Nitrogen Fixation and Crop Productivity

Crop productivity is correlated with the amount of available nitrogen. This nitrogen comes from mineralization of soil organic matter, application of fertilizer nitrogen, and biological fixation of N₂. The amount of nitrogen annually mineralized is dependent on the soil and ranges from negligible to about 200 kg of N per hectare per season. Almost all (90 +%) of fertilizer nitrogen is produced by the fixation of N₂ by the Haber-Bosch process, with ammonia and urea as the dominant forms. Biological fixation of N₂ is catalyzed by nitrogenase, which occurs in some bacteria and blue-green algae. Statistical information on nitrogen contents of crops (Table 1, Figures 1 and 2), nitrogen inventories (Tables 2 to 5), fixed nitrogen sources (Tables 6 and 7, Figures 3 to 5), fertilizer nitrogen (Figures 6 to 8), and biological N₂ fixation (Tables 8 and 9, Figures 9 and 10) relevant to crop production are given in the following pages. 105FIGURE 1 The distribution of nitrogen among the above-ground parts of corn (A) and soybeans (B) as a function of time. (From Hanway, J. J., <italic>Agron. J.,</italic> 54, 217, 1962; Hanway, J. J. and Weber, C. R., <italic>Agron. J.,63,</italic> 406, 1971. With permission of the American Society of Agronomy. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351072878/38527347-c5ad-4144-b03a-1c6a17eaf960/content/fig8_1.tif"/> 106FIGURE 2 Relationship between number of N deficient corn leaves showing characteristic tip burn at tasseling and yield. Plants without visible evidence of N deficiency on the leaves at tasseling may yield 3 tons less corn per hectare than plants with sufficient N. (From Viets, F. G., Jr., <italic>Soil Nitrogen,</italic> Bartholomew, W. V. and Clark, F. E., Eds., American Society of Agronomy, Madison, Wisconsin, 1965, 503. With permission.) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351072878/38527347-c5ad-4144-b03a-1c6a17eaf960/content/fig8_2.tif"/> Table 1 Nitrogen Content of Various Crops<xref ref-type="bibr" rid="ref8_1"> ¹ </xref>

Crop

Protein in seed (%)

kg plant N/ton seed ^a

Soybeans

42

100

Other grain legumes

23—28

56—68

Wheat

14

33

Sorghum

12

29

Corn

10

25

Rice

00

20

a

Assumes a nitrogen harvest index of 2/3, i.e., 2/3 of N is in the harvested part, seed, and 1/3 is in the nonharvested part. This harvest index is representative of the better varieties, while some lesser varieties may have a nitrogen harvest index of 1/10. Genetic and chemical approaches may improve the nitrogen harvest index.

From Hardy, R. W. F., Research for Food in Century ///, Proc. 24th Annu. Meeting of the Agricultural Research Institute, Agricultural Research Institute, Washington, D.C., 1975, 115—130. Table 2 Earth’s Nitrogen Reserves<xref ref-type="bibr" rid="ref8_5"> ⁵ </xref>

Source

Mass (metric tons)

Primary rocks

193 × 10¹⁵

Sedimentary rocks

0.4 × 10¹⁵

Deep sea sediments

0.5 × 10¹²

Atmosphere

3.9 × 10¹⁵

Land-sea pool

24 × 10¹²

From Burns, R. C. and Hardy, R. W. F., Nitrogen Fixation in Bacteria and Higher Plants, Springer-Verlag, Berlin, 1975. With permission. Table 3 Atmospheric Nitrogen Inventory<xref ref-type="bibr" rid="ref8_5"> ⁵ </xref>

Component

Mass (metric tons)

Annual input (metric tons)

Mean residence time

N₂

3.9 × 10¹⁵

250 × 10⁶

16 × 10⁶ years

N₂O ^a

1.0—2.0 × 10⁹

20—150 × 10⁶

10—100 years

NO

2 × 10⁶

20 ×10 ⁶

35 days

NO₂

4 × 10⁶

30 × 10⁶

36 days

NO₃ ^-/NO₂ ^-

0.2 × 10⁶

60 × 10⁶

1 day

NH₄ ⁺

4 × 10⁶

140 × 10⁶

10 days

NH₃

27 × 10⁶

>170 × 10⁶

<60 days

a

Concern over the possible significant destruction of stratospheric ozone by the N₂0 formed by denitrification of the additional fixed nitrogen required for increasing crop production has been expressed, but the inadequate information on rate of production and mean residence time preclude assessment of the problem.

