Monday, June 13, 2011

How's Your Moisture

I grew up in a place where during the growing season it was commonplace to announce yourself to friends (especially at the coffee shop) not with "Hello!" but with how much moisture you may or may not have gotten during the last rain storm. One memorable time the morning after a particularly potent thunderstorm I entered Timmies by bellowing "Inch and a half !" which got nods of approval from all my farmer buddies but quizzical looks from the counter girls, one of whom hollered back at me, " Don't believe I'd BRAG about that !"

Moisture was much on my mind when I farmed in Ontario but I think it's actually a bigger deal in Tennessee than it ever was up home. In this part of the world I've learned over time that we average somewhere around 50 inches of rainfall a year divided fairly evenly among each of the twelve months with a slight maximum in late winter and early spring. Given this, and given that our yearly average rainfall is nearly twenty inches more per annum that it was where I grew up in Ontario, it might surprise you to know that the biggest stressor for farmers, their crops and their pastures in this part of the world is drought !

Droughts are seldom a problem in the cooler months down here partly due to relatively low evapotranspiration rates but mostly due to the type, freqency and intensity of our cool season rainfalls. In every season but summer (and early fall) it tends to rain in dollops....a little bit every few days which helps keep the soil moist.

Summer around here is a different ball game. With 24 hour four inch soil temperatures at or above 90 degrees evapotranspiration rates are incredibly high. Cold fronts cease to arrive sometime around the first of June and between that date and the fall solstice, most of our moisture comes in the form very random afternoon thundershowers which can drop a month's worth of rain in a few minutes and then disappear for weeks at a time. Even on the days when it rains and in years when we get normal levels of precipitation it's hot and sunny most of the time. High soil temperatures and sporadic summer precipitation are pretty hard on C3 grasses, so as I mentioned in greater detail in another blog post, this is where C3 grasses give way to C4 tropical species.

And coffee shop conversations ? Well, in my dotage you'll be proud to know I've become more circumspect. I usually wait to get seated these days before I beller out to my farmer friends how much moisture the latest rain has provided.