Saving Nitrogen

 Dr. Gene Stevens, crop production specialist
 at the Fisher Delta Research Center discussed the
 latest information on nitrogen management in rice and corn.

 Photo by John LaRose, Jr.

Specialist Presents Ways To Fight Volatilization In Crops

MidAmerica Farmer Grower

   The latest information on nitrogen management in rice was presented recently by Dr. Gene Stevens, crop production specialist at the Fisher Delta Research Center. He also related some tips about nitrogen in corn.
   “Nitrogen fertilization is an important part of corn and rice production,” he began. “This spring, we started a new extension project with farmers collecting soil and plant samples from fields to help them improve nitrogen management. Since the tests were developed by scientists at other locations, this project is giving me an opportunity to have firsthand experience using them under local conditions.”
   This spring, Stevens went to 10 different corn fields, collected both stalk and soil samples, and had David Dunn at the Delta Center Soil Lab run the Iowa State pre-sidedress nitrogen tests and stalk nitrogen test for corn. This was an unusual spring, with cool and wet weather. The corn grew slow with nitrogen concentrated in smaller than normal plants. The plants were pale green or yellow, but the stalk test showed high tissue nitrate levels. “Without a soil test showing low N, I might have recommended reducing the rates of side-dress N based just on the tissue test.
   “The soil tests did really well for corn and rice,” Stevens said. “We tried the Arkansas N-STAR test on Missouri rice fields. We took samples from nine different rice fields, clay and silt loam soils, on each side of Crowley’s Ridge. According to University of Arkansas recommendations, on the clay soils we sampled down to 12 inches and for the silt loam soils we sample down 18 inches. Most of the tests showed the amount of nitrogen we’re recommending is on target except for two fields. One of them is here at the Missouri Rice Research Farm and it showed that we’re applying too much nitrogen, which explains the results we’ve been getting from some other experiments. Last year we had a variety test where we evaluated three different nitrogen rates for each variety and found that the lowest N rate was our highest yield; that explains why the N-STAR test showed that we were applying too much nitrogen, so those two things made sense of what we’re learning.”
   Even though Stevens has been emphasizing nitrogen loss processes in extension programs, he finds some farmers are still confused about urea volatilization.
   “The ideal scenario for cutting N loss from urea is to apply it on dry soil and push the fertilizer into the soil with irrigation or rainfall; that would be your best case situation for saving the most nitrogen,” he said. “The worst case scenario is to put urea on wet soil and let it stand there for several windy days allowing the pellets to melt and the urea to be lost as a gas by volatilization. There are several bacteria in the soil that produce enzymes that break the bonds in urea fertilizer and they’re more active on the soil surface in a warm, moist situation than in dry soil conditions.
   “I have found that this concept is very easy to get reversed in your mind, because farmers see the urea pellets melt on the soil surface and think it’s safe.  At the risk of sounding like a broken record, I will keep teaching people how it works at meetings and field days.”
   Stevens also discussed research that measures the amount of urea volatilization loss. Additives are available to farmers to reduce losses. In his studies, big plastic tubes  were pounded into the soil in two rice fields.  Urea with two additives (Agrotain and Limus) were tested at several rates and compared to urea applied at the same rates with no additive. The urea treatments were placed on the soil surface in each tube at green ring 10 days before rice flooding at first tiller. In the top of the tubes, foam disks were impregnated with a chemical to catch the amount of urea being lost. We found that urea without any additive for protection had the highest amount of urea loss. Here at the Missouri Rice Farm we did the same experiment as at the Delta Center and there were major differences between locations. So the difference of the soil moisture at the time we put the urea on, the temperature, the wind, all these different factors come into play and it’s just really hard to predict in advance to know how much loss you’re going to get. However, using those additives, either the Limus or Agrotain, helped reduce the amount of N loss.”
   In summary, for 2015, the pre-sidedress soil nitrogen test for corn this year did better than the stalk test on the nitrogen. The Arkansas N-STAR test worked really well and showed that in most fields farmers are putting on the correct amount of fertilizer anyway; but there were a couple of fields that were short on nitrogen, and putting additives to urea helps provide an insurance policy to prevent nitrogen losses. ∆
   BETTY VALLE GEGG-NAEGER: Senior Staff Writer, MidAmerica Farmer Grower

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