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Sensor-based irrigation

Sensor-based irrigation is the next step in building a better farming enterprise for South Carolina grower, Bradley O’Neal of Coosaw Farms. Using the right amount of water makes sense in a number of ways, he says.

“It allows us to answer environmental questions before they are asked, lets us produce high quality crops that help us build and maintain marketing outlets for those crops, and it reduces stress on crops, thus reducing crop protection costs.”

O’Neal, who heads Coosaw Farms, began the operation in the late 1970s. After graduating from Clemson University, where he played football for legendary coach Frank Howard, he worked for several years for the Federal Land Bank and farmed on the side. By the 1980 he was farming full-time.

Today, Coosaw Farms is a team/family operation. Bradley, and his wife, Louise; their son, Brad; and their daughter, Angela, continue the O’Neal family farming tradition.

Brad, who studied agricultural economics, and Angela, who studied graphic design, now work on the family farm. Brad handles much of the field and packing house operations while Angela fills in a lot of the business and marketing functions — from food safety, to HR, to customer service and sales. Both have helped develop new marketing strategies that keep the farming operation young, according to the senior O’Neal.

“Having a wonderful family is great. Having a great family who enjoy working on the farm is a real blessing,” he says.

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When Brad and Angela returned after graduating from Clemson, they brought a new vibrancy to Coosaw Farms, he says. “They returned with a little different view of technology and marketing, and both have been a big part of our growth and continued success.”

“Our main crops are watermelons, blueberries and cabbage,” Bradley notes. “We’ve moved away from row crops, although we maintain some cotton and corn, primarily to allow better rotation for our produce crops.”

Their operation, with headquarters at Fairfax, S.C., spreads across two small South Carolina counties and includes acreage in Florida.

Precision technology at Coosaw Farms goes back to 2002, with a John Deere Starfire GPS system, followed by a more sophisticated RTK system that allows repeatability to within one-fourth inch under ideal conditions.

“We use the GPS for just about everything; we even spread our lime and apply fertilizer with it. Using a sensor-based irrigation system is the next logical step in increasing precision in our operation,” says Brad.

“It’s like building a house — you have to start with a good foundation, and then everything builds from there. For example, with the repeatability precision-based applications afford, we can offset our trickle tape a couple of inches when we’re laying plastic. At planting, we can then use the middle of the row with no problems. As the crop grows, we don’t have to worry about overlap with a spray, because the row spacing is right. One thing builds on the other.

“We got involved with soil moisture sensors because we wanted to get away from picking up a handful of dirt and making a critical crop decision based on the way it felt — is this enough water at this particular moment? Making that kind of educated guess 15-20 times a day is not the most efficient way to grow crops.”

With the sensors, the first of which were installed four years ago, they can constantly monitor the water uptake of the plants, he notes.

“The sensors provide excellent information, but you do have to learn how to use the information and apply it to its best use for a particular crop in a particular field.”

They now use three different types of sensors. A mobile sensor made by WaterMark can be placed in the soil and connects to a data logger via a cable. Information that goes into the data logger can be taken in the field and downloaded to a computer back the farm office. During the growing season, that system can be used every day to monitor progress of the crop.

They are also using a handheld sensor that looks like a two-pronged fork, which gives a water reading from 0-8 inches. It allows them to check different parts of a field to back up information attained from the WaterMark system.

“Collectively, the moisture monitors allow us to address stress on plants before it is visually apparent,” Brad says. “By the time you see a stress-related problem, you’ve already lost yield and quality. Now, we can correct it within an hour, instead of a day or two down the road when the damage is already done.

“By knowing exactly how much water the soil can hold, along with salinity measurements, we’re able to maintain our fertilizer and not flush it through. With the cost of fertilizer these days, that allows us to be more efficient.

“We’re also able to reduce disease control costs by keeping plants out of a stressful environment. We want to use as much water and fertilizer as we need — but never more than we need.”

The O’Neals have worked closely over the past few years with Clemson University Vegetable Specialist Gilbert Miller. This fall, Miller will expand that relationship thanks to a federal grant that will provide valuable irrigation information to fruit and vegetable growers in South Carolina and the region.

“There are several different types of sensors that can be placed in a field and can be automated to read moisture level in the soil. This allows the grower to determine when and how much irrigation water they want to apply,” Miller says.

“Previously, we didn’t have a good tool for the plant to tell us how much water it need. Tensiometers are valuable for monitoring irrigation, but not so good as a triggering device because they are very difficult to automate and fluctuate so much in different soil types.

“The new sensors we’re using measure the volumetric moisture of the soil, or the percent water in the soil at different levels. This allows the grower to determine the optimum amount of moisture needed by the crop to achieve maximum growth and maximum quality.”

To attain maximum productivity, most crops need close to field capacity for moisture. For example, watermelons on a certain field at Coosaw Farms require field capacity of 17 percent. Brad can program the irrigation system, based on sensor readings, to begin applying water when field capacity reaches 15 percent. The irrigation will run until it makes up the two percent difference.

“What you don’t want to do,” Miller says, “is take field capacity up to 17 percent, then have a rain that produces runoff, loss of nutrients, and potential environmental problems, not to mention the loss of valuable and limited irrigation water.”

The sensor sends a radio signal to a receiver that has a 24 volt relay which tells the relay to close, which signals the valve to open. Using the radio signal makes it practical to place one sensor in a large field to provide the irrigation information needed for optimum water management.

“You could put multiple sensors in a field to read the mean value of the sensors and provide an average on which the irrigation system is triggered,” Miller notes. “But right now, the cost (about $1,800, including software and connectivity to a grower’s computer) of the type sensors I’m using makes it too expensive for most growers to use multiple applications.

“We are using Sentek sensors in our research and the third type sensor used by Coosaw Farms. There are a number of companies that produce irrigation control systems using Sentek sensors, which are called capacitive sensors.”

In addition to measuring water, these sensors monitor salinity levels of the soil, allowing a grower to better monitor nutrients in the plant.

“We’re still experimenting with water-sensor systems to try and determine which one, or which combination of systems, is best for our operation,” Bradley O’Neal says. “Once we do that, we’ll have more of them in the field to further improve production efficiency, yield, and quality of our crops.”


TAGS: Management
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