Biomass inputs drive agronomic management impacts on soil health

Numerous conservation and regeneration practices are recognized as effective strategies in the management of soil health (SH), a critical factor for ensuring the sustainability of food production systems. Despite their acknowledged importance, the multifaceted impacts of these practices often lead to confounding effects, and reliance on generic categorization of agronomic practices often falls short in portraying the drivers of SH. We advocate for a paradigm shift from a label-centric approach to one rooted in processes. Our study underscores the pivotal role of aboveground biomass cycling as an indicator for assessing the potential of agronomic management practices to instigate shifts in carbon balances, and, consequently SH. Drawing on soil physical, biological, and chemical SH data from three Uruguayan long-term experiments on Pampas region Mollisols we (i) present quantitative evidence of the importance of evaluating SH through biomass inputs, and (ii) illustrate the applicability of the proposed framework for evaluating different scenarios of land management for the region. Management-induced variations in aboveground biomass inputs accounted for 50 % of the observed changes in a composite soil's physical and biological SH index and helped explain the inconsistent effect of management practices. Raising the SH Index by ten points required an increase in biomass inputs of over 50 Mg ha⁻¹. Based on this concept, substantial enhancements in SH can be made by narrowing yield gaps and intensifying cropping sequences over many years. The benefits of practices such as increased crop diversification, integration of perennial and cover crops, or reduced tillage in promoting SH depend in part on their ability to augment biomass production. This nuanced understanding underscores the importance of aligning agronomic strategies with the fundamental processes driving SH dynamics.