Soil nitrogen left behind by Indiana's drought-stricken 2012 corn crop could mean that the state's wheat growers might be able to apply less fertilizer this spring, a group of Purdue Extension agronomists say. Corn plants stressed by extreme heat and too little water yielded less grain andleft more nitrogen in soils than in normal years. Wheat has more potential to scavenge the nutrient than a subsequent corn crop.
In a new publication, "Carryover Nitrogen - Potential Impact on WheatFertilization," Shaun Casteel, Jim Camberato and Chuck Mansfield discuss the topic and why it's good news for wheat growers who might not have to buy as much fertilizer.
"Spring fertilization rates necessary to optimize yield may be lower thanwhat is needed following normal corn crops," Casteel explains. "Wheat planted inthe fall has an advantage in that it will accumulate some nitrogen prior todormancy. Wheat'sprimary advantage is the established root system that cantake up nitrogen in the early spring before corn is even planted."
In a more normal year, Indiana wheat growers don't have to consider leftovernitrogen because winter and spring precipitation removes it from the croproot zone, Camberato says.
"Most of the nitrogen remaining in the soil at the end of the season is ahighlyleachable form of nitrate," he says. "Nitrate is repelled by soilparticles, soit moves downward with water. Indiana typically receives 18to 24 in. of rainfall between October and April, which is sufficient toremove most of the nitrate from the root zone of the state's soils."
This year, parts of Indiana have received less rainfall than that -
especially in the northeastern and northwestern parts of the state whererain has ranged from 10 to 20 in.. Nitrogen carryover potential is much higher in these regions than in southern Indiana.
Soil sampling and lab analysis are the most accurate way to estimate theamount of nitrogen left behind. But because deep soil sampling islabor-intensive, the more common approach to adjusting nitrogen fertilizerrates has been to use young wheat plants as an indicator of soil nitrogensupply instead of sampling soils directly, Casteel says.
Virginia Tech and the University of Kentucky provide guidelines to growersfor sampling wheat and adjusting the fertilization rate based on the tissue nitrogen concentration.
"Sampling wheat at the proper growth stage is important because the tissueconcentration changes rapidly with growth during this time period," Casteelsays.
Casteel, Camberato and Mansfield's full report, including tables and photos, is available for free download at http://www.agry.purdue.edu/ext/soilfertility/news/carryovernitrogenwheat.pdf.
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