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Believe In Soil Biology

Believe In Soil Biology

More accurate soil test accounts for microbe activity.

By Lynn Betts

The mainstream soil tests you're using don't tell you the whole story, and are most likely leading you to over-fertilize. That's the contention of Dr. Rick Haney, a soil scientist with the Agricultural Research Service in Temple, Texas, who has researched soil testing for more than 20 years.

"Standard soil tests miss the mark because they don't account for biological activity in the soil," says Haney. "They use 50-year-old technology from heavily tilled soils, and they miss the organic N and P in the soil, the pool of nutrients available naturally in the soil."

NATURAL TEST: Rick Haney's soil health tool is an integrated approach to soil testing using both chemical and biological soils information. It's designed to mimic nature's approach to soil nutrient availability as best as can be done in a lab, the ARS soil scientist says.

Haney, a farmer in Oklahoma years ago before he went to school to earn a PhD in soil chemistry and microbial ecology at Texas A & M University, has always been bugged by high input costs in farming. "You can't do a lot about some of those input costs, like seed, but you can control the amount of fertilizer you're buying," he says.

"I've always thought we should be able to predict how much organic N is available naturally, so we could reduce commercial fertilizer accordingly," Haney says. "We've known the N is there, but we couldn't detect it."

New test measures microbial activity
That changed for Haney about ten years ago when he developed an enhanced soil test -- the first to account for biology in the soil. His breakthrough came when he began extracting organic nitrogen and phosphorus from the soil by drying and re-wetting it. "Microbes take in oxygen and respire carbon dioxide, just like you and me," Haney says. "If you dry the soil, and then re-wet it, there will be a burst of biological activity in the soil that peaks within the first 24 hours of re-wetting. That burst of bug activity and CO2 respiration is highly related to soil fertility."

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Haney teamed up with Will Britton, the inventor of a patented gel-technology in 1994 that measures CO2 respiration. Called the Solvita Soil Test, the technology uses a digital color reader to measure the magnitude of the flush or "burst" of carbon dioxide released after dried soil samples are moistened with water. The CO2-Burst is proportional to microbial biomass and directly tied to potential carbon and nitrogen mineralization. Solvita is now offered to crop consultants and growers at more than 35 labs across the country.

Soil health tool
Through cooperative research at the USDA/ARS Grassland, Soil and Water Research Laboratory in Temple, Texas and the Woods End Labs in Mt. Vernon, Maine, Haney and Britton developed an open-source, non-proprietary soil fertility evaluation method that goes beyond traditional chemical and physical methods used in most soil tests today.

It's called the Soil Health Tool. "This integrated approach to soil testing mimics nature's approach to soil nutrient availability as best we can in the lab," Haney says. "We don't measure just one thing to arrive at plant available NPK, we use an integrated approach. Dirt, or soil, is alive, and we're going to tell you how alive it is with this tool."

The Soil Health Tool measures the most important nutrient variables, Haney says, including microbial activity, water extractable organic N and P, water extractable organic carbon, and the ratio of carbon to nitrogen.

"When we test soil samples using the soil health tool, we put the raw data in an Excel file for the producer or consultant," Haney says. "We include the amount of N, P2O5, and K2O presently in your soil in pounds per acre. That includes both, the inorganic NH4-N, NO3-N, and PO4-P, as well as the amount of organic N and P that soil microbes will provide based on the Solvita test. Then we give you a dollar value of the nutrients currently in your soil, factoring in current fertilizer prices."

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The Soil Health Tool requires the user to use an online calculator to enter crop type and yield goal. The tool will then calculate N, P2O5, and K2O needs in pounds per acre to produce the stated yield goal. The spreadsheet also includes amounts for nitrate-only needed, the figure most standard soil tests provide. "The producer or consultant will get a figure for the amount of nitrogen saved in dollars per acre by fertilizing according to the test that accounts for microbial activity and organic N and P available in the soil," Haney says.

