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V. Accumulation of Legume Nitrogen

V. Accumulation of Legume Nitrogen

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Table IV

Abovegound N Accumulation by Green Manure (GM) Crops Grown in Lowland Rice Fields



Species and

country

Aeschynomene afraspera

Philippines



Asfrugalus sinicus

Japan

Crotalaria juncea

India



Duration0.'

(d)



Dry herbage

yield (tiha)



N accumulation

(kdha)



CIN

ratio



N



P



K



42

49

56



2.2, 3.9

3.1, 1.8

4.3, 7.2



17,78

155,204

138, 149



13, 16

-



0

0

0



0

0

0



0

0

0



FB



4.3



I38



13



0



0



0



50-55

50-55

50-55



91

120

149

110

85

I20

144



17

16



30

45

60



3.4

4.0

4.8

5.4

3.1

6.0

7.6



24

-



0

I5

15

0

NA

NA

NA



0

0

7

26

NA

NA

NA



0

0

0

0

NA

NA

NA



60



3.8



87



22



0



26



0



4



30

45



1 .o



60



3 .O



35

62

16



-



NA

NA

NA



NA

NA

NA



NA

NA

NA



5

5

5



60

Philippines



Cyamopsis tetragonoloba

India

Lablab purpureus

Philippines



Fertilization of GM'

(kdha)



1.9



15



Reference"



2



(continued)



Table IV (continued)



Species and

country

Indigofera tinctoria

Philippines



Sesbania aegyptica

India

Sesbania aculeata (syn:

S . cannabina)

Bangladesh



Duration'.'

(d)



Dry herbage

yield (t/ha)



N accumulation

(kdha)



C/N

ratio



45

45

60

60

178



0.5

1.2



-



1.7

4.7

13.3



19

25

58

267



-



57



-



39



-



0.85

2.0

6.3

0.23

2.0

2.3

3.4

3.7

4.6



24

70

170

8

58

57

87

98



5.0



108

120

132

81

143

173



16

16

16

22



30

45



India



60

30

45

50-55

50-55

50-55



Philippines



60

60

60

60

30

45

60



4.8

5.6

3.9

6.7

8.0



110



104



-



-



Fertilization of GM'

(kdha)



N



P



K



NA

0

NA



NA

0

NA

0



NA



5



0



NA

0



0



0



6

5

7

6



NA



NA



NA



8



0

0

0



0

0

0



0

0

0



36

26

0



15

I5



0



0

0

0

0

0

0

0



9

9

9

10

10

3

3

3



0

0



NA

0

NA

0



NA

NA

NA



7

NA

26

NA

26

NA

NA

NA



0



NA

0

NA

0



NA

NA

NA



Reference"



'*



11



4

12

10

5

5

5



Sesbania cannabina

India



Philippines



-



60



98

147

I65

43-128

58-132

79

98-151

131-171



57



-



24



57



-



45

42

48'

48

49

49

49

49

49

49

49

56

60'

60



606



Sesbania grandiflora

India

Sesbania glabra

India

Sesbania sp.PL se-17

India

Sesbania rostrata

Philippines



18

20

23



3.1

5.3

7.3

1.8-3.6

2.5-4.1

4.9

4.9-6.3

6.7-7.2



45

55

60

4tIb

48

48



0

0



22

22

22

0

0



0



13

13

13

14

14

14

14

14



0



0



0

0



0

0



0

0

0

0

0

0

0



-



NA



NA



NA



8



27



-



NA



NA



NA



8



-



81-108



-



0



22



0



15



2.1, 2.6

2.5, 3.7

2.6, 5.3

5.0

6.0

6.3

6.4

11.2

12.4

8.4, 11.2

4.1, 5.4

6.9, 6.8

7.2,7.7



55,50

68, 111

89, 167

103

125

142

143

194

252

155, 194

83, 117

148, 179

176, 219



-



0

0

0

0

0

0

0



0



0

0

0

0

40

0

40

0

0

0

0

0

0



-



-



I



22, 24

-



-



0

0

0



0



30

0

0

0

0



0

0

0

0



40

40

0

0

0



0

0

0



1



14

14

16

16

16

16

16

16



16

16

14

14

(continued)



Table IV (continued)



Species and

country

Thailand



Dry herbage

yield @/ha)



N accumulation

(kdha)



