“Way down upon the Swanee River, far, far away, that’s where my heart keeps yearning, yearning – for where the old folks play.”
My mom used to sing these words to me as she tucked me in to sleep at night and I would cry thinking of the old folks far away that I would never see again. Her father, my Grandpa Charlie, sang the song to her when she was a child and now I sing it to my son Charlie as well. In my mind the Swanee River was always an allusion to heaven, not a real place on Earth. Imagine my surprise then, when researching the sources of phosphorus fertilizer, to learn that the Suwannee River actually exists right here in the U.S. – flowing 246 miles from the Okefenokee National Wildlife Refuge in Georgia to the Gulf of Mexico in northern Florida (time to brush up on my southeast US geography!). It turns out also that the original lyrics to the song (which references “darkies” living on the plantation) are quite different from those passed down from generation to generation in my family. I imagine Grandpa Charlie changed his version long ago so that the words are now as sad and sweet as the melody that they accompany. But what does this have to do with fertilizer, you ask?
Commercial fertilizers contain three vital nutrients – nitrogen (N), phosphorus (P), and potassium (K). The Suwannee River Mine, which opened in northern Florida in 1965, was once one of our nation’s most productive sources for rock phosphate, the raw material used to manufacture phosphoric acid (phosphorus). It was purchased by Potash Corporation of Saskatchewan, Inc. in 1995 and appears to be lying fallow at the moment, though several other mines are still operating in Florida. In the U.S., 80% of all rock phosphate mining is done in North Carolina and Florida, though there are also reserves in Utah and Idaho. Worldwide, China and Morocco are the only two countries that mine even more rock phosphate than the U.S..
To obtain phosphoric acid for commercial fertilizers, rock phosphate is either treated in an electric furnace, creating a pure and expensive phosphoric acid called white or furnace acid, or it is treated with acid through a wet process that creates gypsum as a by-product. The phosphoric acid is then heated to reduce the water content, creating a superphosphoric acid. To create a complete fertilizer, ammonia is added to the superphosphoric acid (N), followed by finely ground potash (K), to create liquid or dry material with nitrogen, phosphorus and potassium.
In a farm field or natural environment, phosphorus adheres to soil particles or is taken up by plants, so it generally stays put on the landscape as long as the dirt and vegetation remain. Because the phosphorus is taken up by plants, leaves, stems, seeds, flowers, and fruits contain the nutrient, and it is also passed on to humans and animals that eat plants. Hence, manure, compost, and sewer sludge are three common organic fertilizers that are used as alternatives to inorganic commercial products. (Incidentally, agricultural research suggests that using manure as fertilizer can often result in too much phosphorus and potassium, while bio-solids can have too much nitrogen. In other words, it is much more difficult to apply exactly the right amount of an organic fertilizer.)
Unfortunately, in a human-built environment, soil and vegetation don’t always stay put. Erosion from farm fields and construction sites send phosphorus-rich sediment into nearby streams, lakes and rivers. In the water, the phosphorus feeds algae and aquatic plants, turning the water green. Leaves and grass clippings washed into storm sewers create a similar effect when they break down and release phosphorus into the water. In 2005, Minnesota passed a law making it illegal to use phosphorus fertilizer on lawns due to concerns that too much phosphorus was making its way into lakes and rivers. Despite this change, however, phosphorus continues to wash off the land and Minnesota lakes continue to turn green.
Once phosphorus reaches a waterway, it might settle at the bottom of a lake or wetland (feeding algae for decades to come), or it might continue it’s journey from lake to stream to river. Large rivers like the Mississippi carry phosphorus from the center of the continent out to the Pacific and Atlantic Oceans where it eventually settles on the ocean floor. Some of this would happen naturally – the rock phosphate mined out of the swamps in Florida today are the remains of ancient sea beds that turned to rock thousands of years ago – but we’ve accelerated and amplified the process, creating a nutrient super-highway. After phosphorus flows down the Mississippi River and into the Gulf of Mexico, it becomes inaccessible to us, for all practical purposes. For this reason, preventing erosion and composting yard waste is as important for our long term prosperity as it is for water quality.
Learn more about erosion control at: http://www.mnwcd.org/land/erosion-control/
Learn more about using compost for farming and gardening at: http://www.extension.umn.edu/garden/fruit-vegetable/using-manure-and-compost/
Visit the Suwannee River at: www.floridastateparks.org/park/Big-Shoals; www.floridastateparks.org/park/Stephen-Foster; https://www.floridastateparks.org/park/Suwannee-River; https://www.floridastateparks.org/park/Lafayette-Blue-Springs; https://www.floridastateparks.org/trail/Suwannee-River-Wilderness-Trail; https://www.floridastateparks.org/park/Troy-Spring or about a dozen other Florida State Parks.