Shifting climate requires smart manure management

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This spring's extremely wet start could have a big impact on how farmers manage manure. And it will not just matter this year. As climate changes, as it always does, farmers will need to pay more attention to every step in their manure management processes, including maintaining adequate storage capacity and being flexible with manure application timing.

Global Climate Change: http://nca2014.globalchange.gov/highlights/overview/overview

Figure 1. Changes in heavy precipitation.

As we all know, manure management does not end when the manure leaves the barn. Manure is stored and then transported and applied to crop fields where it benefits the soil and the crops. This seems simple until you get into the details. A changing climate is making those details more difficult.

At the University of Minnesota, we are urging farmers to prepare for these changes as we anticipate more variable weather in the future. Weird and variable weather patterns cannot always be clearly quantified, yet every farmer knows they exist. Just ask a retired farmer how the weather has changed over his or her lifetime. However, some trends are very clear; for the Midwest, historic trends indicate a 37% increase in the heaviest precipitation events (Figure 1) and longer frost free dates (Figure 2).

Smarter manure management begins with an understanding of the climate trends in your area as precipitation and temperature are critical parameters for good manure management. What are historic trends in rainfall and temperature? What seasons are getting drier or wetter? Do these climate trends impact the windows of time for manure application?

Outside Manure Storage: Manure storages are sized based on the amount of manure and runoff entering the system, the balance of rainfall and evaporation, and the planned frequency of pumping. Unexpected rainfall can lead to overtopping of manure storage or result in emergency manure pumping. A full manure storage is vulnerable to any intense rainfall event. Overtopping can mean fines for polluting and expensive cleanup. Outside manure storages are more vulnerable to intense rainfall events if they are capturing runoff from barns and other farm areas (roofs, lawns, fields and drives). If you are building a new storage, make sure it is designed with new rainfall data.

Smart manure management means maintaining your manure storage 1 to 2 feet below design capacity or what might be needed to handle a heavy rainfall event. This is defined as a 25-year, 24-hour storm event at any time of the year. Remember we have had several of these large 25-year events within the last few years. Extra freeboard provides flexibility when rains are heavy and unexpected. This may require that manure storages are pumped more than once per year.

Kunkle et al. Temporal Variations in Frost Free Season 1895 to 2000, 2004. Geophysical Research Letters, Vol. 31.

Figure 2. Frost-free days

Buffers and Treatment Areas: More intense rainfall events mean higher runoff from open feedlots. Buffer treatment areas may not be designed for volatile weather. Buffers work best when the grasses in the buffers are growing and the soils are thawed. Early and intense spring rains will increase the flow of feedlot runoff to the buffers at a time when the buffers are not very effective. Make sure your buffers are big enough to handle the increased rainfall and are maintained properly. Intense rainfall events can cause erosion and gully formation.

Manure Application: Fall seasons are becoming longer and warmer. When the soil is warm, nitrogen is volatilized leaving less nitrogen for your crops in the spring. Leaving manure application until spring is an option, but the window between winter and first planting dates is short. An ill-timed spring rain can easily result in a full manure storage basin with no place to pump. Waiting until late fall when soils are cool to apply manure is an option but there have been some recent early snow events that make this risky also.

One option that allows more flexibility is applying manure on pastures. This may take special application equipment but really allows for flexible manure management. Also, when fertilizer prices are high and corn prices are low, designating some crop acreage for manure application can be a cost effective method to reduce your risk. Simple calculations on profit per acre of cropland provide you the cost of this option versus the liability of pollution cleanup caused by an overflowing manure storage system.

The Bottom Line: Farmers need to pay attention to the shifting climate and adapt practices so they are not caught off guard. The first step in that process is education. The University of Minnesota is part of a national effort to build a community of trained professionals engaged in using the best climate science to create a profitable and climate resilient animal agriculture community. (For more information go to www.animalagclimatechange.org.)


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