Arkansas

Nitrogen fertilizer offers great benefits for yields, but it is the nutrient most difficult to manage effectively, said Dr. Rick Norman, professor of soil fertility for the University of Arkansas Division of Agriculture.

"Preflood nitrogen sets the yield, so we have to do it right," Norman said.

Urea, a common source of nitrogen, has to be applied and incorporated into the soil within three days to minimize nitrogen loss, Norman said. Producers incorporate it into the soil by flooding fields, but many don't have the well capacity to get a flood across a field within three days.

"When flooding is delayed, urea nitrogen losses of 25 percent to 35 percent in five to 10 days is common," Norman said.

Division of Agriculture scientists, supported by the Arkansas Rice Research and Promotion Board, are studying alternatives and additives that can help reduce nitrogen loss. One of the most promising is a commercial additive called Agrotain, Norman said.

Agrotain is an enzyme inhibitor that reduces the breakdown of urea into ammonia gas. It is applied as a coating for urea that minimizes nitrogen loss and improves nitrogen uptake by plants, Norman said.

"When it takes more than three days to flood across a field, Agrotain reduces nitrogen loss 60 to 70 percent and can increase yields by up to 25 bushels," said Dr. Chuck Wilson, Extension rice specialist "Farmers say the fields stay green longer."

"This Agrotain thing has been great," Norman said. "We're doing tests now to see how it works on muddy fields."

Urea needs to be applied in contact with the soil, so it works best when used in dry fields, Norman said.

"If preflood fertilizer application is delayed because of rain, Agrotain reduces nitrogen loss from urea when applied to wet ground," he said. "It looks better than urea alone on wet ground, but not as good as urea with or without Agrotain on dry ground."

Norman and Wilson are also trying to see if Agrotain offers benefits when used on clay soils.

Ammonium sulfate is an alternative fertilizer that offers reduced loss of nitrogen, but it is more expensive than urea, Norman said.

"Ammonium sulfate is the best source for minimizing nitrogen loss and ensuring uptake," Norman said. "Agrotain is not as good, but it's close enough when balanced against price."

He is conducting research to see if blending ammonium sulfate with urea is a cost effective means of using nitrogen more efficiently.

Date: 2/24/05

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