Improvement of soil properties maps using an iterative residual correction method

Accurate mapping of soil properties is vital for many applications, yet existing models for digital soil maps often underestimate their spatial variability or prediction uncertainties, which introduces risk for applications such as irrigation and drainage management. This study introduces an approach, iterative residual correction (IRC), to update existing probabilistic soil maps when new soil observations become available. We demonstrated its application for enhanced soil mapping performance using a Californian case study. To implement this, we first generate prior probabilistic soil property maps using a pruned hierarchical Random Forest (pHRF) method. These prior estimates are then refined by integrating additional soil profile data and iteratively adjusting residuals of distribution of soil properties (reducing differences between observations and prior predictions) pixel by pixel. For this purpose, we employed Random Forest regressors to gradually adjust the soil property distributions and incrementally correct prior bias. Updated soil maps were evaluated over California and at 1 km resolution to test the methodology, using additional soil observations from the World Soil Information Service, the Soil Characterization Database, the University of California Riverside, and the United States Department of Agriculture Agricultural Research Service. Posterior soil texture predictions achieved an RMSE below 10, a 7 % relative reduction in errors (mass fraction of the fine-earth fraction) over priors. RMSE and spatial representation for soil organic matter and bulk density also improved. Furthermore, the method reduced prediction uncertainties (narrower prediction intervals compared to the priors) and enforced physical constraints on soil property bounds. Looking forward, this IRC method offers a scalable pathway to improve existing probabilistic soil maps, providing a strategy for the evolution of digital soil products as new soil observations emerge.

Duke Scholars

Author Nathaniel Chaney Civil and Environmental Engineering