Deciding when to irrigate is a daily judgment call that requires commercial growers to consider many variables, with weather being a key one. With the intensifying effects of climate change, weather patterns have only become more unpredictable and extreme. Rising temperatures, erratic rainfall, and increasing water shortages are just a few of the hurdles growers face in key agricultural regions across the world.
Access to accurate, real-time weather data allows growers to make cost-effective water management decisions, mitigating the risks of over-irrigation and drought stress, while helping crops thrive—no matter what the weather brings.
Water uptake and plant transpiration
Water is vital for plants, driving key processes that ensure their growth and survival. One such process is transpiration, where water moves from the roots to the leaves and escapes through small pores called stomata. This regulates the plant's temperature, aids in nutrient absorption from the soil, and helps maintain water balance within the plant. Environmental factors can directly influence transpiration rates, affecting how much water a plant needs. Below, we'll explore the key weather data points that impact this process.
Diagram of the transpiration process in a substrate-grown plant
Key weather data points
Temperature: Temperature directly influences the water demand of growing crops. As air temperatures rise, both soil evaporation and plant transpiration rates increase, resulting in higher water requirements to maintain healthy plant growth and prevent water stress. Monitoring peak temperatures is essential to ensure that crops receive adequate water during these critical periods.
Evapotranspiration: Evapotranspiration (ET) is the combined process by which water is lost to the atmosphere through both evaporation from soil and plant surfaces, and transpiration from plants. It represents the total amount of water used by a crop. Over the growing season, daily ET fluctuates in response to weather patterns and crop development. It is influenced by factors such as crop type, growth stage, and weather variables, including temperature, solar radiation, humidity, and wind. The daily ET demand of a crop can be estimated using predictive models that incorporate measurements of these weather variables.
Using ET data allows for precise irrigation scheduling, ensuring that water application closely matches the crop's needs. In periods of high ET, frequent watering may be needed, while in low ET conditions, less irrigation is required to prevent over-watering.
Radiation: Solar radiation is another variable that influences crop water use, or evapotranspiration. Plants use energy from sunlight to drive the transpiration process, converting liquid water into vapor (evaporation) and causing water loss. As a result, evapotranspiration tends to increase with higher levels of solar radiation. Growers can monitor accumulated solar radiation to assess how much sunlight their crops are receiving over a given period. Additionally, shading techniques can be used to manage sunlight exposure and reduce excessive water loss.
Humidity: Humidity is the measurement of water vapor in the air. It affects how and when plants open the stomata on the bottom of their leaves to transpire. In environments with low humidity, transpiration rates in a plant increase as the moisture content inside the leaves is much higher than the surrounding air. When conditions are too humid, it may prevent the plant from evaporating water or drawing nutrients from the soil. When this occurs over a prolonged period, the plant eventually rots. Protected cropping growers should aim to maintain humidity levels below threshold values both day and night to ensure optimal plant transpiration.
Vapor pressure Deficit (VPD): Vapor Pressure Deficit (VPD) is an important driver of plant health, growth, and productivity, as it directly impacts transpiration rates. VPD measures the difference between the maximum moisture the air can hold at a given temperature (saturation vapor pressure) and the actual moisture content of the air.
Monitoring this parameter is important because high VPD levels (dry conditions) can lead to excessive water loss in plants through transpiration and cause wilting. In contrast, heavy irrigation in low VPD environments can keep the growing medium wet overnight, as transpiration and evaporation slow down. In controlled environments like greenhouses, growers can adjust irrigation, ventilation, and temperature to maintain an optimal moisture balance, ensuring healthier crops and higher productivity.
Rainfall: Incorporating rainfall data into irrigation planning allows growers to maintain soil moisture levels and optimize nutrient availability. Excessive watering after a rainfall event can result in soil leaching, washing away vital nutrients like nitrates that crops rely on for growth. By proactively adjusting irrigation schedules based on forecasted rainfall patterns, growers can optimize water usage and protect soil health.
How to use your daily weather forecast
Utilizing daily weather forecasts in your irrigation planning is essential for efficient water management and optimal crop health. Growers should aim to Monitor daily accumulated radiation, humidity levels, peak temperatures, vapor pressure deficit (VPD), and evapotranspiration rates; analyze evapotranspiration trends by comparing today's data with past (e.g., yesterday) and forecasted values to anticipate changes in crop water demand; and incorporate daily rainfall forecasts into your irrigation decisions. If significant precipitation is expected, consider reducing or delaying irrigation to prevent overwatering.
Source: WayBeyond
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WayBeyond
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