If you live in an area where livestock outnumber people, manure being used as a fertilizer source is simply common practice. Collected manure needs to go somewhere, and the available nutrients can be put to good use in soil where crops are grown. Manure flows through draglines or travels by tankers to fields nearby.
The scene is much different in other parts of the country. In places where corn and wheat fields span as far as the eye can see, manure is often not easily accessible. In fact, according to numbers from the United States Department of Agriculture (USDA), just under 8% of the 240.9 million acres planted to the seven major field crops of corn, soybeans, wheat, cotton, barley, oats, and peanuts received manure as a nutrient source in 2020.
That number seems small, considering the millions of farm animals that live across the country. Yet, maybe it is not that surprising given that one of manure’s biggest hurdles for use is transportation.
In a USDA report released earlier this year, titled “Increasing the value of animal manure for farmers,” the authors noted that manure has a low nutrient value-to-mass ratio. This is partly due to water content, which can be up to 90% of the manure’s weight in some cases. The sheer volume makes transportation and application costly.
Also, while manure supplies nitrogen, phosphorus, and potassium, it does not come with a guaranteed analysis, and the nitrogen-to-phosphorus ratio is lower than what is required by crops. So, while manure can be a wonderful complement, it is not always a perfect substitute for commercial fertilizer.
Because animal production and manure management differ by region, the amount and type of manure used to fertilize certain crops varies. A breakdown of what type of manure is applied to each of the major crops can be found on page 15.
Corn acres are most likely to receive manure, in part because more acres are planted to corn than any other field crop. Of the acres that receive manure, 78% are planted to corn. More details about this are available on page 21.
Of the 3,109 counties in the contiguous United States, an estimated 390 counties generate more manure-supplied phosphorus than crop production can use, and about 100 counties generate excess nitrogen. The uneven distribution of manure does not make it a hot commodity, though. The authors of the report explained that, if manure-supplied nutrients exceed crop needs, the growers will not demand the extra nutrients, actually lowering the overall value of manure.
To capture more from manure, the report highlighted several opportunities for farms to enhance the fertilizer value or lower its cost of use. This included subsurface application to conserve nitrogen, ration formulation that affects the characteristics of manure excreted, manure additives that can enhance the end-products’ fertilizer value, and composting to remove water and condense the final product. The authors also pointed to liquid-solid separation as a practice that provides several benefits for the high moisture content manure that comes from dairy and hog farms. Other technologies that remove liquid from manure to make it easier to transport are also intriguing options.
Beyond fertilizer, the report also gave a nod to the nonfertilizer uses, including energy production. The feasibility of these potential income streams, however, often depends on the incentives and financial support provided by governmental or private industry sources.
The bottom line is that there are more acres that could utilize the benefits of manure, if we can find ways to move these nutrients farther. If you would like to view the whole report, it can be found at this link: bit.ly/valueofmanure. It is an interesting read and highlights the challenges of manure — and the opportunities that await.
Until next time,
This article appeared in the August 2023 issue of Journal of Nutrient Management on page 4. Not a subscriber? Click to get the print magazine.