Research Shows Variability in Manure

OMAHA (DTN) -- Those who use manure as a fertilizer source need to know that nutrient availability ranges widely depending on the livestock species. Manure from hogs and poultry has higher amounts of nutrients, while manure from beef and dairy cattle has less.

It is important to test manure for nutrient levels to ensure it is not overapplied or underapplied, advised a manure specialist.

DIFFERENT NUTRIENT LEVELS

In a presentation at the 2022 Minnesota Nutrition Management Conference last month, Melissa Wilson, a University of Minnesota Extension manure management specialist, discussed nitrogen and phosphorus crediting. The latest research from the University of Minnesota on manure was also discussed.

Manure from different animal species produces different nutrient contents, she said. Manure in Minnesota is mainly from swine (liquid), poultry (solid), beef (solid) and dairy (liquid).

In their research, Wilson and her team looked at the nutrient content of the manures from different species and found swine and poultry manures had the higher levels, while beef and dairy had lower levels. Also, liquid manures tended to have higher levels of nutrients than dry manure.

In nearly 50,000 samples, swine manure averaged just under 50 pounds per 1,000 gallons of total nitrogen (N), 25 lbs. of ammonium N, 20 lbs. of phosphorus (P) and 30 lbs. of potash (K) available. Poultry had similar numbers as swine with over 50 lbs./ton of total N, 10 lbs. of ammonium N, 45 lbs. of P and 35 lbs. of potash in 9,000 samples.

Beef manure only had about 15 lbs./ton of total N, 1 lb. of ammonium N, 10 lbs. of P and 15 lbs. of potash in just over 5,000 samples. In nearly 11,000 samples, dairy manure had 20 lbs./ton of total N, 10 lbs. of ammonium N, 10 lbs. of P and 20 lbs. of potash.

Wilson said the samples show varying amounts of nutrients in different manures. The ratios of N/P/K are not always where we think they need to be, she said.

"This is why it is so important to get your manure tested regularly," Wilson said.

MINNESOTA MANURE STUDIES

The University of Minnesota has conducted field experiments during three growing seasons. At two locations (Waseca and Lamberton), corn was planted in strips after six different manures were applied. The six types of manure were: composted chicken pellets, swine, raw dairy, separated dairy, turkey and bedded beef pack.

Wilson said the manure was applied at an N-based rate of 140 lbs. of plant-available N per acre. The first year, manure was applied, while the second and third years, no fertilizer was applied to see what levels of nutrients were still present.

At harvest time for the first year, corn yields were mostly high for swine, chicken and turkey manure -- all three had yields over 160 bushels per acre (bpa), she said. The beef and dairy manures ranged from just over 100 bpa to 150 bpa.

The study also showed how much N and P were available in that first year, Wilson said.

Nitrogen fertilizer equivalent (lbs. N/acre) ranged from 29 lbs. in bedded beef pack to 118 lbs. for the composted chicken manure. Phosphorus in lbs. P/acre ranged from 21 lbs. for the bedded beef pack to 77 lbs. for the composted chicken manure.

In the second year of the study, corn was planted after corn, but again no more manure was applied. Yields were significantly lower, right around 80 bpa.

Nitrogen available ranged from 7 lbs. in swine manure up to 19 lbs. in the composted chicken manure. Available phosphorus ranged from 1 lb. in the swine manure to 17 lbs. in the composted chicken manure.

The third year of the study showed yields were at about the same levels as year two. Nitrogen available that year ranged from 6 lbs. in swine manure to 33 lbs. in composted chicken manure, while phosphorus spanned zero lbs. in dairy manure to 7 lbs. in turkey litter.

WEATHER AFFECTS MANURE

Wilson said there are two main points to consider regarding her team's research.

One is the manure was applied in the spring in two extremely wet years in the study, which probably affected the amount of nutrients available. Nitrogen availability was lower than expected in the first year, but higher at Waseca than in Lamberton, she noted.

The other important point was where the N and P went in the last two years of the study. Low second- and third-year availability suggest the N was lost in the first season, probably from being denitrified or leached.

"I would guess some in-season soil samples may shed some light on this," she added.

Wilson said the study shows how variable N and P uptake is and how important soil sampling is, especially in years following manure application. Producers should also soil sample after applying manure, she said.

Her manure research will continue but with some additional areas of study, Wilson said. This includes a closer look at spring versus fall manure applications, alternative methods of determining nitrogen availability and realizing that manure N availability is always variable.

Russ Quinn can be reached at russ.quinn@dtn.com

Follow him on Twitter @RussQuinnDTN

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