C/N

ratio



N



P



K



0.46-0.85

1.7

2.8-4.0

5.1

0.7, 1.1

2.0,2.1



16-24

66

76-100

116

21

62.48



-



0

0

0

0

0

0



0

22

0

22

0

22



0

0

0

0

0

42



17

17

17

17

17

17



60

84



2.9

3.4

4.7

4.9

4.4



91

112

130

156

83



-



0

0

0

0

NA



0

0

0

0

NA



0

0

0

0

NA



14

14

14

14

18



MAT



3.4-4.8



72-106



-



NA



NA



NA



19



60

60

30

45

45

45

45



2.8

6.9



13

113

21

62,70

63

67

74

34

80



32

-



NA

0

NA

0

NA

0

NA

0

NA



NA

26

NA

20

NA

0

NA

0

NA



NA

0

NA

0

NA

0

NA

0

NA



12

4

5

20

5

21

22

14



Duration'l.b



(4

46

46

61

61

61

61



13

0



Sesbania sesban

Philippines



48b

48



w



Sri Lanka



Trifolium subterraneum

U.S.A.

Cowpea

India

Philippines



Fertilization of GM'

Wha)



48



60



0.1



2.3, 2.5

2.4

2.5



-



1.8

3.6



15

15



-



Referenced



5



Mung bean

Philippines



Pigeonpea

Philippines

Soybean

Philippines



54

41-50

75-102

115

I36



-



60



2.3

4.5

4.7



45

60



1.3

3.6



45



2.6

4.8

7.9



30

30

40

45



60

60



-



NA

NA

NA

NA

NA



NA

NA

NA

NA

NA



NA

NA

NA

NA

NA



5

22

22

5

5



33

76



-



0

0



0

0



0

0



7

7



67

134

141



-



NA

NA

0



NA

NA

0



NA

NA

0



5

5

7



-



Abbreviations: FB, full bloom; MAT, crop maturity.



z



* Green manure crop was grown on flooded soil for the last 25 days before incorporation.

NA designates that information was not available in the reference.

1, Becker et a / . (1990b); 2, Ishikawa (1988); 3, Sharma and Mittra (1988); 4, Ben et al. (1989a); 5, IRRI (1986, p. 403); 6, Bantilan et a / . (1989);

7, Meelu et al. (1985); 8, Ghai et al. (1985); 9, Bhuiyan et al. (1989); 10, Khind et al. (1983); 11. Ben et al. (1989b); 12, Khind e r a / . (1982); 13, Bhardwaj

andDev(1985); 14, M o m s e t a l . (1989); 15,Ghaietal. (1988); 16, Beckeretal. (1990a); 17, Hemeraetal. (1989); 18, Palmetal. (1988); 19. Dabneyetal.

(1989); 20, John et al. (1989~);21, John et al. (1989b); 22, M o m s et al. (1986a).



22



R. J. BURESH AND S . K. DE DATTA



The growth and yield of legumes, like those of other upland crops, can

be limited by nutrient deficiencies and soil acidity, which are serious crop

production constraints in southeast Asia (Craswell et al., 1987). Food

(Saraf, 1983; Craswell et al., 1987; Veeranna, 1987) and green manure

legumes (Alberto, 1989; Table IV) frequently respond to P fertilization.

Herrera et al. (1989) reported that P application to Sesbania rostrata on an

infertile Aeric Palequult in northeast Thailand was essential for high N

accumulation. They speculated that on soils highly deficient in P, it may be

more effective to apply P to the green manure rather than to the following

rice crop. In Punjab, India, the P fertilizer recommendation in a S. cannabina green manure-rice sequence is to apply the P recommended for rice

to the legume and then omit P application to the succeeding rice (Gill,

1989). In winter green manure-rice sequences in China, it is reportedly

more profitable to apply P to the legume than to rice (Chen, 1988; Wen,

1989).

A starter dose of 20 to 25 kg N/ha is frequently recommended for

tropical food legumes (Chatterjee and Bhattacharyya, 1986). Reports show

that starter N can increase N accumulation of green manure legumes

(Sharma and Mittra, 1988; Becker et al., 1990a) and yield of food legumes,

particularly on infertile coarse-textured soils (Carangal et al., 1987)and for

inoculated soybean (Sekhon et al., 1984). Increases in soybean seed yield

can be much greater with inoculation than with N fertilizer, especially in

environments where soybean is newly introduced (Duong et al., 1984;

IRRI, 1987, pp. 490-491).

