Weight = (mass) x (gravity)
Weight = (8 x 10⁻⁴ kg) x (10 N/kg) = 0.008 Newton
It's not true.
The crucial principle for a scientific experiment is to keep only ONE variable at a time.
In this case, the variable of this experiment is actually the tomato is in sunny part or in shady part, instead of whether applying Ca fertilizer.