The Climatology of Soil Moisture, Atmospheric Evaporative Demand, and Resulting Moisture Stress Days for Corn at Ames, Iowa

Abstract

The average seasonal march and frequency of soil moisture in the com root zone at Ames, Iowa, during a 30-yr period was estimated for a well-drained 5-ft soil profile holding 9 inches of available water at field capacity. Average seasonal marches of soil moisture in the top 5 ft were also prepared from simulated water balance computations for soils with three different available field capacities (6, 9 and 12 inches) and, for each capacity, three different 1 April soil moisture profiles (20, 60 and 100 per cent of available field capacity) from which to begin the moisture budget calculations. The average seasonal march and frequencies of evaporation from a Weather Bureau Class A evaporation pan and from com with soil moisture not limiting were estimated. Using an experimentally derived atmospheric-soil moisture stress relation for com, the climatology of potential evapotranspiration from corn was expressed as the soil moisture necessary in the corn root zone to prevent moisture stress in com on any day of the season. The estimation of moisture stress in corn showed at least some stress days to occur in every one of the 30 years and an average of 40 non-stress days in the critical 63-day period for corn six weeks before silking to three weeks after silking.