May 10, 2013
WEST LAFAYETTE, Ind. - Extra nitrogen left in the soil after drought reduced corn yields last year has likely been lost with excess soil moisture in the winter and spring, a Purdue Extension agronomist says.
Most leftover nitrogen was in the form of nitrate, which is easily lost with soil moisture and to the air.
"A dry winter and spring would have allowed some of the nitrate to carry over to the upcoming corn crop," Jim Camberato said. "Unfortunately, in most of Indiana the winter and early spring have been anything but dry."
Between October and April, most of Indiana had more than 15 inches of precipitation, 4-8 inches above normal for a majority of the state.
If corn growers want to determine nitrogen levels in their soils, Camberato said sampling is an option.
Growers need to sample soils from representative field areas at depth intervals of 0-1 foot and 1-2 feet, and keep samples cold or spread thin to air dry shortly after sampling to minimize changes in the nitrogen levels, he said. The samples should then be sent to a soil-testing lab for NO3 analysis.
"Nitrogen fertilizer is one of the most expensive and important inputs in corn management," Camberato said. "Excess applied nitrogen reduces profit and negatively impacts the environment. Insufficient nitrogen reduces yield and profit.
"If you believe carryover nitrogen from last year's drought-stricken crop is likely in your fields, then soil sampling for nitrogen as a basis for a reduction in this year's fertilizer application is wise."
Growers who don't think nitrogen carryover is likely can follow nitrogen recommendations in Purdue Extension's Nitrogen Management Guidelines for Corn in Indiana available at http://www.agry.purdue.edu/ext/corn/news/timeless/NitrogenMgmt.pdf.
Unlike the nitrate left behind from last year's drought, nitrogen applied in the fall and spring in the form of anhydrous ammonia is unlikely to have been lost so far this spring, Camberato said. Anhydrous ammonia stays in the soil in the form of ammonium for several weeks after application. The colder the temperatures, the longer it stays in the ammonium form.
More information about nitrate carryover, anhydrous ammonia and soil sampling, including rainfall charts, are available in Camberato's article, "Plentiful Winter and Spring Precipitation - Nitrogen Carryover Unlikely for Most of Indiana" at http://extension.entm.purdue.edu/pestcrop/2013/issue4/index.html#plentiful.