Researchers Lower Nitrogen Recommendation in Sugarbeets

By: Carol Ryan Dumas, Capital Press
March 15, 2016

JEROME, Idaho — Improvements in genetics and overall management have significantly reduced nitrogen needs in today’s sugar beet production, according to researchers at the USDA Agricultural Research Service and Amalgamated Sugar Co.

Research in the 1990s resulted in recommendations of 7 to 8 pounds per ton of sugar beets. But researchers theorized changes in sugar beet genetics might be changing nitrogen requirements for optimal sucrose yield, said David Tarkalson, an ARS soil scientist and agronomist at ARS Northwest Irrigation and Soil Research Lab at Kimberly.

Not only did research bear that theory out, it resulted in a significant decrease in nitrogen recommendations.

The new recommendations for maximum yield and maximum sucrose levels average 4.5 pounds of combined nitrogen in spring soils and applied fertilizer per ton of sugar beets, Tarkalson told those attending the University of Idaho Nutrient Management Conference last week.

That translates to 158 pounds of nitrogen per acre for a yield of 35 tons of beets per acre, significantly less than the previous recommendation of 245 to 280 pounds, he said.

The ARS and Amalgamated research was performed from 2005 to 2010, and yields are still moving up with the new, lower recommendations — which can allow growers to maximize sugar yield and save money on fertilizer, he said.

Nitrogen fertilizer is an expensive input with environmental implications, and nitrogen management is an important factor in row crop production. But it is especially important in sugar beets, with too little nitrogen harming yields and too much hindering sucrose extraction, he said.

That’s why researchers were concerned with fine-tuning nitrogen recommendations, he said.

Like most crops, yields in sugar beet production are increasing all the time, and that increase has gotten steeper since the 1990s, he said.

Nitrogen use efficiency has also improved, as yields are increasing with the same amount of nitrogen. The increase in nitrogen use efficiency implies decreased potential of nitrogen losses to the environment and increased economic returns for growers, he said.

The research showed applying nitrogen to meet the previous recommendations resulted in excess applied nitrogen at 13 of the 14 test sites. Assuming an excess of 90 pounds per acre, the per-acre monetary loss ranged from $30 to $64.

Curiously, sucrose yields did not increase in eight of the sites as the nitrogen supply increased, even when soil tests showed nitrogen fertilizer was needed, he said.

Researchers don’t really understand that, but Tarkalson theorizes the response was microbial driven with adequate nitrogen being released from organic matter in the soil, he said.

Along with the new recommendations, Tarkalson advised growers to sample spring soils to a depth of 3 feet and no less than 2 feet, as beets are readily pulling nitrogen from those depths.

He also noted that heavier textured soils — sandy loams to clays — might need a little more nitrogen, but no more than 6 pounds per ton of sugar beets. Coarse-texture, sandy soils might require up to 7 pounds, he said.

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