Answers from on-farm research

To help farmers navigate these challenges, there is Discovery Farms, a farmer-led research and outreach program of the UW-Madison Division of Extension focused on the relationship between agriculture and water quality. The Wisconsin-based program works on privately owned farms throughout the state to conduct unbiased research.

Our neighbor and close partner, Discovery Farms Minnesota, is coordinated through the Minnesota Agricultural Water Resources Center. Data collection methods from both states are compatible in order to capitalize on combining data and create a robust set of on-farm water quality data to inform farmers on topics like manure management, soil erosion risks, and other crop nutrient questions.

Managers of manure in the Upper Midwest or other seasonally frozen areas must take into account the two main runoff periods in winter (February and March) and spring (April, May, and June). Discovery Farms has worked with over 100 farmers in Wisconsin and Minnesota over the past 19 years to understand the challenges and solutions in the intersection between agriculture and water quality. Wisconsin and Minnesota farms are included in this information, which consists of 250-plus site years of data. The on-farm research data helps to show the stark differences in the risk of runoff earlier in the winter compared to later in the season.

The highest risk

Runoff is mostly likely in late winter months like February and March and spring months like April, May, and June. In November, December, and January, the average monthly surface runoff is less than 0.1 inches. However, February and March average 0.4 and 1 inches, respectively. The average monthly runoff for March is twice as high as the next closest month (June) and almost three times higher than February, April, May, and July.

There is less risk for runoff in November, December, and January, and this relates to the amount of precipitation during that time period as well as the risk of snowmelt or rain. The average date that the soil freezes is December 9, according to Discovery Farms soil temperature observations. There is rain and/or snowmelt in November, but rain or melting snow during November is more likely to infiltrate into the soil than rain or snowmelt during February and March when the soil is frozen or only partially thawed. The average thaw date is March 28.

One of the drivers of dissolved phosphorus loss in the winter is manure application, especially manure applied shortly before runoff or during late winter. Phosphorus is a valuable manure nutrient for crop production, but it is a concern for water quality as it creates algal blooms and excessive plant growth, harming the fishery and recreational resources. Manure application during February and March significantly elevated dissolved phosphorus loss when compared to manure application earlier in the winter or other times of the year.

Manure application during the time period when runoff is more likely raises the risk for nutrient loss associated with runoff. Research has indicated that when manure does not have time to adhere to the soil, dissolved phosphorus loss can increase by two to four times. Applying manure onto a snowpack or shortly before the snowmelt, especially later in the season, leaves little chance that manure will make contact with the soil and a greater chance that nutrients will be lost in runoff.

Dissolved phosphorus drives phosphorus loss on frozen soils, and late winter manure application can increase losses by two to four times compared to early winter application or no winter application. Manure application on frozen ground shortly before a snowmelt or rain drives the largest losses.

Farmers must adjust

Concerns with winter spreading can be addressed if farmers understand the risks associated with varying soil conditions and consider weather forecasts prior to spreading on frozen ground. Spreading just before snowmelt or a winter rain event significantly raises the risk of manure and nutrient movement. The key to reducing nutrient loss during winter manure application is to understand the local conditions and have a detailed spreading plan in place for winter and throughout the year.

Working to apply manure during a low risk time period can mean that farmers need to alter rotations or consider options that allow them to manage manure during the lowest risk time periods. Especially for farmers with stored manure, managing the storage throughout the year is the best practice to make sure there is no ‘need’ to spread when conditions are ripe for runoff.

Utilizing other tools, like the Runoff Risk Advisory Forecast in Wisconsin, allows farmers a real-time look at the runoff risk no matter the season. This forecasting tool is a joint effort by several state agencies, including Discovery Farms and other state and federal partners. Investigate the options available for your area, and work to utilize the best tools available to reduce the risk of loss from winter manure application.