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Use caution when spreading manure in summer

The alfalfa is in the bunker, the sun is shining, the ground is dry – should you start hauling liquid manure?


Summer hauling liquid manure on just harvested alfalfa fields in East Wisconsin is considered by many dairy farm operators as a way to fertilize and reduce the fall workload. No doubt there are benefits.  Alfalfa and grass respond to the addition of nitrogen, phosphorus and potassium,  and a little moisture.  There are some pitfalls that all farms should be aware of before hauling on hard dry soils.

Tile drained fields.  Most liquid manure is 95% water or more.  Processed manures are more watery, 98% or more.   Field tile lines are designed to move water.  In local fine texture soils, soil cracks develop  immediately above tile lines.  It seems the dryer the weather, the deeper and wider the cracks.  Often, cracks, worm holes and root channels will extend down to the tile line.  The result is liquid manure can move almost unimpaired into tile drainage systems.  Most tile drain systems empty to streams and ditches.    It doesn’t take a tile blowout to get manure water into the line.

Tile drain location. Of course, tile lines usually are in the lowest portion of the landscape within a crop field.  They are designed to move water away from wet areas.   Any manure liquid that pools, even for a short while, may be immediately over tile lines and may move into the tile system.

Bedrock?  Is your alfalfa over a bedrock area with shallow soil?  Keep in mind that if manure passes through soil cracks to the bedrock below, there is little or no filtering beyond that.

Slopes.  Freshly harvested alfalfas leaves a field that is low in residue, and are relatively smooth.  When soil becomes so dry, it functions similarly to pavement.  Rapid additions of liquid to sloped areas can quickly begin flowing, resulting in pooling at the base of slopes, or runoff.  Remember, tile lines are in the low areas.  7,000 gal/ac is roughly equal to ¼ inch of water added to land.  ¼ inch applied within seconds is a very rapid rate, and is sometimes too fast for soil to absorb without runoff occurring.

Warm hot summer is a time of low water flow and high stress in area streams in lakes.  Even small spills or runoff can kill a stream.

Are you getting your fertilizer bang for the buck?  Alfalfa needs no added nitrogen and will make its own nitrogen fertilizer if it needs it.  Extra nitrogen from manure will be used by alfalfa, but it will not stay in the soil for later.   Check your soil test and your alfalfa stands to determine if Phosphorus and Potassium are needed.  If you grow corn you may be money ahead if you save your manure to fertilize next years corn crop.  Your corn crop will use nitrogen, phosphorus and potassium.  Is your manure more valuable as fertilizer, or ¼ inch of water?

Minimize impact of summer manure applications on water resources.

•      Apply at light rates.

•        Scout your tile drained crop field for  surface inlets and blowouts. Setback applications 300 feet upslope from surface inlets.

•        Set back applications 300 feet from streams, and 50 feet from other channels.  Setback 1000 feet from lakes.

•       Do not over apply. Heavy applications of manure liquid in summer can burn out the alfalfa.  Applications after regrowth begins can also damage the stand by burning, smothering or wheel traffic.

•       If soil cracks are present, monitor tile outlets.  If runoff occurs, take action to collect the runoff.

•        Fields with heavy residue such as winter wheat stubble resist runoff and encourage infiltration of manure liquids.

(Source – http://dairybusiness.com/archive/?p=3596)

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