Changes in field-level cropping sequences: Indicators of shifting agricultural practices

Farmers implement an assortment of management practices to ensure the sustainability, economic viability, and resilience of their operation. Dryland farming practices dominate in the semiarid regions of the US northern Great Plains, where historical practice has been to rotate small-grain cereals with whole-year summer fallow; however, pulse crops (e.g., lentils) have become increasingly common in these regions as an alternative to fallow. The area of fallow in northeastern Montana, for example, has decreased by one-third, while the area of pulse crops has increased more than five-fold. Our objectives were: (1) to characterize the principal cropping sequences in northeast Montana during the period of regional pulse crop adoption (2001–2012); and (2) to identify changes in the relative proportions of these sequences during the same period. We identified crops at the field-level by class (cereal, pulse, fallow, or cereal–fallow strips) for 2001–2012 using multitemporal Landsat imagery in conjunction with the cropland data layer, cadastral data, ground reference data, and local producers’ records. The annual crop classifications were combined into a 12-character string for each field that represented the sequence of crop classes for 2001–2012. We then searched these strings for specific 2- and 3-year crop sequences with a string-matching algorithm. The most abundant sequences involved continuous cereal, block-managed cereal–fallow, and cereal–pulse. We also observed a steady decrease in the abundance of cereal–fallow sequences managed by strip-cropping that were coincident with increases in block-managed cereal–fallow sequences and with increases in pulse production. We conclude that, over the studyʹs time frame, regional producers grew more cereal crops and fallowed fields less frequently, but did not appear to strongly adhere to specific sequences. Furthermore, strip-cropping as a management practice has declined substantially.