Stratified substrates enhance rhizosphere oxygen exchange and root growth

Stratified substrate systems (i.e., layering substrates of differing physiochemical properties within a container) can increase crop growth and quality by improving the profile hydraulic properties; however, no research has examined if these systems enhance gas supply to the rootzone. In this study, we used a one‐chamber gas diffusion apparatus to understand how peat‐based stratified systems (7:3 by vol. peat:perlite layered over unscreened bark; 1:1 depth layer ratio by vol.) influenced gas exchange when compared to a non‐stratified control (100% of a container filled with 7:3 by vol. peat:perlite). We also examined if relative gas diffusivity ( D s / D 0 ) was modified for different rooting levels (0, 14, and 28 days of growth of a Helianthus annus Lemon Queen crop) and relative wetness of maximum water storage (<10%, ∼50%, and ∼75% of container capacity values). Crops grown in the stratified system generally exhibited more root growth compared to those grown in non‐stratified systems, including longer roots and greater surface area and volume. The linear increase in rooting measured through time within treatments had negligible effects on D s / D 0 ; however, D s / D 0 varied with relative wetness for both substrate profiles. When moisture was present, stratified systems supplied the rhizosphere with oxygen faster than non‐stratified systems. Stratified systems can (1) improve rootzone environments through reduced waterlogging, (2) better resupply oxygen, and (3) decrease peat inputs by nearly 50%.