Hi! Jamie Patton here with the Nutrient and Pest Management Program. Here to talk a little
bit about soil pH. If you ask a soil scientist, "What one piece of information they would want to
know about a soil in order to make interpretations about how it's functioning?", many soil scientists
would say, "Give me soil pH!" And the reason for that is soil pH is going to dramatically influence
not only the biological, but the chemical, and physical processes going on within a particular
soil. So that soil pH influences so many different properties. It's going to influence soil health
and it's going to influence how well our crops are going to grow under agronomic situations.
So in times of high fertilizer prices, such as we're experiencing right now, it is imperative
that we keep our soil pH in a range that's ideal for a particular crop. And the reason for that
is kind of explained in this chart. I really like this chart because it's really visual. So visual,
when we look at the bottom axis you notice the pH's are ranging from four to ten and
there are listed different soil nutrients within the chart and those nutrients are contained within
bars. When those bars are wide and they're green that means that those nutrients are more available
for plants. As those bars begin to get thinner and change from green to yellow to red color that
means that nutrient availability is decreasing. So just because a nutrient is contained within a
soil does not mean that a plant can take it up. That nutrient has to be dissolved in water but
soils are complex and there are lots of different chemical reactions going on. So by maintaining
a soil pH within a particular range, for a particular nutrient, we're going to help ensure
that that nutrient stays dissolved, not solid but rather dissolved, so that the plant root can take
it up. What's really interesting is when we look at those nutrients, macro versus micronutrients,
they're going to follow different patterns within the soil. So if you look at the top six
nutrients in this figure, nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium,
all of those are considered macronutrients. You'll notice that their bars are widest and greenest
when that pH is near seven. So when soils are near neutral our macronutrients are most available.
Alternatively our micronutrients, so that's iron, manganese, boron, copper, and zinc,
are going to be more available when that ph is closer to 5.5. Molybdenum doesn't follow
the typical micronutrient pattern, but a majority of those micros, as you notice those five listed
right there, are going to be most available at those lower pH's. So for us, as agronomists trying
to balance this complex chemical environment and maintain the availability of both macro
and micronutrients is essential to ensuring not only fertilizer use efficiency but also
crop growth and productivity. So in the state of Wisconsin, you're going to see many of our target
soil pHs for particular crops are going to range somewhere between six and seven. So the target
pH range for corn and wheat in Wisconsin is 6.0, for soybeans at 6.3, and for alfalfa that's 6.8.
Our legume crops, such as alfalfas and clovers, are going to have that higher target pH because
not only are we trying to maintain nutrient availability but we're also trying to create an
environment that's conducive for rhizobium growth. So those nitrogen-fixing bacteria that live with
those legumes are going to like those higher pH's and be more prolific and more productive at those
higher pH's. In addition, alfalfa is very very sensitive to aluminum. Aluminum becomes toxic
as those pH's drop near 5.5 or below. So there's a lot of complexity in managing the soil chemistry
within a given environment in order to maintain nutrient availability. In times of high fertilizer
prices, it is essential that we maintain soil pH so that the little bit of fertilizer that we may
be applying, because either supplies are limited or we are choosing not to buy as much nutrient
as we would have in the past because of higher prices, it is essential that we're applying those
to soils that have a pH that's going to maintain that availability for crop uptake. So when we look
at liming our soils, in order to make those lime recommendations and figure out how much lime we
need to apply, in order to bring that soil pH up into that target ph range for my crop rotation,
I'm going to need to have an up-to-date soil test. That soil test is going to give me lime
recommendations for oftentimes the 60-69 effective neutralizing material limes as well as that 80-89
effective neutralizing material lime. Common liming materials in Wisconsin include calcium and
or magnesium carbonates, so the calcite as well as dolomite limestones, which are mined from the
ground to a particular fineness and then applied to the field. So it's important to note that when
we look at these lime applications when we use lime products such as calcium chloride and calcium
sulfate, also known as gypsum, are not limiting materials. Limes must contain a base cation but
also neutralize acidity. So gypsum for example, contains calcium, contains that base cation,
but the sulfate portion doesn't neutralize that acidity and pH doesn't change. It's
also important when we're looking at our potential lime options, that these materials must be applied
in sufficient amounts. So there are a lot of products out there that say you only need to apply
maybe 100 pounds of this product to see that that pH go up. Most often times that is not true. We're
oftentimes applying tons of the material a ton or more plus of the material in order to neutralize
that acidity. There's a lot of acid out there as that pH drops below that target pH of six,
so we need to apply an appropriate lime to neutralize it. So if the product seems too
good to be true, it probably is. But if you don't know, go ahead and ask your agronomist,
extension agent, state extension specialist, and we can help you with those questions. So in times
of high fertilizer prices, such as now, what is the key takeaway from this presentation? PH
is important! So the old adage, the first dime on lime, may hold true. If we want to make sure
that that nutrient stays that we're spending a lot of money on, stays soluble, and available
for nutrient uptake, we need to ensure our soil pH is in a range that allows for that.