MO-28F
Influence of Soil Applied Magnesium on the Uptake and
Partitioning of Potassium in Rice Plants
David J. Dunn
University of Missouri-Delta Center
P.O. Box 160
Portageville, MO 63873
573-379-5431
dunnd@missouri.edu
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MO-28F
Introduction
Successful rice production requires a consideration of soil fertility. Proper K nutrition is
critical to maximize rice production. Potassium deficiency in rice can reduce grain yields
and increase lodging. Visual symptoms of K deficiency in rice first appear in older
leaves. These symptoms include a yellowing of leaf tips, decreased disease resistance,
and reduced yields Increased stalk strength and decreased lodging are associated with
proper K nutrition. Studies of K nutrition of rice are rare compared to those of nitrogen.
Tissue K levels in rice are affected by the stage of growth. The uptake of K by rice plants
closely parallels the accumulation of dry matter from emergence until anthesis. Estimates
of critical levels in rice leaf tissue are a function of plant growth and developmental
stage. Adequate K in rice tissue during the late vegetative and early reproductive stages
is important for producing optimum yields. During these growth stages, rice plants
rapidly accumulate K in leaf and stem tissue. After seed development begins, K uptake
slows dramatically. Transfer of K from lower leaves largely account for K accumulation
in the hull and seed.
Studies of the role of Magnesium in rice production are even rarer. Magnesium is found
at the center of the chlorophyll molecule. An estimated 20% of the Mg is used in this
role. The remaining Mg is distributed through out the plant and is relatively mobile in
the phloem. Since this pool of Mg is mobile deficiency symptoms are first developed in
older tissue. These symptoms are caricaturized by an interveinal yellowing of the leaf
blade that progresses from the edge to the center of the leaf. The typical pattern of Mg
deficiency is green conductive tissue surrounded by a yellow background. Ultimately the
leaves become stiff and brittle with the veins becoming twisted. Magnesium toxicity is
rarely observed in field conditions.
The interaction of soil applied K and Magnesium (Mg) fertilizers with K and Mg uptake
in rice plants has not been previously studied. This study compares the uptake of both K
and Mg in rice plants fertilized with KCl or K2SO4 . 2MgSO4 at equivalent K rates.
Methods and Materials:
A rice study was conducted on a field at the Missouri Rice Research Farm (36oN, 90oW)
in Dunklin County, Missouri in 2003. Rice was planted on a Crowley series (fine,
montmorillonitic, thermic Typic Albaqualf). The soil has a silt loam eluvial horizon
which overlies a thick silty clay loam argillic horizon. This is a typical soil for producing
drill-seeded rice in Southeast Missouri. The soil pHwater of the surface horizon was 6.2.
The soil test value for K was 55 mg kg-1, P was 45 mg kg-1, Mg was 147 mg kg-1, Zn
was 1.9 mg kg-1 and the CEC value was 17.9 cmolc kg-1. There was no record of
potassium fertilizer ever being applied on the site. The soil test values for P, Mg, Zn, and
pH are considered to not be limiting yields. The University of Missouri soil test
recommendation for K was 56 kgha-1 of K2O. Rice was cultivated in 2002 and the field
was conventionally tilled prior to seeding rice in 2003. The experimental design was a
randomize complete block design with four replications was employed. Three pre-plant
rates of K from two different K sources were applied by hand to a K deficient soil.
These rates were 0, 56, and 224 kgha-1 of K20. The sources of K were KCl and K2SO4 .
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MO-28F
2MgSO4 (K-Mag®, IMC USA Inc. Forest Lake IL). The rice variety Cocodrie was
cultivated using standard cultural practices. Four times during the growing season tissue
samples were collected from each plot. These times were first tiller, maximum tillering
inter-node elongation, and harvest. These tissue samples were then analyzed for total dry
matter and K & Mg content. From these determinations total K and Mg uptake was
calculated. Rice plants from 30 cm from the outside drill row from each plot were
collected. These samples were dried at 100 Co. After being weighed the samples were
ground and digested using H2SO4 and H2O2, and analyzed for K and Mg content using a
Perkin-Elmer AA. The results of these two analyses were then compared. The field was
drained on September 10, 2004. All plots were harvested on October 15, 2004. An
ALMACO plot combine was used to harvest the middle five feet of each plot. The
harvested grain was weighed, moisture % measured and yields were adjusted to 13%
moisture for final yield. Statistical analyses of the data were preformed with SAS (1990)
using General Linear Modeling procedures. Fisher’s Protected Least Significant
Difference (LSD) was calculated at the 0.05 probability level for making treatment mean
comparisons.
