Do your homework and you can ensure spreading septage is good for the farmer and doesn’t harm the environment.
One of the benefits of land application is improved crop growth from nutrients in the septage, the primary nutrient of interest being nitrogen. This is why pumpers can enter into contracts with nearby farmers to land-apply screened and stabilized septage. The nutrients help the farmers’ bottom line because they don’t have to purchase nitrogen from other sources. It’s even better if a part of your operation as a pumper involves farming, because you can keep it on your own land to receive the value while reducing your expenses.
Federal 503 regulations lay out in detail the requirements for land application of domestic septage on nonpublic sites including cropland. The rules are less restrictive for lime-stabilized septage. Usually some additional state requirements must also be followed, so pumpers who land-apply need to be aware of all of the rules and regulations.
BY THE NUMBERS
As a pumper and as a farmer, two things relative to nitrogen need to be considered: the maximum allowable application rate and how it relates to the crop being grown at the site. A pumper who is not the farmer wants to apply as much septage as possible to a given site to avoid contracting for additional acreage. The farmer, on the other hand, wants to know if the amount applied is going to meet the crop needs. If it doesn’t meet those needs, the farmer will have to make up the difference with purchased fertilizer.
Maximum annual volume of septage that can be applied to cropland depends on septage nitrogen content, the amount of nitrogen required by the crop and the estimated crop yield. This information is usually provided through your state university and state Department of Agriculture, and varies state to state.
A simple calculation is used to estimate application rates according to federal guidelines. The Annual Application Rate (gallons/acre/year) = pounds of nitrogen required for the crop (based on crop yield goal) ÷ 0.0026. The 0.0026 constant is derived from the average nitrogen content in domestic septage. This fact is a good reason to store and mix different loads when land-applying to meet crop requirements.
Nitrogen requirements of the crop depend on expected yields for the area, actual temperature, growing degree days and rainfall. Local county extension offices can help determine the appropriate nitrogen application rates. Those rates can vary from 10,000 gallons/acre/year to 100,000 gallons/acre/year.
There are some environmental concerns about applying nitrogen as well. In my area, the concern is excessive nitrogen applications that may leach to groundwater, creating health concerns for infants and vulnerable adults when the concentration exceeds 10 mg/L (parts per million).
In coastal areas, the concern is not only for human health, but nitrogen is the limiting nutrient for algal growth in estuaries. This has led some entities to reduce the allowable application rates to the point that they cannot be used for crop production.
This is why I was interested to read about a study in Virginia that looked at application rates of biosolids to winter wheat. The purpose was to see if fall application rates were appropriate or if those rates needed to be reduced. The authors reviewed 10 studies in two areas of Virginia, the Coastal Plain, and Ridge and Valley (think Shenandoah Valley).
They found that lime-stabilized biosolids increased grain yield and nitrogen recovery (recovery means it did not leach through the soil) compared with similar applications (100 kgN/ha) of urea-split applied in coarse-textured soils without aquic properties. This means that the soils were coarse-textured sands that were well drained without high water tables. For fine-textured soils or coarse-textured soils with aquic characteristics, the two methods — biosolid and split urea applications — resulted in equal yields and nitrogen recovery.
The authors concluded that “lime-stabilized biosolids benefit winter wheat in coarse-textured soils and do not clearly benefit or damage winter wheat in fine-textured or aquic soils.” The recommendation was that fall biosolid applications of 100 kgN/ha were appropriate and should be permitted.
BEST PRACTICES RULE
These are important kinds of studies for our industry. They show our methods are based on sound scientific principles and studies, and are not just best guesses. This does not mean, though, that we should stop looking for ways to become more efficient in our applications. We should also continue to be concerned about protecting human health and environment.