By John Lea-Cox, April 12, 2015
Spring has taken a while to come to the Mid-Atlantic region this year. After an unusually cold February, March turned wet and grey. But early April brought some warmth and finally the daffodils, forsythia, cherries and even a few early dandelions are now in full bloom. Talking to my colleague Bob Rouse, he estimates we are between 5% and 10% bloom for strawberries in the southern parts of Maryland, while those a little farther north are perhaps 7-10 days behind.
For many, spring is a welcome relief; for our strawberry growers, it’s typically a time of anxiety because the last frost date in the Mid-Atlantic is between May 1st and 15th, which is a full month away. So all eyes are on the weather forecasts, in anticipation of early mornings when they rise at 3 or 4 am to check temperatures in their fields, and if that critical 32.5°F is reached, then the overhead sprinklers get turned on to save those precious flower buds.
But this year, thanks to NSSI funding, a couple of Maryland growers have a little extra help with getting both flower and leaf temperature data delivered in real-time to their cellphones, from advanced radiation frost detectors (Apogee Instruments, Inc.) located right in their strawberry canopies. Eight of these sensors (pictured left) are located in each quadrant of the field. The floral thermistor is just visible as a black wire in the center of the picture; the leaf thermistor is at right. The data from these sensors and the weather station on site is transmitted via wireless radio nodes (Decagon Devices, Inc.) to a radio base station and computer located in the barn at the farm.
The base station and Sensorweb software (Mayim, LLC) receive that data every 5 minutes, where it is accessible over the internet via a password-protected website for the farm. As an example (see figure below), we can plot the average leaf (green) and flower (orange) temperature and compare that to the weather station air temperature (black line), and relate that to the photosynthetic radiation (blue line) during the day. Note that air temperature reached 34.5°F early on the 12th April, but leaf and flower temperatures reached a minimum of only 39.6°F and 38.6°F respectively — a 4 to 5°F differential from the air temperature.
Perhaps more useful to the growers is that they can set various threshold temperature alerts in the software that will automatically text their cellphone when that temperature is reached. For example, a grower can get a text when the temperature from a flower sensor located in a frost pocket reaches 38°F. We’re hopeful that this information will help them rest a little easier this spring!
But that’s only part of the story. The real reason we are using sensor networks is to use sensor-controlled irrigation in the fields – not only to save water (which is critical for our California growers), but also to keep nutrients in the root zone for as long as possible and reduce leaching. This is critical for growers in Florida as well as the Chesapeake Bay. We are doing that with a combination of soil moisture and electrical conductivity sensors, again providing that information to our growers in real-time to help them make more informed irrigation decisions.
We’ll keep you posted on those results, as we progress through spring and early summer. You can also learn more about our project objectives and our grower partners from our website at http://sensingberries.net.