The long term negative impacts of inorganic, synthetic fertilizers on soil, water, and air are now well established facts. Hundreds of peer-reviewed scientific papers – dating as far back as 1930 – have described the environmental damage caused by using these chemicals to grow food and other plants, yet nitrogen and phosphorous-heavy fertilizers still persist in home gardens and farms. The reality is that in gardening, organic methods are far superior, and in the case of farming, can deliver equivalent yields. But marketing targeted at homeowners and the corporate stranglehold on the farm system drowns out this message.
Compost is a safer fertilizer than synthetic chemicals
Nitrogen, phosphorous, and potassium (N-P-K) are the “big 3” chemicals required in varying ratios by plants. Synthetic fertilizers and compost both supply these chemicals, but their actions and impacts are considerably different.
Compost gradually feeds N-P-K to plants along with additional, supporting nutrients over a period of months. This gradual feeding also supplies the soil food web as well – the bacteria, fungi, and insect and animal life necessary to sustain plants. Synthetic fertilizers on the other hand, are concentrated, water soluble, man-made versions of these chemicals. Most formulations only contain these three chemicals, but some also contain pesticides and herbicides.
When applied, whatever the roots of garden plants or lawn don’t take up is washed away into local watersheds where these excess chemicals cause significant damage. These fertilizers are salt-based solutions which acidify soil with long-term use, rendering it inhospitable for microbial life. Adding to the problem are the gardeners and homeowners who don’t read the package directions and apply a heavier dose of fertilizer than the manufacturer recommends, which increases the impact on the environment.
But the problem extends beyond backyards and local waterways.
Nitrogen and Phosphorous runoff creates algae blooms
The central interior of the United States and parts of Canada – the area between the Rocky Mountains and the Appalachian Mountains – is like a vast funnel that drains into the Mississippi River. Every local creek, stream, river, and lake in this region eventually winds its way into the massive river which drains into the Gulf of Mexico. It’s in the Gulf that we see the effect of this overuse of synthetic fertilizers.
Every summer in the Gulf of Mexico, an area estimated to be the size of Connecticut becomes choked with algae and phytoplankton blooms. This is due mostly to the massive runoff of nitrogen and phosphorous carried by the Mississippi River. Algae and phytoplankton, necessary to sustain higher forms of marine life, feed on these chemicals and reproduce in vast numbers very quickly, a population explosion which overwhelms the ecosystem. Marine life is unable to consume the suddenly plentiful algae and as it dies and decomposes, uses up available oxygen. This renders the area uninhabitable for fish or any other marine life and creates a dead zone. Called algae blooms, they discolor water, form huge, rancid-smelling piles on beaches, and in some cases kill fish and coral.
Synthetic fertilizers reduce organic matter in soil
A team of researchers at the University of Illinois, led by professors Richard Mulvaney, Saeed Khan, and Tim Ellsworth, published two papers describing how fertilizers use up organic matter in the soil. Initially they concluded, nitrogen fertilizer stimulates soil microbes, which consume organic matter. But these microbes consume more organic matter than what is added to the soil from crop and plant residue. As the volume of organic matter decreases, the soil’s physical structure changes as well, losing its sponge-like ability to hold water, air, and organic nitrogen. Water leeches through the soil, carrying nitrogen into local waterways where it fouls the water. The free nitrogen also enters the atmosphere as Nitrous Oxide (N2O) , which has three hundred times the heat-trapping power of carbon dioxide. Then, with less oxygen available, soil life slows and the intricate ecosystem in the soil becomes dysfunctional.
And this becomes a vicious cycle. The soil, with less and less organic matter every season, becomes dense and compacted, allowing more water and nitrogen to run off into waterways and escape into the air. Plant roots have a hard time anchoring in dense clay, making the soil more vulnerable to erosion and able to hold even less water. As garden plants and lawns struggle for survival, inexperienced gardeners conclude that they need to apply more fertilizer, a message reinforced by marketing, and they unwittingly perpetuate the cycle.
The answer is that you rarely need more fertilizer, synthetic or organic. What you usually need is more organic matter from compost. The rule of thumb is to feed your plants (including grass) much as they would be fed if they were growing in the wild – rotted leaves, decaying plant and food residue, and animal manures. Add compost, composted manure, and leaf mold to your garden and lawn and the plants will take care of themselves.