Years ago, if our industry had a lawn that just wouldn’t green up, the answer was to apply a synthetic fertilizer with increased nutruients and hope for the best. A majority of the time, you would get a visual improvement - but it wouldn’t last long. This was the most comon in homes under 10 years old because of the builders sand used during construction. The problem with builder's sand is there were no soil nutrients to feed the lawn between synthetic applications and no one ever added anything to build the soil's nutrient-levels or beneficial bacteria. The answer was to keep bombing with synthetic nutrients.
That's bad for your lawn long-term, bad for your soil, and bad for the enviornment as a whole. Unfortuneately, that's still common by some of the larger pest control companies today.
This is why we use bio-stimulant applications that add carbons, probiotics, beneficial bacterias, and micro-organizms back to your soil, in addition to organic-based lawn fertilizers. We are essentially “rounding out” the old school basic lawn fertilizer program by supplementing the soil with nutrients for long-term health.
Think of this like you taking vitamins. You can get 100% of your daily recommended vitamins and minerals from daily synthetic supplements (vitamins, fish oils, etc.) but you still have to eat something of substance or you will starve to death. You can’t live on vitamin supplements and water alone for very long, and the better you eat a well-balanced diet - the more natural vitmins, minerals, and oils you are getting, lessening the need for the synthetics vitamins.
Soil is the same way - we need to give it some substance and that is where the sea kelp, humics, biochar, and other fun stuff come in. Even our old friend Milorganite is a soil building suuplement because it is derived from microbes that have consumed waste materials. It is organically derived. This is why we do an intial soil test on every lawn before we ever begin a lawn program.
Now, this is going down a deep rabbit hole into soil and plant science, and we are probably starting to approach information overload, but I'm a lawn nerd. Sorry I'm not sorry. :)
Also, when we get too “sciencey” about 80% of people just tune us out because it’s too complicated. So I'll just say, “Trust me, if you use soil ammendments that we recommend, you will be building your soil over time. More and more elements and nutrients will be present there, naturally by having a nutrient-rich soil.”
But if you do want to get deeper and improve your understanding, John Perry from Greene County Fertilizer did an entire series last year on soils. Here's a YouTube playlist of that series for you here.