Nutrients from manure

Gloria Hafemeister
Now Media Group


Farmers are bombarded with information about water quality and conservation, leaving them wondering what will really work on their farm.

Prioritizing can be a challenge as growers try to look at their bottom line while also being good stewards.

Amber Radatz, co-director of the University of Wisconsin Discovery Farms program, understands the challenge and knows first-hand that there is no one-size-fits-all recommendation.

Discovery Farms program has discovered a lot from studying the interaction of nutrient loss and field management on private farms for the past 15 years, according to Radatz. During Discovery Farms fourth annual conference in Wisconsin Dells recently she described the dataset of Wisconsin specific information that has brought to light some interesting conclusions.

She said the Discovery Farm on-farm research has indicated that reducing soil loss does not always reduce phosphorus loss. It has to do with timing, placement and more.

'When soil is frozen, soil does not erode but phosphorus loss still happens,' she illustrates. 'That's why we have developed the runoff risk advisory forecast for use by farmers around the state.'

She points out, 'As we get into winter, we know conditions are unpredictable. We can expect some combination of snow, frozen ground, ice, warmer periods and even a bit of rain in any given year.'

She notes, 'Factors including soil and landscape, influence the volume and timing of runoff, but weather conditions in the local area play the most significant role.'

Discovery Farm findings

The UW-Discovery Farms program has monitored enough locations and conditions to show that when manure is applied one week or less before a runoff event, losses of nitrogen and phosphorus are significantly increased even with relatively low application rates.

She suggests that farmers pay attention to the amount of snowpack present and the weather forecast. A rapid and dramatic temperature increase, clear sunny skies or a layer of ice over the soil often lead to higher runoff volumes during the winter months. However, a deep snowpack doesn't always mean that a large amount of that water will end up as surface runoff.

Conditions that encourage infiltration of melting snow include the absence of concrete frost in the soil, temperatures just above freezing during the day and cooler at night and foggy or overcast conditions.

She suggests, 'If you must spread manure during these months, look ahead in the forecast for days that favor infiltration instead of runoff of melting snow.'

Rain on frozen/snow covered ground also prevents challenges. Discovery Farms data shows that almost all winter runoff events in December and January are the result of a rain event on frozen ground. During February and March, warmer temperatures during the day lead to more frequent rain events than earlier in winter. That's why it's important to monitor the weather forecast before spreading.

Going into this winter with saturated ground increases the chances of concrete frost or ice crust, she points out.

Whether it is solidly frozen soil, referred to as concrete frost or a layer of ice on the soil surface, rain, melting snow, or manure from a recent application cannot infiltrate into the soil in these conditions, she points out.

'Some evidence exists that fields with vegetative cover through the winter freeze less solidly,' she says. 'In a must-spread situation, try to target fields that have had vegetative cover throughout the winter and try to get the manure onto the ground surface if possible when a snowpack is present.'

Regarding this year's saturated soil, she says soil moisture is a primary factor influencing runoff. When soil is at or near saturation, additional water from precipitation or liquid manure application cannot infiltrate, and thus begins to run off from the soil surface.

Trying to spread manure during these times also increases compaction and puts ruts in the field.

Targeting fields that are relatively flat and dry out more quickly are good ways to manage runoff risk when saturated soil conditions are present.

She stresses the importance of working with advisors to identify the low risk fields for the high risk periods and watch the weather for rain or melt events. If possible, find areas with little snow cover or plow an area to try and get the manure as much contact with the soil as possible.

She stresses, 'Don't start planning for winter manure application in February. Start tweaking your system and develop a strategy much earlier so that if an emergency situation arises, you have gone the extra mile to protect yourself and the water quality around your farm as much as possible.'

She reminds farmers, 'The key to reducing nutrient loss during winter manure application is to understand the local conditions and have a winter spreading plan in place.'

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