Previous crop has a large effect on spring soil water content (see the graph below). For each of the last eight springs (1996-2003), the soil has been wettest after fallow (11.4 in./4-ft), intermediate after wheat (9.7 in./4-ft), and driest after safflower (8.4 in./4-ft). The variation among years has been much less following fallow (10.6 to 12.3 in./4-ft) compared to following wheat (7.8 to 11.7 in./4‑ft) or following safflower (6.5 to 10.5 in./4-ft). This explains, in part, why yields are generally more consistent following fallow compared to following wheat or safflower. Producers need to determine if the higher yield potential resulting from increased soil water after fallow compensates for the loss of production from fallowed land.

The difference in water content between treatments is less when the soil is wet compared to when the soil is dry. This is because the soil has a limit to the amount of water it can hold, which is called its “field capacity”. The data presented here suggests the field capacity of the top 4 ft of this soil is about 13.5 inches. In this soil, about 4 inches of soil water is not available to a crop. Thus, the available water holding capacity of this soil is about 9.5 inches.

This past spring (2003), the soil was wetter than the 8-yr average, ranking as the second wettest  spring when the treatments were combined. When the treatments were ranked individually, each was the third wettest of the eight-year period. This spring, following fallow the soil was near the 8-yr average wetness, whereas following wheat and safflower the soil was wetter than the 8-yr average.

These data have been collected during the past eight years as part of a crop rotation study. Each data point is the average of three plots.