Previous crop has a large effect on spring soil water content. The graph below illustrates data collected during the past ten years (1996-2005) as part of a crop rotation study.  Each spring, soil water is measured in plots of three different treatments: plots that were fallowed the previous year, plots where wheat was grown the previous year, and or plots where safflower was grown the previous year. Each data point is the average of three field plots.

This spring (2005), as in most previous springs, the soil was wettest after fallow, intermediate after wheat, and driest after safflower. For the ten-year period, the amount of water in the top four feet of soil has averaged 11.0 inches after fallow, 9.5 in after wheat, and 8.5 inches after safflower. For the last two years (2004 and 2005), the differences among the three treatments have been unusually small.

This spring (2005), the soil was drier than any other spring of the 10-yr history in both the fallow treatment and the wheat treatment, and for the three treatments combined. It was the second driest ever for the safflower treatment.

During the 10-year period, the year-to-year variability in soil water content has been less after fallow than it has been after wheat or after safflower. 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.

¹ NDSU Williston Research Extension Center, Williston, ND