Abstract
With increasing canola (Brassica napus L.) acreage in the Inland Pacific Northwest of the USA, we investigated the effect of this relatively new rotational crop on soil microbial communities and the performance of subsequent wheat (Triticum aestivum L.) crops. 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 SW yields following winter wheat (WW). Using soil samples collected and analyzed every year 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 associated with SW yield response. Microbial biomass and community composition were determined using phospholipid fatty acid analysis (PLFA). The WC-associated microbial community contained significantly less fungi, mycorrhizae, and total microbial biomass than WW. Additionally, reduced fungal and mycorrhizal abundance in SW following WC suggests that the canola rotation effect can persist. A biocidal secondary metabolite of canola, isothiocyanate, may be a potential mechanism mediating the decline in soil microbial biomass. These results demonstrate the relationship between soil microbial community composition and crop productivity. Our data suggest that WC can have significant effects on soil microbial communities that ultimately drive microbially mediated soil processes.
Highlights
Soil microorganisms are an integral part of many soil processes in agroecosystems
Crop rotation did not have a significant effect on the soil pH, electrical conductivity (EC), or gravimetric water content, which averaged 5.30 (±0.11) and 5.33 (±0.14), 97.90 (±1.97), and 96.59 (±1.49) μS cm−1, and 0.20 ± 0.09 and 0.21 ± 0.11 kg kg−1 for the winter canola (WC) and winter wheat (WW), respectively
For the ensuing spring wheat (SW), BGA was significantly greater in SW following WW (SW-WW) vs. SW following WC (SW-WC) in three of the five crop years
Summary
The soil microbial community plays a key role in aggregate stability (Duchicela et al, 2013; Graf and Frei, 2013), mineralization and stabilization of organic matter (Lützow et al, 2006; Schmidt et al, 2011), nutrient cycling (Kennedy and Papendick, 1995; Talbot et al, 2013), soil ecological function, and biological stability (Griffiths and Philippot, 2013). These processes can be altered by shifts in the activity and composition of microbial communities caused by environmental. A combination of edaphic and dynamic factors, including crop rotation, residue management, soil type, tillage, and climate, all interact to influence the microbial community (Bünemann et al, 2008; Gil et al, 2011; Zhang et al, 2014)
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