By Jay Capasso and Bob Hochmuth – UF/IFAS North Florida Research and Education Center – Suwannee Valley
Watermelon production relies on precise irrigation management for optimal growth. Getting the duration and frequency of irrigation right is crucial for using water efficiently and achieving a successful harvest.
Understanding Irrigation Duration
Based on our experience, utilizing drip tape with a flow rate of 0.4 gallons per 100 feet per minute, it’s important not to irrigate longer than a duration of 1 – 1.5 hours in any single irrigation event (do not count the time it takes to pressurize the drip irrigation system in the total run time). Since watermelon roots typically extend to depths of 12 – 15 inches, irrigating longer than 1.5 hours at this flow rate leads to water leaching below the root zone in our sandy Suwannee Valley soils. When water leaches below the root zone it is no longer useful to the watermelon crop and risks leaching nutrients.
Irrigation Frequency: Twice (or thrice) is Nice
Instead of irrigating once a day for 3 or 4 hours a strategy of shorter, more frequent, irrigation events is more beneficial. Dividing daily irrigation into two 1 – 1.5 hour sessions throughout the day better aligns with the watermelon’s ability to absorb water in the root zone; this strategy also minimizes the risk of leaching. Some growers may benefit from irrigating even more than two events a day. See image 1 below of soil moisture sensor data showing how a watermelon grower increased the amount of irrigation water in the root zone by switching from two long irrigation events to three shorter irrigation events daily. As a result, he was able to better maintain a stable level of soil moisture in the root zone.
Tailoring Irrigation to Different Drip Tape Flow Rates
Not all drip tape flow rates are the same. With reduced flow rates, it takes longer to saturate the watermelon root zone adequately, extending the necessary irrigation time. For growers using lower drip flow rates, such as those ranging from 0.22 to 0.25 gallons per 100 feet per minute, growers should avoid irrigating more than 2.7 hours (approximately 2 hours and 40 minutes).
How Can I Tell if I am Irrigating Correctly?
A soil moisture sensor can help you determine if your irrigation event is too long or too short. With a soil moisture sensor containing sensors at various depths, you can run an irrigation event and determine how deep sensors record increased moisture content from the irrigation event. If irrigation is not reaching the 12-15 inch depths you are not sufficiently irrigating the entire watermelon root zone. This is more problematic later in the season when roots are fully grown, and temperature/evapotranspiration have increased. Large increases in moisture content below the 12-15 inch depth indicate that water is being wasted and moving nutrients below the root zone. Blue dye can also be used to determine how deep water percolates in the soil via an irrigation event.
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