Figure 1. Theoretical (not actually measured data) crop response to nitrogen fertilization. There were 5 replicates of each N rate (some data points are hidden behind others). Note the rapid increase in yield with the first few increments of N fertilization, then a leveling off, and possibly an indication of yield reduction with excessive fertilization. Also, note there is some yield with zero fertilization, in this case approximately 20% of the maximum yield. We will use the term "percent relative yield" to express this percentage of the maximum yield. There appears to be no further increase in yield after 150–200 lbs/acre N. This example is used for illustration purposes; typically in field experimentation, there is more variation among the replications, especially at the lower rates of fertilization.