A. SYMBIOTIC

N FIXATION

For legumes to maintain or increase the soil N pool as desired, they must



fix large amounts of atmospheric N2. However, estimates of NZfixation by

legumes on ricelands are limited, particularly for food legumes other than

soybean. Moreover, because legumes on ricelands are frequently grown

under marginal conditions with limited inputs and management, researchers’ measurements of N accumulation by legumes and total legume N from

fixation in well-managed experimental plots may overestimate the contribution of N2 fixation in farmers’ fields.



I . Food and Forage Legumes

Factors affecting NZfixation by legumes include soil mineral N, inoculation, water regime, and soil and crop management. Root nodulation

(Brockwell et al., 1989) and N2 fixation (Bergersen et al., 1989) dramatically decrease as plant-available soil N increases. Using results from



NITROGEN IN RICE-LEGUME CROPPING SYSTEMS



23



soybean experiments in Australia, Herridge and Bergersen (1988) showed

that for soybean the percentage of N derived from symbiotic N2 fixation

(Ndfa) correlated inversely ( r = - .88) with nitrate N, expressed in kg

N/ha in the top 120-cm soil layer. Increased rates of inoculation can

diminish but not eliminate the adverse effects of plant-available soil N on

N2 fixation (Herridge and Brockwell, 1988). Peoples and Herridge (1990)

used results of Herridge and Brockwell (1988) to illustrate the strong

relationships (R2 = 0.80) between Ndfa and number of Bradyrhizobium

japonicum in the seed zone at sowing and soil nitrate to 90-cm depth at

sowing.

Soil nitrate following a flooded rice crop is normally very low or undetectable (Figs. 1 and 2 ) . Therefore, in terms of suppressing symbiotic N2

fixation, soil nitrate conceivably may be a much less important factor for

legumes following lowland rice than for legumes following a fallow or

upland crop.

Water deficit is known to dramatically decrease N2 fixation by legumes

(Kirda et al., 1989). K u c ~ yet al. (1988b) showed that biweekly irrigation,

as compared with weekly irrigation of soybean in Thailand, did not seriously reduce yield or N2 fixation, but delaying irrigation until symptoms of

water deficit appeared on soybean markedly reduced yield and N2 fixation.

Because legumes in tropical lowland rice environments are typically

grown only on residual soil water, water deficit may be an important factor

influencing Ndfa and total legume N from fixation in tropical rice-based

cropping systems.

Tillage generally increases soil nitrate N which, in turn, can suppress N2

fixation. Herridge (1986) observed greater nitrate N in the top 120-cm soil

layer following a cultivated fallow (214 kg N/ha) than following a no-till

fallow (185 kg N/ha). Soybean fixed more N following the no-till (236 kg

N/ha) than following the cultivated fallow (132 kg N/ha). Nitrogen fixation

exceeded N removal in the grain following the no-till fallow (54 kg Nlha),

but not following the cultivated fallow (-29 kg N/ha). Rennie et al. (1988)

reported that zero tillage rather than conventional tillage for establishment

of soybean increased soybean yield and N2 fixation in two of three field

trials in Thailand.

Nitrogen fixation by food legumes in the tropics and subtropics is highly

variable and inconsistent. For example, N2 fixation measured by "N

dilution on dry-season soybean at two sites in Thailand ranged from 32 to

161 kg N/ha, and Ndfa ranged from 21 to 79% depending on soybean

cultivar, Bradyrhizobium japonicum strain, and location (Kucey et al.,

1988a). A literature review by Peoples and Herridge (1990) on N2 fixation

by legumes in the tropics and subtropics revealed a large range in estimated Ndfa: 0 to 95% for soybean, 8 to 89% for cowpea, 22 to 92% for

groundnut, and 10 to 88% for pigeonpea. The amounts of N2 fixed ranged



24



R. J. BURESH AND S. K. DE DATTA



from 0 to 450 kg N/ha. Estimated Ndfa tended to be higher for forage

legumes than for food legumes. In the studies reviewed by Peoples and

Herridge (1990), the Ndfa for forage legumes ranged from 50 to 100%.

Among food legumes, soybeans normally give the most consistent response to inoculation. The greatest successes with inoculation have been

achieved when a legume is newly introduced to a site and when rhizobia

numbers in soil decrease greatly between legume crops (Henzell, 1988).

Anaerobic conditions during growth of lowland rice between legume crops

may result in depletion of soil rhizobia (Wood and Myers, 1987). Henzell

(1988) listed identification and exploitation of situations in which inoculation of legumes gives economic benefit as a priority of applied biological

nitrogen fixation research. Lack of effective inoculants to developing

country farmers remains a constraint (Craswell, 1990).



