maintaining low soil temp?

[Mark Johnson]

As some of you may know, it have been hot and VERY humid in the Midwest this summer (dewpoints of over 78 for a long stretch of time).

As a result at our club and several other, there has been considerable debate on golf course maintenance protocol.  Several courses including my own have been watering much more than normal in order to maintain a lower soil temperature, resulting in a few places where it is very wet.

My question as an uninformed person -- is this worth it and what are the tradeoffs involved?

[Ben Sims]

Mark,

I'll take a stab at it.  Waiting for professionals to correct me.

Yes, it's worth it.  I assume you have cool season grasses at your course.  In the summer, cool season grasses lose root length and strength due to a process known as photorespiration.  Photorespiration is essentially when oxygen replaces CO2 in photosynthesis and occurs in cool season grasses when temps get high.  It causes the plant to use up--or not be able to access--its carbohydrates (energy).  This causes the plant to become weaker and weaker as the summer goes on.  It's very common for cool season grasses under heavy temperature stress to go from 7 inches or more of root in spring to less than 3 inches of root by summer's end.  The weakness--or stress--of the grass through a hard summer is why many places with cool season grasses typically play faster in the late summer.   

It is arguable whether rootzone temps or air temps contribute more heavily in this loss, but that debate isn't relevant to this discussion.

Bottom line, high temps with excessive root loss equals dead turf.  You're maintenance meld is likely a result of trying too hard to prevent that. 

[Sean Remington (SBR)]

Mark,

I don't know were you are located so I can't speak to what is happening in your area.  All I can do is tell you is what my approach is.  As you know every course is very different.

What I do know:  Water is slower to warm but once it is warm it is slower to cool.  A wet soil will have less oxygen, roots need oxygen.  The plant will cool itself by transpiration if the soil has adequate moisture and enough oxygen so that the roots are still working and bring moisture into the plant and then up into the leaves.  If you can keep the soil profile some what consistent in moisture the roots seem to hang in there a bit deeper, longer.  Once we get into June I try to keep the soil profile as even as I can so as to avoid the stresses on the plant.  I used to be a dry it down to wilt and then try to get the profile wet again guy.  I found that the repeated stress on the plant would shorten the roots faster than normal environmental stress.  That said I don't like soft greens. You can maintain soil moisture without being wet.  If you can aerate and topdress enough your greens will stay firm.  We have so many great tools these days.

Basically what this boils down to is that each morning we check our greens for moisture levels.  Experience tells us how much and where to put the water with the hose.  If we run the irrigation heads we always under water with them and then suppliment and even out with the hose.  If by 10:30AM we have done our job that's it,  we are done for the day.  So far this summer we have not had to syringe. There are several contributing factors but giving the plant the moisture it needs it the biggest part of this. 

One more thing I know:  Grass dies deader, wetter.   This is why the summer thunderstorms can present such a big problem.  If is it really hot and you get a 2 3" downpour the whole game is changed.  Know you want to get the moisture out as soon as you can.  This is were needle tine aeration and slicing come in.