What’S All This About Chemical Nitrogen Leaching Into Groundwater From Lawn Fertilizers?

One of the best illustrations of the huge network of roots produced by grass plants is illustrated here. The turf was planted on an extreme slope and nylon mesh was installed to hold it in place until the network of roots could get established. In only a few months the root system will virtually guarantee no erosion of the turf or soil. Author photo.

The matter of nitrogen leaching into our rivers and streams, and possibly into groundwater, as a result of the fertilizing of home lawns, seems to be a major topic in the general media again. This is an old complaint, usually made by those who would have us use nothing but “natural” elements in plant fertilizing, rather than chemical elements. 

First, if it is your desire to use only natural elements, that is certainly possible. Most fertilizer companies offer balanced fertilizers made from wholly natural (organic) elements, as well as those with mixed (chemical and organic) elements, in addition to the all-chemical types. 

Keep in mind that no research has ever been able to show that plants can tell the difference in the source of their nutritional elements. And, generally, the chemical fertilizers are the most economical on a unit-of-plant-food basis.

The inference that only organic (natural) fertilizers should be used on lawns and gardens because only they do not pollute the ground water is absolutely false. One study, conducted over four decades by the University of Iowa, tracked the leaching of nitrogen from agricultural land all along the Iowa River through the state. The study began in 1945 and ended, or was last reported on in 1988.

Coincidentally, one sampling station was situated on the river just above the city of Des Moines, and the next, just below. At the time the study began, there was no fertilizer being applied to home lawns. In fact, as internationally noted and distinguished turf expert, Dr. James Beard, said in commenting upon the study, “no nitrogen was being used in the making of fertilizer--all of it had been going into the manufacture of bombs for use in Europe!”

By the time of the 1988 report, like all Canadian and US cities, Des Moines had grown immensely, and fertilizer applied to home lawns in the city and suburbs was extremely common. What did the data from the sampling stations show? Interesting! Absolutely no increase in nitrogen (from leaching or other sources) detected at the lower sampling station than there was at the upper. Simply put, there had been no leaching of nitrogen into the ground water (or river) resultant from the fertilizing of lawns and gardens in that city.

Now, the amount of leaching from the agricultural lands was significant throughout the testing years. But that is quite easily explained by erosion and over-application basically to bare (un-cropped) soils. My point, and that of James Beard, is that there is absolutely no evidence of leaching of fertilizer elements from home lawns (and gardens) into ground water. There is likewise no evidence of pesticides getting into our ground water in any significant amounts.

One of the reasons home lawns are so efficient in retaining fertilizer (and pesticide) elements (as well as soil-bound air pollutants) until they are broken down, is their efficient root systems. Grass plants generally have in excess of 2,400,000 plants or shoots per hectare (six million to 20 billion plants per acre). This is an amazing natural network that traps and retains all types of pollutants, both natural and man-made. 

Grass root systems are also the single most efficient plants on earth in “manufacturing” organic matter. So, if yours is a new home in a subdivision where the good topsoil has all been removed, establishing a lawn for the first few years prior to making a garden is the best way to go. When you do start making specific garden areas be sure not to remove the grass, simply turn it over and incorporate its high organic matter into the soil.