Cropland Reference Ecological Unit: A land classification unit for comparative soil studies

There is a growing consensus on a need for measuring the dynamic soil properties of croplands and even comparisons with a reference state or native land. These measurements and paired comparisons will create the capacity to determine soil health management effects and targets. However, the complex soil heterogeneity and climate variations make soil health potential variable and confound the effects of land-use and management practices and comparisons between soils from different sites. Identifying a discrete landmass unit where all soils have similar health potential will be critical in conducting meaningful comparative studies and measuring the impact of conservation practices. This methodological paper proposes and discusses a land unit, Cropland Reference Ecological Unit (CREU), that accounts for soil genoform and climate variabilities and covers an area with a presumably similar soil health potential. An example CREU has been developed, for one Major Land Resource Area (MLRA) in Nebraska, which is an area delineated based on the standard United States Department of Agriculture – Natural Resources Conservation Service (USDA-NRCS) hierarchical land classification system. This example portrays an actual difference in soil health for different land use and agronomic management practices can be determined by comparing sites under the framework of CREU. Evaluation of management effects on soil health indicators in a CREU will adequately illustrate the beneficial impact of such practices without being confounded by agroecological variations. This proposed framework addresses researchers' current interest in comparing soil health parameters among croplands and reference sites to benchmark soil health measurements, set soil health targets, and determine the effects of different management practices.