With corn prices expected to be lower this season, no-tillers may find themselves planting more soybean acres and focusing on growing a better soybean crop. That includes paying more attention to the soybean’s fertility needs and ensuring it has the nutrients it requires.
Monsanto technical agronomist Lance Tarochione and Mycogen Seeds commercial agronomist Jason Welker share their advice for avoiding common fertility mistakes, checking nutrient levels and helping increase soybean yields.
Sample the Soil.
Creating an accurate fertility plan for soybeans starts with taking a soil test to find out where nutrient levels are.
“It’s not expensive to pull one sample for a field to at least have an idea where you are in nutrients, because the worst thing you can do is start depleting your soil of valuable nutrients,” Welker says.
He recommends no-tillers soil test every year and take multiple samples to get a good idea of fertility levels in fields. He likes to split fields into quadrants during sampling so he’s not taking cores just from the high- or low-producing areas.
Tarochione recommends no-tillers soil test at least every 4 years and stay consistent in how they pull their samples by soil testing after the same crop, at the same time of year, and preferably under the same soil moisture conditions.
No-tillers can achieve even more accuracy by taking grid or zone samples so they can variable-rate fertilizer.
That’s a practice Norman Deets has implemented on his Milledgeville, Ill., no-till corn and soybean operation for the last 10 years.
Deets grid samples a third of his farm every year, so every field gets soil-tested every 3 years. He takes 6- to 8-inch-depth samples right after harvest and waits for the results before making an application. In the fall after corn harvest, he has his local co-op variable-rate broadcast diammonium phosphate (DAP) based on the soil test results.
“It’s saved money and increased the consistency of the fertilizer application throughout the field,” Deets says, estimating that he’s cut his fertilizer bill by a third with this approach.
Check the pH.
Soil pH is often the overlooked aspect of soil fertility, Tarochione says, because the availability of nutrients and chemistry in the soil is impacted by pH, as is soybean nodulation.
“In a lot of situations, a farmer has a soil that’s testing low in phosphorus (P) and potassium (K) and it’s pretty easy to focus on those major nutrients,” he says. “But some situations you really ought to start with adjusting the pH.”
For soybeans, he says the best availability occurs between a pH of 6.3-6.7. No-tillers will want to avoid getting over 7, as they may see problems from the pH being too high. Tarochione warns this may happen in the first few inches of the soil after a lime application, since no-tillers don’t incorporate it.
“If you drop 3-4 tons of lime on an acre, you might raise the pH of the top inch to 7.5 or 8,” he explains. “Over time it’s going to work its way down through, but lime stays pretty close to where it’s applied.
“If I was a continuous no-tiller, I would apply lime more frequently in smaller amounts. I’d be putting on 1 ton or 1½ tons — no more than 2 — maybe every year for a few years in a row.”
It’s been a common practice in corn-soybean rotations to apply 2 years worth of nutrients ahead of the corn crop and hope there’s enough left for the soybeans, Tarochione says. But fertilizing before each crop will ensure plants have access to needed nutrients, and it can also be more cost effective.
“You can maximize the plant availability of your macronutrients by making more frequent and smaller applications,” he says.
Tarochione cites research that has shown if a single, large application is made once compared to that same amount being applied in increments over 10 years, the plot that received the smaller applications will have higher nutrient levels in the end. Larger applications mean the nutrients are more likely to get tied up in the soil.
On his own farm, Tarochione makes an application of P, K and sulfur every fall based on what the previous crop removed in nutrients, which he can determine from his yield averages.
Sulfur is frequently an overlooked nutrient, and no-tillers should keep in mind it’s still a macronutrient — even if it’s a smaller one, he says. Because federal clean-air initiatives have removed a large amount of sulfur from rainfall, he’s seeing more sulfur deficiencies in soils, especially those with low organic matter.
A 75-bushel soybean crop will remove about 15 pounds per acre of elemental sulfur, he says, and there are a lot of ways to get sulfur on the farm — whether it’s applying gypsum or blending in a sulfur product with other fertilizers.
Welker likes to see P and K levels around 18 and 120 ppm, respectively, but he recommends checking soil tests to see what the soil lab says to aim for.
In addition to a fall application, he also recommends no-tillers put fertility down during planting, to help the microbes work faster in cool, no-till soils.
P, K and sulfur aren’t the only nutrients soybeans need. Welker says zinc should be at least 1 ppm for soybeans. If soil levels are below that, then no-tillers can add dry zinc in with their dry P application, or use chelated zinc with their liquid fertilizer.
“But a chelated zinc will only apply for that crop year. It’s not going to raise it in your soil profile,” he says.
Other micronutrient deficiencies may occur, depending on the type of soil and location. Tarochione says deficiencies are most common in sandy soils, and soils with low organic matter.
“Organic matter is a wonderful thing to have in the soil, and if you have high organic matter levels you won’t often find micronutrient deficiencies,” he says.
The best way to determine if soybeans are experiencing a micronutrient deficiency is to take tissue samples, Tarochione says, because soil samples aren’t as reliable for micronutrients and don’t necessarily indicate that they’re available to the plant.
“If you want to know what’s in your plant, you need to test your plant, not the soil,” he says, adding there may be times when the crop isn’t showing symptoms of deficiency but it can still benefit from additional nutrients.
He recommends tissue testing anytime through the vegetative part of the growing season, sometime around late spring and early summer.
There are some options in applying foliar nutrients to soybeans, such as with manganese. But if no-tillers find a problem at that point, it’s likely too late to correct it that season. Tarochione says tissue samples are more to determine if there is a deficiency, so no-tillers can incorporate that nutrient into future fertility.
While soybeans fix their own nitrogen (N), Tarochione says they actually use more than they fix.
“Soybean nodules stop fixing N earlier than we’d like,” he says. “About the time the plant starts to produce seed, N fixation and production of the nodules drops off dramatically.”
The easiest way to ensure soybeans are producing enough N is to help them nodulate through seed inoculation.
In previous research on applying N to soybeans, Tarochione says the benefit comes later in the season when the crop is no longer producing its own N, but researchers are still working on whether this is an economical practice.
One practice that may help provide N later in the season is the use of a cover crop, particularly cereal rye.
“Cereal rye basically sucks all of the available N out of the soil, ties it up and releases it later in the summer when it decomposes,” Tarochione says. “That might explain why soybeans into cereal rye has consistently worked well for people.”
He adds there’s been some concern that too much N early in the season may be detrimental to soybeans, as they won’t nodulate if there is available N in the soil. If the cereal rye is taking up that unused N, that may push soybeans to nodulate more.