In dry years the biomass of producers is significantly decreased what would the effect be on a rodent population

The rodents like rats will be highly affected by the decline in the number of the producers during the dry spell. The rodents consume the grasses and other small insects like the grasshoppers and beetles that live on them. When the producers die, the amount of food available for the rodents goes down. This affects the survival as the food is required by the rodents for maintaining their body metabolism.

i think that is new experiments yield untrustworthy data and should be carefully considered, because you don't know what will happen with the experiments.