Agriculture Reference
In-Depth Information
TABLE 7.2
Quantity of N Fixed by Principal Legumes
Crop Species
N
2
Fixed (kg ha
−
1
Crop
−
1
)
Reference
Peanut (
Arachis hypogaea
L.)
40-80
Brady and Weil (2002)
Cowpea (
Vigna unguiculata
L. Walp.)
30-50
Brady and Weil (2002)
Alfalfa (
Medicago sativa
L.)
78-222
Heichel (1987)
Soybean (
Glycine max
L.)
50-150
Brady and Weil (2002)
Fava bean (
Vicia faba
L.)
177-250
Heichel (1987)
Hairy vetch (
Vicia villosa
Roth.)
50-100
Brady and Weil (2002)
Ladino clover (
Trifolium repens
L.)
164-187
Heichel (1987)
Red clover (
Trifolium pratense
L.)
68-113
Heichel (1987)
White lupine (
Lupinus albus
L.)
50-100
Brady and Weil (2002)
Field peas (
Pisum sativum
L.)
174-195
Heichel (1987)
Chickpea (
Cicer arietinum
L.)
24-84
Heichel (1987)
Pigeon pea (
Cajnus cajan
L. Huth.)
150-280
Brady and Weil (2002)
Kudzu (
Pueraria phaseoloides
Roxb. Benth)
100-140
Brady and Weil (2002)
Chick pea (
Cicer arietinum
L.)
24-84
Heichel (1987)
Greengram (
Vigna radiata
L. Wilczek.)
71-112
Chapman and Myers (1987)
Lentil (
Lens culinaris
L.)
57-111
Smith et al. (1987)
Source:
Adapted from Brady, N. C. and R. R. Weil. 2002.
The Nature and Properties of Soils
, 13th edition. Upper Saddle
River, New Jersey: Prentice Hall; Chapman, A. L. and R. J. K. Myers. 1987. Western Australia.
Aust. J. Exp. Agric
.,
27:155-163; Heichel, G. H. 1987.
Energy in Plant Nutrition and Pest Control
, pp. 63-80. Amsterdam: Elsevier
Scientific Publishers; Smith, M. S., W. W. Frye, and J. J. Varco. 1987.
Adv. Soil Sci
. 7:95-139.
7.5.1 a
CetYlene
r
eduCtIon
a
ssaY
The acetylene reduction assay depends on the ability of nitrogenase to reduce acetylene to ethylene,
which is then released from the enzyme and measured by gas chromatographic procedures (Gibson
and Jordan, 1983). In simple words, it is a technique for demonstrating or estimating nitrogenase
activity by measuring the rate of acetylene (C
2
H
2
) reduction to ethylene (C
2
H
4
). The standard acety-
lene reduction assay method involves enclosing detached nodules or the nodulated root system in
airtight containers and exposing them to an atmosphere containing C
2
H
2
. Gas samples are taken
after a certain period of incubation and analyzed for ethylene by using gas chromatography. This
technique is widely used in the research of dinitrogen fixation due to its high sensitivity and simplic-
ity (Peoples and Herridge, 1990).
It is simple and relatively cheap to use, very sensitive, and many assays can be done in a short
period of time. However, Peoples and Herridge (1990) reported that when results of dinitrogen
fixation by this technique are compared with other techniques under field conditions, the acetylene
reduction assay technique greatly underestimated N
2
fixation activity. Several factors may affect the
C
2
H
2
reduction to C
2
H
4
, that is, plant and nodule age, plant stress, soil fertility level, especially NO
3
and NH
4
, and changes in O
2
partial pressure, making quantitative comparisons of N
2
fixation based
on long-term C
2
H
2
accumulation misleading (Peoples and Herridge, 1990).
In addition, Gibson and Jordan (1983) reported that the amount of dinitrogen fixation by this
technique may lead to under- or overestimates. This may happen due to the overestimation of nitro-
genase activity by this method, including the suppression of endogenous ethylene oxidation by
acetylene in some soil system (Witty, 1979), and the apparent stimulation of nitrogenase activity by
acetylene during longer-term assays (David and Fay, 1977), while a change in pO
2
conditions dur-
ing the course of the assay may give overestimates or under-estimates of activity depending on the
