Very few field crops yield as large returns to the acre as do potatoes during favorable years, and but few crops are as greatly affected in quality and yield by soil and seasonal conditions. The potato is particularly sensitive to soil moisture. For this reason yields under irrigation, where the moisture can be controlled, are usually much higher than where the moisture supply is irregular.
Harris, F. S., "Bulletin No. 157 - The Irrigation of Potatoes" (1917). UAES Bulletins. Paper 123.