Is your irrigation scheduling method reliable or is it reducing yields?
By Amanda Huber
The need to reduce costs in a time of down prices is easier said than done. What input can you possibly cut and still provide the crop what it needs, including protection from disease, insects and weed competition? According to Wes Porter, UGA Extension irrigation specialist, it could very well be irrigation. Studies he has conducted over the last two years show that producers might be irrigating too much and to the detriment of peanut yield.
“Typically in the South, we run the irrigation system a couple times a week or whenever we can get to it,” Porter says. “But I am wondering if we can do better than that.”
“Irrigation scheduling is one option for maximizing yields and increasing profitability,” he says. Irrigation scheduling is a technique that involves determining how much water is needed and know when to apply it to the field to meet crop demands.
“The main purpose is to increase profitability and/or quality of the crop by increasing the efficiency of using water and energy or by increasing crop productivity,” Porter says. “That means getting it to the crop at the proper time. Irrigation timing affects quality and profitability.”
Unfortunately, surveys from USDA National Agricultural Statistics Service find that producers often base irrigation scheduling decisions on visible stress, feel of the soil or simply based on the calendar.
“If you wait until visible stress, yield has already been lost,” Porter says.
“Using a soil moisture sensor or testing the soil with a soil probe allows for better accuracy when determining moisture in the soil and whether you should irrigate.”
The goal of irrigation management should be to apply water at specific times to meet crop demand and minimize water loss due to runoff and deep percolation.
When considering irrigation, Porter says you have to take into account the efficiency of that system.
“Efficiency usually ranges from 60 to 95 percent. When talking about efficiency, if your system is only at 60 percent efficiency, keep in mind that means only six-tenths of an inch is getting down to the crop.
“Those in the 60 percent range are usually older systems, solid-set systems, travel guns and systems that perform at high pressures. Newer, low-pressure systems can be around 90 to 95 percent efficiency,” he says.
Other considerations are soil water holding capacity, which can be from six-tenths to 1.8 inches per foot, and the crop growth stage.
Porter suggests the use of sensors for more precise estimation of soil moisture, and to split the application of weekly water rates to help improve efficiency.
Knowing what’s going on in the soil is an important place to start in irrigation scheduling.
Soil has an infiltration rate and a soil water holding capacity. The crop has a rooting depth. Porter gave the following example: How much moisture can be stored from a rain event that had 1.5 inches per hour intensity and two hour duration? While three inches were caught in the rain gauge, the infiltration rate is one inch per hour and the soil water holding capacity is .8 to one inch per foot. In the example, the soil has the ability to infiltrate or “catch” approximately two inches of the rain event. However, with roots only 12 inches deep, only one inch of the rain event would be available to the crop. In this situation, only one inch of this rain event should be considered in calculating the need for irrigation.
“You have to remember where your roots are,” Porter says. “Think about what’s going on in the soil first.”
Porter began a study of irrigation scheduling methods in 2014, a dry year, and continued in 2015, a year with much more rainfall.
In 2014, looking at peanuts under irrigation treatments, they studied the University of Georgia Smart Sensor Array (UGA SSA), smart crop, which is a method in development, the traditional checkbook method, UGA EasyPan, UF PeanutFarm, a web-based irrigation scheduling tool, and then rain fed.
Porter says in 2014, a dry year, the highest yield was achieved from the UGA SSA, putting out only 9.40 inches of irrigation for a total of 21.73 inches of water and achieving an yield of 6,052 pounds per acre.
What surprised Porter is the amount of irrigation called for in the checkbook method and the effect on yield.
“This really made me start thinking that we need to adjust the checkbook method; maybe we are over applying. It called for 15 inches of irrigation for a total of 27 inches of water, and there was a reduction in yield of about 1,000 pounds below the best method and 600 to 700 below other methods.”
In 2015, the study was repeated and additional methods included; however, weather conditions made it a wetter year. Irrigation scheduling method has less effect on yield in the wet year, but again the checkbook method called for more than 12 inches of irrigation.
“We don’t want to over irrigate in a wet year,” Porter says. “It may not reduce yields as in a dry year, but it is costing money in pumping water that isn’t helping the crop.”
Porter will continue the study again in 2016, but whether it will be a wet year, dry year or somewhere in between remains to be seen.