As we get to the heart of land application season my thoughts always drift to the same concepts. How can we do better at moving manure from farmstead to field, quickly, safely, and environmentally consciously? Manure has long been considered a valuable input to the soil for crop production and in its broadest sense manure management is the science of figuring out the most appropriate use of animal manure and how to get the most benefit for the least expense while protecting air, soil, and water quality. When it comes to manure utilization it seems like every year is a discussion of how we can get 10-billion gallons or so of liquid manure applied quickly, safety, accurately, and as cost effectively as possible. There are several ways to do this: bigger equipment, more people in the manure business, extending application seasons either by planting crops with different harvest windows or developing technologies that allow application during the season.
Today I’m going to focus on just one little aspect though – nutrient delivery rates with drag line systems for dairies and pig finishing manure. My costs are all approximate as lots of factors can influence cost, but right now we are going to take a look at why application rate may be important.
Say we have two farms, one a dairy and the other a finishing swine farm, who each generate the same amount of available nitrogen for land application every year. Let’s say this is a 4800-head swine farm so it will generate about 1.75 million gallons of manure a year or about enough manure from 695 acres (approximately 60 lb N/1000 gallons). At this farm we’d have an application rate of about 2500 gallons per acre. At a dairy the manure would have closer to 10 pounds of N per 1000 gallons so we’d apply right around 15,000 gallons per acre and would be dealing with closer to 10 million gallons of manure.
For illustrative purposes, I’m going to ballpark $500,000 in equipment costs (pumps, hose, drags, and a toolbar) but that is all dependent on what you are using. In the case of swine manure let’s assume we have a 30-foot bar and can drive through the field at 7 mph, this means they can cover an 0.42 acres per minute and to get 2500 gallons per acre the flow rate would be about 1060 gpm. This means to get all 1.75 million gallons applied would take 27.5 hours and assuming the crew was about 50% efficient it would take about 55 hours overall. Just for fun in estimating, let’s assume run time costs about $500 an hour (tractors, fuel, wear and tear, etc.). If we figure a 5-year equipment life and that 1.75 million gallons is about 10% of the total gallons they apply every year, then or cost for manure here would be about $37,500 or about $0.02 a gallon of manure applied or about $0.36 per pound of N applied.
Now let’s take a look at the case of the dairy. Here we are covering the same number of acres and would have the same number of sets so let’s assume that setup time was again 27.5 hours, however we have lots more gallons to apply so the application will take a bit longer. In this case we can probably pump around 3000 a minute if everything is set up well so we’d take about 57 hours of application time so with setup time we’d have about 84 hours in application time. As we are applying more gallons this might represent 50% of the annual gallons this crew would apply. If you work this about we have about $42,000 in variable rate cost related to application time and about $50,000 in equipment depreciation for a total of $92,000. This would work about to about a $0.01 per gallon application cost or about $0.88 per pound of nitrogen applied.
So when you think about what your manure application, remember there is a lot that goes into that per gallon price and application rates can play a big role in that, but it’s important to also think in terms of fertilizer benefit you are providing.