N2fixed
Time period (days)
Grain legume kg ha-1 % Country Methoda Ref.b
Arachis hypogaea
Cajanus cajan
Cicer arietinum
Glycine max
Lathyrus sativus Lens
culinaris
139–206 85–131 32–120 43–72 68–116
101 100–152 152–189 21–58 101–130
c150–200c
c102c
c46c 68–88 150–166
0–76 30–131 13–163
– 1–39 60–84 67–85 0–124 0–99
c35–80c
<20–91<
85–154 14–15 15–170 114–188 42–83 149–176
26–57
c108–152c 68–174
147 –
c19–83c
c16–83c 4–38
55–64 47–53 22–49 45–67 54–78
– 86–92 61–85 16–53 59–64 72–77 68 62 88 63–86
0–36 59–87 42–85
c52–88c 64–100 60–80 63–81 0–79 0–81 66–96 21–95 70–80 36–39 12–100 84–87 46–87 69–74 78–87 66–68 38–74 84
c85–91c 62–85 55–91 9–46
120 144 140 90–106
110 – 89 118–137
– 90–110 106–119
88 87–97
– – 95–210
– 120
– – 160 170 – – – – 110
40 – 66 36–75 70–84 64–73 97–104
72 77 – – – –
Australia Australia Australia Australia Brazil Ghana India India Indonesia Thailand Thailand Thailand Thailand India India India India Malawi Nepal Zimbabwe Australia Australia Australia Australia Nepal Pakistan Brazil Congo Nepal Nigeria Nigeria Philippines Thailand Thailand Thailand Thailand Nepal Nepal Pakistan Pakistan
NA NA NA NA ID Diff ID NA/Diff ID/NA ID ID ID ID ID ID NA NA NA NA NA NA NA NA NA NA NA ID ID NA ID/Diff ID ID NA ID Ureide Ureide NA NA NA ID
1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 1 20 21 22 23 24 4 25 18 26 27 28 1 10 29 30 18 18 31 32 Table 8.2. Estimates of N2-fixation by grain legumes grown as sole crops in the tropics. All are examples where small amounts of N-fertilizers, and generally adequate amounts of phosphorus, were applied.
N2fixed
Time period (days)
Grain legume kg ha-1 % Country Methoda Ref.b
Phaseolus vulgaris
Vigna radiata
V. mungo V. unguiculata
25–65 3–32 4–45 25–115 18–36
9–50 12–125 74–91 44–50 0–108 34–85
7–81
c8–26c 0–55 64–66 58–107
c10c 119–140
0–55 9–51 201 47–105 66–120
c63c
37–68 15–72 12–53 27–60 32–47 24–50 22–73 43–52 60–73 0–58 30–57 13–56 40–51 0–100 89–90
– 25 95–98
0–100 32–74
– 61–76 54–70 65
60–90 61 60–92
– 56 63–70
– 74 91 – – 86–116
75 – 57–64
– 87–97
66 – 110
– 66 57 87–89
Brazil Brazil Brazil Chile Colombia Colombia Guatemala Kenya Mexico Mexico Mexico Peru Tanzania Pakistan Thailand Thailand Thailand Thailand Pakistan Brazil Ghana Nigeria Nigeria Thailand
ID ID ID ID ID ID ID ID ID ID ID ID ID NA NA NB ID NA NA ID Diff ID/Diff ID ID
33 34 35 35 36 37 35 38 39 35 40 41 42 31 1 43 12 1 31 4 5 26 44 10
aI D =15N isotope dilution; NA =15N natural abundance; NB = N balance; Diff = N difference; Ureide = ureide method.
b1: Peopleset al., 1991b; 2: Peopleset al., 1992; 3: Bellet al., 1994; 4: Boddey et al., 1990; 5: Dakoraet al., 1987; 6: Gilleret al., 1987; 7: Nambiaret al., 1986;
Yoneyamaet al., 1990a; 8: Cadischet al., 2000; 9: McDonaghet al., 1993; 10:
Toomsanet al., 1995; 11: McDonaghet al., 1995b; 12: Toomsanet al., 2000; 13:
Kumar Raoet al., 1987; 14: Tobitaet al., 1994; 15: Kumar Raoet al., 1996b; 16:
Kumar Raoet al., 1996a; 17: Sakalaet al., 2001; 18: Maskeyet al., 1997; 19:
Mapfumoet al., 1999; 20; Herridgeet al., 1995; 21: Herridgeet al., 1998; 22:
Schwenkeet al., 1998; 23: Aliet al., 1997; 24: Aslamet al., 1997; 25: Mandimba, 1996; 26: Eagleshamet al., 1982; 27: Sangingaet al., 1997; 28: Georgeet al., 1995; 29: Guafaet al., 1993; 30: Yinboet al., 1997; 31: Shahet al., 1997; 32:
Hafeezet al., 2000; 33: Ruschelet al., 1982; 34: Duqueet al., 1985; 35:
Hardarsonet al., 1993; 36: Kipe-Nolt and Giller, 1993; 37: Kipe-Noltet al., 1993;
38: Ssali and Keya, 1986; 39: Peña-Cabrialeset al., 1993; 40: Castellanoset al., 1996; 41: Manriqueet al., 1993; 42: Gilleret al., 1998; 43: Firthet al., 1973; 44:
Awonaikeet al., 1990.
cMeasurements made in experiments on farmers’ fields, or in farmers’ crops.
