Soil biology a long term tactic

If anyone doubted that soil biology is a long term tactic, the following graph that I discovered recently, from the Rothamstead agricultural research station illustrates this.

"FYM" stands for farm yard manure, and it took some 40 years for soils to respond to applications.

Apparently, the initial aims of these plots were to show that artificial fertilisers could match the traditional applications of farm yard manures. These graphs indicate that to some extent, this can true in the short term, but not in the long term.

We still have a lot to learn about this. Any comments or further detail would be greatly appreciated.