Diversifying cropping systems enhances productivity, stability, and nitrogen use efficiency

Long-term field experiments are useful for determining cropping system productivity, yield stability and resource use efficiency. Using 12 years (2004 – 2015) of data derived from five cropping systems in a long-term experiment in Swift Current, SK, Canada, comparisons were made of grain yield, protein yield, yield stability, nitrogen fertilizer use efficiency and available nitrogen use efficiency. After three complete rotation cycles, the study showed that the average grain yield and protein yield were greatest for the wheat (Triticum aestivum L.)-canola (Brassica napus L.)-wheat-field pea (Pisum sativum L.) (W-C-W-P) rotation, being 2244 and 372 kg ha1, respectively. These yields were 1438% and 3366% higher, respectively, than the continuous wheat (ContW), summer fallow-wheat-wheat-wheat (F-W-W-W), F-W-W, and lentil (Lens culinaris Medik) green manure-wheat-wheat (GM-W-W) rotations. The rotations with summer fallow were the most stable, well-adapted to poorer growing conditions, possibly low moisture availability, but less productive overall. The GM-W-W rotation was the least stable and poorly adapted. The ContW system had fairly good stability, but was better suited for optimum growing conditions for grain yield. Finally, the W-C-W-P rotation consistently produced better than average grain and protein yields, and was best suited for optimum growing conditions. Available nitrogen use efficiency for grain yield was highest for the ContW, while for protein yield, it was highest for the W-C-W-P rotation. The GM-W-W rotation had the lowest available nitrogen use efficiency for both grain and protein yield. Nitrogen fertilizer use efficiency was the reverse of available nitrogen use efficiency. Overall, our results showed that diversified cropping systems that include pulses can more consistently produce high grain and protein yields regardless of growing conditions than most other systems, with the added benefit of requiring lower nitrogen fertilizer inputs, thereby potentially reducing the negative environmental consequences associated with nitrogen fertilizer application.