Iron Content of Soybean Grain as Affected by Soil pH and Carbonates.
Background
Natalia Rogovska, Graduate Assistant, and
Alfred Blackmer, Professor.
Department of Agronomy
Iowa State University.
What was found
Soybean plants tend to have yellow leaves and grow poorly on calcareous
calcareous soils,
and the symptoms are commonly described as iron deficiency chlorosis
chlorosis (IDC).
No significant relationships were observed between the soil ASI
and P, K, Mg, Ca, S, Na, B, Cu or Zn concentrations in grain.
Grain Fe, mg kg-1
In the past, it was difficult to attain predictable relationships
relationships between factors
that cause IDC and final yields. One possible explanation is that
that symptoms of
IDC are non specific and can be easily mistaken for other nutrient
nutrient deficiencies,
toxicities or pest damage.
The concentrations of Fe in grain were negatively
correlated with soil ASI. Coefficient of determination for
individual sites ranged from 0 to 0.87 and had a mean of
0.47. When data were pooled, the soil ASI explained 34%
of variability in Fe grain concentrations.
We developed a new soil alkalinity index (ASI) that considers both
both
measured soil pH and calcium carbonate equivalent (CCE) to establish
establish
relationships between soil factors and final yield (Rogovska N. 2004. Soil
pH and carbonate effects on soybean yield. M.S. thesis. ISU).
60
40
20
30
20
8
9
10
11
40
8
9
10
11
12
Soil ASI
40
7
60
7
-1
80
Grain Mn, mg kg
Our objective in this poster is to
evaluate the newly developed index
by assessing how much variability in
grain nutrient composition it can
explain.
100
The concentrations of Mn in grain were
positively correlated with soil ASI.
Coefficient of determination for individual
sites ranged from 0 to 0.87 and had a
mean of 0.40. When data were pooled,
the soil ASI explained 10% of variability
in Mn grain concentrations.
12
Soil ASI
How it was done
0
Means
79%
6.0
7.5
60%
28%
9.0
10.5
14%
12.0
Soil ASI
Aerial
erial images of 12 soybean fields having marked spatial
variability in plant growth were taken during the growing
season.
amples were taken from small plots selected to represent a wide
Soil and plant samples
range in plant heights and yields as indicated by the aerial image.
image. Eight to 20
samples per field were taken. Geographic locations of sampling areas
areas were
recorded using a GPS unit.
Soybean plants were cut from 3 ft2 areas. The plants were dried and
shelled. Grain was weighed, and relative yields were calculated. Soil
samples were taken at the same locations after the harvest.
Color of the aerial image often corresponds
to height, vigor and final yield (3D image) of
the soybean plants as determined by yield
monitor. Yield range from 0.9 Mg ha-1 (dark
blue) to 4.5 Mg ha-1 (dark red).
Grain samples were analyzed for 11 essential nutrients including P, K,
Mg, Ca, S, Na, B, Cu, Zn, Mn and Fe. Soil samples were analyzed for pH
and calcium carbonate equivalent percentage.
Flooded areas
The FeFe-toto-Mn concentration ratio in
grain showed a better relationship
with the soil ASI than did either Fe or
Mn alone. Coefficient of
determination for individual sites
ranged from 0.61 to 0.95 and had a
mean of 0.77. When data were
pooled, the soil ASI explained 60% of
variability in FeFe-toto-Mn ratio.
5
y = 7.5-0.6x
r2 = 0.60, P<0.001
4
Grain Fe/Mn ratio
Relative Yield, %
The soil ASI = pH+0.14CCE.
The ASI explained 45% of
variability in relative yield
(percentage of the highest yield
within a field) observed across
12 fields. We consider this
relationship to be good because
many different factors influence
yield under field conditions.
80
20
y =10.9+2.1x
r2 = 0.10, P<0.001
50
y = 148.5-9.5x
r2= 0.34, P<0.001
100
3
2
1
0
7
8
9
10
11
12
Soil ASI
What was concluded
Iron deficiency chlorosis in soybean seems to involve more than just deficiency
of Fe. Mn seems to interact with Fe in a way that we cannot explain.
explain. Other
authors have observed Fe and Mn interactions in grain and suggested
suggested that there
is an optimal FeFe-toto-Mn ratio for plant growth.
The observed relationships between FeFe-toto-Mn in grain and new soil ASI adds
support to the conclusion that soil ASI is a useful tool for learning
learning more about
iron deficiency chlorosis.