Previous Cropping Effects on Spring Soil Water

James A. Staricka, Soil Scientist, WREC

Previous crop has a large effect on spring soil water content (see the graph below). For each of the last nine springs (1992-2000), the soil has been wettest after fallow (11.0 in./4-ft), intermediate after wheat (9.6 in./4-ft), and driest after safflower (8.3 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.

In terms of soil water content, this spring ranked as the second driest of the nine-year period. Among the safflower stubble treatments, this spring was the driest ever. The difference in soil water content among the three treatments was also exaggerated, being greater this spring than any of the previous eight. This was a great contrast from the previous spring (1999), when the soil was the wettest ever, and the difference among the treatment was the smallest ever. This change is attributable to the small May-October 1999 rainfall amount (8.35 inches), which was the second smallest amount of the nine-year study period. This past year (2000), May-Oct rainfall was only 9.01 inches, the third smallest for the study period. From September 27 until December 6, 3.76 inches of precipitation occurred. Of this, 2.23 inches was rain which occurred before snow cover was established. This late season precipitation should have helped replenished the soil water reserves for the 2001 growing season.