Nitrogen Use Efficiency of Staygreen Sorghum Under Three Soil Water levels
Sylvester Addy *, M.R. Reddy and Carl Niedziela
North Carolina A&T State University,
Abstract
Introduction
Nitrogen Use Efficiency comprises recovery of fertilizer N, either in grain or in total
above ground biomass in the current crop, and a part of the applied N that is
immobilized in the soil (Ladha et al., 2005). N fertilization has been a powerful tool
in increasing grain yield especially for cereals such as sorghum. Concerns on
groundwater quality, public health and rising energy costs have moved economic
concerns to the forefront. Farmers must therefore optimize the application of N
fertilizers to minimize and avoid pollution by nitrates and to preserve their
economic margin while producing economic yields. Sorghum [Sorghum bicolor (L)
Moench] hybrids containing the stay-green trait retain more photosynthetically
active leaves under drought than do hybrids that do not contain the trait. Yield
increases in stay-green types have been attributed directly to maintenance of
photosynthetic capability during the grain filling period. NUE has been studied for
rice (Singh et al., 1998; Ladha et al., 1998), wheat (Ortiz. et al., 1997), and maize
(Hirel et al., 2001).However, information is limited on sorghum.
Results and Discussion
0.3 bars
40
35
a
a
0.8 bars
1.8 bars
a
a
a
25
a
a
20
a
15
a
a
a
a
a
ab
10
a
a
c
5
0
2
3
Grain weight was also significantly (P=0.05) reduced by 20% at both 0.8
and 1.8 bars. Chlorophyll readings did not significantly differ for the
three N levels during post anthesis period. Plants maintained similar
chlorophyll level throughout the grain filling period even under limiting
water supply. Borrell et al., (2000) reported this phenomenon and
explained that as early as 40 days after emergence, more N is allocated to
the leaves of staygreen hybrids compared with their senescent
counterparts, resulting in a higher specific leaf nitrogen.
Conclusion
a
30
a
a
a
10
a
5
b
Water stress below 1.8 bars decreased the NUE and grain yield of
staygreen sorghum BTx642. This genotype however maintained similar
physiological characteristics under the three water stress levels. It is
important to use N efficient sorghum cultivars to produce sustainable
yields and reduce environmental contamination.
0
Leaf
Fresh
w eight
Leaf Dry
Weight
Leaf
Water
Content
Root Dry
Weight
Stover Dry
Weight
Grain
Yield
Figure 2. Relationship of soil water levels on growth and yield of staygreen sorghum
Chlorophyll meter readings
67 kgha-1
100 kgha-1
134 kgha-1
50
40
30
20
10
0
_
9-May
15-May 24-May
31-May
6-Jun
12-Jun
24-Jun
Time
Figure 1. sorghum study in the greenhouse
15
Figure 4. Effects of N and water levels on NUE
There was no significant interaction observed between N and water stress
levels. Water stress significantly (P=0.05) decreased NUE by 45% and
41% at 0.8 and 1.8 bars respectively. This agrees with the report of
Eghball and Maranville (1991) that NUE generally parallels water use
efficiency (WUE) in corn. Single factors N and water did not significantly
reduce leaf fresh weight, dry weights of Ieaf, stover, root, leaf water
content, LAI and SPAD Chlorophyll readings.
Materials and Methods
The experimental design was a 3 x 3 factorial in a randomized complete block
with four replications.
a
a
20
1
Objective
To evaluate the NUE and physiological characteristics of staygreen sorghum under
different soil water treatments.
Effect of N rates on NUE
Effect of Water levels on NUE
25
NUE
The soil used was Enon sandy loam. The pots (25cm diameter) were
filled with 10 kg of soil. Seeds of sorghum variety (BTx642) were planted
in march and grown to grain filling stage. N fertilizer rates of (67, 100
and 134 kgha-1) were applied at 3, 6 and 9 weeks after planting. Three
soil water treatments of 0.3, 0.8 and 1.8 bars were applied from anthesis
until harvesting. Data were collected for leaf fresh weight, dry weights of
Ieaf, stover, root, grain and leaf water content. Leaf Area Index (LAI) and
SPAD Chlorophyll readings were taken on the second leaf from the flag
leaf before anthesis till harvest. NUE was calculated as the ratio of grain
weight to N applied.
(Weight gpot-1)
Nitrogen use efficiency (NUE) for cereal production worldwide is approximately
33% with the remaining 67% representing a $15.9 billion annual loss of Nitrogen
(N) fertilizer. Many parts of the world are becoming more arid due to climate
change. In this light, methods that increase NUE and water use efficiency farmer
profitability are no longer simply commendable, but required. Breeding programs
have identified certain adaptations that present great promise for the development of
crops that are tolerant to low levels of N and soil water. The Staygreen character of
sorghum is a unique example of these adaptations. A greenhouse study was
conducted at NCA&T State University to determine the nitrogen use efficiency of
staygreen sorghum variety (BTx642) at 67, 100, 134 kgha-1and soil moisture levels
of field capacity(0.3 bars), half-field (0.8 bars) and one-third field (1.8 bars)
capacities. Moisture levels significantly (P=0.05) decreased NUE by 45% and 41%
at 1.8 bars and 0.8 bars respectively. Grain weight was also significantly (P=0.05)
reduced by 20% at both 1.8 and 0.8 bars. However, NUE was similar under different
rates of N. Leaf fresh weight, dry weights of Leaf, stover, root and leaf water content
were not significantly affected by N and soil moisture levels.
Figure 3. Chlorophyll meter readings under N rates during post-anthesis.
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