Dense subsoils limit winter wheat rooting depth and soil water depletion

Abstract

Dense subsoils pose a challenge to dryland winter wheat (Triticum aestivum L.) production in the Palouse region of the semiarid northwestern United States. Subsoils, commonly fragipans and argillic horizons, may restrict root growth and limit crop access to critical stored soil water, but this phenomenon is not well characterized in the Palouse. During the 2017–2018 growing season, an on‐farm study of soil profiles in two commercial winter wheat fields in eastern Washington and northern Idaho was established to observe the effects of soil bulk density on winter wheat root system depth and subsoil water depletion. At harvest, grain yield, root density, soil bulk density, and postharvest soil water and nitrogen content were measured to 120 cm at 15‐cm segments in the profile. Root‐restrictive depth (RRD) was defined as the depth where root density was less than or equal to 0.25 intersections cm−2 cross‐sectional area. Soil bulk density negatively affected root density and consequently increased the probability of shallow RRD. Shallow RRD was common, with 38% of profiles having RRD less than or equal to 105 cm. Postharvest soil‐water content at the bottom of the measured profile (105–120 cm) was 41% higher in profiles with RRD of 90 cm than nonrestricted profiles. Yield declined with increase in postharvest soil water content at 105–120 cm depth. Findings indicate that dense subsoils can reduce stored soil water depletion by limiting root density and root system depth that, in turn, limits yield.

Can Crop Models Identify Critical Gaps in Genetics, Environment, and Management Interactions?

“…Structural-functional models of root systems have been incorporated in models that, however, do not simulate full crop cycles (Schneider and Lynch, 2018), are not integrated in comprehensive crop models, and like any model carry the risk of conflating model assumptions with emergent properties. These models are far from representing the uneven exploration of soil layers by roots and the impact of compacted soil layers on actual water use patterns (Breslauer et al, 2020). New efforts at mechanistically modeling water uptake in soil layers with clusters of roots (uneven root distribution) are fortunately emerging in the literature (Graefe et al, 2019).…”

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

“…Most studies that investigate how management or climate impacts soil health indicators focus on the upper 30‐cm depths (e.g., Morrow et al., 2016; Schlatter et al., 2022; Thapa et al., 2023). However, the health of soil layers deeper than 30 cm is important to study as water and nutrient availability in subsoils impacts plant productivity (Breslauer et al., 2020; Kennedy & Schillinger, 2006; Schlatter et al., 2020).…”

“…Deep soils in the Palouse River watershed support high yielding and high‐quality rainfed winter wheat as one of the most productive wheat growing regions in the world (Breslauer et al., 2020; Duffin, 2007). The Palouse River watershed of eastern Washington and northern Idaho constitutes the largest dryland cropping region in the western United States (Kruger et al., 2017; Schillinger & Young, 2004).…”

“…Most studies that investigate how management or climate impacts soil health indicators focus on the upper 30-cm depths (e.g., Morrow et al, 2016;Schlatter et al, 2022;Thapa et al, 2023). However, the health of soil layers deeper than 30 cm is important to study as water and nutrient availability in subsoils impacts plant productivity (Breslauer et al, 2020;Kennedy & Schillinger, 2006;Schlatter et al, 2020). Soil profile gradients of moisture, pH, nutrient availability, and aboveground and belowground plant and microbial biomass can influence soil organic matter (SOM) decomposition and C cycling (Blanco-Canqui et al, 2021;Gross & Harrison, 2019).…”