Weather, and especially rainfall, is the most important factor affecting crop yields in Iowa. The moisture used by crops comes from two sources- crop season rainfall and soil reserves. Here's how we stand for 1963.
Shaw, R. H. and Duncan, E. R.
"Crop Yield Prospects for 1963,"
Iowa Farm Science: Vol. 17
, Article 7.
Available at: https://lib.dr.iastate.edu/farmscience/vol17/iss7/7