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UNL scientists propose a novel land classification method for comparative soil studies

In collaboration with the USDA Natural Resources Conservation Services, Bijesh Maharjan, associate professor and Extension specialist, Department of Agronomy & Horticulture, University of Nebraska-Lincoln, and Saurav Das, research assistant professor, Department of Agronomy & Horticulture, University of Nebraska-Lincoln, have been furthering the science of soil health.

In 2020, Maharjan and Das proposed the “Soil Health Gap” concept that compares soil health in cropland and native undisturbed land, and is a measure of soil health decline in croplands since cultivation began, and simultaneously sets potential soil health targets and goals (Figure 1). However, comparing croplands with reference sites or among themselves can be confounded by agroecological variations, including the vast heterogeneity in soil and climate. Differences in precipitation and soil types can create distinct inherent soil properties and soil health potential. These local factors allow the soil to respond differently to management practices. Therefore, comparative studies in soil health should consider limiting the scope in which comparisons can be made.

Das and Maharjan, in their recent publication in September 2022, proposed and discussed a new landmass classification unit, a Cropland Reference Ecological Unit (CREU), for an unconfounded comparison of land use and management. In a CREU, cropland of different managements and the identified reference sites can be compared under a homogenous boundary of soil and climatic factors. Cropland Reference Ecological Units, together with the Soil Health Gap concept, will offer a method to describe the true soil health potential of land. The effectiveness of conservation practices would be illustrated better if evaluated within the scope of this method.



The CREU will provide a leveled platform for comparative studies where soil health can be assessed and compared for a group of sites that have a similar soil health potential. If measured in the same CREU, soil health at different sites will provide actual differences due to land use or conservation practices. The CREU provides a geographically universal framework for comparative studies by accounting for the different native potentials based on the soil and climate.

The Cropland Reference Ecological Units are created using the existing NRCS land resource hierarchy (Figure 2), where Major Land Resource Area (MLRA) are segregated into Benchmark Ecological Sites, which are ecological sites paired and categorized by benchmark soil. The benchmark ecological sites are further divided into Dominant Ecological Sites, which represents ecological sites relevant to more than 90% crop cover in the MLRA. Identified Dominant Ecological Sites are divided as a function of soil association and precipitation to create the CREU (Figure 2).



Workflow for the development of Cropland Reference Ecological Unit and subsequent pairing of reference sites and cropland for comparative studies. Courtesy graphic

The manuscript published in the Elsevier Journal, Ecological Indicators, illustrates the methods of developing a CREU. This proposed framework addresses the current interests in comparing soil health parameters among croplands and reference sites in a homogenous boundary of soil and climate to set attainable soil health targets. The manuscript can be downloaded at https://doi.org/10.1016/j.ecolind.2022.109468.


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