Submitted to: Manitoba North Dakota Zero Till Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 14, 2011
Publication Date: January 9, 2012
Citation: Tanaka, D.L., Liebig, M.A. 2012. Crop rotation principles for the northern Plains. P. 31-32. IN: Proc 34th Annual Zero Tillage Workshop and Trade Show, 9-11 Jan 2012. Minot, ND. Manitoba North Dakota Zero Tillage Conference Proceedings. Interpretive Summary: Crop rotations serve as a major component of sustainable cropping systems. Since the establishment of wheat-based crop rotations in the northern Plains over 150 years ago, cropping systems have evolved considerably to the point where use of fallow is limited to the driest areas of the region and a broad diversity of crops are currently grown. Selecting and sequencing crops over time can be fixed (i.e., a repeating rotation of predetermined length) or dynamic. A dynamic approach to crop selection and sequencing requires decisions be made annually in order to optimize production, economic, and resource conservation goals. Dynamic cropping systems are location-specific, with unique crop portfolios (i.e., adapted crop species) within an ecoregion, and require a thorough understanding of short-term (1 to 3 yr) crop sequencing effects on relevant agronomic and environmental factors. Use of dynamic cropping systems in the northern Plains has been shown to result in greater and less variable crop yields over time compared to fixed-sequence crop rotations. Such an outcome suggests dynamic cropping systems can achieve greater production consistently within variable environments.
Technical Abstract: Crop selection and sequencing serve as a cornerstone of sustainable cropping systems. Among the many options available to select and sequence crops, a fixed-sequence system, whereby crops are sequenced in a consistent, unchanging pattern, is the most simple. Fixed-sequence systems, however, can compromise soil function, contribute to the development of pest and disease infestations, be less responsive to weather conditions, and may limit the potential to take advantage of market opportunities. To increase cropping system responsiveness to externalities, opportunity/flex crop sequences were developed to allow for adjustments in cropping intensity and/or diversity using critical information at planting, such as soil water status. Even greater flexibility in annual crop sequencing may be realized through the application of a dynamic cropping system concept, where crop sequence decisions are made annually in order to optimize production, economic, and resource conservation goals. Application of dynamic cropping systems in the northern Plains has resulted in greater crop yields that are also less variable. Evaluation of data from the Area IV SCD Research Farm found spring wheat grain yield to vary the least in a dynamic cropping system compared to other less diverse crop sequencing approaches. Moreover, grain yield in the dynamic system was 20 and 17% greater, respectively, compared to three and five year rotations containing spring wheat. Yield responses across cropping systems were driven largely by differences in precipitation-use efficiency, which was greatest in a dynamic system. Such outcomes suggest an inherent resilience of dynamic cropping systems to achieve greater production consistently within a variable environment.