Clemson researchers develop new technology to help vegetable growers



Most South Carolina vegetable growers know that fertilization and irrigation are important for crops. But a recurring issue is just how much fertilizer is enough?

Clemson University Cooperative Extension Service researchers have solved this issue by creating a calculator that figures the amount of liquid fertilizer needed using a drip irrigation system. This process is called “drip fertigation.” The Clemson Drip Fertigation Calculator is helps vegetable farmers grow the best crops while still protecting the environment.

Developed by Justin Ballew, Kendall Kirk, Rob Last and Zack Snipes, this free web-based calculator app, helps farmers determine just how much fertilizer to apply to their vegetables. This will help save money and increase crop productivity.

“By adding liquid fertilizer to irrigation systems, plants are given a little bit of fertilizer each time farmers water their crops,” said Snipes, assistant program leader for the Clemson Cooperative Extension Service horticulture team and an area horticulture agent. “This reduces runoff and leaching as compared to granular applications.”

According to the developers’ instructions, to use the app, growers select the fertilizer formula to be used, by calculating pounds of nitrogen needed per acre per day and the amount of acreage to be fertigated. The calculator determines how many gallons of fertilizer are needed to supply proper nutrients through the drip system. The app has a drop-down menu for users to input the dates crops were planted to help determine fertilizer needed at that stage of development.

“This app makes use of published data for nutrient requirements throughout a crop’s life,” said Last, a Clemson Extension horticulture agent. “Development stage of crops always has an impact,” he said. “For example, the amount of fertilizer to be applied to younger vegetative crop will generally be lower than a more mature crop. Nutritional status of a crop can also play a role. For example, in strawberries, if the petiole nitrogen content is low then additional nitrogen should be applied. This reduces the risk of nutrients becoming limited and limiting yield potential. The same calculations generated by the app can be done manually and give the same results.”

Clemson Extension vegetable specialist Gilbert Miller said that fertigation is an “excellent method” for meeting the daily nutrient needs of fruit and vegetable crops, adding if the drip irrigation cycle time is not too long, nutrients provided via fertigation will remain in the crop root zone and be readily available.

“Growers should make sure they use a high-quality liquid fertilizer that will not clog up the drip irrigation emitters,” Miller said. “Also, it is generally not recommended to apply phosphorous through a drip irrigation system because of the possible precipitation of phosphates and consequential clogging of drip emitters. Phosphorous does not move freely through the soil so it can be easily applied pre-plant with a granular fertilizer.”

A grower’s perspective

Jim Basara, coordinator of a 6-acre community farm on Spring Island, said the Drip Fertigation Calculator helps make his job easier.

“When we started with fertigation, calculating the fertilizer dosage was one of things I was hesitant about,” Basara said. “It was a big unknown. I think there are farmers out there like us who are hesitant due to a number of unknowns and this calculator knocks down a big barrier to adopting fertigation.

“With this calculator and other opportunities offered by the Clemson Extension Service, we have advanced the quality of our farm beyond anything we could have imagined two years ago. We are producing healthier crops for our members and we are much more confident in what we are doing, and as a result, we are having more fun doing it.”

In addition to the Drip Fertilizer Calculator, other calculators and web applications (apps) available from the Clemson Extension Precision Agriculture Group can be found at


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