From Burns, R. C. and Hardy, R. W. F., Nitrogen Fixation in Bacteria and Higher Plants, Springer-Verlag, Berlin, 1975. With permission. Table 4 Land-Sea Pool Nitrogen Inventory<xref ref-type="bibr" rid="ref8_5"> ⁵ </xref>

Component

Land (metric tons)

Sea (metric tons)

Soluble nitrogen

1 × 10⁹

660 × 10⁹

(NO₃ ^-, NO₂ ^-, NH₄ ⁺)

Insoluble inorganic

100 × 10⁹

—

Coal nitrogen

100 × 10⁹

—

Organic nitrogen

550 × 10⁹

650 × 10⁹

Animals

1 × 10⁹

3 × 10⁹

Plants

10 × 10⁹

1 × 10⁹

N₂ dissolved in sea

—

22 × 10¹²

Note: C. C. Delwiche, in a personal communication, proposes 9.9 × 10¹⁰ metric tons for soluble nitrogen and 9.6 × 10” for plants and animal nitrogen in the seas. Confidence limits are about ±50% for most values in Table 4. From Burns, R. C. and Hardy, R. W. F., Nitrogen Fixation in Bacteria and Higher Plants, Springer-Verlag, Berlin, 1975. With permission. 107Table 5 Examples of Total Amounts of Nitrogen and Other Primary Nutrients in Temperate-Region Mineral Surface Soils (%)<xref ref-type="bibr" rid="ref8_6"> ⁶ </xref>

Range

N

0.02—0.50 ^a

P₂O₅, 0.02—0.40

K₂O 0.20—4.00

Norfolk fine sand, Fla.

0.02

0.05

0.16

Sassafrass sandy loam, Va.

0.02

0.02

1.54

Ontario loam, N.Y.

0.16

0.10

1.95

Ely loam, Neb.

0.10

0.18

2.90

Hagerstown silt loam, Tenn.

0.27

0.16

0.91

Cascade silt loam, Ore.

0.08

0.16

2.11

Marshall silt loam, la.

0.17

0.12

2.23

Summit clay, Kan.

0.09

0.09

2.42

a

A nitrogen content of 0.1% is equivalent to 1.8 metric tons per hectare furrow slice.

From Soils of the United States, Part 3, Atlas of American Agriculture, U.S. Department of Agriculture, Washington, D.C., 1935. Table 6A Estimated Annual Amounts of N₂ Fixation in 1975<xref ref-type="bibr" rid="ref8_5"> ⁵ </xref> <xref ref-type="fn" rid="fntable8_4"> ^a </xref>

Land use

ha × 10^-6

kg N₂ Fixed/ha year ^a

Metric tons × 10⁶ N₂ fixed/year

Biological N₂ Fixation

Agricultural

4,400

Arable under crop

1,400

Legumes

250

140

35

Non-legumes

1,150

Rice

135

30

4

Other

1,015

5

5

Permanent meadows

3,000

15

45

Forest and woodland

4,100

10

40

Unused

4,900

2

10

Ice covered

1,500

0

0

Total land

14,900

139

Sea

36,100

1

36

Total

51,000

175

Abiological N₂ Fixation

Lightning

10

Combustion

20

Industrial

Fertilizer

40

Industrial uses

10

Total

80

Total N₂ Fixation

255

a

Another recent report containing estimates of N₂ fixation ⁷ is based on the preceding estimates with the following changes: forest and woodland, 50 × 10⁶ tons; ocean, 1 × 10⁶; industrial-used as fertilizer, 39 × 10⁶; industrial-industrial uses, 11 × 10⁶; industrial-inefficiencies (losses), 7 × 10⁶, and a total of 237 × 10⁶ tons. Another, ⁸ gives the following estimates for N₂ fixation: land, 99 × 10⁶ tons; ocean, 30 × 10⁶; atmospheric, 7.4 × 10⁶; industrial, 40 × 10⁶; combustion, 18 × 10⁶. Confidence limits are about ±50% for all values except that of industrial fixation.

108Table 6B Reported Rates of N₂ Fixation by Specific Systems

N₂-fixing system

kg N₂ fixed/ ha × yr

N₂-fixing system

kg N₂ fixed/ ha x yr

Soybean

94

Soil, Canadian

2—200

84

Soil, algal film

To 6

57

Under rye grass

55

Soybean, groundnut

91

Natural grassland

1—2

Pulses

50—60

Irrigated lawn

5

Peas, lentils, vetches

85

Grass

112—145

Cowpeas

84

Sand dune vegetation

0.1

Groundnuts

47

Beech forest

0.4

Cereal legumes

50

Coniferous forest

50

Clovers

105—220

Pine forest

0—23

137

13—39

150—160

Soil under Douglas fir

13—38

104—149

Douglas fir, phylloplane

7—23

Lucerne

128

Alnus

156

208

85

158

150

300

56

Lupin

150

Wppophae

179

169

2—15

Mixed legumes

125

Acacia

270

Pasture legumes

118

Casuarina

58

Rice paddy

10—55

Ceanothus

60

27

Myrica

9

45

Gunnera-Nostoc

To 72

Wheatfield soil

4

Desert crust, Arizona

41

Cornfield soil

90

Desert crust, Australia

2—3

Soil, cultivated layer, U.S.S.R.

