Information from 1999 Missouri Rice Research Update, February 2000.

Effect of Soil Calcium: Magnesium Ratios and Hormones on Potassium Uptake and Rice Yields

Tina Gladbach, Gene Stevens, Alan Sheckell and David Dunn

Abstract

An investigation of the effects Ca:Mg ratio and plant hormones on plant nutrient uptake and yield in rice is being conducted. Different rates of epsom salt (MgSO4), red lime (dolomite), and white lime (calcite) were applied to plots to create different soil Ca:Mg ratios. Additionally, Agri-Cal, and Agri-Gro were applied as foliar treatments. Red lime did not decrease the Ca:Mg ratio. Results did not show significant differences between treatments in either tissue nutrient concentrations or yield.

Introduction

The Basic Cation Saturation Ratio concept has recently received attention in Missouri. This method of soil test interpretation was developed through a series of publications in the late 1940's based on work done in alfalfa. The ideal ratio promoted in these early works was for saturation of the cation exchange complex at 65% Ca, 10% Mg, 5% K, and 20% hydrogen (H) (Eckert 1987). Nearly a decade later, Graham (1959) presented the saturation ranges of 65-85% Ca, 6-12% Mg, 2-5% K rather than a specific ratio for optimum production in Missouri soils. No research has been conducted with Ca:Mg ratios on flooded soils. In 1999, an experiment was begun in Missouri to study the relationships between cations ratios in the soil, plant uptake and rice yield.

Materials and Methods

A randomized complete block design with four replications was used. Magnesium sulfate, white lime, and red lime treatments were applied on April 29 to establish variations in soil Ca:Mg ratios. Plots were also established with no soil amendments for testing foliar Agri-Gro and Agri-Cal treatments. Treatments included an untreated check, 3 applications of MgSO4 (2,4, and 6 tons/acre), red lime (3 tons dolomite /acre) white lime (3 tons calcite /acre), Agri-Gro (32oz at 6-leaf stage+ 16 oz at joint growth), Agri-Cal (3 gallons 6-leaf), one combined treatment of Agri-Cal and Agri-Gro (Agri-Cal 3 gal +Agri-Gro 32 oz 6-leaf +Agri-Gro 16 oz joint ). Drew rice was planted on May 12. On May 25, Stam (1 gal/acre) and Facet (8 oz/acre) were applied for weed control. Soil samples were collected on June 7. On June 8, 75 lb N/acre was applied on all plots followed by flooding. On June 11, treatments with Agri-Gro and Agri-Cal at 6-leaf growth stage were sprayed. Tissue samples were collected at mid-tillering on June 25. On July 15, 30 lb/acre mid-season fertilizer was applied and internode elongation tissue samples were collected. On July 21, Agri-Gro and Agri-Cal treatments were sprayed at joint growth stage and a second mid-season fertilizer application 30 lbs/acre was applied. Tissue samples were collected at early boot on July 27. Tissue samples were analyzed using H2SO4 and H2O2 digestion with a Hach Digesdahl. Plots were mechanically harvested for yield on September 14. Samples were milled with a McGill mill for percent head and total.

Results and Discussion

The epsom salt and white lime treatments were effective in altering the soil Ca:Mg ratios in plots. The results from the soil samples collected on June 7 are shown in Table 1. The red lime increased the soil Mg level but it also increased soil Ca by the same factor. The net effect was that the Ca:Mg was slightly reduced from red lime.

Table 1. Effect of epsom salt (MgSO4), and white and red lime on soil Ca, Mg, and K.

  Treatment       Salt     Ca:Mg         Ca      Mg      K
                   pH      Ratio       -------lbs/acre------
Untreated         5.3       3.2         1608     501     132
MgSO4  2ton/A     5.1       1.5         1574    1031     152
MgSO4  4 ton/A    5.4       1.0         1569    1646     136
MgSO4 6 ton/A     5.2       0.8         1729    2066     166
Dolomite3 ton/A   6.1       3.1         2034     656     169
Calcite 3 ton/A   6.9       5.4         2804     517     142

The differences in soil Ca:Mg ratio did not significantly affect the plant concentration of potassium at any of the three growth stages (Tables 2, 3, and 4). Some salt injury was observed in the highest rate of epsom salt (6 tons/acre). This was reflected in the lower yields in this treatment (121 bu/acre). Rice yields and milling results are in Table 5.

Table 2. Effect of treatments on tissue concentrations of Ca, Mg, and K at mid-tillering growth stage.

                  Soil        Ca    Mg    K
  Treatment       Ca:Mg     --------%-------
                  Ratio
==============================================
Untreated          3.2       0.31  0.24  2.22
MgSO4  2 ton/A     1.5       0.28  0.32  2.38
MgSO4  4 ton/A     1.0       0.28  0.34  2.27
MgSO4   6 ton/A    0.8       0.28  0.38  2.12
Dolomite  3 ton/A  3.1       0.29  0.38  2.26
Calcite  3 ton/A   5.4       0.29  0.28  2.47

Table 3. Effect of treatments on tissue concentrations of Ca, Mg, and K at internode elongation.

                  Soil        Ca    Mg    K
  Treatment       Ca:Mg     --------%-------
                  Ratio
==============================================
Untreated          3.2       0.20  0.24  1.7
MgSO4 2 ton/A      1.5       0.24  0.28  1.8
MgSO4  4 ton/A     1.0       0.24  0.32  2.0
MgSO4 6 ton/A      0.8       0.28  0.28  2.2
Dolomite 3 ton/A   3.1       0.20  0.24  2.0
Calcite 3 ton/A    5.4       0.28  0.24  1.8
Agri-Gro             -       0.28  0.24  1.9
Agri-Cal             -       0.24  0.28  2.1
Agri-Cal +Agri-Gro   -       0.20  0.24  2.3

Table 4. Effect of treatments on early boot tissue analysis.

                  Soil        Ca    Mg    K
  Treatment       Ca:Mg     --------%-------
                  Ratio
==============================================
Untreated          3.2       0.38  0.28  1.4
MgSO4  2 ton/A     1.5       0.32  0.28  1.8
MgSO4  4 ton/A     1.0       0.44  0.32  1.5
MgSO4  6 ton/A     0.8       0.36  0.32  1.6
Dolomite 3 ton/A   3.1       0.40  0.28  1.9
Calcite 3 ton/A    5.4       0.28  0.28  1.4
Agri-Gro             -       0.40  0.24  1.7
Agri-Cal             -       0.36  0.20  1.6
Agri-Cal + Agri-Gro  -       0.44  0.24  1.4

Table 5. Effect of treatments on rice yield and milling.


                       Milling %    Rice Yield 
  Treatment          Head   Total    Bu/Acre
----------------------------------------------
Untreated             63     71        158
MgSO4 2 ton/A         54     66        165
MgSO4  4 ton/A        58     69        165
MgSO4 6 ton/A         50     64        121
Dolomite 3 ton/A      50     65        140
Calcite 3 ton/A       59     69        152
Agri-Gro              59     68        157
Agri-Cal              51     65        148
Agri-Cal + Agri-Gro   60     70        160

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