Soil pH and nutrient stratification and spatial variability: A review of drivers and agronomic implications

Soil pH and nutrient stratification, as well as spatial variability, pose a problem for diversified no-till systems in the Canadian Northern Great Plains (CNGP). Therefore, we conducted a review aimed at (1) summarizing the evolution of soil pH stratification and variability from conventional to no-till systems, (2) reviewing the contributing factors to soil pH and nutrient stratification, (3) discussing the implications of soil pH stratification on pest management, and (4) deliberating on challenges and opportunities for managing stratified pH in CNGP no-till systems. Reviewed literature indicates that historical tillage practices have redistributed soil downslope, exposing carbonate-rich or acidic subsoils on convex slopes and depositing organic matter in lower positions, contributing to spatial pH variability. The shift to no-till production has intensified cropping systems and led to soil pH and nutrient stratification resulting from seeding and fertilizer application practices, and, to a lesser extent, from crop residue and manure management practices. Soil pH stratification and variability may affect herbicide efficacy, weed pressure, and the incidence of soil-borne diseases, as well as their management. Changes to standard soil sampling practices and fertilizer recommendations are key to managing soil pH and nutrient stratification. Liming plus strategic tillage are potential remedial solutions, but the cost-benefit trade-offs associated with these interventions remain uncertain.