Agriculture Reference
In-Depth Information
B072044
AB112092
B072085
Without lime
With lime
Without lime
Without lime
With lime
With lime
FIGURE 8.30
Root growth of upland rice with and without lime.
Moll et al. (1982) reported that N use efficiency differences among corn hybrids were due to the dif-
fering utilization of N already accumulated in the plant prior to anthesis, especially at low N levels.
Eghball and Maranville (1991) reported that N use efficiency generally parallels water use efficiency
in corn. Hence, both N use and water use efficiency traits might be selected simultaneously where
such parallels exist. Kanampiu et al. (1997) reported that wheat cultivars with higher grain harvest
indexes had higher N use efficiencies. Cox et al. (1985) reported that wheat cultivars that accumu-
late large amounts of N early in the growing season do not necessarily have high N use efficiency.
Plants must convert this accumulated N into grain N and also assimilate N after anthesis to produce
high N use efficiency. Forms of N uptake (
NH
4
+
vs.
NO
3
−
) may also have effects on N use efficiency
(Thomason et al., 2002). Plants with a preferential uptake of
NH
4
+
during grain fill may provide
increased N use efficiency over plants without this preference (Tsai et al., 1992). Ammonium N
supplied to high-yielding corn genotypes increased the yield over plants supplied with
NO
3
−
during
critical ear development (Pan et al., 1984). Salsac et al. (1987) reported that
NH
4
+
assimilation pro-
cesses require 5 ATP (adenosine triphosphate) mol
−1
of
NH
4
+
, whereas
NO
3
−
assimilation processes
require 20 ATP mol
−1
NO
3
−
. This energy-saving mechanism may be responsible for higher N use
efficiency in
NH
+
−
N.
4
BRS Monarca
B062037
BRS CIRAD 302
Without lime
With lime
Without lime
With lime
Without lime
With lime
FIGURE 8.31
Root growth of upland rice with and without lime.
