Rice producers in Louisiana and other Mid-South states frequently split their nitrogen fertilizer applications between one made just prior to permanent flood establish and another at mid-season or when the rice reaches the green ring stage.
Of the two, the first is most important because typically two-thirds of the nitrogen is applied at that time, according to Dustin Harrell, agronomy project leader at the LSU AgCenter’s H. Rouse Caffey Rice Research Station.
Over the years researchers have found that applying a compound called NBPT on the urea fertilizer recommended by the LSU AgCenter for application in rice will help prevent the urea from turning into ammonia gas and “simply float off the field if it is left exposed on the soil surface for an extended period of time.”
Dr. Harrell told visitors to the Rice Research Station’s annual field day on June 28 he had begun to believe he would never see a compound that worked better in rice than those containing NBPT, but he “had about decided to change his mind after working with a new product.”
The new material, which doesn’t have a name yet, could be introduced by Koch Agronomic Services in 2018 if it receives approval from EPA in time for the 2018 use season.
10 days to flood
“Unfortunately, in commercial rice production in Louisiana, it may take 10 or more days for a flood to be established on some of the larger fields,” says Dr. Harrell. “In these situations, a urease inhibitor containing NBPT is recommended.”
Research at the H. Rouse Caffey Station has shown that farmers can lose 17 to 30 percent of the soil-applied urea when it is left on the field for 10 days before permanent flood. That’s a potential for 30 percent of a rice producer’s fertilizer dollar to be lost before he ever gets water on the field.
“The urease inhibitor, N (n-butyl) thiophosphoric triamide, basically slows down the breakdown of urea to the ammonium-N form, which is available to plants,” he said. “Because it temporarily delays the breakdown of the urea, it also temporarily delays the potential for ammonia volatilization losses.
“We recommend that when we apply this preflood fertilizer that we apply it on dry ground, and that we get the flood on that field as soon as possible,” said Harrell. “The reason we recommend that is that the longer that urea sits on the soil surface the more losses you’re going to have through ammonia volatilization.”
If the grower applies the nitrogen on moist or damp ground, the urea will break down faster and more ammonia volatilization can occur, said Dr. Harrell, who also serves as Louisiana’s Extension rice specialist.
Experimental compound tested
“Last year, in 2016, I had the opportunity to look at an experimental urease inhibitor,” he said. “This experimental compound was created by scientists with Koch Agronomic Services. Koch is the company that bought the rights to Agrotain, one of the original urease inhibitors with NBPT in it.”
The scientists have taken NBPT and formaldehyde and put them together under certain conditions to create a new molecule that works better than NBPT alone under certain situations.
“The situation where it really excels is on acid soils,” said Dr. Harrell. “One of the things we know about NBPT is that it can break down a little faster on acid soils. So this is where this new urease inhibitor really has an advantage.”
In a greenhouse study, which allowed him to control the environmental factors, Harrell said plots not treated with NBPT or the new compound lost about 32 percent of the nitrogen applied in the test. With Agrotain Ultra, an older product with NBPT, the researchers lost about 15 percent of their nitrogen. Plots treated with the new Koch experimental compound only lost about 11 percent of their nitrogen.
“So this new molecule basically has about a 26-percent advantage over the original NBPT treatment at least on this acid soil,” he said. “This soil has a pH of about 5.5.”
Koch has filed for a patent for the new molecule and has asked EPA to register the product. They hope to have the label approved in time for the 2018 season.