Caution issued on applying manure to fields with dry, cracked soils

With the winter wheat harvest well under way or soon to begin in most of Wisconsin, many landowners might be thinking about applying manure on what will be open land once the straw is removed.

But, given the long period of dry weather, a manure application might pose an environmental hazard in many cases, Outagamie County Extension Service agents Zen Miller and Kevin Jarek pointed out in a recent advisory to farmers, crop consultants, and custom manure applicators.

In the two months since most of Wisconsin's major wheat growing area has had substantial rainfalls, wide and deep cracks have developed in many of the fields, Miller and Jarek point out.

With similar cracking in the past, there is a history of having both surface and injected manure flow very deep into those cracks - 17 feet in one Wisconsin incident a few years ago, they warn.

This means that manure applied in such conditions has a direct path to field drain tile, groundwater, or the subsurface water table - not to mention the loss of the nutrients in the manure for growing subsequent crops, the Extension Service agents explain.

If there is any doubt about such a direct connection to field tile, that doubt was erased when smoke bomb demonstrations were conducted in fields in several east central Wisconsin counties a few years ago, they note.

The risk of a rapid flow of manure from the soil surface to field tile is normally highest when the solids content of the manure is less than 2.5 percent but that number might not apply with the wide cracks that were in place at the start of July this year, Miller and Jarek indicated.

Citing a Calumet County incident during June in which surface applied liquid manure entered drain tile, they're asking everyone involved to "be careful with all manure applications, regardless of the solids content."

Research by federal agencies and Ohio State University has shown that pre-working the soil in order to fill in the cracks can be fairly effective in preventing a direct rapid to field tile and groundwater, Miller and Jarek observe.

If the manure is to be injected, however, they emphasize that the soil would need to be tilled to below the depth of the injection.

Jarek also "highly recommends" monitoring the outlets of field drainage systems before, during, and for several days after a manure application.

Should there be significant rainfall after that period, he adds, monitoring of outlets should resume because of the possibility that manure could still enter the field tile several days or even weeks after an application.

In a state-level Extension Service report, small grains specialist Shawn Conley indicated that the winter wheat plot near Janesville was harvested during the last week of June.

The preliminary data shows that yields averaged 85 bushels per acre, with a top of 108 bushels, and that test weights were 60 pounds or better for all varieties despite the lack of rainfall during most of the latter half of the crop's growing season.