Current Nitrogen Fertilization Strategies for Corn in Nebraska Richard Ferguson Bob Caldwell

Nebraska Nitrogen Rate Algorithm for Corn Strengths Strengths Fairly extensive research database Fairly extensive research database Goal of minimizing nitrate leaching below root zone Goal of minimizing nitrate leaching below root zone Weaknesses Weaknesses Reliant on accurate preplant soil testing Developed at yield levels ≤ 200 bu/acre NR = 35 + (1.2*EY) – (8*NO 3 -N) – (0.14*EY*OM) EY = Expected yield (bu/acre) NO 3 -N = Root zone soil residual nitrate-N (ppm) OM = Soil organic matter (%) Additional credits for legumes, irrigation water and manure. EY = Expected yield (bu/acre) NO 3 -N = Root zone soil residual nitrate-N (ppm) OM = Soil organic matter (%) Additional credits for legumes, irrigation water and manure.

Mid-Nebraska Demonstration Project N Rate Response Over Years

Mid-Nebraska Demonstration Project N recommendation algorithm under- recommended N approximately 14% of the time (24 of 170 sites from 1990 – 1997, at which REC+ yield was statistically greater than REC yield). N recommendation algorithm under- recommended N approximately 14% of the time (24 of 170 sites from 1990 – 1997, at which REC+ yield was statistically greater than REC yield). N recommendation algorithm over- recommended N approximately 52% of the time (88 of 170 sites where REC- yield was statistically the same as REC yield). N recommendation algorithm over- recommended N approximately 52% of the time (88 of 170 sites where REC- yield was statistically the same as REC yield). N recommendation algorithm under- recommended N approximately 14% of the time (24 of 170 sites from 1990 – 1997, at which REC+ yield was statistically greater than REC yield). N recommendation algorithm under- recommended N approximately 14% of the time (24 of 170 sites from 1990 – 1997, at which REC+ yield was statistically greater than REC yield). N recommendation algorithm over- recommended N approximately 52% of the time (88 of 170 sites where REC- yield was statistically the same as REC yield). N recommendation algorithm over- recommended N approximately 52% of the time (88 of 170 sites where REC- yield was statistically the same as REC yield).

Nebraska Fertilizer Nitrogen Use Efficiency for Corn Statewide average corn yield for grain, and surveyed average N rate – irrigated and dryland Nebraska Agricultural Statistics Service Statewide average corn yield for grain, and surveyed average N rate – irrigated and dryland Nebraska Agricultural Statistics Service

Nitrogen Fertilizer Use in Nebraska Primary Sources Nitrogen for all crops Nebraska Agricultural Statistics Service Nitrogen for all crops Nebraska Agricultural Statistics Service

Chemigation: in-season whole- field N application

Producer Approaches to N Timing for Corn Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug % % Fall NH 3 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug % % Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug % % Preplant NH 3 Fertigation NH 3 UAN Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug % % Sidedress

Summary Current N recommendations for corn in Nebraska have led to measured increases in N use efficiency and reductions in groundwater nitrate concentrations. Current N recommendations for corn in Nebraska have led to measured increases in N use efficiency and reductions in groundwater nitrate concentrations. Current approach – Current approach – Relies on accurate preplant soil sampling. Relies on accurate preplant soil sampling. Is not sensitive to application timing – ie increased efficiency with fertigation. Is not sensitive to application timing – ie increased efficiency with fertigation. May not be valid for yield levels above 220 bu/acre. May not be valid for yield levels above 220 bu/acre.