It’s getting dry out there...

 It’s getting dry out there. How do I know? Simple. Soil moisture sensors! Well, not really so simple! For starters, at the UMass Orchard in Belchertown, MA I have two sets -- one pictured below -- of WaterMark soil moisture Tensiometry sensors attached to My Toro Tempus Ag. As of June 8, Monday afternoon they read (Tensiometry) 20.32 and 35.11 kPa’s at 8 and 18 inches depth respective in my NC-140 Honeycrisp row, and 0 and 6.8 kPa’s at 8 and 18 inches depth respectively in my B3 Test Apples block. I have been told 30 is the threshold to turn water on. Whoa, wait a minute, B3 is down from 15.7 and 19.38 earlier today (Monday) so maybe they turned the trickle on here! Hee Haw! BTW, I can see all this sitting in my cozy office chair thanks to My Toro Tempus Ag! Tuesday PM update, Tensiometry readings are 38.19 (dry), 21.12 (getting dry), 4.39 (irrigated) and 0 (irrigated). Time to turn the irrigation on the NC-140 Honeycrisp!

WaterMark soil moisture (Tensiometry) sensors installed at 8 and 18 inches soil depth in the 2014 NC-140 Honeycrisp apple rootstock planting at the UMass Orchard, Belchertown, MA

I also have a water potential sensor in my NC-140 Honeycrisp attached to a Onset/Hobo/Licor weather station via Hobonet. It says -17.5 kPa which is interesting, they must use a different direction away from zero (which is soaking wet), but it is close to that 20.32 reading via the WaterMark sensor mentioned previously. Tuesday PM update, it’s now -20.2, time to turn the water on there like I said.

Hold tight, not so simple, I also have no fewer than 9 (maybe only 8 currently working) soil moisture content sensors attached to Onset/Hobo/Licor weather stations via the Hobonet. They measure water content in terms of cubic meter of water per cubic meter of soil. Not terribly useful is it? Or is it? Kind of depends on the soil type and water holding capacity. Let’s just say when charted the soil moisture content slope it is downhill right now, ranging from 0.169 to 0.366 cubic meters of water per cubic meter of soil. I have been told that about 1/3 water content (0.34 cubic meters) in soil is good? You can actually look at those charts (including water potential as mentioned above) at OrchardWatch. Wednesday PM update: 0.168 o 0.361, so dropping (less water content) a bit over 24 hours. 

What are I missing? Oh yea, NEWA’s Apple Irrigation Model. Assuming in Belchertown, 3 foot by 12 foot tree spacing, a mature tall-spindle orchard, and ditto spacing for 0.6 mph trickle emitters, the model says I am currently (June 9) at a cumulative water deficit of 37,473 gallons per acre. Yikes! If I ran that trickle for 24 ours it would distribute 17,424 gallons, not nearly making up that deficit, it’d still be circa 20,000 gallons cumulative deficit and not advisable anyways -- you need to start irrigation when the deficit starts, see example below where I turned on the trickle on May 27 for 8 hours doling out 5,808 gallons per acre bringing the deficit down to 1,007 gallons per acre from what would have been a deficit of  6,815 gallons. The idea is to keep it close to no/minimal deficit.

My key points for you? Up to now, despite the drought status, trees have not been under a lot of water stress (unless newly planted, roots not established.) But NOW we are entering a period where they will be under stress unless adequate water is applied. Especially important for Honecyrisp for calcium uptake from the soil. You ought to pay attention to the NEWA Apple Irrigation Model and start watering and recording to keep the Cumulative Water Balance from not becoming too negative (from which you will likely never recover). And you should be monitoring soil moisture in as many or your orchard blocks as you can, those WaterMark sensors are a reasonable start point available from Brookdale Farm Supply. Thanks to Trevor Hardy at Brookdale for this white paper How to Measure Irrigation Needs with Soil Moisture Sensors.