How Targeted Soil Testing Can Benefit Crop Health and Farm Finances

The foundation of a grower’s operation is their soil. In addition to providing structural support, healthy soil provide crops with the vast majority of the essential micro- and macro-nutrients they need to thrive. They hold water, store excess carbon, and provide important habitat for beneficial microbes and fungi. 

The best way for growers to get to know their soil — what it has, what it needs, and how best to support both soil and crop health — is through periodic soil testing. 

“You can test for all the micro and macro nutrients, you can test for salinity — you can get the full spectrum,” says Sarah Taylor, Sales Agronomist with Sound.

Most growers use soil tests to determine what kind of amendments they might need. If testing reveals a grower’s soils are too acidic or too alkaline, different methods can be used to help bring the soil to a more optimum, neutral pH and ensure plants have access to important nutrients, like phosphorus. In both alkaline and acidic soils, plant-available phosphorus forms strong bonds with minerals and soil particles and becomes inaccessible to plants. 

“There’s a lot of value in understanding what’s going on in your soil,” says Sarah. ​“If you’re applying phosphorus, but your plants still have a phosphorus deficiency, there’s no way to tell what’s going on without a deeper dive, and soil testing will get you there.”

Sound takes a very precise approach to soil testing. First, growers interested in Sound’s SOURCE™ for Corn or Soy can use three key soil parameters — pH, organic matter, and cation exchange capacity (CEC) — to predict where the microbiome activator will perform best. For certain fields of interest, the agronomy team then conducts targeted tissue and soil tests to find indicators of where SOURCE is performing well. By conducting these tests in the same area, Sound’s agronomists can paint a better picture of what is happening above and below the soil. 

“If a tissue test shows higher levels of phosphorus, that’s great because it means more phosphorus is reaching the plant, but we want to know why,” Will Llewellyn, Senior Sales Agronomist. The team also takes soil samples at the plant’s root zone in order to directly correlate SOURCE’s impact on plant and soil health with yield data collected at harvest — it helps them better understand the big picture.

“It’s hard to build a full understanding around a piece of data in a tissue test by itself,” he explains. ​“If there’s a higher pH in this area, phosphorus is also tied up in the soil. SOURCE may be stimulating the microbes that free tied-up phosphorus and bring it to the plant — it’s doing this job effectively. But you need all that data together to be able to tell that story.” 

Because SOURCE stimulates the soil microbiome, Sound’s agronomists are also interested in understanding the health of those microbes, and there’s a test for that too — the Haney Test. Standard soil tests provide growers with the CEC, pH and OM, but the Haney Test can be used to estimate microbial activity. 

Will explains that the Haney Test measures CO2 or soil respiration. Microbes provide plants with important nutrients found in the soil in exchange for sugars that microbes eat. Since CO2 is the byproduct of the microbes’ metabolism, the test can act as a proxy for the amount of microbial activity in the soil. 

The Haney Test provides a Soil Health Score which is calculated using multiple soil measurements. ​“A high Soil Health Score score can mean either that there are fewer microbes working at high efficiency or a lot of microbes working at a normal level, but either way it’s a good signal that a grower has healthy soils,” says Sarah. 

“We want to be tuned into that information,” says Will. ​“With SOURCE, if a treated field is able to increase microbial activity, then we want to see if there is a correlation in these soil respiration measurements.”

Growers seeking to understand how their soil health is changing over time and their soils’ microbial activity may find that the Haney Test can provide useful information as they try to influence respiration rates, says Will. 

“For growers curious about soil health and who want to go more in depth, a Haney Test is a good way to get a baseline for that respiration rate or microbial activity across their fields,” says Will. ​“It’s a way to get that baseline and then start looking for ways to improve.”

Soil tests can be a useful way to track changes over time, whether that’s across a single season or several years. Sarah says some may think that pH, OM, and CEC do not change within a season, but they can, especially if growers are widely applying amendments.

“If a grower is flooding their fields with manure, they may not know what their OM is going to look like,” she says. ​“You also might not be able to predict what the effect on pH is going to be.” 

In general though, most growers use more infrequent grid sampling of larger field areas to identify problem areas where soil health is poor or key nutrients are missing and then focus in on those spots.

“Grid sampling is a common practice, but it’s also a big investment,” says Will, adding that most growers have results on file from within the last five years or so. Problem spots can then be tested more frequently to monitor specific deficiencies. Since altering soil health or pH can take time, ​“growers will likely want to track those trends and see if they need to make additional adjustments,” he explains.

Sarah adds that growers may already know the spots in their fields where crops don’t thrive, and soil sampling in those specific locations can help them gain a better understanding of what those areas need.

“That’s where precision ag wins,” Sarah says.

Soil testing can also be a way to reduce input costs by ensuring applications are precise and necessary. For example, targeted mid-season soil and tissue testing could help growers assess nitrogen levels and decide whether a late nitrogen application is really needed. 

“If you look at your soil test results and they seem really depleted, but when you look at your plant tissue results and they are healthy, with the nutrient levels they need, then you know that the soil’s nutrients are going in the right direction,” she explains. 

Sarah says there’s also a significant opportunity for growers to use soil tests to reduce input costs by applying fertilizer efficiently, especially this year. In addition to bottom line benefits, reducing nitrogen application can also boost on-farm soil health and sustainability, but when nitrogen costs are low growers may apply fertilizer more liberally as an insurance measure.

This year, however, fertilizer prices have skyrocketed. High input costs for producers, impacts of the COVID-19 pandemic, and increased demand have all helped drive prices up. 

“Because it’s going to be more expensive to buy fertilizer, it’s important to understand what is already in your soils,” she says. Then, SOURCE may be able to help unlock nutrients already existing in the soil and make them available to the plants.

Although there’s an upfront cost to having a soil test done, Sarah says growers who know what is in their soil will only have to pay for only what they need, granting some independence from the supply chain impacts this season.

“This year specifically is going to be a big year to start testing your soil in order to better understand what you’re doing and how to minimize input usage.”