Root growth and turnover in perennial forages as affected by management systems and soil depth

Abstract

Aims: Extensive knowledge of perennial forage root systems is essential, given their critical role in below-ground C input. Methods: Root length and diameter were quantified periodically from 2016 to 2018 with minirhizotrons in a field experiment with three forage management systems: mixture of timothy (Phleum pratense L.) and tall fescue (Festuca arundinacea Schreb.) fertilized with (i) dairy cattle slurry or (ii) calcic ammonium nitrate, and (iii) mixture of timothy, tall fescue, and alfalfa (Medicago sativa L.) without N fertilization. Root biomass was measured yearly by coring. Results: Management systems with the two fertilization sources did not differ in root elongation, but the management system with alfalfa resulted in a slower root elongation after the first defoliation and a lower root mortality in the fall. Root length turnover was greater in the topsoil with dairy cattle slurry than with calcic ammonium nitrate. Fine roots dominated the surface soil and coarse roots the deeper soil layers. Conclusions: Root growth and mortality were more contrasted between systems that differed by the presence of alfalfa than by fertilizer source. As many root characteristics are drivers of soil C storage, the choice of perennial species in mixtures appears as a key management factor for sustainable farming systems.