2 . Green Manures

Stem-nodulating legumes have received considerable recent examination for their potential as green manures in lowland rice environments

prone to soil waterlogging. Stem nodulation has been reported in three

genera of legumes: Sesbania, Aeschynomene, and Neptunia. Ladha et al.

(1990) indicated that 17 species of Aeschynomene, 3 of Sesbania, and I of

Neptunia are now reported to bear stem nodules. High acetylene reduction activity (ARA) is reported for stem nodules of S . rostruta (Dreyfus

and Dommergues, 1981), A. scabra (Eaglesham and Szalay, 1983), and A .

afruspera (Alazard and Duhoux, 1987). Whereas flooding adversely affects ARA of root nodules, stem nodules continue to actively fix N2 under

flooded soil conditions (Saint Macary et a f . , 1985; Ndoye and Dreyfus,

1988). Soil mineral N reduces N2 fixation by root nodules, but stem nodules of S . rostrata (Dreyfus and Dommergues, 1980; Becker et al., 1990a),

A . scabra (Eaglesham and Szalay, 1983),and A . afruspera (Becker et al.,

1986) effectively fix N2 at high mineral N concentrations in soil. Becker et

a f . (1990a) speculated that stem-nodulating legumes may effectively increase total soil N through N2 fixation, even on high-N soils. The unusual

properties and potential benefits of stem nodulation are reviewed by

Ladha et al. (1990).

Pareek et a / . (1990) reported that Ndfa in well-nodulated S . rostrata and

S . cannabina increased with plant age. Ndfa, estimated by the isotope

dilution method, increased from 50 and 75% at 25 days after seeding to

about 70-95% at 45 to 55 days. Between 45 and 65 days, nearly 100% of

Sesbania N came from air. Ndfa was similar for S. rostrata and S . cannabina, but total N from fixation was greater for S . rostrata than for S .



NITROGEN IN RICE-LEGUME CROPPING SYSTEMS



25



cannabina because of higher N accumulation for S. rostrata. Ndfa reported by Pareek e f al. (1990) is greater than the 35 to 51%, estimated by

isotope dilution, in a study by Ndoye and Dreyfus (1988) in which uninoculated Sesbania was the reference.

Reports on the benefit of inoculation are conflicting (Ladha et al., 1990).

Inoculation of S . rostrata has been reported both to increase N accumulation (Ndoye and Dreyfus, 1988; Ladha et al., 1989a)and to have no effect

on N accumulation (Rinaudo et al., 1983). Ndoye and Dreyfus (1988)

reported that inoculation of S . sesban increased N accumulation under

drained but not under waterlogged soil conditions.

A. afraspera is less photoperiod sensitive than S . rostrata (Visperas et

al., 19871, making it superior in N accumulation to S. rostrata during the

short-day period (Becker et at., 1990b). The higher N concentrations and

lower biomass production of A. afraspera than of S . rostrata may offer the

advantage of reduced labor for incorporation (Becker et al., 1990b),which

is a major determinant of profitability for green manure use in rice cropping

systems (Garrity and Flinn, 1988). Nitrogen fixation by leguminous green

manures in the tropics is reviewed in greater detail by Ladha et al. (1988).

Legume winter green manure crops reportedly derive most of their N

from symbiotic Nz fixation. In China, estimated Ndfa was 84% for milk

vetch and 88% for common vetch (Vicia satiua L.) (Wen, 1989). Comparable Ndfa values ranging from 67 to 84% were estimated for various

winter legumes in the United States (Smith et al., 1987). Estimated Ndfa

was lower, 36 to 40%, when legume growth was poor (Smith et al., 1987).



B. N REMOVAL

WITH LEGUME

GRAIN

When legumes are grown in situ solely for green manure production, N2

fixed by the legume and added to the soil represents a net gain of soil N,

provided that soil and legume N are not lost as gases or by leaching. Food

legumes are capable of fixing large amounts of N2, but removal of seed or

green pods can constitute an export of considerable N .

The quantity of N in aboveground residues remaining after grain harvest

(Table V) depends on the total N accumulation of the legume and the

harvest index for N (NHI) (Myers and Wood, 1987).The NHI, which is the

proportion of N removed in seed, varies considerably among species and

cultivars of the same species. Soybean tends to have a higher NHI than do

other species (Myers and Wood, 1987; Table V).

Levels of N2 fixation are often not sufficient to offset the N removed

with harvested grain. For example, estimated Ndfa in an experiment in

Indonesia was 33% for soybean and 12 to 20% for cowpea (Sisworo et al..



