Farm Progress is part of the Informa Markets Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Serving: East
Corn+Soybean Digest

New Ways to Evaluate Soil


Soil quality is the most important base layer for all farm production decisions. That includes decisions about yield goals, plant populations, fertility programs and hybrid genetics, says Clay Mitchell, a Harvard-educated corn and soybean grower, futurist and new technology guru from Buckingham, IA.

In the past, farmers and landowners have tended to base both their management decisions and farmland sales on soil surveys that are at least a generation old, but now that’s changing rapidly, he says.

"There is no other physical asset that trades on its condition from a long, long time ago," says Mitchell. "In a modern farming paradigm, agriculture will require higher resolution analysis of soil capacity to effectively index farmland values and to determine what it is that we're buying after all."

New, analytical techniques to measure soil quality, nutrient content, texture and, ultimately, productive capacity will soon help to support land investment premiums and more productive, sustainable farm-management decisions, he says. "With recent technological advancements in soil analysis, we can measure nutrient content and physical properties of soil in ways that we haven't been able to before," says Mitchell. "This includes both how soil samples are collected and how those samples are prepared and analyzed."

Determining the nutrient profile in the rooting zone, typically considered to be at least 4 ft. deep, is the best place to start when evaluating a new farm's production potential, Mitchell advises. "You want to look for the depth at which nutrient levels change," he says.

Soil probes can easily mount on a pickup and take samples as deep as 4 ft., he says. "Using this technology is a way to inventory soil productivity of farms for resale value for buying and selling farmland," Mitchell says.

Deep soil samples are important for land sales, but most management decisions can be made with shallower sampling, he adds. "Shallow sampling can be fine as long as people are consistent with depth when making year-to-year comparisons and aware of the depth at which their soil fertility changes," says Mitchell. "Then the shallow sampling can work for annual sales."

Still, the marketplace is eager for even more accurate ways to factor soil-nutrient levels and stewardship into farm leases, he adds. "There is increasing professionalism falling into place affecting how leases are written for farm-investment groups," Mitchell says. "However, certain protocols need to be followed if specific soil-nutrient expectations are written into a lease."

If a farmer fails to maintain soil nutrient levels, landowners would like to be able to hold the farmer liable, and that is what drives the demand to specify soil-fertility levels in a farmland lease, explains Mitchell.

"At nearly $100/acre for fertilizer replacement levels on high-productivity grain farms, the fertilizer cost is between 20% and 40% of annual rent," he says. "A farmer who mines the soil is effectively lowering the returns to the landowner by that amount. Furthermore, if the farmer adds to soil erosion, soil fertility is lost in a way that wouldn’t be accounted for if the lease simply required application records."

Soil sampling

On the other hand, inaccurate soil-nutrient measurements can create financial headaches for both landowner and farmer, says Mitchell. In particular, soil-sample depth and lab error are two potential pitfalls that could hurt people who aren't careful when agreeing to these types of leases, he add.

"When landowners get soil samples, the assumption is that the nutrient value is the same, no matter the depth, and sometimes it is," he says. "However, the reality is that on most fields you can get drastically different results, depending on how deep the soil samples are taken."

Mitchell notes that on some new ground he recently sampled, the fertility levels drop off rapidly beyond the 0-6-in. depth. "On this ground, the topsoil is only several inches deep, but it had three times the nutrients than the soil at 6-12 in. in depth," he says.

The nutrient stratification that occurs on this ground tends to be fairly common in no-till situations, compared to fields where tillage mixes the nutrients more deeply into the soil profile, he says. However, even in situations with more tillage,  there's generally a drop-off in fertility below the 12-in. depth, he adds.

"So, if the landowner takes soil samples at a 12-in. depth after the farmer has applied fertilizer based on soil samples from a 6-in. depth, it may look like the farmer has cut the fertility application in half," says Mitchell. "In this case, the farmer might be held liable for what appears to be extreme changes in soil fertility, due to differing nutrient levels at two different depths. For strip-till farmers, there's also a potential liability issue, depending on whether soil samples are taken in the row, where nutrients are applied, or out of the row, where they are not applied."

Soil testing quality, depending on the lab, is the other significant challenge, adds Mitchell. "Landowners want to look at the old soil-nutrient levels and see the changes over time," he says. "However, if the quality of that data is bad, the implications can be huge."

What method a lab employs to test soils can result in highly variable outcomes, cautions Mitchell. "Using field-moist sample preparation methods can be much more consistent and accurate than the air-dried or oven-dried soil methods that many labs have been using for decades, but are now outdated," he says. “Keeping field samples in their naturally moist state preserves the integrity of the sample, and allows us to measure what the plant actually sees."

There is also an emerging class of soil measurements developing which can isolate soil particle-size distribution, providing a new level of insight into a field’s structure and productive capacity, says Mitchell. "These new, high-resolution soil-texture measurements are vastly superior to the two basic methods (the hydrometer and sieving approaches) used to determine soil texture in the past," he says. "The old methods only approximate soil texture based upon percent sand, silt and clay, not particle-size distribution."

Soil texture is critically important for properly managing soil water-holding capacity through irrigation scheduling, tillage considerations and variable-rate adjustments, adds Mitchell. "Soil texture is soil’s single most important physical property," he says. "A better understanding of a field's soil texture alone can provide critical information regarding water flow potential, water holding capacity, nutrient efficiency, compaction risk and (field) traffic load capacity."

Other factors to consider when evaluating land would be to look at maps generated by real-time kinematic (RTK) technology and radioactive, radiometric and electrical conductivity measurements. "These technologies can detect changes in slope and elevation due to erosion," says Mitchell. "Soil erodes from higher elevations to lower areas of the fields. And RTK maps can show where the soil has moved. We can also use RTK maps to compare where we have scraped out waterways and added the soil somewhere else in a field."

A very strong relationship exists between yield and topsoil depth, Mitchell says. "Sadly, the U.S. has lost half of all its topsoil and half of all its organic matter since being used for agricultural purposes," he says. "Yet, now we can measure and manage erosion using these new mapping technologies to see, verify and validate how much soil is moving and benchmark a farm's conservation efforts. Adopting this technology should also help motivate people to act in their own best interest."

Editor’s note: With this issue, Corn & Soybean Digest begins a periodic column featuring the latest thoughts and practices of Clay Mitchell, a fifth-generation farmer, Harvard University biomedical engineering graduate and Saltonstall Fellow at Cornell University. Mitchell farms approximately 2,800 corn and soybean acres with his great uncle Philip near Waterloo, IA. Together, they leverage technology and innovative soil conservation techniques to increase productivity, minimize cost and preserve the environment for future generations.

Mitchell is known for “thinking different,” a hallmark of Apple’s Steve Jobs, and what ultimately characterizes Americans in a competitive marketplace.

 Given American agriculture’s pre-eminence globally, “thinking different” can solidify our strengths in the marketplace.

TAGS: Soybeans
Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.