Sampling soybean roots: A comparison of excavation and coring methods

Accurate estimates of soybean root productivity are needed to estimate carbon (C) inputs to soil. Soil excavation and coring methods were compared where soybean was subject to ambient, elevated carbon dioxide (CO2) and ozone (O3) treatments. We evaluated within-season changes in biomass and shoot-root production, labor requirements, and damage to plots. Estimates of root biomass were similar, but excavation-based estimates required less total time. Core-based estimates provided similar levels of precision, allowed sampling of deeper depths, and reduced both plot disturbance and the amount of effort devoted to tasks performed in the field. Correlations between root and shoot biomass were weak and varied with time of sampling. Collectively, results suggest caution should be exercised when making predictions about C allocation to roots or soils based on shoot-root ratios or when scaling up field-based findings to predict larger or longer-scale trends.