Previous crop has a large effect on spring soil water content (see the graph below). For each of the last eleven springs (1992-2002), the soil has been wettest after fallow (11.0 in./4-ft), intermediate after wheat (9.8 in./4-ft), and driest after safflower (8.2 in./4-ft). The variation among years has been much less following fallow (10.5 to 11.9 in./4-ft) compared to following wheat (7.3 to 12.0 in./4‑ft) or following safflower (7.1 to 10.8 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 (2002), soil water content was near average, ranking as the seventh wettest of the eleven-year period. The fallow and wheat treatments were the fifth wettest of the eleven-year period, but the safflower was only the eighth wettest. The difference in soil water content between the fallow and wheat was the sixth greatest of the eleven-year period, but the difference in soil water content between the wheat and the safflower was the second greatest of the eleventh-year period. Only in 2001 was there a greater difference between wheat and safflower. The difference between fallow and safflower was greater this year than any other year.

The crop rotation study where these data were obtained was discontinued this year. Future installments of this article will use data from a similar study, which was started in 1995.