What happens if I spread manure today?

Available nutrients next spring depend on how and when manure is hauled this fall.

Surface applied manure:

If manure is surface applied, the MSU Extension recommends incorporating it the same day. Immediate incorporation retains the most nitrogen, reduce odor and reduce the risk of runoff. Same day incorporation is more important when the weather is hotter and less important as the temperatures cool. Manure that has more nitrogen in the ammonium form is always more important to incorporate the same day. Manure test can tell you the amount and form of nitrogen. When sending in manure samples, always be sure to request both the organic and ammonium N test.

A light rain is good and helps incorporate surface applied manure. A big fast rain may not be good, increasing the risk of runoff. Be mindful of field selection for surface applied manure, always choosing the least risky fields.

Injected manure:

Injecting manure reduces odor and nitrogen losses to the air. Injection and surface applications after the soil temperatures go below 50F is beneficial in maintaining the manure nitrogen in the ammonium form, binding it to the soil, and holding it in the root zone over the winter. Conserving this nitrogen has direct impact on fertilizer savings the following spring.

Fall cover crops are another way to keep nutrients in the root zone and available for the next crop. This practice is increasing as cover crop acreage is growing in Michigan. Beyond all the long time noted benefits of cover crops (soil tilth, organic matter, compaction reduction, etc.) the root system of cover crops helps create a more absorptive area for liquid manure to infiltrate and then provides a growing plant to take up the nutrients, helping to hold them until next season.

This winter:

Even the best laid plans for manure applications can be trumped by the weather. If manure was surface applied during the winter, there is concern of whether it soaked in during freeze and thaw events or if the thaw was fast and furious creating runoff. Any surface applied manure in the winter should be to fields with the very least risk of runoff: no areas where slopes lead to surface waters. Leaving any field rough tilled or with heavy residue this fall will provide greater safety for winter applications. And cover crops would be an excellent addition too.

Next Spring:

When the soils begin to warm up in the spring, the ammonium form of nitrogen will begin to convert to nitrate forms that are available for plant uptake and for leaching. Under a typical spring, the nutrients will stay well within the reach of future corn roots. Under extreme spring rain events, those that generate rain faster than the soil can hold or infiltrate, nitrogen losses can occur on sandy soils by leaching or on heavy, saturated soils by denitrification. Neither is profitable for the farmer.

Keep records of manure hauling, including the weather conditions. Pull new manure samples at the time of hauling and be sure soil tests are up to date (less than three years old). This will put valuable information in your hands this winter for planning next year’s crop fertilizer needs.

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