Nitrogen Use Efficiency as Influenced by Crop Response Index. G.V. Johnson, W.R. Raun, R.W. Mullen, R.L. Westerman and B.B. Tucker Department of Plant and Soil Sciences Oklahoma State University R.A. Olson Department of Agronomy University of Nebraska G.V. Johnson, W.R. Raun, R.W. Mullen, R.L. Westerman and B.B. Tucker Department of Plant and Soil Sciences Oklahoma State University R.A. Olson Department of Agronomy University of Nebraska

RI > 1.5 RI < 1.5 RI > 1.5 RI < 1.5 Higher NUE Lower NUE Higher NUE Lower NUE Apply more N Apply less N Apply more N Apply less N Potential for increased yield Response Index

Improving Nitrogen Use Efficiency for Cereal Production  Raun and Johnson Agron. J. 91:  Worldwide NUE = 33 %  1 % change = $234,658, 462  Raun and Johnson Agron. J. 91:  Worldwide NUE = 33 %  1 % change = $234,658, 462

Improving Nitrogen Use Efficiency for Cereal Production  Potential Improvements  Crop Rotations  Forage Production Systems  Hybrid or Cultivar  Conservation Tillage  NH 4 -N Source  In-Season and Foliar-Applied N  Fertigation  High Resolution Precision Management  Potential Improvements  Crop Rotations  Forage Production Systems  Hybrid or Cultivar  Conservation Tillage  NH 4 -N Source  In-Season and Foliar-Applied N  Fertigation  High Resolution Precision Management

Improving Nitrogen Use Efficiency for Cereal Production  Cause of low NUE  Soil-Plant system leaks  Loss increases with excess mineral-N  Cause of low NUE  Soil-Plant system leaks  Loss increases with excess mineral-N

Leaching Denitrification NO, N 2 O Fertilizers Plant Uptake Nitrification NO 3 - NH 4 + N2N2 N2N2 + H 2 O NH 3 + OH - Harvest + OH - NH 3 Volatilization Loss of N from soil-plant system

Harvested-N 1 - Harvested-N 0 Fertilizer-N 1 X 100 = NUE

Influence of year on NUE winter wheat receiving 90 kg N/ha.

Unfertilized yield is variable over time. Unfertilized yield is variable over time. y = x C.V. = 30.4 % y = x C.V. = 30.4 % Control plot yield of winter wheat (Lahoma, OK):

Fertilized yield is variable over time. Fertilized yield is variable over time. Y = 23.95x C.V. = 20.5 % Y = 23.95x C.V. = 20.5 % Maximum yield of winter wheat (Lahoma, OK)

Are fertilized and unfertilized wheat yields related?

What is the temporal variability of fertilizer-N response?  Response Index (RI) RI = Max yield N x / yield N 0  RI = Indication of the degree to which N, external to the growing environment, is needed to support potential yield.  Response Index (RI) RI = Max yield N x / yield N 0  RI = Indication of the degree to which N, external to the growing environment, is needed to support potential yield.

Temporal variability of wheat response to N

Relationship of fertilized and non fertilized yield to R.I.

Irrigated maize and sorghum

Response Index for irrigated maize and sorghum over time.

Conclusions  NUE of wheat is usually < 70 % at low fertilizer-N rates and decreases with increasing N input.  NUE for maize and sorghum is usually < 50 %.  Supply of non-fertilizer N to crop changes greatly from year to year.  Soil moisture and temperature variability?  NUE of wheat is usually < 70 % at low fertilizer-N rates and decreases with increasing N input.  NUE for maize and sorghum is usually < 50 %.  Supply of non-fertilizer N to crop changes greatly from year to year.  Soil moisture and temperature variability?

Conclusions:  Response to fertilizer-N is influenced more by external N inputs and mineralized soil-N (N 0 yield) than by potential yield, in a given year.  Since this is found for soil that has not received fertilizer N for over 20 year, it is even more likely to occur in fields that have a history of receiving fertilizer-N each year.  Response to fertilizer-N is influenced more by external N inputs and mineralized soil-N (N 0 yield) than by potential yield, in a given year.  Since this is found for soil that has not received fertilizer N for over 20 year, it is even more likely to occur in fields that have a history of receiving fertilizer-N each year.

Conclusions  NUE may be improved by knowing the response index and avoiding excess fertilizer-N.  Identify potential yield each year.  Identify non-fertilizer N contributions.  Apply fertilizer-N in-season.  NUE may be improved by knowing the response index and avoiding excess fertilizer-N.  Identify potential yield each year.  Identify non-fertilizer N contributions.  Apply fertilizer-N in-season.