1) If you are using synthetic, you can be pretty sure that your grass is getting enough N,P,K. I think thatÂs a true statement. The P and the K requirements are dictated by accurate soil analysis. And you control the amounts of NPK applied.
2) If you are going organic, I am wondering if I will need tests to make sure that I get the right amount of the three. And if I were only putting something like soy bean meal down, won't I run into a major P and K deficit at some point? I have heard and believe that soil testing is far less important with an organic lawn care program. I like to diversify the organics by using corn meal, soybean meal and alfalfa pellets. All the autumn leaves get mulched into the lawn and piled onto the beds. Homemade compost gets spread across most of the lawn throughout the summer and fall as it becomes available. I donÂt worry about NPK at all. My KBG lawn is very dark and thick. Now the fine fescue in the shady areas is a still a challenge but is much better than when chemical fertilizers were used exclusively and the leaves went to the landfill (or to my horror, burned). Bill Hill

Synthetic fertilizer has N, P, and K. Organic fertilizer has everything in it to include all the trace minerals not included anywhere else.

1) If you are using synthetic, you can be pretty sure that your grass is getting enough N,P,K.

I've always wondered about the N part of that, anyway. One good heavy rain after feeding and what percentage washes away? Nobody seems to know. You can lose K the same way, but at least the P binds a bit better and only leaves via erosion.

2) If you are going organic, I am wondering if I will need tests to make sure that I get the right amount of the three. And if I were only putting something like soy bean meal down, won't I run into a major P and K deficit at some point?

I'm debating about bothering with it myself. The optimal nutrient proportion is around 4-1-2, with soybean being 7-1-2 (or 7-2-1, reports differ). However, there's a point where close enough is good enough, and 7-1-2 should be in that range.

Besides, all the happy bacteria and fungi will be supplying P and K from mineral sources that a synthetically-fed lawn won't have available to nearly that extent.

My philosophy tends to be that if it looks good and grows well, it is good. If I have a problem, then I start looking deeper.

Depending on the test N levels can vary widely
in a very short period of time. A better indicator,
for my money anyway, is amount of organic matter in
the soil.