LESSON 1a: WEATHER EFFECTS ON CROP YIELDS

OVERVIEW

The primary concern in this discussion is the influence of weather on crops and on crop production. Weather is the major uncontrollable factor that influences the development of crops. Initially, we will look at some of the historical trends in crop yield. We often hear about deviation from yield trend. This is a concern as we have been seeing greater deviation from yield trends during the past few years than were experienced during the 1960s and the early 1970s. We attribute much of this to changing weather patterns and the interaction of the weather with the soils and the crops.

YIELD TRENDS

The United States Department of Agriculture (USDA) publishes several charts that have to do with yield trend. Typically, the USDA depicts yield trend as a straight line, averaging the yields of the past several years, usually a 20- or a 30-year period. The most recent USDA trend estimate for corn and soybeans was from 1970 through 1996 (Fig. 1.1a).

Fig. 1.1 U.S. Corn and soybean yield trends from 1970-1996 (bushels/acre).

State-wide average corn yields from 1900-1996 are depicted in Figures 1.1 and 1.2. Notice the change in yield thoughout the century. Study the figure and answer the discussion questions that follow.

Fig. 1.2 Iowa state wide average corn yields.