Agriculture Reference
In-Depth Information
TABLE 7.3
N Fertilizer Equivalence (NFE) of Legume Cover Crops to
Succeeding Nonlegume Crops
Legume/Nonlegume Crop
NFE (kg ha
−
1
)
Hairy vetch/cotton
67-101
Hairy vetch + rye/corn
56-112
Hairy vetch/corn
78
Hairy vetch/sorghum
89
Hairy vetch/corn
78
Hairy vetch + wheat/corn
56
Crimson clover/cotton
34-67
Crimson clover/corn
50
Crimson clover/sorghum
19-128
Common vetch/sorghum
30-83
Bigflower vetch/corn
50
Subterranean clover/sorghum
12-103
Sesbania/lowland rice
50
Alfalfa/corn
62
Alfalfa/wheat
20-70
Arachis
spp./wheat
28
Subterranean clover/wheat
66
White lupin/wheat
22-182
Arachis
spp./corn
60
Pigeon pea/corn
38-49
Sesbania/potato
48
Mungbean/potato
34-148
Chickpea/wheat
15-65
Source:
Compiled from Smith, M. S., W. W. Frye, and J. J. Varco. 1987.
Adv. Soil
Sci
. 7:95-139; Kumar, K. and K. M. Goh. 2000.
Adv. Agron
. 68:197-
319; Fageria, N. K., V. C. Baligar, and A. Bailey. 2005.
Commun. Soil
Sci. Plant Anal
. 36:2733-2757.
(
Trifolium pretense
L.) into small grains is a common practice in the northeastern United States
(Singer and Cox, 1998), and such practice can provide up to 85 kg N ha
−1
to the subsequent corn
crop (Vyn et al., 1999). Researchers in the southeastern United States have estimated that legumes
such as hairy vetch can supply well over 100 kg N ha
−1
to the following corn or grain sorghum
crops (Hargrove, 1986; Blevins et al., 1990; Oyer and Touchton, 1990). On prairie soils in Kansas,
Sweeney and Moyer (2004) found that grain sorghum following an initial kill-down of red clover
and hairy vetch yielded as much as 131% more than continuous sorghum with estimated fertilizer
N equivalencies exceeding 135 kg ha
−1
.
7.5.6 n
ItroGen
I
sotopIC
t
eChnIque
N has two stable isotopes that are designated as
14
N and
15
N. The
15
N isotope occurs in atmospheric
N
2
at a constant abundance of 0.3663 atom% (Peoples and Herridge, 1990). If the isotopic concen-
trations are different in two sources of N (soil N and atmospheric N
2
), the proportion P of plant N
