Two people with agricultural affiliations responded in an expected manner to my commentary, "For 'biggest bang for the buck' ban land application of manure" (May 2009).

It is unfortunate the editors used the word "manure" rather than the phrase "animal waste." In most people's minds, "manure" applies to feces from large animals such as horses and cattle. The practice of allowing these kinds of animals to forage on fields, which are then rotated to grow crops in subsequent years, is not a large source of nutrient pollution in the Chesapeake Bay because so few animals are raised that way any more. In fact, the practice is desirable at low densities of animals, as the grazier who responded in "Throwing away manure is like throwing away money" (July-August 2009) advocates.

Massive pollution from animal waste is caused because almost all of the solid waste, including waste from humans-and especially poultry-is produced in localized areas such as confined animal feeding operations, wastewater plants or poultry sheds.

The huge amounts of waste must be disposed of, and the cheapest disposal method is by land-application elsewhere, so excuses are manufactured to justify the practice. Animal waste is disposed by land application on less than 5 percent of agricultural land in Virginia, so a huge pollution problem is caused on a very small fraction of farm acreage.

First, some facts must be established so readers are not misled by excuses such as "recycling a valuable resource," promoting the "rural life" and protecting farmland from conversion to "other uses." It has been known for one-third of a century that inefficiencies in agricultural fertilization practices is the largest source of nutrient pollution of Chesapeake Bay. Subsequent studies have confirmed that original 1973 Army Corps of Engineers finding.

Chesapeake Bay nutrient pollution can be summarized simply because the total nitrogen and phosphorus pollution load can be divided into four approximately equal-size quarters:

  • Conventional agricultural chemical fertilization,
  • Disposal of animal waste by land application,
  • Water discharged from wastewater treatment plants, and
  • Everything else, including stormwater runoff (especially combined sewage overflow), homeowner fertilization practices, acid rain, septic systems, etc.

The president of the Maryland Farm Bureau wrote: "Nutrients are not pollution and, when properly applied, represent the most effective and efficient means to recycle this valuable resource," in "Manure-nature's fertilizer predates nutrient woes," (July-August 2009).

It is impossible for any kind of fertilization to be 100 percent efficient, so all mechanisms of fertilization cause nutrient pollution. Nutrients become pollutants when their excess is released into the environment because they are not sequestered in the crop.

Typical chemical fertilization is rarely more than about 80 percent efficient, meaning that if 120 pounds of chemical nitrogen are applied to a field, 96 pounds are removed with the crop and 24 pounds are released into the environment.

More pollution occurs when nutrients are applied according to crop needs using animal waste as fertilizer. The nutrients in animal waste are contained in organic material, which must be decomposed by microbes to release the nitrogen and phosphorus for plant uptake. Microbial decomposition takes time, so the absolute amounts of nitrogen and phosphorus applied to grow a crop must be larger than what is needed for chemical fertilizers, which contain nutrients that are immediately available to the plants. In Virginia, nutrient management plans assume that between 30 percent (lime-stabilized sewage sludge) and 60 percent (poultry litter) of the nitrogen is available to the crop immediately after land application. So if the crop needs 120 pounds of nitrogen per acre, 400 pounds of nitrogen must be applied in sewage sludge. What happens to the excess 280 pounds of nitrogen over and above what would have been applied using chemical fertilizer? When a corn crop is drying in the field in late summer, what happens to the nutrients not being taken up by the dead corn that are released into the environment as microbes decompose the sludge particles at summer soil temperatures? Is this "the most effective and efficient means to recycle this valuable resource"? I think not. It is a highly inefficient way to use a very small fraction of the nutrients in the waste, and it is responsible for one-quarter of Chesapeake Bay nutrient pollution.

Does the Bay have no value to society? "Value" does not relate solely to a farmer's bottom line. Efficient recycling is obviously a desirable goal, but as long as our society throws non-renewable resources like aluminum cans in landfills, rather than recycling them, worrying about efficient recycling of a renewable resource (animal waste) is just a hollow excuse.

Reflect on the fact that agricultural practices are responsible for roughly half of the Chesapeake's nutrient pollution, and that the pollution caused by the land application of animal waste is roughly the same magnitude as that caused by all the wastewater treatment plants in the watershed. Reflect on the cost of banning the land application of animal waste relative to the cost of upgrading wastewater treatment plants and stormwater disposal systems. It is long past time to accept the scientific consensus that agricultural fertilization practices are the largest source of the Bay's nutrient pollution and to stop believing that voluntary actions by farmers will significantly reduce pollution. They haven't.

We must concentrate resources on reducing the biggest source of pollution and spreading the inevitable costs widely and equitably, despite the powerful resistance of agricultural interests and their lobby. Why can't chemists develop timed-release fertilizers to provide nutrients as the plants need them? A single application of conventional chemical fertilizer is inefficient because so much of the fertilizer washes out of the soil before the maturing plants can use it. Side-dressing or split fertilizer application uses less fertilizer and is more efficient than a single application of fertilizer, but costs more in time and fuel.

Nitrogen-laced groundwater beneath agricultural fields is proof-positive of the inefficiencies in agricultural fertilization, and the groundwater discharges into the Chesapeake Bay.

Abysmal water quality in the Bay exists because we continue to do everything as cheaply as possible. Unless citizens agree to pay for the changes needed to improve water quality-higher wastewater bills, taxes to pay the debt on municipal bonds that improve infrastructure, more expensive chicken-no progress is possible. "Throwing away manure is like throwing away money" may apply to a very small percent of Virginia farmers, but using manure as a highly inefficient "free fertilizer" costs all of society in reduced commercial and recreational fisheries, lost jobs for watermen and reduced property values because of water pollution. Farmers are not the only people who matter.

The Bay's water quality matters too, and will be better served when all animal waste is used as biofuel, replacing some imported fossil fuel and its emissions that are the cause of global warming. It is time for the EPA to mandate that action, especially in the case of municipal sewage sludge-where the grazier and I agree-because of additional concerns about human health and the dissemination of antibiotics and other chemicals, including pharmaceuticals, into the environment.