allow even smartphone thermal imaging to detect early water stress signs in crops like pumpkins or cereals.

Managing Water Deficits: Short-Term and Long-Term Solutions

Short-Term Solutions:

• Apply seaweed extracts, phosphites, amino acids, or humic acids to stimulate root growth.
• Avoid foliar fertilizers during hot, sunny days to prevent leaf scorch.
• Monitor calcium levels, as this nutrient becomes limited under water stress.

Long-Term Strategies:

• Build up organic matter through cover crops, compost, and reduced tillage.
• Adopt regenerative practices like no-till or min-till to retain soil structure and water.
• Invest in water-efficient sensors and trial new practices via government grants like the adopt programme.

The Role of Technology and Breeding

Although water deficits are a major threat, there’s still limited breeding for drought resistance—mainly because water stress isn’t consistent year-to-year. However, hydroponic research and speed-breeding technologies are making waves in breeding crops that use less water or mature quickly.

Hydroponics, for example, use 5% of the water required in field-grown crops and are being used to breed arable crops faster. Still, full-scale hydroponic wheat is not on the immediate horizon for arable farmers.

Conclusion: Adapting for a Resilient Future

As dry periods become more common, farmers must adapt. Regenerative practices, better soil management, smart use of bio-stimulants, and investment in monitoring tools can help reduce the impacts of water deficits.

While we can’t control the weather, we can prepare our soils and crops to weather the storm—or in this case, the lack thereof.

Article by Dr Russell Sharp

Stay tuned to the Cereal Killers podcast for more insights, or check out Hydroponics Daily if you’re a grower looking into soilless systems.

Cereal Killers Podcast: https://t.co/eSEbBkTVHl

Hydroponics Daily Podcast: https://open.spotify.com/show/207T7p7fw9sPjINfSjVXW2