GVJ seminar 2000

Temporal Variability in Nitrogen Use Efficiency and Crop Response Index of Cereals.: 

Temporal Variability in Nitrogen Use Efficiency and Crop Response Index of Cereals. G.V. Johnson, W.R. Raun, 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

Improving Nitrogen Use Efficiency for Cereal Production: 

Improving Nitrogen Use Efficiency for Cereal Production Raun and Johnson. 1999. Agron. J. 91:357-363. Worldwide NUE = 33 % 1 % change = $234,658, 462

Improving Nitrogen Use Efficiency for Cereal Production: 

Improving Nitrogen Use Efficiency for Cereal Production Potential Improvements Crop Rotations Forage Production Systems Hybrid or Cultivar Conservation Tillage NH4-N Source In-Season and Foliar-Applied N Fertigation High Resolution Precision Management

Improving Nitrogen Use Efficiency for Cereal Production: 

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

Slide5: 

Loss of N from soil-plant system

Why is NUE so low for conventional N-fertilized production systems?: 

Measurement / Calculation? Applying too much fertilizer-N? Why is NUE so low for conventional N-fertilized production systems?

Calculating System Efficiencies: 

Calculating System Efficiencies For a particular system:

Calculating NUE: 

Calculating NUE Crop use of fertilizer-N:

Calculating NUE: 

Calculating NUE Correction for non-fertilizer contributions:

Reliability of NUE calculations?: 

Reliability of NUE calculations? Is mineralized N overestimated from N uptake for NO? Continual crop removal stimulates mineralization in NO. Fertilizer additions stimulate microbial activity, causing ‘priming effect’.

Is mineralized N overestimated from N-uptake for NO?: 

Is mineralized N overestimated from N-uptake for NO?

Reliability of NUE calculations?: 

Reliability of NUE calculations? Calculations for a single year may be misleading. Annual variations in mineralized soil-N may be large. Annual variations in crop response to fertilizer-N may be large.

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

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

Some conclusions about NUE for winter wheat.: 

Some conclusions about NUE for winter wheat. When corrected for mineralized-N, NUE still decreases with increasing fertilizer input. Long-term average NUE for dryland wheat ranges from about 50 % at low N input to 30 % at highest input.

Are farmers applying too much N?: 

Are farmers applying too much N? Enough N = amount required to support potential yield – N supplied from non-fertilizer sources. Yield Goal based recommendations assume potential yield and non-fertilizer inputs of N are near constant. Excess N is stored in soil.

Reality: 

Reality Unfertilized yield is variable over time. Control plot yield of winter wheat (Lahoma, OK): y = -15.78x + 1910 C.V. = 30.4 % 745 1974

Reality: 

Reality Fertilized yield is variable over time. Maximum yield of winter wheat (Lahoma, OK) Y = 23.95x + 2581 C.V. = 20.5 % 3045 3088

Are fertilized and unfertilized wheat yields related?: 

Are fertilized and unfertilized wheat yields related?

What is the temporal variability of fertilizer-N response?: 

What is the temporal variability of fertilizer-N response? Response Index (RI) RI = Max yield Nx / yield N0 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: 

Temporal variability of wheat response to N

Slide23: 

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

Some conclusions about wheat response to N.: 

Some conclusions about wheat response to N. Response to fertilizer-N is influenced more by external N inputs (N0 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.

How much fertilizer-N is needed?: 

How much fertilizer-N is needed?

NUE of winter wheat (502) as influenced by R.I. and N rate.: 

NUE of winter wheat (502) as influenced by R.I. and N rate.

Irrigated maize and sorghum: 

Irrigated maize and sorghum

Slide28: 

Maximum yield of irrigated maize: C.V. = 15.7 %

Slide29: 

Control plot yield of irrigated maize: C.V. = 34.3 %

Influence of year on NUE of irrigated maize receiving 180 kg N/ha.: 

Influence of year on NUE of irrigated maize receiving 180 kg N/ha.

Response Index for irrigated maize and sorghum over time.: 

Response Index for irrigated maize and sorghum over time.

Improving NUE.: 

Improving NUE. Manage input in relation to need. Difference between N uptake of maximum yield and unfertilized irrigated maize.

Slide33: 

Economics of excess N.

Economics of low NUE’s: 

Economics of low NUE’s At maximum yield. Value of yield increase / N cost = 1.7 / 1 Marginal ‘profit’ is $60/ha. At maximum profit. Yield is decreased by only 47 kg/ha. Marginal ‘profit’ is $4.55 / ha greater. N rate is 21 kg/ha less. NUE is 4.5% greater (33.6 to 38.1) Worldwide = $1.06 billion

Slide35: 

Economics of excess N. If N is 21.4 % in excess of N for maximum yield. Marginal ‘profit’ is reduced by $14 / ha. Yield is reduced by only 47 kg/ha. NUE is 4.5 % less.

Economics of low NUE’s: 

Economics of low NUE’s At maximum yield. For winter wheat: Value of yield increase / N cost is 1.7 / 1 Marginal ‘profit’ is $60/ha. For irrigated maize (NE) Value of yield increase / N cost is 2.8 / 1 Marginal ‘profit’ is $178/ha. NUE’s for maize and wheat are 3 to 4 % less than at maximum $ marginal return There is little or no economic incentive to manage for less than maximum yield.

Improving NUE’s: 

Improving NUE’s Avoid excess fertilizer-N. Identify realistic Yield Goal. 5-year average + 25 %. Calculate N requirement ~ 1 kg N / 50 kg maize. Subtract ‘soil test-N’ or ‘estimated’ available soil-N. Assumes final yield is predictable. Assumes N from soil is minimal and constant.

Summary: 

Summary 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 %. NUE and economic return from fertilizer use may often be improved at N rates slightly less than that for maximum yield. Supply of non-fertilizer N to crop changes greatly from year to year.

Summary: 

Summary The key to improving NUE is to avoid excessive N input. Realistic yield goals that take into account seasonal and spatial variability. Develop understanding of seasonal changes in crop utilization of soil-N. Future research?

Effect of Response Index on NUE of maize.: 

Effect of Response Index on NUE of maize.