Spring crops in three year rotations reduce weed pressure in winter wheat

• Published in: Field crops research Vol. 233; pp. 12 - 20
• Main Authors: San Martín, Carolina, Long, Dan S., Gourlie, Jennifer A., Barroso, Judit
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2019
• Subjects: Barley; Brassica carinata; carinata; Crop diversification; Downy brome; Hordeum vulgare; Triticum aestivum; Weed cover reduction; Weed density reduction; Wheat yield; carinata; Barley; Downy brome; Crop diversification; Hordeum vulgare; Weed cover reduction; Weed density reduction; Brassica carinata; Wheat yield; Triticum aestivum
• DOI: 10.1016/j.fcr.2018.12.017
• ISSN: 0378-4290

•Intensification of wheat-fallow systems with a spring crop improves weed control.•Diversification of winter wheat-fallow systems reduces grass weed infestations.•Environmental conditions and crop rotation impacted weed infestations in the PNW. Downy brome (Bromus tectorum L.) is a problematic weed for the conventional fallow/winter wheat (F/W) production system in the low precipitation-region (<350 mm yr−1) of the Pacific Northwest. A 4-yr field experiment was conducted to determine if incorporating spring barley (B, Hordeum vulgare L.) or spring carinata (C, Brassica carinata A. Braun) into 3-yr crop rotations with W would benefit weed management. The experimental design was a split-plot with four replications where each phase was present every year for the following rotations: 1) F/W, 2) F/W/B, and 3) F/W/C. Reduced tillage, consisting of a single undercutting operation with a wide-blade sweep, and herbicides were used to control weeds during the fallow period. The seeded plots were subdivided in three different weed management areas: a weed-free area where weeds were pulled by hand, a weedy area with no weed control and a general area where weeds were chemically controlled. Weed density and cover per species and W yield were evaluated in each rotation. Grass cover and density after one and two complete cropping cycles were significantly higher in F/W than in F/W/B and F/W/C. Reduction in density and cover of total weeds was found after two cycles. However, differences in community biodiversity were only found between F/W, and F/W/B or F/W/C in 2017. Winter wheat plots of F/W had more downy brome than F/W/B or F/W/C indicating the greater capacity of the latter to control this weed. In 2018, the 3-yr rotation with barley had greater winter wheat grain yield compared with F/W when weeds were not present though weeds were more competitive in F/W/B. Intensifying the F/W cropping system into a 3-yr crop rotation of W followed by spring barley or spring carinata may reduce weed infestations of winter annual grasses that are difficult to control in W and the most competitive due to larger similarities in their life cycle with this crop.