Ecophysiological Root Traits Asses of Maize and Soybean Under Contrasting Field Conditions in Iowa.

Crop root traits below 60 cm depth are infrequent but could improve the ability of process models predict production and environmental performance. The objective of this study was to quantify the following root traits at the begining of grain filling: root mass, root:shoot ratio, root C:N ratio, and specific root length in corn and soybean. During 2016, we carried out twelve experiments in six representative croplands in Iowa. Experiments included common crop management practices (N rate, plan density and tile drain treatments) and were replicated three times. Root sampling was taken in-row and center-row. In some experiments, maximum root depth exceeded 180 cm. Root traits in-row and center-row differed across sites. Corn produced ~50% more root mass than soybean. For corn and soybean respectively, root mass across the entire profile ranged from 0.69 to 4.4 Mg ha^-1 and 0.54 to 2.34 Mg ha^-1; R:S ratio from 5.2 to 50.7 and 13.5 to 48.5; root C:N ratio from 21.3 to 31.5 and 10.5 to 20.40; and, specific root length ranged from 77.5 to 172.7 mm mg^-1 and 142.4 to 203.8 mm mg^-1. Root C:N ratio was relatively constant from surface to subsoils.