They have 72 experimental plots. Thats not 72 experiments. They have 3 x 2 = 6 different approaches being evaluated It is divided into 3 overarching systems:

They have 72 experimental plots. Thats not 72 experiments. They have 3 x 2 = 6 different approaches being evaluated It is divided into 3 overarching systems: organic manure, organic legume, and conventional. Each system is further divided into two: tillage and no-till, for a total of 6 systems. There are a total of 72 experimental plots. It is likely that the 6 main approaches have been divided into smaller plots to act as a control for natural soil variations within the area, or, e.g. one side of the field being nearer to a river than the other. This is normal for agricultural experiment design I believe.