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Magnesium Recommendations

The optimum magnesium (Mg) level varies with the crop.

The optimum Mg is given on the crop sheet for each crop in this handbook. Look in the left hand column and find the soil test Mg level in ppm as reported on the bar chart in the middle of the soil test report then go across to the appropriate "Optimum Mg" column for that crop to determine the amount of Mg recommended.

Since the most common source of Mg is magnesium containing limestone, the Mg recommendation is also given on the soil test report as the percent Mg required in the recommended limestone to meet the Mg requirement. To calculate this percentage divide the Mg recommendation determined from this table by the limestone recommendation determined from table 1 and multiply by 100.

Recommendations are given as elemental Mg because limestone is required by Pennsylvania law to be labeled with the elemental Mg analysis. You can convert the the Mg recommendation to MgO by multiplying the Mg recommendation times 1.6.

Table 2. Magnesium Recommendation (lb Mg/A)
Soil Test
Mg Level
(ppm)
Optimum Mg Level (ppm)
50 60 100 120
0 100 125 200 250
5 95 110 190 240
10 90 105 180 230
15 85 95 170 220
20 80 80 155 205
25 75 75 150 200
30 70 60 140 190
35 60 50 125 175
40 60 45 120 170
45 50 30 105 155
50 0 20 95 140
55 0 15 90 140
60 0 0 75 125
65 0 0 65 105
70 0 0 55 105
75 0 0 45 95
80 0 0 30 80
85 0 0 25 75
90 0 0 15 60
95 0 0 0 50
100 0 0 0 45
105 0 0 0 30
110
0 0 0 20
115 0 0 0 15