What is Daily Light Integral (DLI)?
Daily Light Integral (DLI) refers to the total amount of photosynthetically active radiation (PAR) that a plant receives throughout the day, influencing the grass's ability to maintain its density, health, and performance. DLI is a more comprehensive measure than light intensity, as it accumulates light received throughout the day, expressed in moles of light per square meter per day (mol/m²/day). For turfgrass, optimal DLI ranges from 25 to 30 mol/m²/day during the growing season, but grasses can survive in as low as 12-15 mol/m²/day for golf greens and 10-12 mol/m²/day for sports pitches. Lower DLI levels can lead to reduced growth, weaker roots, and susceptibility to diseases, while excessive light can cause stress.
Several factors influence DLI:
Geographical Location: Locations closer to the equator receive more light, while those in northern and southern regions may experience lower DLI
Time of Year: Day length and solar angle change with the seasons, affecting DLI
Shade: Trees, buildings, and landscape features can reduce DLI, leading to uneven growth
Weather Conditions: Cloud cover, fog, and precipitation reduce light reaching the turf, especially during the growing season
Insufficient DLI can results in lower rate of photosynthesis leading to slower growth and turf thinning, poor root development making turf more vulnerable to stress, recovery from wear, is more susceptible to turfgrass diseases, and has a negative Impact on playability i.e. the speed, smoothness, and firmness of playing surfaces.
How to Calculate DLI
DLI is calculated by measuring the total amount of photosynthetically active radiation (PAR) a plant receives throughout a day. PAR represents the range of light wavelengths that plants use for photosynthesis, typically between 400 to 700 nanometres. DLI is expressed in moles of light per square meter per day (mol m-2 day-1), capturing the cumulative effect of light over time.
Steps to Calculate DLI:
1. Measure Instantaneous PAR: DLI calculation starts by measuring the instantaneous PAR at specific intervals during the day. This can be done using a PAR sensor, which measures the intensity of light in micromoles per square meter per second (µmol m-2 s-1). PAR fluctuates throughout the day based on factors such as cloud cover, shading, and time of day.
2. Average PAR Over a Set Interval: To estimate DLI, record the PAR values at regular intervals (e.g., every minute or every 15 minutes) throughout the daylight period. These values are then averaged for each interval. Data can also be sourced from subscription weather websites, such as the UK Meteorological Office, which can be historic or forecast data.
3. Convert to Moles of Light: To convert PAR (measured in micromoles) into DLI (moles of light per day), the following formula is used:
DLI= PAR × number of seconds in the day
1,000,000
This formula takes into account the total number of seconds in a 24 hour period. For example, if the average PAR is measured over a 24-hour period and is found to be 500 µmol·m²·s⁻¹, you would use this formula to determine how many moles of light are delivered per square meter over the entire day.
4. Account for Daylight Hours: Since daylight hours vary with season and latitude, you must multiply the average PAR by the number of seconds during the actual daylight period, not the full 24 hours. The formula then simplifies to:
DLI=∑PAR readings during daylight × number of seconds of daylight
1,000,000
Example Calculation:
The table on the right shows a spreadsheet of hourly PAR readings for the 18th February 2024:
Using the above calculation:
DLI = Mean PAR x ((No. of hours of daylight) x 60 minutes x 60 seconds)
1000000
= 9.15 mol/m²/day
Using published data for a 15-day forecast, the chart below can be produced:
The red bars show the days expected to be below the optimum DLI for healthy turfgrass growth, i.e. all days! As can be concluded, there will be a weakening of the grass and a reduction in the quality of the playing
For just £175 per year, South West Agronomy provides a bi-weekly service providing the above information for your golf course and sports surfaces. Contact us for more details using the options at the end of this article.
Managing DLI for Optimal Turfgrass Performance
To manage DLI, turf managers can monitor light levels using sensors, manage shading by pruning trees, adjust cultural practices, and, when necessary, employ supplemental lighting as in sporting arenas.
The Role of PAR+
PAR+ contains 5-Aminolevulinic Acid (5-ALA) that enhances turfgrass performance in low DLI conditions by promoting chlorophyll production, improving photosynthetic efficiency, and boosting stress tolerance. It is a precursor in chlorophyll biosynthesis, allowing turf to utilize limited light more effectively.
Enhanced Chlorophyll Production: 5-ALA stimulates chlorophyll production, improving the grass’s ability to capture light and photosynthesize.
Increased Photosynthetic Efficiency: 5-ALA supports both light-dependent and independent reactions, helping turf maximize available light.
Improved Stress Tolerance: 5-ALA boosts antioxidant activity, reducing the negative effects of stress, such as heat or drought.
Enhanced Nitrogen Utilization: 5-ALA improves nitrogen metabolism, maintaining turf colour and density in low light.
Stronger Root Systems: 5-ALA promotes root growth, making the turf more resilient and capable of recovering from wear.
Faster Recovery from Wear: By improving energy production and photosynthesis, 5-ALA helps turf recover faster after high-traffic events.
PAR+ should be integrated into a comprehensive turf management program, applied during low light periods or after heavy wear to improve recovery. PAR+ can be used on golf greens or sports turf to enhance overall turf health and performance.
Conclusion
DLI is a critical factor in turfgrass management, with optimal light levels necessary for maintaining density, health, and resilience. Managing DLI through shade control, cultural adjustments, and supplemental lighting can improve turf performance. PAR+ is a valuable tool for enhancing turf health under low light conditions, supporting better photosynthesis, stress tolerance, and recovery. Incorporating PAR+ into a broader management strategy can help maintain year-round, high-quality playing surfaces.
Contact South West Agronomy on how we can help you make the transition from chemical to bio-based turfgrass management.
Email: enquiries@swagronomy.com
Office: +44 (0)822 369005
Mobile: +44 (0)7900 692052
Web: www.swagronomy.com
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