Farmers could certainly do a better job of soil conservation and nitrogen runoff. Vast majority of nitrogen in the water comes from farms. That's a scientific fact.
There is a point to royalcy on the lawn runoff too though. We care about our lawns wayyy too much in this country and heavy rains drive nitrogen runoff into storm sewers. I am remembering a thread on here where someone was putting fertilizer on their lawn 4 times a year. If you are one of those people you would be extremely hypocritical to criticize farmers as they use very calculated rates. Precision agriculture with soil testing is improving excess use somewhat. Most people applying on their lawn have no idea what thier soil profile is.
On your tech point - I have a computer program that I can build variable rate prescriptions from. These scrips are made using Cation Exchange Capacity (nutrient holding capacity), historical yields, and soil test levels on different nutrients. I do this on 2.5 acre grids so on a 160 acre field there are 64 different amounts of fertilizer applied to match the productivity in each of those 2.5 acre tracts within the larger field. It’s pretty incredible how far some of this stuff has come.