Crop Rotations to Complement Winter Wheat.

Dryland crop production in Montana is dominated by a winter wheat (ww) – fallow (F) crop sequence due in large part to limited annual precipitation that ranges from 250 to 400 mm. The majority of these 1.3 million hectares are established under no-tillage conditions. It is likely that increased diversity in crop selection could improve crop management aspects such as weed control, and water and nutrient use efficiency. Increased acreage of pulse crops such as dry pea (p) and lentil (l) in the region have provided an opportunity to include these crops in the traditional system. Additionally an oilseed crop, camelina sativa (c) has shown promise as an alternative crop for dryland production. In 2008 a field study was established to evaluate increased cropping intensity using pulse and oilseed crops on the productivity and economic return of dryland winter wheat production in Montana. The only treatment was crop rotation, arranged in a randomized complete block with four replications. There were eight treatments: ww – F; ww – spring wheat (sw) – F; ww – p – F; p – ww – F; ww – sw – l; ww – sw – l (as a cover crop); ww – sw – c; and ww – l – sw – c. Growing conditions varied across the years with three years wetter than average and two years drier than average. Total annualized grain yield averaged over the five years of the study was not significantly different for 7 of the 8 rotations. Only rotation 8 ( ww – l – sw – c) provided significantly lower annualized grain yield. A limited economic analysis using only input costs and grain sales followed the same trend. Additionally the ww – F rotation was less variable in income over the years than rotations that included alternative crops except for ww – p – F which had the lowest economic variability of all rotations. It is apparent that without some other benefit, such as an improvement in soil health, enhanced nutrient efficiency, or some measure of environmental degradation associated with fallow, or a significant change in grain prices, that winter wheat – fallow rotations will continue to dominate dryland production in Montana.