Monday, July 2, 2012

ET - What is it?

ET (Evapotranspiration) is a value that is used to describe how much water evaporates from the soils.  This is typically expressed in a daily amount.  It is a reference; an estimate based on calculations from a weather station.  Actual amounts can vary considerably depending on soil type, plant/crop and local conditions (under a tree - full sun).  But a useful tool to get an idea as to how drying a day, week or month was.



For the month of June we had a ET rate of 5.59" with 0.63" of rainfall recorded from the weather station on the course.  This leaves an estimate of nearly 5" shortfall in water, which is impossible to replace without error using a modern day irrigation systems.

How do we use ET?
Based on the previous days ET, we use it to adjust the irrigation system up or down.   The system is also adjusted based on weather forecast for the coming day (manually) and this is where things get tricky.  If there is a high chance or rain the next AM, we may hold off or back off on the irrigation - but if the next day is looking hot and dry we may up it a bit so we can make it through the next day.

Mother Nature sometimes doesn't play fair.  Sometimes the forecast looks like rain, but never shows.  Then there is the no rain is forecast and a storm pops up.  Once the irrigation system runs at night, no undoes.  To hedge our bets, sometimes we run a light cycle at night and do catchup in the AM.  But even this has its drawbacks - water running when the first groups tee off.

To add one more complication, at Biltmore we have two very different types of soils - peat and clay.  Nearly 60% of the golf course is on peat and not all the peat is the same.  Some fairways are half peat and half clay.  Some peat has degraded into a rich topsoil while other areas are very much like true peat (has the consistency of a sponge and made up of compressed cattails) and vary in depth, up to 30' in some areas.   If it is not peat, then clay is the norm at Biltmore (very little good topsoil).  If I had my choice, I would take clay over peat any day of the week!  But that is what makes it fun - the challenge.

Forecast for the week:
The forecast is for a chance t-storms daily, highs in the mid 90's and lows in the 70's with high humidity.  Turf diseases which have been absent for most of this year are starting to show up (in the rough right now) and I would expect become worse this week.  The ten day looks promising, it is just getting through the next 7 days.