Table 8.2. continued
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quickly is particularly important for short-duration genotypes. In some grain legumes, such as soybean and P. vulgaris, the timing of nodule senescence often coincides with seed development, and the period of active N2-fixation will be longer if senescence of the nodules is delayed so that N2-fixation continues during pod-fill.
By contrast, no decline in rates of N2-fixation during pod-fill occurs in groundnut (Bell et al., 1994). There is strong evidence that rates of N2-fixation in legume nodules are limited by the supply of oxygen (Minchinet al., 1996) and the strength of the sink for carbon in nodules will depend partly on the efficiency with which carbon is utilized for N2-fixation. Factors contributing to the overall efficiency of carbon use for N2-fixation include the provision of reductant and electrons to nitrogenase, the electron allocation to hydrogen production by nitrogenase and the costs associated with assimilation and transport of fixed N to the shoot (Neves and Hungria, 1987) (Chapter 3).
The proportion of a plant’s N that is derived from N2-fixation (sometimes referred to as the %N derived from atmosphere, or %Ndfa) is strongly influenced by the amount of combined N that is available for uptake by the plant, and the ability of the plant to capture and utilize that N. Where the amount of N available in the soil is very limited, grain yield will be directly proportional to the amount of N2fixed. The proportion of N derived from N2-fixation will be smaller when large amounts of soil N are available. The sensitivity of legumes to high concentrations of N in soil can vary substantially. In soybean andP. vulgaris, nodulation and N2-fixation are readily suppressed by N-fertilizer applications and, in fact,P. vulgarisis even more sensitive to N than soybean (George et al., 1988; Abaidoo and van Kessel, 1989). Other legumes, notablyV. faba, groundnut (Nambiaret al., 1986) and perhapsM. geocarpum (Dakoraet al., 1992), are less sensitive to high concentrations of mineral N.
It must also be remembered that many of these plant characteristics can vary depending on the particular strain (or strains) of rhizobia with which the N2-fixing symbiosis has been established.
Character Contributing factors Duration
Vigour Nodulation Physiology of
N2-fixation Fertilizer use
Time to maturity; time to flowering; early nodulation; delay of senescence
Plant size; photosynthetic area; plant architecture; N sinks Number, size and longevity of nodules; host/rhizobial strain speci- ficity for nodulation; nodulation in the presence of combined N Efficiency of carbon utilization for N2-fixation; specific nitrogenase activity of nodules; oxygen transport mechanisms
Ability to exploit or ignore soil and fertilizer-N; rooting characteristics
Table 8.3. Characteristics determined by the plant genotype which are important in determining the amount of N2fixed by the symbiosis.
Comparative ability of grain legumes to fix N2
It is difficult to make useful generalizations as to the N2-fixing ability of the different grain legumes. Across all of the grain legumes for which data is presented in Table 8.2, optimal rates of N2-fixation are 1–2 kg N ha-1day-1, with all of the legumes recorded to fix more than 120 kg N ha-1within a cropping season in at least one case.
As discussed in Chapter 5, these fast rates should be considered as thepotentialof the grain legumes for N2-fixation within a given environment. The wide variations in N2-fixation within a given crop are found for a variety of reasons.
Cases where no N2-fixation has been observed, or very small %N from N2-fixation, are largely due to drought (C. arietinum), some other environmental constraint such as high temperatures (P. vulgaris), or perhaps nutrient limitations where the measurements were made in farmers’ crops. The largest amounts of N2-fixation have been recorded where there have been long, favourable growing seasons, generally on research stations.
Early-maturing pigeonpea varieties appear to nodulate and fix N2poorly com- pared with long-duration varieties (Kumar Raoet al., 1995, 1996b). In Australia, pigeonpea exhibits highly variable nodulation even when inoculated and is often con- sidered to fix N2poorly (Brockwellet al., 1991), although estimates from India and Africa show that it can often fix large amounts of N (Table 8.2). The smaller amounts of fixation withV. unguiculataandP. vulgaristend to be for shorter-season, determite types and the larger amounts are found with spreading or climbing varieties.
P. vulgaris has often been judged to be poor in N2-fixation (e.g. Piha and Munns, 1987a); yet under optimal conditions estimates of N2-fixation of up to 72%
of N derived from fixation have been obtained (Table 8.2) and in longer growing seasons amounts up to 125 kg N ha-1fixed have been recorded (Rennie and Kemp, 1983). These are comparable to estimates for soybean, which is considered to fix N2
abundantly. Under controlled conditions in growth rooms,P. vulgarisnodulates well and fixes N2at similar high rates to other grain legume species (Eaglesham, 1989). In relatively cool, long seasons in Austria, three climbing varieties ofP. vulgarisfrom the African highlands were among the best in terms of largest amounts of N accumulation and N2-fixation (Hardarsonet al., 1993). The success of grain legumes in N2-fixation in the field will be strongly influenced by the prevailing environmental conditions, and sensitivity of grain legumes to environmental stresses may be the overriding factor influencing the amount of N2fixed. This may partly explain why P. vulgarishas been classed as a poor N2-fixer. However, whereas soybean may often be able to meet all its requirements for growth and high yields from N2-fixation (e.g. Hungriaet al., 2000),P. vulgarismay still respond to N fertilizer even under conditions where it grows and fixes N2well (Redden and Herridge, 1999).