Results and Discussion:
At first tiller dry matter accumulation was greater for K-Mag treatments than KCl at
equivalent K rates (Figure 1a). This may be due to the sulfur contained in the K-Mag
product. Potassium uptake at first tiller was affected by K rate and not by K source
(Figure 2a). Magnesium uptake at first tiller was affected by K source and K rate (Figure
3a). K-Mag treatments produced greater rates of Mg uptake the equivalent KCl
treatments. At maximum tillering all K treatments produced dry matter accumulations
that were greater that the untreated check (Figure 1b). Potassium uptake at maximum
tillering was affected by K rate and K source (Figure 2b). Magnesium uptake at
maximum tillering was affected by K source and K rate (Figure 3b). K-Mag treatments
produced greater rates of Mg uptake the equivalent KCl treatments. At inter-node
elongation the 212 kgha-1 K as K-Mag produced dry matter accumulations less than all
other treatments (Figure 1c). Potassium uptake at inter-node elongation was affected by
K rate and K source (Figure 2c). The high K rate as K-Mag had lower K uptake and may
be explained by the decrease dry matter accumulation. Magnesium uptake at inter-node
elongation was affected by K source and K rate (Figure 3c). K-Mag treatments produced
greater rates of Mg uptake the equivalent KCl treatments. Dry matter accumulation at
harvest was effected by both K rate and K source (Figure 1d). Potassium uptake at internode elongation was affected by K rate, but not by K source (Figure 2d). Magnesium
uptake at harvest was affected by K source and K rate (Figure 3d). K-Mag treatments
produced greater rates of Mg uptake the equivalent KCl treatments.
Rice grain yields and harvest grain moisture for K treatments are presented in Table 1. K
source significantly effected grain yields and harvest moisture. Both KCl treatments
produce grain yields significantly greater that the untreated check. Both K-Mag
treatments produced grain yields that were statistically equivalent to the untreated check.
Both K-Mag treatments produce harvest grain moisture levels that were statistically
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MO-28F
greater than the untreated check and both KCl treatments. This indicates a delay of
maturity effect of K-Mag.
Conclusions
•Magnesium fertilization did not affect total K uptake at harvest.
•Magnesium fertilization did result in higher rates of Mg uptake at all growth stages
studied.
•Only at first tiller did Mg rate effect Mg uptake.
•During reproductive growth stages Mg fertilization tended to decrease dry matter
accumulation at the same K rates.
Maximum tillering
Dry matter (kg/ha)
Dry matter (kg/ha)
First tiller
300
250
200
150
100
2000
1500
1000
Check 50 lbs K 50 lbs K 200 lbs K 200 lbs K
as KCL as K-Mag as KCl as K-Mag
Check 50 lbs K 50 lbs K 200 lbs K 200 lbs K
as KCL as K-Mag as KCl as K-Mag
K treatment
K treatment
Harvest
dry matter (kg/ha)
Dry matter (kg/ha)
Inter-node elongation
2500
2000
1500
8500
8000
7500
7000
Check 50 lbs K 50 lbs K 200 lbs K 200 lbs K
as KCL as K-Mag as KCl as K-Mag
Check 50 lbs K 50 lbs K 200 lbs K 200 lbs K
as KCL as K-Mag as KCl as K-Mag
K treatment
K treatment
Figures 1 a, b, c, & d. Dry matter accumulation for K treatments for rice growth stages.
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First tiller
Maximum tillering
K uptake (kg/ha)
K uptake (kg/ha)
•
10.0
8.0
6.0
4.0
2.0
55.0
50.0
45.0
40.0
35.0
30.0
Check 50 lbs K 50 lbs K 200 lbs K 200 lbs K
as KCL as K-Mag as KCl as K-Mag
Check 50 lbs K 50 lbs K 200 lbs K 200 lbs K
as KCL as K-Mag as KCl as K-Mag
K treatment
K treatment
Harvest
K uptake (kg/ha)
K uptake (kg/ha)
inter-node elongation
70.0
60.0
50.0
40.0
30.0
150.0
100.0
50.0
Check 50 lbs K 50 lbs K 200 lbs K 200 lbs K
as KCL as K-Mag as KCl as K-Mag
Check 50 lbs K 50 lbs K 200 lbs K 200 lbs K
as KCL as K-Mag as KCl as K-Mag
K treatment
K treatment
Figures 2 a, b, c, & d. Potassium uptake for K treatments for rice growth stages.
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Maximum tillering
Mg uptake (kg/ha)
Mg uptake (kg/ha)
First tiller
1.0
0.8
0.6
0.4
0.2
0.0
Check 50 lbs K 50 lbs K 200 lbs K 200 lbs K
as KCL as K-Mag as KCl as K-Mag
3.0
2.0
1.0
Check 50 lbs K 50 lbs K 200 lbs K 200 lbs K
as KCL as K-Mag as KCl as K-Mag
K treatment
K treatment
Harvest
5.0
4.5
4.0
3.5
3.0
2.5
2.0
Check 50 lbs K 50 lbs K 200 lbs K 200 lbs K
as KCL as K-Mag as KCl as K-Mag
K treatment
Mg uptake (kg/ha)
Mg uptake (kg/ha)
Inter-node elongation
22.0
20.0
18.0
16.0
14.0
12.0
10.0
Check 50 lbs K 50 lbs K 200 lbs K 200 lbs K
as KCL as K-Mag as KCl as K-Mag
K treatment
Figures 3 a, b, c, & d. Magnesium uptake for K treatments for rice growth stages.
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Table 1. Rice grain yields and harvest moisture % for K treatments, 2004.
K treatment
Yield
Grain Moisture
(Bu/acre)
(%)
Check
168 a
14.3 a
50 lbs K
190 b
14.6 a
as KCL
50 lbs K
167 a
16.6 b
as K-Mag
200 lbs K
192 b
15.0 a
as KCl
200 lbs K
170 a
16.8 b
as K-Mag
Values followed by the same letter are
statistically equivalent at the alpha =
0.05 level.
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