Manure Application Timing Drives Energy Absorption for Snowmelt on an Agricultural Soil

Reducing agricultural runoff year-round is important, in particular during snowmelt events on landscapes that receive wintertime applications of manure. To help inform manure guidelines, process-level data are needed that link management scenarios with the complexity of snowmelt, hence runoff. Albedo and radiative energy fluxes are strong drivers of thaw, but applying these mechanistic measurements across multiple, plot-scale management treatments over time presents a logistical challenge. The objective of this study was to first develop a practical field approach to estimate winter albedo in plot-scale field research with multiple management scenarios. The second objective was to quantify the radiative drivers of snowmelt by measuring fluxes after wintertime liquid manure application. Six management treatments were tested in south-central Wisconsin during the winters of 2015–2016 and 2016–2017 with a complete factorial design: three manure application timings (early December, late January, and unmanured) and two tillage treatments (conventional tillage versus no-tillage). A multiple linear regression model was developed to estimate albedo with digital imagery and readily-obtained site characteristics. Manure timing had a significant effect on radiative energy fluxes and tillage was secondary. January applications of liquid manure produced an immediate and lasting decrease in albedo, which resulted in greater net radiation absorbed by snowpack and subsequent energy available for snowmelt. Later applications of liquid manure accelerated snowmelt, which increased runoff losses and posed a challenge for nutrient retention from the liquid manure during thaw

Quantifying the Impact of Seasonal and Short-term Manure Application Decisions on Phosphorus Loss in Surface Runoff

Agricultural phosphorus (P) management is a research and policy issue due to P loss from fields and water quality degradation. Better information is needed on the risk of P loss from dairy manure applied in winter or when runoff is imminent. We used the SurPhos computer model and 108 site–years of weather and runoff data to assess the impact of these two practices on dissolved P loss. Model results showed that winter manure application can increase P loss by 2.5 to 3.6 times compared with non-winter applications, with the amount increasing as the average runoff from a field increases. Increased P loss is true for manure applied any time from late November through early March, with a maximum P loss from application in late January and early February. Shifting manure application to fields with less runoff can reduce P loss by 3.4 to 7.5 times. Delaying manure application when runoff is imminent can reduce P loss any time of the year, and sometimes quite significantly, but the number of times that application delays will reduce P loss is limited to only 3 to 9% of possible spreading days, and average P loss may be reduced by only 15% for winter-applied manure and 6% for non-winter-applied manure. Overall, long-term strategies of shifting manure applications to low runoff seasons and fields can potentially reduce dissolved P loss in runoff much more compared with near-term, tactical application decisions of avoiding manure application when runoff is imminent

Temperature and Manure Placement in a Snowpack Affect Nutrient Release from Dairy Manure During Snowmelt

Agricultural nutrient management is an issue due to N and P losses from fields and water quality degradation. Better information is needed on the risk of nutrient loss in runoff from dairy manure applied in winter. We investigated the effect of temperature on nutrient release from liquid and semisolid manure to water, and of manure quantity and placement within a snowpack on nutrient release to melting snow. Temperature did not affect manure P and NH4–N release during water extraction. Manure P release, but not NH4–N release, was significantly influenced by the water/manure solids extraction ratio. During snowmelt, manure P release was not significantly affected by manure placement in the snowpack, and the rate of P release decreased as application rate increased. Water extraction data can reliably estimate P release from manure during snowmelt; however, snowmelt water interaction with manure of greater solids content and subsequent P release appears incomplete compared with liquid manures. Manure NH4–N released during snowmelt was statistically the same regardless of application rate. For the semisolid manure, NH4–N released during snowmelt increased with the depth of snow covering it, most likely due to reduced NH3 volatilization. For the liquid manure, there was no effect of manure placement within the snowpack on NH4–N released during snowmelt. Water extraction data can also reliably estimate manure NH4–N release during snowmelt as long as NH3 volatilization is accounted for with liquid manures for all placements in a snowpack and semisolid manures applied on top of snow

Dynamics of Measured and Simulated Dissolved Phosphorus in Runoff from Winter-Applied Dairy Manure

