Why recommend 2 lb N/bu wheat?

Micah Humphreys, Jagadeesh Mosali, Jamie Patton, Roger Teal

Assumptions:

1 bu wheat = 60 lb

N in wheat grain = 2%

N in wheat straw = 1%

Harvest Index = 60

For 1 bu wheat yield

1 bu * 60 lb/ bu * 2% N in grain = 1.2 lb N in grain

(1 bu * 60 lb grain/bu) * 1.67 lb biomass/1 lb grain = 100.2 lb biomass

100.2 lb biomass * 1% N in straw = 1 lb N in straw

1.2 lb N in grain + 1 lb N in straw = 2.2 lb N needed for 1 bu wheat

General NUE Calculations

10 lb N/ acre added by lightening +

100 lb N/ acre added by mineralization (soils with 1 % OM) +

120 lb N/ acre added by fertilizer (60 bu/acre* 2 lb/bu) =

230 lb N/ acre additions

132 lb N/ acre used by plant (60 bu * 2.2 lb N needed grain and straw)

72 lb N/ acre used by plant (60 bu * 1.2 lb N needed grain only)

NUE (grain and straw) = 132/230 = 57 %

NUE (grain only) = 72/230 = 31%