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Liquid Manure Application and Drought

12:31PM Aug 30, 2012

Extremely dry weather has chapped and cracked Midwestern soils. Liquid manure application during a drought can be tricky, but understanding how liquid manure is absorbed into drought ravaged soil will help keep your application from running off, leaching or escaping through drainage tile.

Runoff and leaching are always a concern but in the majority of Midwestern farmland, soils are dry enough to soak up liquid manure almost as fast as farmers can spray it this year. The concern comes when the soil's moisture capacity is met. This occurs when all of the pores in the soil are completely filled with moisture. Saturation takes around 10-12 inches of liquid per square foot to infuse the soil profile to a depth of 4-5 feet. If more liquid is applied after the soil has reached it's saturation point, surface runoff becomes a real threat.

To avoid oversaturating dry soils, Iowa State Extension Agronomist Mahdi Al-Kaisi recommends, "Liquid manure should be applied more carefully under such dry conditions by using a low application rate to allow more time for liquid manure to be absorbed and infiltrate [the soil] at a slow rate and to minimize surface runoff".

Most cracks in the soil reach 6-15 inches deep. With most tile resting somewhere between 3 and 5 feet deep, liquid applications on the surface will have a long way to go before finding tile. Al-Kaisis continues, "For those few soils with continuous cracks or fractures extending to the depth of drainage tiles, the cracks and fractures would have to be directly above the tile line".

Application rates will be the key to avoiding surface runoff, and the majority of soil cracks and fissures are much to shallow for liquid to immediately reach drainage tile. Growers may want to consider multiple applications of thin layers of liquid manure this fall to maximize soil fertility potential.

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