Fertilizing rice in a very wet year: Part II

LSU Ag Center and University of Arkansas scientists recommend farmers apply nitrogen fertilizer for their rice on a dry soil, just ahead of the establishment of a “permanent” flood on their fields, normally three or four weeks after rice emergence.

Research shows putting on the flood helps incorporate the nitrogen into the soil and can help prevent the loss of up to 30 percent of the N through a process called volatilization. Dr. Justin Harrell, Extension rice specialist for Louisiana, talked about the recommendations during a tour stop at the LSU Rice Research Station Field Day.

“In Louisiana, if we’re talking about a drill-seeded or a dry broadcast or any type of a delayed-flood rice production system, we’re going to recommend you apply your nitrogen at two application timings,” said Dr. Harrell. “We will recommend you apply your first timing generally before the permanent flood is established when the rice is about 4 leaves to the first tiller stage of development.

“We’re going to recommend you apply the second shot at mid-season when the rice is at the green ring stage of development. That’s what we will use to make our determination to call the airplane and make that mid-season application.”

The scientists recommend growers apply two-thirds of the nitrogen at the first pre-flood timing and one-third at the mid-season timing, says Harrell.

“The first application is the most important because this is where we have the greatest potential for nitrogen loss,” says Harrell. “We will tell you we want you to make that first application on a dry soil. Then we’re will recommend you get the flood across the field as soon as possible after that application.”

As water moves across the field not only does it move laterally, but it also helps push the nitrogen into the soil, “incorporating” it where the rice plants can make optimum use of the fertilizer as they continue to develop.

“We know that if we can incorporate that nitrogen deeper into the soil, once we get anaerobic conditions, it’s going to stabilize that nitrogen,” he says, “and that’s exactly what we want to do.”

If, on the other hand, if the flood is delayed, “We’re going to leave that nitrogen exposed to the environment, and, in that situation, we have a lot of nitrogen loss through a process called ammonia volatilization.”

Research has shown that up to 30 percent of the nitrogen applied can be lost if it is not incorporated into the soil as quickly as possible. “That’s up to 30 percent of a farmer’s nitrogen dollars that are gone if the nitrogen is not moved into the soil.”

If farmers need more than two or three days to get the flood across their larger fields, LSU soil scientists recommend they treat their urea with a urease inhibitor or a product containing a product called NBPT. The NBPT delays the breakdown of the urea and thus limits nitrogen losses through ammonia volatilization.

To read more about urease inhibitors, go to http://link.springer.com/article/10.1007/BF00025060#page-1

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