5

Lichens, mountains

39—84

Soil, Nile valley

15

Lake, Wisconsin

4

Fallow soil, Calif.

3.5

2.4

Under native vegetation

2

Lake, England

0.4—3

Under grasses, iris

45—66

8

Soil, Quebec (anaerobic)

To 73

Lake, Tropical

44

Under mustard

24

Marine angiosperms, rhizosphere

700

From Burns, R. C. and Hardy, R. W. F., Nitrogen Fixation in Bacteria and Higher Plants, Springer-Verlag, Berlin, 1975. With permission. 109Table 7 Selected Examples of Seasonal Amounts and Percentages of Total N Fixed Symbiotically by Field-Grown Soybeans

kg N₂ Fixed/ha × Season

N Fixed(%)

Method or conditions

Untreated

Soil amended

Untreated

Soil amended

Inoculated vs. uninoculated soybeans

29

_

—

—

Nodulated vs. nonnodulated soybean isolines

0 kg N/ha (good growth conditions)

155

40

—

56 kg N/ha as NH₄NO₃

—

110

—

29

112 kg N/ha as NH₄NO₃

—

77

—

20

168 kg N/ha as NH₄NO₃

—

69

—

16

45 ton/ha as corn cobs

—

280

—

72

Nodulated vs. nonnodulated soybean isolines

0 kg N/ha

51

—

34

—

225 kg N/ha as NH₄NO₃

—

18

—

9

Nodulated vs. nonnodulated soybean isolines

0 kg N/ha

103

—

48

—

112 kg N/a

—

62

—

27

224 kg N/ha

—

21

—

10

449 kg N/ha

22

—

10

Acetylene reduction

¡00

—

—

—

Acetylene reduction

164

—

35

—

Acetylene reduction

0 kg N/ha (first-year soybeans)

8

—

—

—

280 kgN/ha as NH₄NO₃

—

<1

—

—

12.7 ton/ha as corn cobs

—

57

—

—

Acetylene reduction

0 kg N/ha

—

—

6

—

200 kg N/ha as NH₄NO₃

—

—

—

<1

Acetylene reduction

Field-grown soybeans

84

—

25

—

Outdoor chamber-grown soybeans

76

—

26

—

Outdoor chamber-grown soybeans + CO₂

—

427 ^a

—

84

Average

86

31

a

No soil amendment was used. The CO₂ level in canopy varied between 800—1200 ppm between 0800—1700 hr vs. ambient CO₂ for the untreated chamber-grown soybeans.

