The article, MD tough phosphorus tool may be joined by revisions of other Bay states (January-February 2016), should have clarified that the “tools” must apply to poultry litter and sewage sludge as well as manure. And Maryland’s tool is very far from being tough, which is what agricultural interests want and have so far achieved.
The article states that Maryland, Virginia and Pennsylvania trigger their respective tools at phosphorus levels of 150, 127, and 200 parts per million in the soil. According to the 2006 Mid-Atlantic Nutrient Management Handbook, the critical phosphorus level for the Mehlich 3 soil test is around 30 ppm for mid-Atlantic soils. If the results are less than 30 ppm we would expect a profitable crop increase if we add phosphorus. But if the test result is higher than 30 ppm, no yield response is expected. [my emphasis] Obviously, the tools favor cheap phosphorus disposal, only kicking in at phosphorus levels much greater than what is necessary for the crop.
None of the tools require that phosphorus application be limited to a “crop-removal” rate. Applications at this rate would not impact crop yield because that is how inorganic phosphorus is applied. In Virginia, “Phosphorus applications from inorganic nutrient sources shall not exceed crop nutrient needs over the crop rotation based on a soil test.” (Source: Virginia Nutrient Management Standards and Criteria from the Virginia Department Conservation and Recreation)
Demanding that the use of organic phosphorus follow the same rule would require more acreage, create more hassle for the waste producers and require more bureaucrats to regulate the disposal process. More importantly, additional nitrogen fertilizer would need to be applied because an application of phosphorus in animal waste at a crop-removal rate would not supply enough nitrogen for the crop. Such a rule would protect water quality and crop yield, but not the profits of waste producers.
In certain situations, Virginia and Pennsylvania continue to allow the land application of organic waste to be nitrogen-based, guaranteeing a massive over-application of both nitrogen and phosphorus and proving that agricultural economic concerns continue to trump concerns about water quality.
Pollution is an externality and its real cost is never accounted for. In Virginia, dairy manure is applied assuming that 35 percent of the nitrogen is available to the next crop because it takes time for microbes to decompose the organic material in the waste and release the nutrients for plant uptake.
What happens to the other 65 percent of the nitrogen? Unless nitrogen fertilizers are considerably reduced for subsequent crops — which is not required and rarely done — much of the excess nitrogen is pollution. It is easy to understand why animal waste — poultry litter, sewage sludge and manure — accounts for half of all agricultural nutrient pollution, or a little more than a quarter of Bay nutrient pollution because less than half of the disposed nitrogen and phosphorus ends up in the crop.
For those who want round numbers, assume a yield of 175 bushels of grain per acre and that each 56 pound bushel contains about 0.4 pound of phosphorus pentoxide and 1 pound of nitrogen. To supply 175 pounds of nitrogen for the crop, 500 pounds (175/0.35) of nitrogen in manure must be applied per acre, accompanied by several hundred pounds of phosphorus as determined by the nitrogen/phosphorus ratio in the waste. The grain harvested from an acre contains 175 pounds of nitrogen and 70 pounds of phosphorus, so the disposal results in the application of 325 pounds of excess nitrogen and about 200 pounds of excess phosphorus per acre, depending on how much phosphorus was already present in the soil.
Why shouldn’t phosphorus application be limited to a crop-removal rate? Why should the use of organic phosphorus be any different from the use of inorganic phosphorus, except to promote cheap waste disposal? Even better for the Bay, why not ban the disposal of manure, poultry litter and sewage sludge by land application? This could be accomplished with the stroke of a pen (and lots of litigation) if any political entity really valued Bay health over agricultural profits. The waste is better used as biofuel and the phosphorus recovered. A ban would ultimately have more effect on improving Bay water quality than all the expensive wastewater treatment plant upgrades we have paid for, and which have not resulted in significant Bay water quality improvements because their impact is overwhelmed by the agricultural pollution. Unless agricultural nutrient pollution is significantly reduced, no meaningful improvement in Bay water quality is possible. Period.
Or, will we continue to sanction the cheap disposal of animal waste for a few powerful special interests — paying lip service to pollution with highly permissive regulations so that we might enjoy less-expensive food?