Does Tillage Increase Frozen Soil Infiltration?.

Wintertime land-applications of manure are a longstanding practice for many dairy producers, but the presence of frozen soil and snowpack increases the potential for nutrient transport through surface runoff processes. Previous research was historically confounded by observational study designs that could not account for variability in weather patterns or the complexity of frozen, agricultural soils. Therefore, while testing management techniques for fields with winter-applied manure, the objectives of this study include: 1) quantifying water balances to identify the mechanisms that control infiltration and runoff on frozen agricultural soils and 2) quantifying energy balances to link changes in melt rates to management practices. A replicated field study will be conducted for three years (2015-2018) under conventional and no tillage with three manure application timing treatments: unmanured controls, early applications to frozen ground (prior to snowfall), and mid-winter applications to snow-covered ground. 18 plots, each 5 x 15 m, were installed using a 2 x 3 complete factorial arrangement in triplicate on a 5% slope. The plots are monitored for atmospheric (net radiation, wind speed, precipitation, air temperature and vapor pressure), soil (temperature, matric potential, water content, and frost depth), and hydrologic (snow water storage, runoff volume, and flow rates) parameters using a suite of sensors and manual measurements. Nine runoff events occurred in winter 2015-2016, during which 84% of no till plots and 23% of conventionally tilled plots produced runoff in each event and mid-winter applications of manure significantly accelerated snowmelt processes. Tillage created surface depressional storage, which slowed surface water movement and aided infiltration into frozen soil, while mid-winter applications of manure decreased both the albedo and freezing point of snowpack, accelerating runoff processes. Expanding frozen soil research to applied agricultural systems provides a mechanistic context for land management and regulatory decisions that balances environmental and economic viability.