This section considers soil water and its influence on crop stress and crop yield. The first section discussed mainly the variability of crop yield, especially the variability over time. The second section showed the direct effects of weather on crops, particularly monthly average weather, and reviewed how warm temperatures could reduce yield in July or August, and a slightly cooler than usual month could result in a contribution to yield for that month.
Soil water is the amount of water available to a crop from the soil.
Not all water in the soil is crop-available water. Across Iowa, there is variability in the amount of water typically available to the crop. Measurements of crop-available moisture in the state of Iowa are taken in the month of November and also in April. The data from these measurements are summarized in Fig. This assumes that crops have a 5-foot rooting depth and the water in the top 5 feet of soil is the water available to the crop.