Fertilizer Run-Off

Despite the tremendous positive effects fertilizers have had on the human population, its negative consequences are of dire concern. Because farmers desire maximum yield of crops, massive amounts of fertilizers are used to increase the productivity of their crops. Although, as previously shown, this substantially increases the biomass of the crops, much of the nitrogen and phosphorous from the fertilizer doesn’t end up in the crops. Instead, the nutrients which are extremely soluble in water get run off fields (through irrigation systems) into rivers and eventually end up in the ocean.

This is the case for the Mississippi River Drainage Basin, the third largest drainage basin in the world, exceeded in size only by the watersheds of the Amazon and Congo Rivers. The basin covers more than 1,245,000 square miles, including all or parts of 31 states and two Canadian provinces and has a spout (called a delta) at the Gulf of Mexico. Waters from as far east as New York and as far west as Montana contribute to flows in the lower river.

Massive amounts of fertilizers (along with other sources of Nitrogen) run off the farms and get drained into the Mississippi river and its neighboring water systems. Estimates of total annual nitrogen inputs in metric tons to the Mississippi River Basin place a number of 11,602,900 metric tons of nitrogen. To put this in perspective, the amount of nitrogen dumped into the Mississippi River Basin per year is the equivalent of 7,735,266, four door sedans! Although this estimate includes other nitrogen sources such as livestock manure and legumes (nitrogen-fixing plants mentioned earlier), the 51% of nitrogen polluted in the Mississippi Basin from fertilizer is astonishing. What’s important here is that nitrogen-based chemicals are not the only ones that are being drained into the basin. Phosphorus and potassium, both around equally present in fertilizers as nitrogen are key players in the pollution of the Mississippi River Basin.