26



R. J. BURESH AND S. K. DE DATTA

Table V



Nitrogen Accumulation in Aboveground Legume Biomass Remaining after Harvest of Grain in

Lowland Rice-Based Cropping Systems

Grain



Remaining aboveground plant material



N

(kg/ha)



Dry weight

(t/ha)



N

(kg/ha)



-



-



25-52



0.86



4.6



101



Crop and

country



Yield

(t/ha)



Mung bean

Australia

India



0.65

0.9

0.6

0.73

0.38

0.25

0.19

0.4-1.0



3.0

2.5



-



Philippines



Cowpea

Philippines



0.4'

0.9

1.O



-



0.66

0.26

0.39

0.32

0.2-0.9

Lentil

India

Soybean

Australia

India



-



2.6



50

57



30

27

18

17

17-36



3.0

3.7

4.0

3.9

2.8

3.9

I .2



69

54

53

49

61

79



1.7



1.1

I .9



2.7



-



-



-



-



5.7



Reference"



43

60



2.5

2.4

1.1

1.4

1.2-2.3



2.5-4.0



C/N ratio



-



5



27

30

31



8

8

9

7



-



7



19

45-60



-



-



-



-



10

10



30

68

52



-



1



17



-



-



-



7

7

7



I

3



" I , Chapman and Myers (1987);2,Rekhi and MeeIu (1983);3,Prasad and Palaniappan (1987);4,

Maskinaeral. (1990);5,IRRI(1985,p.413);6,

IRRI(1986,p.416);7,Alam(1989);8,

Johnetal. (1989~);

9,John et al. (1989b);10, John et al. (3989d).

Weight of pods.

1990). The N removed by legume grain exceeded N2 fixation in all cases.

Average net N loss was 26 kg N/ha for soybean and 42 kg N/ha for cowpea.

Enhanced N2 fixation or N fertilization would be required to prevent

depletion of soil N levels. Nitrogen fixation and net N contributions of



NITROGEN IN RICE-LEGUME CROPPING SYSTEMS



27



legumes in tropical and subtropical agriculture are reviewed by Peoples

and Herridge ( 1990).



VI. CONTRIBUTION OF LEGUME NITROGEN TO RICE

Many studies have shown that leguminous green manures (Table VI)

and food legume residues remaining after harvesting grain (Table VII)

increase the yield of a subsequent lowland rice crop and reduce the requirements for industrial N fertilizer. The saving in industrial N fertilizer

by using legume N is frequently referred to as the N fertilizer equivalence.

Nitrogen from 50- to 60-day-old green manure (Singh et af., 1990)and from

mung bean haulm (Rekhi and Meelu, 1983) incorporated 1 day before

transplanting on coarse-textured, nonacid soils in Punjab, India, generally

substituted for about an equal or slightly greater amount of urea N. In

environments other than northwestern India, the N fertilizer substitution

was frequently less than the added green manure N (Table VI).

In the limited number of experiments with food legumes listed in Table

VII, N from incorporated haulm of prerice food legumes substituted for

about an equal or somewhat less amount of fertilizer N. Rice yields following cowpea incorporated at the flowering stage as a green manure (66 kg

N/ha, C/N = 15) and cowpea grown to maturity with removal of grain and

pods and incorporation of remaining residue (54 kg N/ha, C/N = 28) were

nearly identical (Fig. 5). Removal of the cowpea residue dramatically

reduced yield of the subsequent rice crop.

Reports on the contribution of soybean haulm to a succeeding rice crop

are not consistent. In India, Rajendra Prasad (1985) reported that incorporation of residue remaining after harvest of soybean pods increased grain

yield of the subsequent rice crop. On the other hand, in a 7-year rice-ricesoybean trial in Taiwan, cited by Morris and Meelu (1989, rice yield was

not increased when soybean haulm was returned rather than removed.

The N contribution of legume haulm and the comparative N contributions for legume green manure versus haulm depend on the NHI. Cowpea

frequently has a lower NHI than do soybean and mung bean (Myers and

Wood, 1987), and cowpea cultivars can vary greatly in NHI. Timsina

(1989), while not presenting data for NHI, reported a range of HI from 16

to 65 for 24 diverse cowpea cultivars. In a study in the Philippines, 40-dayold mung bean incorporated as a green manure accumulated 93 kg N/ha

(26.4 g N/kg), whereas mature mung bean produced 1.1 t/ha grain and

aboveground residue containing 31 kg N/ha (14.8 g N/kg). Yield of the



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