Soil profile health in the Palouse soil series: Carbon, nitrogen, nutrients, and aggregates

Deep soil health (>30 cm) supports deep roots in dryland wheat cropping systems. However, few studies examine how tillage and climate impact soil health indicators deeper than 30 cm in dryland wheat systems. We evaluated how select soil chemical (i.e., nutrients and pH), biological (i.e., carbon [C] and nitrogen [N] fractions and ratios), and physical (i.e., mean weight diameter [MWD] of soil aggregates) health indicators were impacted by depth, tillage, and climate. We sampled soil profiles of the Palouse soil series from 0- to 85 cm in depth at three no-till (NT) and three conventional till (CT) sites across a mean annual precipitation (MAP) gradient (460-660 mm) in the Palouse River watershed. NT sites, compared to CT sites, had higher total C (TC) and N (TN), permanganate oxidizable C, hot-water extractable C and N, and cold-water extractable N (0-5 cm); greater soil moisture (0-29 cm); larger MWD (0-5 cm; 10-85 cm); but lower soil pH (0-10 cm; 59-85 cm); less TC, TN, and NO3- (29-85 cm); less NH4+ and mineralizable soil C (MINC) (29-59 cm); and lower autoclaved-citrate extractable (ACE) protein (0-5 cm; 29-85 cm). Sites with higher MAP had greater soil moisture (0-29 cm), higher MINC (0-85 cm), lower CWC (5-10 cm; 29-59 cm), and lower TC and ACE protein (29-85 cm). The variable effects of tillage and climate on these soil health indicators with soil depth show the importance of evaluating soil health in both surface and subsurface soil depths in dryland wheat cropping systems.