A regional soil classification framework to improve soil health diagnosis and management

Authors: DEVINE, SCOTT - University Of California, Davis; Steenwerth, Kerri; O'GEEN, ANTHONY - University Of California, Davis

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2021
Publication Date: 3/24/2021
Citation: Devine, S.M., Steenwerth, K.L., O'Geen, A.T. 2021. A regional soil classification framework to improve soil health diagnosis and management. Soil Science Society of America Journal. 85(2):361-378. https://doi.org/10.1002/saj2.20200.
DOI: https://doi.org/10.1002/saj2.20200

Interpretive Summary: Recent efforts have promoted the soil health concept as a way to engage growers in practices like cover crops, compost, crop rotations and reduced tillage that can build soil attributes that support a productive agricultural system. This research develops novel methodology to identify where in the soil landscape specific practices to build desirable soil attributes, or soil health indicators, should be implemented for their greatest impact. This is especially important as growers often have limited resources to broadly apply soil health management practices. This work was focused in an internationally important agricultural region, the Central and Coastal Valleys of California, covering 5.6 million hectares. This work has the capacity to increase the productivity of high-value specialty crops found in these valleys, including winegrapes, almonds and other tree crops, citrus, and vegetables. Specifically, we repackaged the USDA-NRCS Soil Survey Geographic

Technical Abstract: The soil health concept highlights soil’s many agroecosystem functions, such as support for crop growth, storage of carbon and water, and habitat for microbes that drive biogeochemical processes. Soil health research has developed soil tests to validate management strategies for healthier soils, such as cover crops, compost, crop rotations, and reduced tillage. Missing in this research agenda are soil health management strategies and diagnostics tailored to unique soils. The Soil Survey Geographic database (SSURGO) offers comprehensive estimates for a wide range of properties linked to soil health indicators. This research employs unsupervised classification of soil surface (0-30 cm) properties and root restrictive layers in an internationally important agricultural region, the Central and Coastal Valleys of California, covering 5.6 million hectares. K-means clustering of ten soil properties derived from SSURGO reveals groups distinct from US soil taxonomy. Clustering metrics, data visualization, and validation tests are used to justify a seven-region soil health conceptual model that divides the landscape into two broad classes, those with and without performance limitations (homogenous soil profiles). There are three pedogenic conditions limiting soil performance: (1) root restrictive layers that develop in wetter climates on stable landforms (2) salinity and alkalinity harmful to crops that develop in drier climates, especially where water converges and evaporates rather than percolates; and (3) shrink-swell properties in alluvial basins, making soils challenging to cultivate. Homogenous soil profiles, soils with restrictive layers, and saline-sodic soils are further divided into textural variants for a total of seven soil health regions. In reality, variation in soil properties is often continuous across the landscape and sometimes fractal in nature, but this research establishes a framework for evaluating soil health diagnostics according to geographically coherent, largely inherent differences in soil properties, demonstrating promise for how soil health management practices can be tailor-made to the landscape.