Six Secrets of Soybean Success
- Foliar Protection
- Seed Treatment
- Row Arrangement
The first "secret," of course, isn’t much of a secret at all. Weather is the dominant factor, dictating
much of the success of any crop. So let's take a look at something the grower can control: fertility,
the second most important factor in soybean success.
According to USDA research of growers in the top five soybean states, almost 80 percent apply neither
phosphorus nor potassium to support the nutritional needs of their soybean crop. And it’s easy to
understand why. Since the 1970s, very little research has actually been done regarding the importance
of crop nutrition for soybeans — especially the importance of micronutrients.
As a part of my Ph.D. work at the University of Illinois, I addressed that void by studying how current
soybean varieties, which produce far greater seed yield, are acquiring and using nutrients.
When examining the subject of soybean fertility, it’s best to start by studying how nutrients are used
by the plant. The table below shows key nutrients, how much of each is required for production, and
how much of that nutrient is removed with the grain. The last column — Harvest Index — illustrates
the percentage of total nutrient uptake that is in the grain. This factor is an indicator of how
important nutrients are to produce grain.
This information matters, because it tells us which nutrients are most important to raise a high-yielding
crop. Nutrients that have high requirements for production — like nitrogen and potassium— are considered
important. So, too, are nutrients that have high harvest index values.
After all, if we’re looking to increase yield, then doing a better job of providing the nutrients
responsible for creating that yield should be a primary goal. This chart shows that
nitrogen (N), phosphorus (P) and sulfur (S) should receive heightened attention for their performance
in that regard.
Are we providing soybean crops enough of those nutrients to reach their potential? Let’s examine
One of three primary nutrients, phosphorus (P) is essential for plant growth, and a plant must
access it to complete its normal production cycle. Plants absorb P from the soil as primary
and secondary orthophosphates (H2PO4- and HPO42-).
usage more closely, as an example.
According to USDA data, the average farmer applies about 90 pounds of P2O5
per acre prior to planting a corn crop. However, 80 percent of farmers don’t follow up
with a subsequent phosphorus application prior to planting soybeans. Let’s say you’re
among that majority, and you raised a 230-bushel-per-acre corn crop, followed by a 60-bushel-per-acre
soybean crop. You will have removed 115 pounds of P2O5 per acre at the end of
the two-year rotation. Because the average farmer didn’t replenish
with an application between harvests, in this hypothetical situation, you’ve depleted your soil by
25 pounds of P2O5 an acre after this two-year crop cycle.
So, you have to ask yourself: Was my soil able to supply enough, or did I run out of phosphorus? Did
this nutrient limitation sacrifice yield, and could it have been prevented?
This graph illustrates the seasonal uptake of P for a 60-bushel soybean crop as well as where it’s allocated.
Here’s the thing with phosphorus: It’s acquired rapidly and throughout much of the growing season.
In fact, soybeans take up P rapidly for 70 days straight. If you’re like the 80 percent of producers
who didn’t apply P before soybean, that means you hypothetically last applied phosphorus 18–20 months
ago. Now it’s July or August, and your crop needs phosphorus badly. It’s anybody’s guess if it will
At the end of the season, the great majority of the phosphorus found in a soybean plant is in the grain,
so when we harvest it, it’s removed forever. That’s why it’s so easy to deplete the soil to levels
that can take years to rebuild.
The Case for K
Potassium (K) is one of the essential nutrients and is taken up in significant amounts by crops.
Potassium is vital to photosynthesis, protein synthesis and many other functions in plants.
It’s classified as a macronutrient, as are nitrogen (N) and phosphorus (P). Plants take up
K in its ionic form (K+).
is also critically important for soybeans. For approximately 50 days, from the 40th through the 90th
day after planting, approximately 3 pounds of K2O per acre per day is acquired, or almost 6 pounds of potash.
Sulfur for All Season
Sulfur (S) is a part of every living cell and is important to the formation of proteins. Unlike
the other secondary nutrients like calcium and magnesium (which plants take up as cations),
S is absorbed primarily as the SO42- anion. It can also enter plant leaves from the air as dioxide (SO2) gas.
is another nutrient that requires discussion.
But not just sulfur — season-long sulfur. Between its mobility in the soil and its propensity
to become unavailable to the plant, S programs require some thought. The most effective sources typically
provide early- and late-season availability. But, since there is a large need for sulfur in making
the grain, it’s worth the extra attention.
Nutrition, A to Zinc
Growers also need to pay attention to
Zinc (Zn) is taken up by plants as the divalent Zn2+ cation. It was one
of the first micronutrients recognized as essential for plants
and the one most commonly limiting yields. Although Zn is required in small amounts, high
yields are impossible without it.
, a micronutrient particularly important during seed filling. If you want to produce high-yield soybean
or corn, you need a lot of phosphate in the grain. Binding to that phosphate is zinc. That relationship
means you can get more out of your phosphorus by making sure Zn is adequately available.
The Official Nutrient of Flowering
If you’ve been hearing more about boron lately, you’re not alone. Growers are finding success with this
micronutrient, and it’s easy to see why.
Boron (B) is a micronutrient that is essential for cell wall formation and rapid growing
points within the plant, such as reproductive structures. Interestingly, while higher
plants require B, animals, fungi and microorganisms do not need this nutrient.
is important all season long, but there is increased significance to its role during flowering.
Boron is basically The Official Nutrient of Flowering, as it plays a critical role in that process.
Since it is needed throughout the season, but isn’t plant mobile, B needs to be accumulated through plant
roots for the greatest impact. Although this isn’t the case for every nutrient, it is for boron,
so ground applications typically work best.
What’s the Bottom Line?
Those who think soybeans are satisfied with scavenging the soil might be raising nutrient-starved soybeans.
Just think about what a soybean acre needs every day during peak growth:
- 4.1 pounds of N
- 0.7 pound of P2O5
- 3.4 pounds of K2O
- 0.3 pound of S
It’s clear. Improved soybean productivity requires a greater demand for plant-essential nutrients, but
solving this puzzle is tricky. Gone is the “wait and hope” era of soybean fertility strategies. Today’s
premium seed technologies require a forward-thinking approach, matched with
premium fertilizer products.
Premium Fertilizer Products
The Mosaic Company offers a suite of advanced crop nutrition products designed to meet your unique
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