Winter Hydrologic and Erosion Processes in the U.S. Palouse Region: Field Experimentation and WEPP Simulation

Abstract

Soil erosion by water is detrimental to soil fertility, crop yield, and the environment. For cold areas, knowledge of winter hydrologic processes is critical to determining land‐use and management practices for reducing soil loss and protecting land and water resources. Adequate understanding of winter processes is also essential to developing models as effective predictive tools. This study evaluated the effects of two contrasting tillage practices on winter hydrologic and erosion processes, and the suitability of the Water Erosion Prediction Project (WEPP) model with a newly implemented energy‐budget‐based winter routine for quantifying these processes. Research plots subject to two tillage treatments—continuous tilled bare fallow (CTBF) and no‐till (NT) seeding of winter wheat (Triticum aestivum L. cv. Madsen) after spring barley (Hordeum vulgare L.)—were established at the USDA‐ARS Palouse Conservation Field Station, Pullman, WA. The plots were monitored for runoff, erosion, soil temperature, water content, and depths of snow and freeze–thaw during October to May of 2003–2004 through 2006–2007. The NT plot generated negligible runoff and erosion (0.5 mm, 0.2 Mg ha−1) compared with CTBF (323 mm, 547 Mg ha−1). Frost occurred more frequently and was deeper in CTBF, probably due to its lack of residue and shallower snow depth. The modified WEPP model could reasonably reproduce major winter processes, yet it cannot represent all the complicated winter phenomena observed in the field. Continued efforts are needed to further improve the ability of WEPP to properly account for soil freeze–thaw and thus transient soil hydraulic properties and hydrologic and erosion processes.

The Cold Vadose Zone: Hydrological and Ecological Significance of Frozen‐Soil Processes

“…This is consistent with the findings of Stadler et al (2000), who demonstrated the preferential flow of water through macropores in a frozen soil column by conducting dye tracing experiments in a controlled laboratory. Because soil tillage disturbs the continuity of the macropore network, agricultural fields under conventional tillage tend to have lower frozen‐soil infiltration capacity than fields under no‐till management (e.g., Singh et al, 2009). Therefore, it is important to better understand the functions of macropores in frozen soil and to effectively represent them in existing models of water and heat transfer (Stähli et al, 1996).…”

“…Freeze–thaw reduces soil cohesive strength and aggregate stability (see above) and consequently increases soil erodibility following thawing of the surface soil. Rainfall or snowmelt on a thawed, bare soil (e.g., after fall cultivation) overlying a solid frozen layer can cause high rates of erosion because the thawed soil has a high water content that reduces its mechanical strength and the subsurface frozen layer impedes infiltration and generates overland flow (Singh et al, 2009). Rills may form on the thawed soil surface, which can substantially increase erosion rates.…”

Effects of experimental snowmelt and rain on dispersal of six plant species

“…As total numbers of seedlings did not differ between the seed mats, there are no strong indications that many seeds moved out of the seed mat or that differences between snow and rain simulations are due to differences in viability. The low dispersal capacity of snow is in line with the minimal erosion because of snowmelt observed in non-tillage plots by Singh et al (2009) but in apparent contradiction with the calculated erosion by snow by Sukhanovskii (2008). However, the latter included soils that were tilled and subjected to quite large volumes of water.…”

“…The low dispersal capacity of snow is in line with the minimal erosion because of snowmelt observed in non‐tillage plots by Singh et al . () but in apparent contradiction with the calculated erosion by snow by Sukhanovskii (). However, the latter included soils that were tilled and subjected to quite large volumes of water.…”

“…Besides, snow will have less impact on seed heads compared with rain and thereby is unlikely to result in ombrohydrochorous dispersal. Snowmelt, on the other hand, is known to cause substantial erosion, especially if the top layer is not frozen (Singh et al, 2009;Sukhanovskii, 2008). That is, snowmelt can induce small, continuous water flows, especially on sloping terrain.…”