Previous crop has a large effect on spring soil water content. The graph below illustrates data collected during the past nine years (1996-2004) as part of a crop rotation study. Each data point is the average of three field plots.

      Generally the soil has been wettest after fallow (11.3 in./4‑ft), intermediate after wheat (9.7 in./4‑ft), and driest after safflower (8.6 in./4‑ft). The only anomalies occurred in 2001 when the soil was wetter after wheat than it was after fallow and in 2004 when the soil was wetter after safflower than it was after wheat. Anomalies such as these are more likely to occur after a wet period when the soil water can be replenished in fields that were cropped during the previous year.

      Because full replenishment occurs only occasionally, the variation in soil water 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.

This past spring (2004), the soil was wetter than the 9-yr average, ranking as the fourth wettest spring when the treatments were considered together. The difference among the three treatments was only 0.7 inches, which was the least ever.

¹NDSU Williston Research Extension Center, Williston, ND