I might disagree that N delivery via rainwater is meaningful. In fact, the studies I did years back showed N from rainwater was almost nonexistent. Rainwater may dissolve soem gaseous N2 from the atmosphere, but N2 isn't plant available. Some plant available N can be made in a reaction with lightning, but this usually adds 0.02 #N/M, so it doesn't add much. Rainwater usually perks up lawns because most irrigated lawns use treated municipal water, which usually has a pH in the mid 8s, which haxs a liming effect each time the lawn is irrigated. Lower pH rainwater helps to bring pH in range for N forms to be more easily available. Like you, I find soil testing for N to be unnecessary and to have little value. But, I was raked over the coals on this board for suggesting that. I wonder if anyone will rake you over the coals for doing the same?