Nitrogen Use Efficiency, Nitrogen Fertilizers, NUE, Nitrogen and the EnvironmentImproving Nitrogen Use Efficiency for Cereal Production
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Agronomy Journal (91:357-363)

W.R. Raun and G.V. Johnson
(Department of Plant and Soil Sciences, Oklahoma State University, Stillwater, OK 74078, USA. Contribution from the Okla. Agric. Exp. Sta. * - corresponding author, E-mail: bill.raun@okstate.edu)
World consumption of N fertilizers for cereal production, N removal in cereal grain and estimated nitrogen use efficiency.

Table 1.

Computation/commodity

 

Production, N Removed, mT

Reference

World consumption of fertilizer-N, 1996

82,906,340

1

Cereal consumption of fertilizer-N (60% of total applied)

 

2

0.60 * 82,906,340 = 49,743,804 MT in cereals

49,743,804

 

World cereal production, 1996

 

Wheat

586,960,900

1

Corn

590,417,900

1

Rice

569,683,000

1

Barley

156,148,100

1

Sorghum

70,667,040

1

Millet

28,857,320

1

Oats

30,881,440

1

Rye

23,022,100

1

Total cereal production

2,056,637,800

 

World cereal grain N removal (production * %N), 1996

Total N, %

Production, N Removed, mT

Reference

Wheat

2.13

12,502,267

3-1, 4

Corn

1.26

7,439,266

3-2, 4

Rice

1.23

7,007,101

3-3, 4

Barley

2.02

3,154,192

3-4, 4

Sorghum

1.92

1,356,807

3-5, 4

Millet

2.01

580,032

3-6, 4

Oats

1.93

596,012

3-7, 4

Rye

2.21

508,788

3-8, 4

Total N removed in cereals

 

33,144,465

 

N removed in cereals coming from the soil and that deposited in rainfall (50% of total)

16,572,232

5

Estimated NUE = ((total N removed in cereals - N coming from the soil)/total N applied)*100

33%

 

N fertilizer savings per year for each 1% increase in NUE (same yield)

 

489,892 mT

 

Value of fertilizer savings using $479/metric Ton of actual N

$234,658,462

 

1 - FAO, 1996

2 - Alexandratos, 1996

3 - Dale, 1977

3-1, average of hard and soft wheat grain; 3-2, corn yellow grain; 3-3, rice grain, rough; 3-4, barley grain; 3-5 sorghum, milo, grain; 3-6, millet, grain, 3-7, oats grain, 3-8, rye grain;

4 - Tkachuk, 1977, to determine %N, crude protein was divided by 5.7, for wheat, barley, sorghum, millet, oats and rye, 6.25 for corn and 5.95 for rice

5 - Keeney, 1982


    Summary of Improved NUE Practices

1. Rotation: Because rotations in dryland production are dependent upon moisture availability, no specific rotation for improved NUE can be recommended. However, we believe that the development of an easily mineralizable organic N fertilizer would be consistent with the continued but low demand for N over the season in dryland production and/or slow release N that would come from an incorporated legume.

2. Production system: Forage production systems when compared to grain are much more efficient in their use of N, since harvest takes place prior to flowering after which gaseous plant N losses become significant. Plant N loss helps to explain why grain production systems are less N efficient.

3. Plant Breeding: Simultaneous selection for improved WUE and NUE, varieties with high HI, low forage yield and low plant N loss

4. Tillage: N fertilizer use efficiency is known to be lower in zero-tillage when N is applied to the surface. Decreased NUE for zero or reduced-tillage compared to conventional tillage can be expected. Although conventional tillage is recommended at this time for increased NUE, it should not be condoned at the expense of increased soil erosion. Surface application of N fertilizer in zero-tillage systems should be avoided.

5. N Source: Provide NH4 supply under low N inputs and NH4+NO3 under high N inputs. Inhibit nitrification under low N input (low yield potential) and stimulate nitrification under high yield potential

6. Preplant and in-season applied N: Applied N as NH3 split for forage production ( at planting and in February). For grain production, no N applied preplant, with NH3 applied once in late February, or UAN knifed in late February.

7. Spring applied foliar N: Rates of foliar applied N, post flowering in wheat should be within 10 and 25 kg N ha-1 and should effectively increase NUE when combined with preplant N rates less than the average required for estimated yield goals.

8. Precision Agriculture and Application Resolution: Sense and treat each 1m2 independently using NDVI at early vegetative stages of growth. N rates used for the first application will not be selected to obtain maximum yields, but rather a first approximation to adjust for the variability present (0- 50 lbs). The second application will apply a similar range of N, but at a time when yield potential can be better defined.