Farm Progress

N-ST*R Nitrogen Soil Test for Rice earns University of Arkansas Division of Agriculture team award from the Rice Technical Working Group. 

March 23, 2012

3 Min Read

The N-ST*R Nitrogen Soil Test for Rice developed at the University of Arkansas Division of Agriculture has earned a team award from the Rice Technical Working Group.

N-ST*R offers field-specific recommendations for nitrogen applications that, in many cases, has the potential to reduce application rates by half or more, said Trent Roberts, research assistant professor of crop, soil and environmental sciences.

"It's about improving the profitability of our growers," Roberts said.

Roberts, soil fertility professors Rick Norman and Nathan Slaton and Extension specialists Chuck Wilson and Jeremy Ross were the lead scientists on the team that received the RTWG's Distinguished Rice Research and Education Team Award.

Collaborating team members from other institutions include Louisiana State University agronomists Dustin Harrell and Brenda Tubana, Mississippi State University agronomist Tim Walker, and Texas A&M agronomist Garry McCauley. The award was presented during RTWG's thirty-fourth gathering Feb. 27-March 1 with rice experts from across the United States and the world.

Before N-ST*R, Roberts said, division recommendations called for 150 units of nitrogen per acre for most rice varieties grown on silt loam soils. "There's a lot of variability among fields. We knew there were areas where you needed different application rates, but we didn't have any way to predict where those areas would occur. With rising fertilizer costs, we needed a better way to know where and how much nitrogen was needed among fields."

The breakthrough that makes N-ST*R possible was developing a means to measure the amount of nitrogen contained in the soil that was available for use by plants. Norman, who has worked on the project for some 20 years, said nitrogen exists in many organic forms in a constant state of change in the soil. The amount actually available to plants has been hard to pin down.

Norman credits Roberts and Ross, who were his graduate students, with finding the correct soil depth to sample and solving the chemistry puzzle by identifying measurable soil nitrogen fractions that reliably predict the amount of soil nitrogen available to plants.

Field trials of N-ST*R in farmers' fields have verified that the site-specific nitrogen rates recommended provide optimum yields and that they frequently vary significantly from the rates a farmer would have otherwise applied.

"We've seen some fields where you can get the same yield with 45 units of nitrogen as you can with 150 units," said Roberts.

A full release of the program was inaugurated in fall 2011 for use in rice on silt loam soils. The N-ST*R lab has processed about 1,500 samples, mostly from Arkansas, Prairie and Lonoke counties. More than 200 samples have come from Louisiana.

N-ST*R recommendations are being used this year in Arkansas Rice Research Verification Program silt loam fields. Soil test data is being collected from the program's clay soil fields.

The research team hopes to extend the program for use in rice on clay soils and wheat on silt loam in 2012. The long-term goal is to extend the technology to corn, cotton and grain sorghum.

"Every soil test method is different," Roberts said. "The method you're using has a lot to do with how deep you have to sample."

N-ST*R requires samples from the entire depth of the plant's root zone. That extends 18 inches deep for rice on silt loams, but only 12 inches for rice on clay soils. Initial tests show samples need to reach 6 inches deep for wheat on silt loams.

"When you step back to look at the potential impact that this technology could have, it could be huge," Roberts said. "If you can cut your fertilizer costs to one-third to one-half of what you're using now, you're talking about being able to keep some farmers in business."

Norman said, "There are going to be fields were N-ST*R increases the nitrogen fertilizer rate over what is currently recommended and in turn increase grain yield. So what is huge about N-ST*R is providing the correct nitrogen fertilizer rate for maximizing profit, minimizing environmental impact, and keeping rice production sustainable."

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