A Tale of Two Grasses and the Hidden Journey of Fertilizer
Every weekend, millions of homeowners engage in the timeless ritual of lawn care. We water, we mow, and we fertilize, all in pursuit of that perfect, lush, green carpet. But what happens to the fertilizer that doesn't stay on the grass? A significant environmental concern lies just beneath the surface: nitrate leaching.
This is the process where water from rain or irrigation carries nitrates—a key nutrient from fertilizer—down through the soil, past the root zone, and into groundwater. This not only wastes your money but can also contaminate water supplies and contribute to algal blooms in nearby ecosystems .
So, the million-dollar question for the eco-conscious gardener is: can we have a beautiful lawn without polluting our planet? Scientists turned to two popular warm-season grasses—'Floratam' St. Augustinegrass and Common Centipedegrass—to find an answer .
Before we dive into the dirt, let's meet our competitors.
The popular kid on the block. Known for its wide, lush blades, rapid growth, and high tolerance for heat and humidity. It creates a thick, dense turf that many find ideal for a luxurious lawn. However, this beauty often comes with a demand for more water and nutrients.
The low-maintenance cousin. It has a slower growth rate, finer texture, and a distinctive light-green color. Centipedegrass is famously "low-input," thriving in poorer soils and requiring less fertilizer. Its motto is often "feed it lightly, or you might harm it."
The central theory scientists wanted to test was whether the grass with a slower growth rate and lower nutrient demands (Centipedegrass) would naturally leach fewer nitrates than the faster-growing, more nutrient-hungry St. Augustinegrass .
To test this theory, researchers set up a controlled experiment that would precisely measure the environmental footprint of each grass.
The experiment was designed to mimic real-world lawn conditions while allowing for precise measurement of water and nutrients.
Researchers planted plots of both grasses in specially designed field lysimeters. These are essentially large, enclosed columns of soil that allow scientists to collect all the water that drains out the bottom—known as leachate. The grass plots were maintained under typical lawn care conditions with regular mowing and controlled irrigation .
A key part of the study was applying a standardized amount of nitrogen fertilizer, tagged with a special isotope (15N), to both grass types. This "tagging" allowed scientists to trace the exact fertilizer nitrogen as it moved through the soil and plant .
Over several months, researchers collected the leachate water from each plot and analyzed it for nitrate concentration. They also regularly assessed the turf quality (a score based on color, density, and uniformity) and measured the growth rate (via clippings collected after each mowing) .
Using sophisticated instruments like ion chromatographs, researchers precisely measured nitrate levels in the leachate. The 15N isotope allowed them to track exactly how much of the applied fertilizer ended up in the grass, soil, or groundwater .
The results painted a clear picture of the trade-off between luxury and sustainability.
The Common Centipedegrass plots showed significantly lower nitrate concentrations in their leachate compared to the 'Floratam' St. Augustinegrass.
St. Augustinegrass had higher turf quality but Centipedegrass showed much better environmental performance.
Using the 15N isotope tracer, scientists could see where the fertilizer ended up. This shows the efficiency of each grass .
This experiment provided concrete, quantifiable evidence that grass selection directly impacts groundwater quality. It demonstrates that "low-input" turfgrasses like Centipedegrass are a viable and effective tool for nutrient management in residential landscapes, helping to reduce the non-point source pollution that comes from urban lawns .
Choose 'Floratam' St. Augustinegrass if your priority is a fast-establishing, dense, high-quality turf and you are committed to managing its higher nutrient and water needs carefully to minimize leaching.
Choose Common Centipedegrass if your priority is a low-maintenance, environmentally friendly lawn that naturally requires less fertilizer and is inherently better at protecting groundwater from nitrate pollution.
The science is clear: our choice of lawn grass has real consequences for the environment. The experiment reveals a direct trade-off. The ideal lawn doesn't have to be a single-species monoculture. By understanding the strengths and weaknesses of different grasses, homeowners can make informed decisions that balance aesthetics with ecological responsibility. The greenest thumb, it turns out, is one that considers what's happening both above and below the surface.