Going beyond the basics | Existing soil tests focus on chemical components, ignoring biological and physical factors
Compared to an actor or astronaut, a soil scientist is not a glamorous profession. Specializing in soil testing is even less glitzy, so research in the area attracts meagre funding.
That could be why soil tests have changed little in the last few decades. Soil labs across North America still measure the basics: nitrogen, phosphorus, potassium, micronutrients and soil pH.
Bianca Moebius-Clune, senior extension associate in the soil sciences department at Cornell University, said the established methods have a role but it’s time to adopt more meaningful tests.
“Standard soil testing has been foundational to our success in agriculture. It has allowed us to identify a very specific (and) fixable constraint: a nutrient deficiency. If this field is low phosphorus, you’re not going to get the maximum yield potential,” she said from her office in Ithaca, New York.
“More and more we’re understanding that beyond nutrient deficiencies… there are really biological and physical soil constraints that we’ve never identified before. Those are largely what are limiting production today and what are limiting our ability to make progress on air and water quality.”
Moebius-Clune is part of a U.S. effort to rejuvenate interest in the importance of soil health. The Farm Foundation, an agricultural think tank located in Illinois, launched a Soil Renaissance project last December in an effort to improve soil health and make it a key factor in land use management decisions.
Neil Conklin, Farm Foundation president, said the project could be a bridge between conventional and organic agriculture.
“We’ve got to start thinking as soil beyond just as a growth medium to stand plants in,” Conklin said. The Farm Foundation has developed a plan to advance the importance of soil, but identifying techniques to measure soil health is key, Conklin said.
“If we can’t explain to producers and to other folks, how do we measure soil health so you have a benchmark and see what it does for you, then it’s going to be very difficult to make progress on these other fronts.”
Moebius-Clune, head of the measurement committee for the Soil Renaissance project, has devised a new method, called the Cornell Soil Health Test, to evaluate the status of soil.
The Cornell Soil Health website notes there are three components to soil health: physical, chemical and biological.
Existing soil testing focuses primarily on the chemical component, mostly nutrients, and ignores the biological and physical properties of soil, the website states.
“We can’t continue to only look at nutrients. We have to look at the rest of the picture,” Moebius-Clune said.
“There are physical processes that have to function well in the soils so we can sustainably grow crops. Without paying attention to that, we’re really missing most of the picture of the status of the soil.”
She said Cornell agricultural extension scientists frequently talk to growers confused about their cropland. Farmers are applying adequate nutrients but the land isn’t as productive as it should be.
The Cornell test measures other soil properties, like compaction, to assess deficiencies in soil productivity.
“Physical and biological processes, in themselves, have a huge impact on crop productivity and crop quality,” Moebius-Clune said.
“If you have a hard pan eight inches down… not only does that impede growth of roots and stress plants, it specifically influences nutrient cycling…. Any water and nutrients that would otherwise be available to that plant that are perfectly available under the pan, the plant can’t get to.”
The Cornell soil test also evaluates the stability of aggregates, or clods of earth within the soil.
Jon Stika, a U.S. Department of Agriculture scientist in North Dakota, has been promoting an on-farm test to evaluate the biological health of soil.
Dropping an aggregate, or clump of soil, in a tube of water and watching how quickly it dissolves indicates the level of biological activity because soil bacteria and fungi produce mucus and other sticky substances.
“In the process of them exploring the soil, they leave the sticky substance behind. Those are the real basic sticky substances that glue the sand, silt and clay particles together,” Stika said. “It’s the biology that makes the glues that holds aggregates together.”
Moebius-Clune said such a test is a useful visual demonstration but it doesn’t provide a number, or a way to measure the soil’s biological activity.
She and her Cornell colleagues have developed a way to measure the stability of soil aggregates: an essential nugget of information for growers.
“If you don’t know whether potassium or phosphorus is low, you don’t know what nutrient to apply,” she said.
“If you don’t know whether you have low stability in aggregates… then you don’t know what (soil) management to apply.”
Rick Haney, a USDA soil scientist in Temple, Texas, said it’s critical to measure the level of biological activity in soil because microbes have a significant role in nutrient cycling.
“The problem is that conventional (testing) tools are not measuring the right soil characteristics,” Haney said in a USDA press release.
“They test for inorganic nitrogen in the form of nitrate but that’s just one form of nitrogen available to the plant.”
Several years ago Haney and his USDA colleague Daren Harmel devised the Haney Soil Test, which involves drying and rewetting the soil to measure all the elements that influence soil fertility.
Harmel conducted a four-year study to evaluate the Haney test’s performance, looking at wheat, corn, oats and sorghum crops in Texas. He applied fertilizer rates based on traditional soil tests and rates according to the Haney Test.
The Haney fertility recommendations reduced fertilizer use by 30 to 50 percent and increased profits by seven to 18 percent for the wheat, oat and sorghum fields.
“The idea here is not anti-fertilizer. The idea is the right amount of fertilizer,” Haney said. “If we’ve been putting on 200 lb. of nitrogen to grow 150 bushel corn and (if) we find out that we can put on 130 lb. to grow 150 or 200 bushel corn, well that’s what we’re after.”
Haney said private labs in Nebraska, Ohio, Maine, California, Tennessee and South Africa are using his soil test.
Some private labs may be using the Haney Test but land grant universities in the U.S. are not.
Haney said conventional soil testing methods are entrenched at major universities and it is difficult to convince scientists to adopt a new approach.
“You’re seeing a lot of pushback from universities because they have all this data…. If you’ve got this nitrate (in the soil) then you need this much nitrogen to get this yield.”
Moebius-Clune agreed that introducing a better mousetrap is a challenge in science, particularly when nothing has changed for decades.
“They (soil scientists) have over 100 years of nutrient recommendations and knowledge and people building their careers on it.”
Haney said he doesn’t want to overthrow and dispose of a century of soil fertility research, but North American farmers are using an excessive amount of fertilizer and that cannot continue.
“Let’s get as much as we can from the natural system by being smart about how we manage soil,” he said.
“This (Haney) test isn’t designed to replace things. It’s designed to tell a better story, more insight into what’s happening in our soils.”