Agriculture Reference
In-Depth Information
Magnesium
Magnesium helps give structure to soil. That's why we need a little more of it on sandy
soils as compared to clay soils, to help that sand glue together a little better. Too much
magnesium in relation to calcium causes soil compaction, a common occurrence.
Magnesium also regulates nitrogen in the plant and helps transport phosphorus, so defi-
ciencies in these nutrients may have to do with excess magnesium. See how intertwined all
of these nutrients are! It's difficult to isolate them as each having their own tasks because
they all work together.
Magnesium is at the center of the chlorophyll molecule, which is responsible for photo-
synthesis. Interestingly, the chlorophyll molecule is almost the same as the molecule that
makes up our red blood cells, except that blood cells have iron at the center instead of mag-
nesium. Magnesium is important for plant health, but often, when we need magnesium, we
need calcium, too, which is why I use calcitic lime much more often than dolomite.
We're looking for 7-15% magnesium on a base saturation test, and a 10:1 calcium to
magnesium ratio on a Reams test. This goes up to 20% magnesium and down to a 7:1 ratio
for grasses and sandy soil. The plant won't take up enough magnesium if there's too little
or
too much in the soil. Most of our soils have too much magnesium, which means the
plant won't take up enough, which may be why our food is so deficient in magnesium. I
like to keep magnesium on the low side because magnesium ties up nitrogen, and I don't
apply much nitrogen. That being said, some people have success keeping magnesium levels
higher. If your calcium to magnesium ratio is low, though, you're probably going to have
nitrogen deficiency problems, compaction, and grassy weeds.
Langbeinite is approximately 27% sulfur, 22% potassium and 11% magnesium. It's also
known as sul-po-mag or K-mag, and is a good, natural product that is useful if a soil test in-
dicates you need sulfur, potassium and magnesium. It's a bit pricey at $30 to $40 for 50
pounds, but Dr. Reams liked it a lot and wanted it to be applied in mid to late summer. It
can be difficult to find and most people will look at you like you just zoomed in from Mars
if you ask for langbeinite. They may have heard of sul-po-mag or K-mag, but they may
substitute a synthetic version so be sure to ask for organic.
Another source of magnesium is epsom salts, also known as magnesium sulfate. It con-
tains approximately 16% magnesium and 14% sulfur, and costs about $10 for a few
pounds. It can be used as a foliar spray or on the ground, when you know you need mag-
nesium and sulfur.
