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Soil fertility is one of the most important factors in soybean productivity, yet many farmers have only a general idea of their soil-nutrient needs. Not fully understanding what the soil holds can be costly due to lost production or unnecessary fertilizer applications.
Experts advise taking the guesswork out of soil fertility by doing regular and thorough soil sampling. There’s no time better than just after harvest.
“Soil sampling should be considered an integral part of every management plan since it impacts the way farmers will implement every other action on their crops,” says Bobby Golden, Ph.D., assistant professor of plant and soil sciences at Mississippi State University.
Samples are typically used to test for phosphorus, potassium and pH levels, plus minor nutrients, organic matter and cation-exchange capacity.
What Lies Beneath
Bernie Paulson, of McPherson Crop Management in Janesville, Minnesota, works with farmers to find out what’s in their soil. At a cost of just a few dollars an acre, Paulson says soil testing is a good investment to help make decisions about applying nutrients that can cost as much as $90 per acre.
“Precise fertilizer recommendations are formulated to provide a return for farmers while minimizing environmental exposure through unneeded nutrients,” Paulson says.
To maximize nutrient value and minimize environmental impact, Paulson follows the four R’s of fertilizer application; the right nutrient in the right place, the right rate and at the right time. He also makes use of university recommendations to ensure application rates are based on economics and environmental impact.
Tighter Crop Budgets
While sampling is always valuable, Paulson believes farmers should be especially aggressive in performing this task during times of low commodity prices so they can proceed confidently with their nutrient-management plans.
“We haven’t seen a drop in input prices, so first importance is understanding the economics of fertilizer applications,” Paulson adds. “Are there enough nutrients in the soil that farmers can forego putting some on, or do they know what they need to apply? With testing, at least they’ll know if they can reduce some of their input costs.”
“Soil sampling doesn’t always mean that farmers should expect to have to build up a lot of nutrients in the soil,” adds Golden. “Sometimes it can just mean a small addition or no addition at all, as long as you’re maintaining natural levels.”
Soil sampling can also reveal the presence of pests, like soybean cyst nematode (SCN). That information can help farmers make seed-variety selections based on SCN-resistance needs.
No Time Like the Present
Soil samples taken more than a few years ago will have limited value for fertilizing next year’s crop, especially if yields have consistently increased or decreased by even a few bushels since the last time you sampled. Increased yields require and use more nutrients; decreased yields require less. Experts recommend sampling every three or four years. Be sure to compare this year’s soil samples to ones taken previously to track your nutrient levels over time.
“When times were good, a lot of farmers built up their soil nutrients,” Paulson says. “Now we’re looking at ways to control the budget and get our cost of production as low as possible. If we’re using old data, we lack the confidence in knowing what the soil really needs.”
Regular soil testing can help farmers better understand soil-nutrient availability, increase crop productivity and become even better stewards of the land.
Soil Sampling: It’s a Simple Process
Soil sampling is the first step toward a profitable crop. Getting a good soil sample is critical to the accuracy of your soil-test results. Below, Illinois soybean farmer Austin Rinker and agronomist David Brummer walk through the soil sampling process.
Why? Soil samples help farmers understand a significant part of the yield equation – the soil’s nutrient status. With proper collection and handling, the results of soil sampling and analysis can result in recommendations to supply adequate fertilization to meet the crop’s nutritional demands.
“Sampling our soils is very important to us,” says Rinker. “Taking a soil sample gives us a baseline to know where our fertility is at and what we need to be applying for nutrients.”
Who? Some farmers sample their soils themselves, although it’s also common for farmers to enlist the help of professionals.
“On our operation we hire someone to do our soil testing,” says Rinker. “When it comes to a field that needs soil tested, we’ll talk with our fertilizer retailer. Then we’ll turn in that work order with our chemical dealer, who will relay that onto our soil testing lab.”
When? Every two to four years.
“Soil tests should be done every four years,” Rinker adds. “If you get into some different cropping systems, or if you make some major management practice changes, probably every two years. But in most instances, four years is satisfactory.”
Where? A specific point in the field you want tested.
“Due to GPS technology, we now do soil sampling on what we call a point-sampling basis, where we drive to a specific point in the field and we take the cores right around that point,” says Brummer. “He will take five steps to the side of the ATV and repeat that step four other times on all four sides of the ATV to create a diamond of about 30 by 30 feet.”
How? Consistent sampling using a soil probe.
“One of the most important factors in getting a good quality soil sample is to take it at the correct depth,” Brummer adds. “In Illinois, we take soil samples at the depth of 7 inches, and every sample needs to be consistently at 7 inches. If we don’t do this, if we are too shallow or too deep, it has a pretty profound impact on the results. Once each core sample has been taken, they go into a bag and the sample is analyzed at the lab.”
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