The days are getting longer

The promise of warmer weather present opportunities for new growth. However, I have begun to wonder how the limited light availability during these periods impacts things?

Daily Light Integral (DLI) is a measurement of the total amount of light that falls in a day, similar to how much rain falls into a rain gauge over the period of 24 hours.

The below graph shows how light levels build over time – these figures are limited by day length and then influenced by cloud cover and intensity of the light.

The green line shown is my first guess at the figures Poa needs to start photosynthesising strongly, the red line is where is suspect we may begin to see some levels of stress.

The amount of light available to the plant has a huge impact on the plants ability to photosynthesise.

Mike Richardson has been doing lots of work in the USA on DLI and although most of it has been done on warm season grasses (which fix Co2 differently). Warm season grasses have a much higher requirement for light and can utilise much higher levels than cool season.

In some recent research he has indicated that Bentgrass needs around 30 DLI a day to maintain healthy turf cover. If that figure stacks up then last year in the epsom area light levels had the potential to reach acceptable levels mid February and potentaily could remain there until early October.

I suspect that Poa has a much lower requirement for light. This work is still in its early phases and I look forward to hearing from people to help me continue piecing this puzzle together.

Of course, all these figures are taken from areas in full sun. There are obvious restrictions to this in many situations in turf, whether that be Stadiums, trees or buildings.

A recent visit to a golf course highlighted to me a typical issue facing turf managers. A high light day but the plants ability to photosynthesis dramatically reduced by dense shade cast by evergreen Yews. In this instance they were reducing light by about 85%!!!!

shade corhampton

Using this example you can see quite quickly that although DLI’s of 30 could be achieved in ideal conditions in mid Febrauary shade can reduce reduce a DLI of 30 down to 4.5 very quickly.

Find out how soil temperature can affect turf growth here.

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