Maize and Soybean Root Traits Measured Under Tile-Drained Soils in Iowa.

Achieving yield gains without environmental degradation is a critical challenge in artificially drained croplands with shallow water tables. Root data can improve our understanding about how crops, soil and weather interact to affect grain production and environmental performance. The objective of our study was to quantify root traits, including: i) maximum root depth, ii) root front velocity, iii) root mass and iv) total root N uptake in corn and soybean grown under tile-drained soils. We carried out twelve experiments in two consecutive years (2016 and 2017) at three Iowa locations spanning northwest to southeast gradients of precipitation and temperature. Root depth was measured every ~14 days using a conventional soil probe. Root tissue was extracted from to 180 cm depth using a hydraulic probe. Overall, corn root depth was 9% greater than soybean. Root depth ranged from 129.5±4 to 152±12 cm for corn and from 108±12 to 154±4 cm for soybean. Pooling all data across years and locations, root depth velocity was better described by a tri-linear model displaying almost similar velocities in the first and second phases (1.20 and 2.74 cm d^-1), and (1.19 and 2.70 cm d^-1) in corn and soybean respectively. Averaging all data across sites during 2016, corn root mass was 4.1 Mg ha^-1 and soybean 1.6 Mg ha^-1. Root N uptake was 44% greater in corn than in soybean, ranging from 54.8 to 68.2 kg ha^-1 for corn and 16.9 to 51.4^- kg ha^-1 for soybean. Our results suggest that under tile-drained soils, roots can take up leached nutrients and water from deep soil profiles.