Clemson leading effort to take stock of state’s water resources

COLUMBIA — With water being vital to the well-being of both South Carolina’s citizens and its largest industry — agriculture — Clemson University is leading the way in taking stock of the state’s water resources.

Sponsored by Clemson Public Service and Agriculture, the biennial South Carolina Water Resources Conference in Columbia brings together state, federal, industry and university water experts to prepare for and meet the growing challenge of providing water resources to sustain and grow South Carolina’s economy, while preserving its natural resources.

Speaking on the opening day of the 2018 conference Wednesday, Clemson associate professor and Extension water resources specialist Cal Sawyer shared preliminary results from the South Carolina Agricultural Water Use and Irrigation Survey, designed by Clemson researchers and Extension agents to gather scientific data on all production agriculture operations using irrigation, regardless of volume of withdrawals or farm acreage.

Agriculture is South Carolina’s largest industry with a $41.7 billion economic impact and 98,000 jobs directly supported. Sawyer said the agribusiness industry has grown 23 percent over the past decade.

“If we can minimize the risk to the yields from that industry, then we felt it was important to try to get some of those answers,” Sawyer said. “Why did we want to conduct a survey? We wanted to get some ideas on what the full balance of agricultural use and what irrigation practices were being used by the farmers, producers and growers in the state.”

Sawyer said the survey was driven by media reports about “megafarm” water demands, increased occurrence of extreme weather events, such as droughts and floods, and increased water demands for the public, industry, agriculture, recreation and the environment.

“We felt like it was important enough that the need for accurate data to inform what tools and data management have to be able to make a confident decision about the allocation of water resources,” he said.

Sawyer said the next steps in future surveys would be to fill data gaps in several critical counties, refine the survey instrument to optimize response continuity, develop dynamic models to more robustly quantify irrigation costs and evaluate other agricultural water uses associated with the production end of agriculture.

“The future likely holds a lot more limitations to water availability and quality,” he said. “In South Carolina, it is becoming increasingly important to use water as efficiently as possible.”

But understanding the state’s water resources isn’t only about conservation. Clemson researchers also work to help South Carolina’s agricultural producers maximize yield while reducing costs. Clemson Extension irrigation specialist Jose Payero discussed using historical weather records to derive water use and irrigation requirements of crops in South Carolina.

While crop water use and irrigation requirement data are needed for on-farm irrigation planning, design and scheduling, long-term water planning and hydrologic watershed water balance studies, Payero said actually measuring it is difficult.

“It’s hard to do. And believe me — I’ve done it,” he joked.

Historical weather data, however, are more readily available and can be used to determine the effects of stress on crops by calculating the estimated runoff based on the amount of rainfall in a given growing season in each of South Carolina’s 46 counties.

“Stress means that a plant is not getting the water that it needs at a given time,” Payero said.

Working to provide farmers a convenient tool to avoid such stress, Payero developed the South Carolina Crop Water Requirement Calculator, a free online application that allows users to determine crop water requirements for different crops in South Carolina by using weather data to estimate crop water use.

Also aimed at helping producers optimize water use to increase profitability, Clemson plant and environmental sciences graduate research assistant Amanda Accampo shared information at the conference about optimizing irrigation scheduling for fruit trees.

South Carolina is the nation’s second largest producer of peaches — behind only California — with more than 14,000 acres of peach orchards. Water plays a major role in ensuring their growth, as a mature peach tree with a full crop needs up to 45 gallons of water day.

“If you consider that there can be anywhere from 100 to 1,500 peach trees per orchard, that’s a lot of water,” Accampo said.

Using instruments — a tensiometer, which measures the amount of soil moisture available to a plant, and a dendrometer, which measures microvariations in trunk diameter — Accampo worked to determine the optimal water status to maximize the growth of peach trees.

“The problem is that there are no guidelines on how to irrigate peach trees,” she said. “There are suggestions from lots of people on what works best, but there’s no best way that is one-size-fits-all. Most of the research that we have on peach tree irrigation are from places like California or Spain that have a semi-arid climate, and in South Carolina we have a subtropical, humid climate. Humidity affects transpiration rates, or a tree’s ability to move water. So, if nothing else, the irrigation schedules for a semi-arid climate should be different from ours, and there are a lot of variables to consider.”

Through a field experiment at Clemson University’s Musser Fruit Research Farm, Accampo’s research concluded that fluctuating environmental conditions make correlation difficult between soil- and tree-based sensors. Thus, if some methods don’t work for peach trees in the South Carolina climate, the same could be true for other fruit trees, meaning further research is needed.

The next step, Accampo said, is to research the effectiveness and reliability of other tree-water status instruments to determine specific irrigation scheduling that works best for fruit trees in humid, subtropical climates.

“We need to find ways to be more efficient with our water so we can use less water,” she said. “In the long run, this will cost growers less money, time and effort.”