Soil scientist Rick Haney has conducted countless traditional field trials and plot tests in his career to compare fertilizer responses on various crops. But, in the back of his mind, he always had this nagging question: "Why does the control plot yield so well with no added nutrients?"
"I kept asking myself, 'How are we growing 60-bushel corn with no [added] nitrogen?' It's coming from somewhere," Haney says.
In 2012, his curiosity led to the development of a unique soil health tool. It's a soil testing so unique, the soil-health community now calls it "Haney's Test."
Soil-health guru Ray Archuleta, a conservation agronomist with the USDA's Natural Resources Conservation Service, says of Haney's test: "The interest continues to grow because of the test's precision and because it considers the whole of the plant's environment in the field. In medicine, we see a blood test as an important tool in 'whole-body' diagnostics. The Haney Test is like a blood test for the soil."
WHAT IT IS
The test measures water-soluble organic carbon and soil biological activity to assess nutrients available to plants. Haney, who is a USDA-ARS soil scientist at the Grassland Soil and Water Research Laboratory, in Temple, Texas, tells its origin story: "As we sought answers to why the control plot could yield 60-bushel corn [with no supplemental fertilizer], we began finding the microbial populations in soil are a vital component in determining what nutrients will be available to the plant through nutrient cycling and carbon mineralization."
Nutrient cycling involves the activity of soil microbes that use atmospheric oxygen, water and soil organic compounds (carbon, nitrogen [N] and phosphorus [P], unavailable to plants in their elemental form) to form plant-available nitrogen and phosphate plus CO2.
"Working with this knowledge, we came to the realization that field conditions in nature and the conditions we have traditionally used in testing soil samples for nutrients in the laboratory are essentially apples and oranges," he says.
HOW IT WORKS
In nature, rainwater -- not the acids used in most laboratories for traditional soil-sample analysis -- is the primary solvent available to initiate mineralization of soil carbon compounds.
"A plant only 'sees' water-soluble carbon, so we use water in our tests for nitrogen," Haney explains. "Also, literature dating back 100 years or more shows scientists in Russia knew there was a link between soil fertility and the release of CO2. That CO2 release is coming from soil microbes doing their job in nutrient cycling. So, we test for that also."
The result is a much more precise look at available nitrogen and nitrogen that likely will be available (given microbial activity) during the life of the crop.
"I like to say soil organic matter is the house microbes live in, while water-extractable organic carbon is the food they eat," Haney explains.
In a further nod to mimicking what the plant root encounters, Haney says his test uses several naturally occurring organic acids in concentrations likely to be encountered in field soils to test for phosphate, potassium [K], calcium, iron and aluminum.
Another factor in overall soil fertility is the wetting, drying and rewetting of soils by natural precipitation, Haney explains. "Research shows microbial activity flourishes during a wetting event then begins to slow with drying, only to flush again with additional rainfall. Therefore, we've included a wetting and drying cycle in our test to measure CO2 release, indicating microbial activity in the sample.
"We're trying to mimic how the soil responds after rainfall in the field. This is much different than what we have been doing in the laboratory," he says.
WHAT'S IN IT FOR ME?
Skeptics of the procedure ask, "Why is all this important? We've been successfully using traditional soil-testing procedures for years."
Haney says the importance is increased precision of the new test and its ability to save significant amounts on fertilizer inputs. (See "Haney Test vs. Traditional" below.)
"Essentially, the research behind the test shows traditional soil-testing methods have been missing nearly half of the nitrogen in the sample for more than 70 years," Haney says. That translates into a lot of wasted dollars for fertilizer.
WHERE CAN I GET ONE?
Growers can send samples -- just like the samples they would pull for traditional soil testing -- to Haney at the USDA-ARS facility or to other soil analysts, such as Ward Laboratories Inc. or Quorum Laboratories LLC.
Haney says the biggest impact of the new test is to give farmers the confidence to try something different, whether that's reducing N, P, K inputs, changing tillage practices or making a focused effort to increase fertility of their soil with the use of cover crops.
"When we return results from our facilities in Temple, the grower gets an Excel file with tabs for N, P, K, Soil Health Scores, Nitrogen and Phosphate, plus an analysis explanation sheet," Haney explains. "The Soil Health Score includes an analysis of organic and inorganic carbon, carbon-to-nitrogen ratios and a look at how efficiently the microbes in the field are converting the carbon present."
The test takes two to three days in Haney's lab in Temple and costs $42 per sample. For a cost calculator using the test's results with your own figures, visit research.brc.tamus.edu/home/index. Or for more information on the test and the peer-reviewed research supporting it, email Haney at Rick.Haney@ars.usda.gov.
Haney Test vs. Traditional
"To give an example," Rick Haney says, "if two soil samples are sent to two labs, one for our test and one for the standard test, we have seen the following results for a yield goal of 200 bushels of corn."
SOIL 1: Standard test would only test for nitrate N:
Nitrate Nitrogen 20 pounds
Soil Respiration 20 parts per million (ppm)
Water-Extractable Organic Carbon 200 ppm
Water-Extractable Organic Nitrogen 20 ppm
N Recommendation: 180 pounds
SOIL 2: Haney test adds additional information to reduce N recommendations:
Nitrate Nitrogen 20 pounds
Soil Respiration 200 ppm
Water-Extractable Organic Carbon 400 ppm
Water-Extractable Organic Nitrogen 40 ppm
N Recommendation: 100 pounds
"Both samples have the same measured nitrate N. But in the standard test, the nitrogen recommendation is 180 pounds, while the Haney Test recommends 100 pounds," Haney says.
"At 40 cents a pound for nitrogen, this is a savings of $32 an acre."
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