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What’s your manure IQ?

April 30, 2013  by Christina Curell Michigan State University Extension

April 30, 2013 – A statement by former Michigan State University Extension educator Natalie Rector noting that “with rising nitrogen prices, manure nutrients are more valuable than ever,” is as true today as it was when she said it five years ago. Manure contains nitrogen, phosphorus, potassium and many micronutrients, but because it doesn’t come in a fertilizer bag with a guaranteed analysis, some producers don’t make use of this resource. How much do you know about manure’s value on your farm? Take this quiz to find out.

True or False: Manure spread during the winter and not incorporated into the soil provides very little nitrogen for the next crop.

False. Winter-applied manure has nitrogen value. When manure is spread during cold weather on soil that contains moisture, much of the nitrogen is held in the soil and is available in the spring. The nitrogen in manure comes in several forms including ammonium (NH4-N) and organic nitrogen. Conversely, manure that is spread during hot weather on dry soils (such as on August wheat stubble), loses much of its ammonium to the air through a process called volatilization that is less likely to occur during cold weather. Manure’s organic components break down slowly. As soon as soils warm up in the spring, a portion of the nitrogen is released and is readily available to the growing crop, even from manure that was surface applied during cooler weather.

True or False: Manure spread in March and April will not be available to crops in June.


False. As the soil warms up in the spring, 25 to 50 percent of the organic nitrogen converts to a form of nitrogen that is readily available to the growing crop.

True or False: Manure composition is too variable to be a reliable source of crop nutrients.

False. Manure is more variable than purchased fertilizer, but it can be managed for efficient crop production. Manure tests will estimate the amount of nitrogen, phosphorus and potassium that can be credited against fertilizer recommendations. Agitating manure in storage prior to hauling it to the fields improves nutrient uniformity. Take several manure samples while emptying a storage system to determine nutrient variation between the first and last loads.

It is important to spread manure as uniformly as possible. If an applicator spreads manure at a steady speed, and avoids random skips and overlaps, manure nutrients will be consistent across the field.

The exception is sand-laden manure stored in a pit, which varies significantly in consistency and nutrient composition from beginning to end of emptying the manure storage facility. Skimming and hauling means the first portion is pumped off as a liquid, a sloppy mix is removed in the middle and the remaining manure removed by tractor-loader and spreader. Take three manure samples from these three different fractions to evaluate the concentration of nutrients at various levels in the manure pit.

True or False: Manure nitrogen is in a form that is not available to plants.

False. Crops cannot tell if nitrogen is coming from fertilizer, livestock manure or green manure cover crops. As mentioned above, manure contains several forms of nitrogen (organic and ammonium), and all forms of manure nitrogen ultimately convert to available forms of nitrogen for plants.

True or False: Manure increases soil organic matter and tilth, but it should not be considered a nutrient source. Full rates of commercial fertilizer should be applied to assure good yields.

False. Manure is a valuable nutrient source that should be credited against fertilizer recommendations. There is a wide range in manure value, so it’s important to take samples as you empty manure pits or during daily haul. This will provide useful information for making the best decisions at fertilizer sidedress time. Liquid manure systems are a valuable source of nitrogen, phosphorous and potassium while straw-packed manure has less nutrient value. 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 3,000; 6,000 or 9,000 gallons per acre. Producers should routinely test soil and manure, and calibrate manure application spreaders.

True or False: When manure is spread on a field for the first time, the manure will be of little nutrient value.

False. Manure has nutrient value beginning with the first application to a field. When manure has been spread on the same field over three years, a significant amount of nitrogen can be slow released. After the third year, nitrogen will still be released from manure that was spread two or three seasons earlier. Applying more manure the third year may provide sufficient nitrogen for a high-yielding corn crop. Use a pre-sidedress nitrogen test to estimate how much nitrogen is available.


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