Your "bank account" of soil moisture can't be "overdrawn" - nature won't advance the funds. Your account for 1957 crops depends on the current balance plus any amount of moisture added, absorbed and held.
Barger, Gerald L. and Shaw, Robert H.
"Soil Moisture Situation 1957,"
Iowa Farm Science: Vol. 11
, Article 4.
Available at: https://lib.dr.iastate.edu/farmscience/vol11/iss7/4