The accompanying graph shows the soil water content for summer fallow, spring wheat, and safflower at approximately 2-week intervals during the 2002 growing season. For each cropping treatment, measurements were taken from three plots and averaged. All the cropping treatments being compared have been grown alternately with spring wheat since 1995. On the graph each bar is divided into four sections that represent the water content in each of the 1-ft depth increments down to 4 feet. Alternating sections have been shaded to improve the clarity of the graph. The amounts of rain received between measurement dates are also listed.

At the start of the growing season, there was little difference in soil water content among the three treatments. The soil water content was 9.4 in./4‑ft in the plots to be fallowed, 10.0 in./4-ft in the plots to be planted to wheat, and 9.0 in./4‑ft in the plots to be planted to safflower. The trend of wetness with depth was the same in all three treatments. The soil was driest at the 3 to 4 ft depth and got wetter at each depth zone closer to the surface, except that the 0 to 1 ft zone was drier than the 1 to 2 ft zone. This irregularity at the 0 to 1 ft depth was probably due to early season evaporative loss from the surface. 

The soil in all treatments gained water until the June 19 measurement.  This was due to rainfall during this period (3.04 inches) exceeding crop water use. After June 19, the soil in all treatments began to dry. In the fallow treatment, the loss was primarily in the 0 to 1 ft depth whereas in the wheat and safflower treatments, substantial water loss occurred from all depths.

By July 31, the wheat had dried the soil to near the wilting point, and little change in water content occurred after that time. Safflower continued to dry the soil until the last measurement date (September 26). From May 21 to September 26 the fallow plots gained 0.4 inches of water, the wheat plots lost 4.6 inches, and the safflower plots lost 4.9 inches. During the same time, 6.5 inches of rain was received at the site. Thus fallow had a net water loss of 6.1 inches, while wheat had a net water use of 11.1 and safflower had a net water use of 11.4 inches.

This data illustrates the inefficiency of fallow at providing additional water for a subsequent crop. This year, the soil under fallow only gained 0.4 inches of water from 6.5 inches of rainfall. While at the end of the season, fallow did have an additional 4.4 inches of water carryover compared to wheat, this may not be much of a benefit. Last fall (2001), fallow had a similar carryover advantage (4.5 inches) compared to wheat. Yet by Spring 2002, that difference was only 1.2 inches, even though rainfall for the period Oct 2001 to April 2002 (3.31 inches) was 0.92 inches less than normal.

Precipitation received this October and November, 1.12 inches, is near normal (1.33) and considerably more than last year (0.41 inches). This fall, the soil in these three treatments had 0.5 inches less water compared to the corresponding treatments last fall. Unless precipitation this winter and next spring is considerably less than normal, soil water content next spring should be favorable for crop production.