Instead of Shade, Let's Talk About Light

Shade from trees, buildings, clouds or mountains affects a lot of turfgrass areas, and shade can make it impossible to produce the desired turfgrass conditions. Rather than talk about the impossible, in this presentation I talk about light. Specifically, I discuss photosynthetically active radiation (PAR), the photosynthetic photon flux density (PPFD), and the daily light integral (DLI). These sound complicated but are quite simple and can be easily measured or estimated. With an understanding and ability to measure and communicate about PAR, PPFD, and DLI, it makes it a lot easier to manage those previously impossible shade problems.

Transcript

1. Instead of Shade, Let’s Talk About Light Micah Woods Chief Scientist Asian Turfgrass Center www.asianturfgrass.com 14 January 2016 Northern Green Expo Minneapolis, Minnesota
2. Shade What can be done? 1. Choose grass species and cultivars that can perform be er than the alternative species under shaded conditions. 2. Remove the source of shade by cu ing trees, pruning trees, removing buildings. 3. Increase the mowing height. 4. Be vigilant in controlling fungal diseases. 5. Be extra careful to control tra ic. 6. Reduce the nitrogen fertilizer application rate. 7. Use plant growth regulators that regulate gibberellic acid: trinexapac-ethyl, flurprimidol, or paclobutrazol. 8. Provide supplemental light.
3. What about light?
4. The terminology: PAR Photosynthetically active radiation (PAR) This is the term for light that grass can use for photosynthesis. It is light with wavelengths from 400 to 700 nanometers.
5. The terminology: PPFD Photosynthetic photon flux density (PPFD) When measuring the PAR, one does so by measuring the PPFD. The PPFD is an instantaneous measurement of PAR, in units of micromoles of photons per square meter per second (µmol m−2 s−1). At night, or in the dark, the PPFD is 0. At midday on a sunny day in summer, the PPFD will be about 2,000.
6. 0 500 1000 1500 2000 00 06 12 18 00 PPFD, µmol m-2 s-1 March 5, 2015 at Sandstone, MN
7. 0 500 1000 1500 2000 00 06 12 18 00 PPFD, µmol m-2 s-1 June 12, 2015 at Sandstone, MN
8. 0 500 1000 1500 2000 00 06 12 18 00 PPFD, µmol m-2 s-1 June 13, 2015 at Sandstone, MN
9. 0 500 1000 1500 2000 00 06 12 18 00 PPFD, µmol m-2 s-1 September 30, 2015 at Sandstone, MN
10. The terminology: DLI Daily light integral (DLI) The DLI is the daily total of PAR. By adding together the PPFD for every second of the day, one gets the DLI. That’s a lot of micromoles, so for convenience the DLI is expressed in units of mol m−2 d−1.1 The DLI ranges from less than 5 to about 60. 11 mole = 106 micromoles
11. 8 19 30 36 36 45 46 36 30 18 10 5 0 10 20 30 40 50 60 1 2 3 4 5 6 7 8 9 10 11 12 Month Average DLI, mol m-2 d-1 Sandstone, MN, 2015
12. 0 10 20 30 40 50 60 Jun 01 Jun 08 Jun 15 Jun 22 Jun 29 DLI, mol m-2 d-1 Sandstone, MN, June 2015
13. 0 10 20 30 40 50 60 Sep 01 Sep 15 Oct 01 Oct 15 Nov 01 DLI, mol m-2 d-1 Sandstone, MN, Sep/Oct 2015
14. 0 10 20 30 40 50 60 Jan 2015 Apr 2015 Jul 2015 Oct 2015 Jan 2016 DLI, mol m-2 d-1 Sandstone, MN, 2015
15. How is this useful? 1. By comparing the actual PPFD to the possible PPFD. 2. By comparing the actual DLI to the possible DLI.
16. PPFD in full sun
17. PPFD with cloud blocking sun
18. In full sun, 2000 µmol m−2 s−1. In shade, 765 µmol m−2 s−1. 765 2000 = 0.38 or 1 − 0.38 = 0.62 That’s either 38% of full sun, or 62% shade.
19. Platja de Pals, Catalonia