Wed. Dec 7th, 2022

In a September 2022 publication, two researchers from the Panhandle Research, Extension and Education Center (PREEC) proposed a natural land classification unit for comparing soil samples.

“First, acknowledgment, understanding how soil is important; it’s not just dirt, it is a life sustaining finite resource we have on the earth. And we need to preserve it, conserve it, I think that’s the whole idea,” Bijesh Mahargan said.

Maharjan, associate professor and PREEC specialist, and Saurav Das, research assistant professor, both serve in the Department of Agronomy and Horticulture, University of Nebraska-Lincoln. They collaborated with the USDA Natural Resources Conservation Service (NRCS) to promote soil health evaluation.

The project initially began in 2020 when the researchers teamed up to tackle soil conservation “from the ground up.” Topsoil, the top six to eight inches, has a finite resource of nutrients that can deteriorate over time.

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“It’s like a movement, suddenly people woke up and felt we need to take care of our soil resources,” Maharjan said. “Topsoil is where the magic happens and soil as a resource needs to be conserved.”

Das said soil health became a hot topic with growing concern about preserving topsoil for future generations and food security. The pair asked the question, how can a farmer determine if his topsoil is good or needs improving?

“There are definite measurements for one pound of rice or one pound of something, but for soil, we don’t have the same kind of measurement or benchmark,” Das said. “I talked to (Maharjan), and he also had some ideas and we sat down to figure out how we can actually put numbers to define soil — is it good or bad?”

The concept, named Soil Health Gap, effectively defined the difference between undisturbed native soil and soil health in cropland systems. Soil Health Gap can be used as a benchmark measurement tool to guide soil health management decisions and goals.

“Let’s say your native land has a soil organic matter of 4% and your farmland has 2%. You know that there is a gap of 2%, during different kinds of management practices, we might have lost the 2% organic matter,” Das said. “That is why we came up with the concept we call Soil Health Gap.”

The two researchers carried the concept further by sampling soil organic matter from grassland, no-till and conventional-till cropping systems and exposed subsoil.

“We saw that there was an exponential decline in soil organic matter across different types of land use,” Das said. “That gave us a set of numbers to define the natural state of soil health which hasn’t had any kind of farming practices and you can compare that to your cropland.”

Soil organic matter (SOM) is a carbon component of soil consisting of plant and animal tissues in various stages of decomposition. Maharjan said SOM was used as a consistent measuring tool because carbon organic matter is central to properties and processes that happen in healthy soil.

“Organic matter precipitously drops from unmanaged land to reduced-till cropland, to no-till cropland, to exposed subsoil land,” he said. “The more you work the soil, the more you are losing (SOM).”

Grassland or undisturbed native pasture was used as the reference land.

“Wherever the minimal disturbance has happened, so pasture and rangeland where there can be grazing, that’s what we call reference land,” Maharjan said. “Now, you’re benchmarking against that. Otherwise, in the past, people can say do this and that and make erroneous, outrageous claims that you can improve your soil. Now, we are setting a ceiling.”

The Soil Health Gap study found that cropping systems should be compared to reference land within the same soil type and climate conditions. Localized differences in soil type and precipitation allow the soil health to respond differently to management practices.

“We realized that healthy soil will be specific to the region. What is healthy in Lincoln may not be possible in the Panhandle,” Maharjan said. “So, we decided soil health has to be benchmarked —Panhandle healthy soil will be referenced with native soil in the Panhandle.”

The Soil Health Gap study encouraged the researchers to further pursue a reference land classification system. Cropland Reference Ecological Unit (CREU) would compare all cropland to identified reference land found in the same ecological area. The comparison system will set a natural framework to compare soil health within the same soil type and climate conditions.

“Can I compare my cropland with native land near Lincoln? Most likely not, it has to be very region specific,” Maharjan said. “The CREU talks about a unit of landmass where you can compare the soils from different sites. It shouldn’t be just geographic like Scotts Bluff County; it should be more natural boundaries.”

The theory will mean all soil within an identified land unit can have similar SOM potential.

Das further explained the significance for developing CREU in Nebraska by noting that the Panhandle receives, on average, half the amount of annual precipitation as eastern Nebraska and the Panhandle soil type is more sandy. If SOM is on average 7% near Lincoln, it is not reasonable to expect the same percent to be achieved near Scottsbluff.

“All the soil has different potential, what (SOM) can be reached, then you can compare each land within this natural boundary,” Das said. “Initially, the soil all has the same potential in the land blocks, then management practices or something has happened which made (SOM) to go down or up.”

The researchers worked with NRCS existing land hierarchy of Major Land Resource Areas (MLRA) as benchmark land sites. The CREU model was established by further segregating MLRA sites by soil characteristics and precipitation.

“The NRCS already has their own land classification system. We are taking that and then divvying it up even further,” Maharjan said.

Once CREU sites are designated and soil samples are compared to the identified reference land or native rangeland. As a result, management practices can be addressed.

Maharjan said that typically cropland in Scotts Bluff County is 1-2% SOM but native land has been found at 4% SOM.

“So, we can do better,” Das said. “When soil is healthy, it can store more water, more moisture for the crop and your production can be better compared to unhealthy soils.”

Maharjan said, “It’s hard to reach (4% SOM), it’s a ceiling but at least now you know. If you manage the land properly, you can shoot for four.”

The researchers both stress the importance of being good stewards of land.

“If topsoil is healthy and rich, it has its own natural system that will cope with severe weather better,” Das said.

The concept of CREU can be used anywhere to promote soil health. Maharjan and Das are moving into the next stage of CREU — demonstrating and validating.

With the aid of funding and in cooperation with NRCS, soil sampling within identified land units and analyzing will be underway. Maharjan said his PREEC lab is currently looking for an assistant to aid with organization and the additional workload.

The researchers said the end goal is to establish a web-based tool for anyone to use.

“Our end goal is an interactive map for the state where anybody can go in and check their land against some reference land and find the (soil health) gap,” Maharjan said. “A soil health interactive map, it will be unique for the nation.”



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