Tools help estimate nitrogen losses

COLUMBUS - Producers in areas that have received excess rains the past several weeks may have a concern about nitrogen loss, particularly those who applied nitrogen in early spring or the previous fall.

Loss potentials increase during mild winters and springs since early-applied anhydrous and other ammonium forms may have converted to nitrate-nitrogen.

Leaching. In the nitrate form, nitrogen is susceptible to loss under the right conditions. Most of this loss potential is from denitrification, but leaching may also occur in sandy soils and soils with gravely subsoils.

Denitrification losses may be significant when relatively warm soils remain saturated for three days.

Standing water is evidence of saturated soils, but even bare soils that an individual cannot walk across without making footprints are saturated.

Tests. There is no test that can precisely determine how much nitrogen has been lost, but there are some options available to producers that can assist in making sound nitrogen management decisions.

One of these options is the pre-sidedress nitrate test, said Ed Lentz, district extension agronomy specialist.

For this test a producer needs to collect 10-15 random soil samples (12-inch depth) from a sampling area no larger than 20 acres, and send to a reputable lab.

The lab will determine the nitrate concentration of the sample.

Any sample that has more than 25-30 parts per million nitrate should have adequate nitrogen for the rest of the season.

If it is less than 25 parts per million the full rate of nitrogen needs to be applied.

Rates. Some states recommend reduced rates of nitrogen between 15 and 25 parts per million.

Ohio State University research, however, showed that soils are too variable for consistent recommendations between 15 and 25 parts per million, and deficiencies may occur later in the season at these reduced nitrogen rates.

A producer also needs to be aware that the soil nitrate level may change by the time they receive the test results.

Most labs have results in several days, but the actual soil nitrate level may be less than the test results if a heavy rain has fallen between soil collection and results received.

Also, this test only determines nitrate-nitrogen.

If a large amount of ammonium type of nitrogen has recently been applied and has not converted to nitrate, the test will not include this nitrogen in the results.

On the ‘Net. For those with internet access, another tool to estimate nitrogen loss is a software program on Ohioline.

This program will ask for inputs on location in the state, soil type, saturated soil events, type of nitrogen fertilizer, time of application, and more.

The software uses long term weather averages as defaults in estimating nitrogen events.

Selecting Nitrogen Transformation and Loss’ at http://ohioline.ag.ohio-state.edu/lines/farm.html#SWARE will download the program.

Not a substitute. Keep in mind that good judgment is still important when using various methods to estimate nitrogen needs, Lentz said.

Also, each field needs to be evaluated individually, he said, adding nitrogen software and point value systems are intended to serve as guides and not as definitive determination of nitrogen needs.