Agricultural P loss from fields is an issue due to water quality degradation. Better information is needed on the P loss in runoff from dairy manure applied in winter and the ability to reliably simulate P loss by computer models. We monitored P in runoff during two winters from chisel-tilled and no-till field plots that had liquid dairy manure applied in December or January. Runoff total P was dominated by nondissolved forms when soils were bare and unfrozen. Runoff from snow-covered, frozen soils had much less sediment and sediment-related P, and much more dissolved P. Transport of manure solids was greatest when manure was applied on top of snow and runoff shortly after application was caused by snowmelt. Dissolved P concentrations in runoff were greater when manure was applied on top of snow because manure liquid remained in the snowpack and allowed more P to be available for loss. Dissolved runoff P also increased as the amount of rain or snowmelt that became runoff (runoff ratio) increased. The SurPhos manure P runoff model reliably simulated these processes to provide realistic predictions of dissolved P in runoff from surface manure. Overall, for liquid dairy manure applied in winter, dissolved P concentrations in runoff can be decreased if manure is applied onto bare, unfrozen soil, or if runoff ratio can be reduced, perhaps through greater soil surface roughness from fall tillage. Both management approaches will allow more manure P to infiltrate into soil and less move in runoff. SurPhos is a tool that can reliably evaluate P loss for different management and policy scenarios for winter manure application

Fall Tillage Reduced Nutrient Loads from Liquid Manure Application During the Freezing Season

Reducing agricultural runoff is important year round, particularly on landscapes that receive wintertime applications of manure. No-tillage systems are typically associated with reduced runoff loads during the growing season, but surface roughness from fall tillage may aid infiltration on frozen soils by providing surface depressional storage. The timing of winter manure applications may also affect runoff, depending on snow and soil frost conditions. Therefore, the objective of this study was to evaluate runoff and nutrient loads during the freezing season from combinations of tillage and manure application timings. Six management treatments were tested in south-central Wisconsin during the winters of 2015–2016 and 2016–2017 with a complete factorial design: two tillage treatments (fall chisel plow vs. no-tillage) and three manure application timings (early December, late January, and unmanured). Nutrient loads from winter manure application were lower on chisel-plowed versus untilled soils during both monitoring years. Loads were also lower from manure applied to soils with less frost development. Wintertime manure applications pose a risk of surface nutrient losses, but fall tillage and timing applications to thawed soils can help reduce loads

Reducing Winter Runoff Losses From Dairy Agroecosystems Through Tillage and Manure Application Timing

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. Therefore, we tested practical management techniques that may reduce runoff on fields receiving winter applications of liquid dairy manure, and used a water-energy balance approach to identify and quantify the key drivers of runoff on frozen, agricultural soils. To test these objectives, a two-year (2015-2017) field study was conducted at the UW Arlington Agricultural Research Station in Arlington, WI, with 18 plots installed on a 6 % slope and planted in continuous corn for silage. Using a 2x3 complete factorial design in triplicate, the management treatments included tillage: a fall chisel plow with a spring finisher versus no-tillage, and three manure application timings: unmanured controls, early applications during the freezing season, and mid-winter applications. Manure was applied at a rate of 37.4 kL ha-1 (4000 gal ac-1) to prevent immediate runoff. The plots were monitored for runoff volume and runoff samples were analyzed for TKP, DRP, and TS. Atmospheric (albedo, wind speed, air temperature, and vapor pressure), soil (temperature, matric potential, water content, and frost depth), and hydrologic (precipitation, snow-water storage) parameters were directly measured. Over the two winter seasons, 19 runoff events occurred and the no-tillage plots, regardless of manure treatment, were twice as likely to produce significant runoff compared to the tilled plots. During the freezing season, cumulative losses of TKP ranged from 0.1 – 0.4 kg ha-1 in the tilled plots and 0.2-3.7 kg ha-1 in the no-tillage plots, while DRP losses ranged from 0-0.3 kg ha-1 in the tilled plots and 0.1-1.6 kg ha-1 in the no-tillage plots. Likewise, TS losses ranged 0.3-84.0 kg ha-1 in the tilled plots and 98.8-836 kg ha-1 in the no-tillage plots. Tillage created surface depressional storage, which slowed surface water movement and aided infiltration into frozen soil, while applications of manure decreased albedo, accelerating snowmelt, hence runoff and nutrient losses. This field study provides a mechanistic understanding of winter processes and a replicated dataset to help inform prediction tools that evaluate nutrient losses from agroecosystems to balance environmental and economic viability

Tillage, Manure, and Winter Runoff

Wintertime land-applications of manure are a common practice because of the high cost of manure storage (Srinivasan et al., 2006). However, the presence of frozen soil and snow creates challenges for on-farm nutrient retention, as up to 75% of annual runoff can occur during thaws (Good et al., 2012). Therefore, we 1) tested practical management techniques that may reduce runoff on fields receiving winter applications of liquid dairy manure, and 2) used a soil physics approach to identify weather and soil properties that control infiltration, runoff, and nutrient losses during thaws

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