Decline in Soil Microbial Abundance When Camelina Introduced Into a Monoculture Wheat System.

Camelina [Camelina sativa (L.) Crantz] of the Brassicaceae family is a potential alternative and oilseed biofuel crop for wheat (Triticum aestivum L.)-based cropping systems of the Inland Pacific Northwest (PNW) of the United States. We investigated the effect of this relatively new rotational crop on soil microbial communities. An 8-year cropping systems experiment was initiated in 2007 at Lind, WA, to compare a 3-year rotation of winter wheat (WW)-camelina (C)-fallow (F) to the typical 2-year WW-F rotation. All phases of both rotations (total = 20 plots) were present every year to allow valid statistical analysis and data interpretations. Monoculture WW-F is the dominant system practiced by the vast majority of farmers on 1.56 million ha of cropland in the PNW drylands that receive <300 mm average annual precipitation. Microbial abundance and community composition were determined using phospholipid fatty acid analysis (PLFA) from soil samples collected during 3 consecutive years beginning in 2010. The abundance of fungi, mycorrhizae, Gram positive and negative bacteria, and total microbial abundance all declined over the 3-year period in the WW-C-F rotation compared to the WW-F rotation. All microbial lipid biomarkers were significantly less in fallow compared to WW of the WW-C-F rotation. The 2-year WW-F rotation demonstrated few differences in microbial lipid abundance and community structure between the rotation phases. Microbial abundance declined and community structure shifted in the 3-year WW-C-F rotation likely due to the combination of a Brassica crop followed by a 13-month-long fallow. The results of this study suggest that camelina in combination with a fallow period may disrupt microbial communities that have become stable under historical WW-F monocropping. Such disturbances have the potential to affect soil processes that have been provided by wheat-adapted microbial communities. However, the disruption appears to be short-lived with the microbial abundance of WW in the WW-C-F rotation, returning to similar levels observed in the WW-F rotation.

Soil Microbial Biomass and Fungi Reduced With Canola Introduced Into Long-Term Monoculture Wheat Rotations.

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.

Phosphorus speciation in manure-amended alkaline soils.

Two common manure storage practices are stockpiles and lagoons. The manure from stockpiles is applied to soils in solid form, while lagoon manure is applied as a liquid. Soil amendment with manure in any form introduces a significant amount of phosphorus (P) that exists in both organic and inorganic forms. However, little is known about P speciation in manure stored under different conditions, or the subsequent forms when applied to soils. We used solution (31)P nuclear magnetic resonance (NMR) spectroscopy and conventional P fractionation and speciation methods to investigate P forms in dairy manure and liquid lagoon manure, and to study how long-term amendment with these manures influenced surface and subsurface soil P speciation. Our results show that the P forms in solid and lagoon manure are similar. About 30% of the total P was organic, mostly as orthophosphate monoesters. On a dry weight basis, total P was much higher in the solid manure. In the manure-amended soils the total P concentrations of the surface soils were similar, regardless of manure type. Total P in the subsurface soil was greater in the lagoon-manure-amended soil than the solid-manure-amended subsurface soil. However, the fraction of organic P was greater in the subsurface of the solid-manure-amended soil. The NMR results indicate that the majority of organic P in the soils is phytic acid, which is enriched in the surface soils compared with the subsurface soils. These results provide insight into P speciation and dynamics in manure-amended soils that will further increase our understanding on how best to manage manure disposal on soils.