Test shows less N needed
Almost every time, Haney says, standard soil tests show more fertilizer is needed than the soil health tool shows. Better soils, those managed for higher microbial activity, show higher savings. "The 14,000 soil samples we've analyzed over 7 years indicate average dollar savings of $27 an acre for nitrogen, $47 an acre for phosphate, and $68 an acre for potassium since 2007," Haney says. "The total value of the nutrients saved by using the tool was more than $100 million, at an average NPK savings of $143 per acre." From his data, Haney believes nitrogen fertilizer could be cut by 15% to 20% with no yield loss on average.

In one experiment a few years back, Haney paid 5 farmers $200 an acre to establish 5-acre control plots on wheat fields that had no fertilizer at all. "To a man, they were disgusted after that experiment," Haney says. "They were all putting on too much fertilizer. One of them believed the data, used the soil health tool, and saved $60,000 in inputs. Every farmer should have test plots for comparisons -- they have to keep seeing the differences over time, I think, to be convinced."

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The tool also uses water extractable organic carbon and nitrogen amounts and organic carbon to nitrogen ratios to calculate a soil health number that can vary from 0 to 50.  "This soil health tool gives you a fix on how badly degraded your soil is," Haney says. "And it gives you a recommendation on what can be done to increase the soil health number -- usually a suggested cover crop mix."

"Cover crops are the missing link to soil health. You have to have something growing in that soil all the time to feed the microbes that build soil," Haney says. "Living plants produce the life underground, and they suck nitrates back into the system." Haney's recommendation for the fastest way to build healthy soil is to use a combination of cover crops, manure, and animals on the land. "You could see a significant difference in as little as three years doing that, but otherwise it could take years to build the organic matter and high level of microbial activity you need for healthy soils," he says.

Betts writes from Johnston, Iowa.

Try it free
To gather data and promote the use of the Soil Health Tool, Haney and the ARS lab in Texas have been running soil samples for producers and consultants for free for five years. They ran about 900 samples in 2011; 3,000-plus samples in 2012; and doubled that last year when they ran 6,200 tests.

"We'd like to hand this off to private or university labs," Haney says. "I know of three labs -- Woods End Labs at Mt. Vernon, Maine; Brookside Labs at New Bremen, Ohio; and Ward Labs at Kearney, Nebraska -- that run the Soil Health Tool, and I'd like to see more of them."

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The test applies to any soil in the country. If you're willing to share your yield and fertilizer inputs with Haney for 3 to 5 years, you can still get up to 40 samples from up to 20 fields tested for Soil Health and NPK for free.

Here's how:

Fill out and submit the online form for the test here.

Take enough 0-6 inch samples to fill a half-quart zip lock bag per field (no cloth bags!). Label each bag with your last name and a field number. Include an accurate, itemized list of not more than 40 samples. Send the samples to Rick Haney, USDA/ARS, Grassland Soil and Water Research Lab, 808 E. Blackland Road, Temple, TX, 76502 (tel. 254-770-6503).

You will receive results in an Excel spreadsheet along with a built in calculator for crop nutrient requirements so you can easily calculate your own fertilizer needs.

Traditional Soil Tests vs. Soil Health Tool:

What they test for

 

Traditional soil tests

Soil Tests in Nature's Image

     

Soil N

NO3-N

NH4-N

NO3-N

WETN*

Solvita**

Organic N

Organic C:N

MAC WEON***

N min

Soil P (phosphate)

ICP P or PO4-P

ICP P

PO4-P

HeA

Solvita

Organic C:N

P min

% Water P/H3A P

% P/FeAl

Ca/FeAl

Soil K (Potassium)

Yes

Yes

Soil pH

Yes

No

% Organic Matter

Yes

No

Microbial Activity

No

Yes

Water Extractable Carbon

No

Yes

Carbon:Nitrogen Balance

No

Yes

* Water extractable total nitrogen

** Microbial respiration/activity

***Water extractable organic nitrogen

TAGS: USDA
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