Potato Plant Nutrition For Growers
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Magnesium Accumulation in Units/Acre in Relation to Yield

Tons/Ac 15 dae 30 dae 45 dae 60 dae 75 dae 90 dae 105 dae 120 dae
25 1.2 5.9 19 26 33 33 33 31
30 1.5 7.1 23 32 40 40 39 38
35 1.7 8.3 27 37 46 47 46 44
40 1.9 9.4 31 42 53 53 52 50

Magnesium is known because of its association with chlorophyll. However, if more than 20% of the plant’s Mg is in the chlorophyll, it will suffer yield potential. This indicates that Mg plays many other important roles in potato development. Due to the high demand of K, magnesium uptake is often suppressed, especially in low CEC soils with low natural levels of Mg. This means that it should be supplied (in sufficient quantity) like other nutrients. Like Ca, magnesium is suppressed by high amounts of K. However, timing is important.

Calcium is taken up more efficiently by newly forming roots (optimum application window = 15 to 35 dae). Potassium is taken up readily, however optimum uptake timing is in the 30 to 60 dae window. Magnesium is accumulated in the leaves from 45 to 75 dae, slightly latter than K. Timing: Calcium > Potassium > Magnesium. Run the last 10-15 units of N with Magnesium Nitrate

Magnesium Facts

  • Mg is mobile in phloem (can move into fruit), unlike Ca
  • Mg uptake is suppressed by; K, NH4, Ca and then Na (in decreasing influence)
  • Calcareous soils (75-85% of CEC as Ca) with less than 15% Mg (less than 20% in CEC lower than 7.0) is a good candidate for water run Mg
  • Mg suppresses degradation of chloroplasts in older tissues. Mg is mobile from old growth to new growth. Supplying Mg late in the season will help keep vines alive longer
  • Starch translocation from the chloroplasts is reduced in low Mg leaves, before visual Mg a deficiency (yellowing) occurs
  • Low Mg results in lower levels of starch (solids) in potato tubers. This is negative affect is greater in higher temperatures, because Mg inhibits oxidation of chloroplasts

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