Skip to main content
ARS Home » Pacific West Area » Pullman, Washington » Northwest Sustainable Agroecosystems Research » Research » Publications at this Location » Publication #349140

Research Project: Improving Air Quality, Soil Health and Nutrient Use Efficiency to Increase Northwest Agroecosystem Performance

Location: Northwest Sustainable Agroecosystems Research

Title: Soil microbial biomass and fungi reduced with canola introduced in long-term monoculture wheat rotations

item Hansen, Jeremy
item SCHILLINGER, WILLIAM - Washington State University
item SULLIVAN, TARAH - Washington State University
item Paulitz, Timothy

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2019
Publication Date: 7/11/2019
Citation: Hansen, J.C., Schillinger, W., Sullivan, T., Paulitz, T.C. 2019. Soil microbial biomass and fungi reduced with canola introduced in long-term monoculture wheat rotations. Frontiers in Microbiology. 10:1488.

Interpretive Summary: A study conducted in eastern Washington reported reduced yields of wheat when planted after a canola crop. We investigated the effect of canola on the soil microbiology to determine if reduced wheat yields could be related to the changes in the soil microbial community. Canola plants contain compounds that can reduce soil pathogens, but can also impact beneficial soil organisms. We found that major portions of the microbial community were impacted by the canola crop and could explain the observed wheat yield reduction.

Technical Abstract: With increasing acreage of canola (Brassica napus L.) in the Inland Pacific Northwest (PNW) of the USA, we investigated the effect of this relatively new rotational crop on soil microbial communities and the performance of the subsequent wheat (Triticum aestivum L.) crop. Canola plants contain glucosinolates, which upon cell rupture and during the decay of residue, hydrolyze to produce isothiocyanates. The production of isothiocyanates is the mechanism responsible for the biofumigation effect, which can reduce the inoculum of soilborne pathogens. However, the non-selectivity of isothiocyanates has potential to also impact beneficial soil organisms. In a 6-year on-farm canola-wheat rotation study conducted near Davenport, WA, grain yields of spring wheat (SW) following winter canola (WC) were reduced an average of 17% compared to yields following winter wheat (WW). With soil samples collected and archived from that study, the objective of this research was to determine the differences and similarities in the soil microbial communities associated with WC and WW, and if those differences were correlated to SW yield response. Microbial biomass and community composition were determined using phospholipid fatty acid analysis (PLFA). The abundance of fungi, mycorrhizae, and total microbial biomass were significantly less in WC compared to WW. The reduction in fungi and mycorrhizae were also observed in SW following WC, indicating a residual affect. These results demonstrate the relationship between soil microbial community composition and crop productivity. Our data suggest that WC can have significant effects on microbially-mediated soil processes such as nutrient cycling that could potentially produce short-term yield declines in subsequent crops.