Yield should be measured for the whole plot, and hills counted.  

 

Usually, yields should not be adjusted for missing hills, because hills may be missing because of varietal differences in seedling vigor or disease resistance. Adjusting yields by counting hills and then multiplying per-hill yield by the number of hills in a plot introduces big errors, because plants growing beside missing hills have more tillers and higher yields.  

Thus, adjusting for missing hills usually overestimates yield, especially when many hills are missing.   

However, if hills are missing because of rat or insect damage, or other random causes, it may be justifiable to make the adjustment.  If there are many replicates within or across sites, it is usually unnecessary.