From Criswell, J. G., Hardy, R. W. F., and Havelka, U. D., in World Soybean Research: Proceedings of the World Soybean Research Conference, Hill, L. D., Ed., Interstate Printers & Publishers, Danville, 111., 1976, 118. With permission. 110FIGURE 3 World nitrogen fertilizer consumption from 1905—1975 and projection for 1975—2000. In 1975 40 × 10^e metric tons of nitrogen fertilizer were consumed and another 10 × 10” metric tons of industrial fixed nitrogen were used for fibers, explosives, animal feeds, etc. Projected nitrogen fertilizer consumption in 2000 A.D. is estimated at 160 × 10’ metric tons. Additional abiological fixation of N₂ occurs by lightning and combustion. (From Hardy, R. W. F., Proc. <italic>1st Int. Symp. Nitrogen Fixation,</italic> Vol. 2, Newton, W. E. and Nymen, C. J., Eds., Washington State University Press, Pullman, 1976, 693—717. With permission.) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351072878/38527347-c5ad-4144-b03a-1c6a17eaf960/content/fig8_3.tif"/> FIGURE 4 Percent of total nitrogen in soybeans obtained from atmospheric Ni, fertilizer, and soil at various rates of soil fertilizer application. Soybeans usually do not increase yield in response to fertilizer nitrogen. (From Johnson, J. W., Welch, T. F., and Kurtz, L. T., <italic>J. Environ. Qual.,</italic> 4, 303, 1975. With permission of the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351072878/38527347-c5ad-4144-b03a-1c6a17eaf960/content/fig8_4.tif"/> 111FIGURE 5 The similar net removal of nitrogen by soybeans and corn at various rates of soil fertilizer application. In contrast to popular belief, soybeans are net removers of nitrogen when no fertilizer nitrogen is applied. (From Johnson, J. W., Welch, T. F., and Kurtz, L. T., <italic>J. Environ. Quai.,</italic> 4, 303, 1975. With permission of the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351072878/38527347-c5ad-4144-b03a-1c6a17eaf960/content/fig8_5.tif"/> FIGURE 6A Idealized response in dry matter production of a non-legume to increments of N fertilizer. Segment A is seldom found in practice. (From Viets, F. G., Jr., <italic>Soil Nitrogen,</italic> Bartholomew, W. V. and Clark, F. E., Eds., American Society of Agronomy, Madison, Wisconsin, 1965, 503. With permission.) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351072878/38527347-c5ad-4144-b03a-1c6a17eaf960/content/fig8_6a.tif"/> 112FIGURE 6B Yield response of corn to fertilizer nitrogen. (From Hoeft, R. G. and Siemens, J. C, <italic>Illinois Res.,</italic> 17, 10, 1975. With permission.) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351072878/38527347-c5ad-4144-b03a-1c6a17eaf960/content/fig8_6b.tif"/> 113FIGURE 7 Relationship between cereal grain yield and nitrogen fertilizer use rate for less developed countries (LDC’s) and more developed countries (MDC’s) for the period 1950—1974. Note that one-half of total nitrogen fertilizer consumption is included since this is the approximate amount used on cereal grains. (From Hardy, R. W. F. and Hav-elka, U. D., <italic>Science,</italic> 188, 633, 1975. With permission of the American Association for the Advancement of Science.) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351072878/38527347-c5ad-4144-b03a-1c6a17eaf960/content/fig8_7.tif"/> FIGURE 8 Energy return in grain per unit of fossil-derived energy input for nitrogen fertilizer manufacture, distribution, and application for various rates of nitrogen fertilization of corn. (From Hoeft, R. G. and Siemens, J. C, <italic>Illinois Res.,</italic> 17, 10, 1975. With permission.) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351072878/38527347-c5ad-4144-b03a-1c6a17eaf960/content/fig8_8.tif"/> 114FIGURE 9 Biological N₂-fixing relationships including asymbioses where the diazotroph (N₂-fixing microorganism) is freeliving and associative symbioses where the diazotroph is associated with another organism. A group of the associative symbioses that are (e.g., nodulated legumes) or may be (e.g., rhizosphere associations) of agricultural significance are designated. (From Hardy, R. W. F., <italic>Research for Food in Century III,</italic> Proc. 24th Annu. Meet. Agrie. Res. Inst., Agricultural Research Institute, Washington, D.C., 1975, 115. With permission.) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351072878/38527347-c5ad-4144-b03a-1c6a17eaf960/content/fig8_9.tif"/> Table 8 N₂ Fixation Parameters<xref ref-type="fn" rid="fntable8_6"> ^a </xref> of Soybeans and Peanuts<xref ref-type="bibr" rid="ref8_16"> ¹⁶ </xref>

Exponential phase

N₂ fixed

Crop

Initiation age (days)

Termination age (days)

Increase %/days

mg N/plant

kgN/ha

Soybeans

26

90

8.3

260

84

Peanuts

42

97

8.5

221

—

a

These parameters will vary with variety, geographic location, soil, etc.

From Hardy, R. W. F., Burns, R. C, and Holsten, R. D., Soil Biol. Biochem., 5, 47—81, 1973. With permission. 115FIGURE 10 Typical time-course of N, fixation by field-grown soybeans and peanuts. (From Hardy, R. W. F., Burns, R. C, Hebert, R. R., Holsten, R. D., and Jackson, E. K., <italic>Plant Soil, Special Volume,</italic> 561, 1971. With permission.) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351072878/38527347-c5ad-4144-b03a-1c6a17eaf960/content/fig8_10.tif"/> Table 9 Relationship between Photosynthate Available to the N₂-Fixing Nodule and N* Fixation<xref ref-type="bibr" rid="ref8_17"> ¹⁷ </xref>

Effect on N₂ Fixation

Factor

Increase

Decrease

Light quantity

Day

Night

Long days

Short days

Supplemental light

Shading

Source size

Additional foliage

Defoliation

Low planting density

High planting density

CO2/O2 ratio in canopy

Increased pCO₂

Decreased pCO₂?

Decreased pO₂

Increased pO₂

Photosynthetic type

C₄(?)

C₃

Competitive sinks

Removal of reproductive

Development of reproductive

structures

structures

Translocation

—

Girdling

Water

—

Drought

From Hardy, R. W. F. and Havelka, U. D., Symbiotic Nitrogen Fixation in Plants, Nut-man, P., Ed., Cambridge University Press, London, 1975, 421—439. With permission.