Manure has value, test and take credit this spring

Manure nutrients vary based on when and how it is applied. But there are always nutrients in it, and benefits to reducing fertilizer.

A red tractor spreading manure on a field.
Tractor pulls a manure tanker side dressing manure into corn. Photo by: Charles Gould

Myth #1: Manure that is spread during the winter and not incorporated has very little nitrogen left for the next corn crop.

Reality: Winter-applied manure will have nitrogen value! When manure is spread during cold weather and the soil has moisture, much of the nitrogen is held in the soil and is available in the spring. Keep in mind a late summer application of manure N on wheat stubble may lose some of the organic nitrogen by next spring’s corn crop.

As soon as soils warm up in the spring, a portion of the nitrogen in the organic fraction is released and is readily available to the growing crop. Nitrogen will be available to the next crop, even from surface applied manure when it is applied during cooler weather.

Myth #2: Manure spread in March and April will not be available to corn in June.

Reality: Nitrogen in manure comes in several forms including ammonium-N (NH4-N) and organic. As the soil warms up in the spring, up to half of the organic nitrogen converts to nitrogen that is readily available to the growing crop. If the manure was injected, this organic nitrogen is available along with most of the readily available ammonium fraction. Manures like open lot beef manure or broiler barn litter, or manure’s that are surface applied have minimal ammonium-N. The organic nitrogen in these manures is a slow-release nitrogen. A fertility program that supplements manure’s organic nitrogen with inorganic fertilizer, possibly a starter fertilizer, can help with early crop vigor.

Some research has demonstrated that peak yields are observed for manure application at rate replacing roughly 75% of the crop N requirements, with supplemental commercial fertilizer used for the balance. Manures with significant ammonium-N content (and injected) may have less need for supplemental fertilizer for the early season vigor.

Myth #3: The nutrients in manure are too variable to be a reliable source of nutrients for crops.

Reality: The nutrients in manure are more variable than in commercial fertilizer if the manure comes from a pit that has not been agitated Agitation puts nutrients in suspension within the manure, which significantly improves the uniformity of nutrients applied in a field, which in turn increases a farmer’s confidence that there will be plant available nutrients when needed by the crop. A manure analysis will estimate the amount of N - P2O5 - K2O that can be credited against the fertilizer recommendations. Sampling manure as the manure pit is emptied and having them analyzed will help you see if there is nutrient variability as the pit is emptied and allow you to make manure application rate adjustments based on the manure analysis.

It is important to spread manure as uniformly as possible. If the applicator tries to spread a consistent distance, drive the same speed, and avoid random skips and overlaps, then the manure nutrients will be quite consistent. It is important to spread manure as uniformly as possible. If the applicator tries to spread a consistent distance, drive the same speed, and avoid random skips and overlaps, then the manure nutrients will be quite consistent.

Sand-laden manure stored in a pit will vary significantly in consistency and nutrient composition from beginning to end of emptying. Be aware if you use the ‘skim and haul’ method of emptying your pit that the first portion removed will have very little nutrient value as opposed to the sloppy fraction in the middle and the remaining manure. to Take three manure tests from these three different fractions to evaluate where and at what concentration the nutrients are located. Agitation of the pit will lead to a much more consistent manure product and requires only one manure test. See "Manure analysis provides accurate account of plant available nutrients" for more information on manure sampling.  

Myth #4: Manure nitrogen is in a form that is not available to crops.

Reality: Corn and other crops cannot tell if nitrogen is coming from fertilizer, livestock manure, or cover crops. Manure contains several forms of nitrogen (organic and ammonium), and all forms of manure nitrogen ultimately convert to available forms of N for plants.

Myth #5: Manure is good for the soil to increase organic matter and tilth, but it should not be considered a nutrient source. Full rates of fertilizer should be applied to assure good yields.

Reality: Manure is a valuable source of nutrients that should be credited against fertilizer recommendations. Straw-packed manure does have less nutrient value, but the liquid systems that are common today are a valuable source of nitrogen, phosphorous and potassium. Manure application rates have a major effect on the amount of nutrients provided to the field. There is a big difference in nutrients per acre when manure is being applied at 3, 6, or 9 thousand gallons per acre. To maximize the benefit of manure, apply manure based on a nutrient management plan and calibrate manure application spreaders.

If you need assistance with nutrient management planning or manure application you can contact MSU Extension educator Sarah Fronczak.

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