Any solid fertility program needs to start with a soil test, showing areas lacking and where improvements can be made. Among the many reasons to test soil, more targeted use of costly inputs is a significant economic benefit.
“It’s generally more economical for farmers to use the right rate of nutrients on the right acre rather than making a blanket application,” says Nebraska-based AgriGold Agronomist Sam McCord.
McCord recommends annual soil testing, especially for high-management, high-yield operations that pull a lot of nutrients from the soil each year. He also encourages farmers to follow the 4Rs of nutrient stewardship to ensure a balanced supply of plant-available essential nutrients and limit nutrient loss.
“If you don’t want to make that investment every year, I recommend at least once every three years,” he says. “But if you harvest a big crop, that’s a good time to go back, test soils again, and evaluate what nutrients were utilized to fertilize the next crop better.”
Fall soil testing is beneficial because “it shows your soil at its weakest point once the crop comes off,” says McCord. Testing soil in the fall also gives farmers more time to think through their fertility program and talk it through with industry partners like agronomists or certified crop advisers. In arid conditions, nutrients like potassium can get even more tied up in the soil. In that case, it may be better to wait until late winter or spring to pull samples when there’s more moisture, resulting in more accurate results.
Drought challenges affect nitrate carryover.
“Having balanced and available fertility is extremely important to making a crop more drought tolerant,” McCord says. “When a crop is short on a nutrient, it pulls in more water than it needs in an attempt to correct that imbalance.” Farmers in Nebraska and other areas dealing with drought may also have high soil nitrates in the fall, which could lessen their 2023 fertilizer needs.
“If you fertilized for a 200-bushel crop and only harvested 120 bushels per acre, your crop didn’t use all the nitrogen you applied,” explains McCord, adding that some nitrogen is mineralized from the soil.
“In those scenarios, I recommend pulling deeper, zero-to-two-foot cores and pulling your zero-to-six-inch/zero-to-eight-inch cores for your topsoil test. There could be more pounds of nitrogen deeper in the soil than you realize, and it’s better to know than to guess.”
Excess nitrates can be washed away by an overly wet winter. But planting a cover crop like rye or wheat can help soils retain more than 25 pounds of nitrogen an acre.
“Those deep-rooted crops capture the nitrates and hold them in the root zone for your crop the following year,” McCord adds, cautioning farmers to terminate that cover crop early in the spring to preserve moisture.
Soil testing methods
McCord prefers grid or zone testing to composite sampling.
“There are 43,560 square feet in an acre, and I often see a lot of variability in just 20 to 30 feet when walking fields,” he says. “The smaller you can make the grids, the better.”
For each grid or zone, he recommends farmers pull 10 to 15 cores.
“When I’m sampling, I’ll jump off the four-wheeler and pull 10 or 15 cores, put them in the bucket, mix them and then dump it into a bag,” McCord explains. “That way, a specific area is covered versus random pulling of cores.”
He recommends farmers do complete soil tests that cover “everything from your macro, micro, and secondary nutrients, along with base saturation and organic matter.”
Putting test results to work
Soil test results typically include measurements and an interpretation value (low, optimum, or high), as well as recommendations for amendments or nutrient application. When analyzing soil test results, McCord recommends using the information to make a realistic yield goal and then figuring out what’s needed in terms of fertility to reach that goal. He prioritizes the test results as follows:
- Soil pH should ideally be in a range of 6.0 (slightly acidic) to 7.0 (slightly alkaline), depending on where you’re located. If pH isn’t in the optimum range, nutrient availability may be negatively impacted. A low soil pH might require lime application.
- Nitrate levels can give you a good idea of carryover nitrogen for the next year, though it’s not exact. To calculate what it is in pounds per acre, simply multiply the parts per million number by two.
- Phosphorus (P) helps plants store energy for growth and reproduction. The optimum level depends on the soil testing method used.
- Potassium (K) is necessary for plant uptake and translocation. Most soils contain a large amount of K, but as discussed, it may not always be available.
- Cation exchange capacity (CEC) indicates how much capacity your soil has to hold cations, aka nutrients and minerals. Look for your CEC to be above ten milliequivalents per 100 grams.
- Base saturation helps ensure you meet all essential mineral and nutrient ratios for better uptake and plant growth. Ideal ranges are 5%-7% K, 75%-80% calcium (Ca) and 12%-15% magnesium (Mg), depending on soil type.
- Micronutrients (boron, copper, iron, manganese, and zinc) ensure that high-value crops have the proper nutrition.
“One of the main things I run into is not enough people give manure credit, particularly for the phosphorous it adds,” McCord says. “If you spread manure on the closest fields for convenience’s sake year after year, it likely will test high for phosphorous. Soil testing can determine where that manure is needed most.”
Optimizing seed selection
“The best way I can learn about a farm is by analyzing soil test data. That helps tell me what corn hybrids will be best on that acre,” McCord says. “Getting the right product on the right acre is the AgriGold advantage.” Don’t hesitate to reach out to your local AgriGold agronomist for support testing soils or putting those results to work specifically for your area.“We never get tired of talking to our farmers about maximizing performance,” says McCord.
AgriGold offers unique hybrids paired with the latest agronomic knowledge and data to achieve exceptional crop performance yearly. Explore our corn hybrids here.