Crop rotation and seasonal effects on fatty acid profiles of neutral and phospholipids extracted from no‐till agricultural soils

Abstract

Analysis of phospholipids (PLFA) and neutral lipids fatty acids (NLFA) was used to characterize no‐till productive agricultural soils associated with different crop rotation levels, replicated across a 400 km transect in the Argentinean pampas, during two sampling seasons, summer and winter. High rotation (HR) management consisted in maize–wheat–soybean intense rotation including cover crops. Low rotation (LR) management trend to soybean monocultures. Soils from nearby natural environments (NEs) were used as references. Fatty acids concentration in soils (nmol/g) decreased c.a. 50% from summer to winter differentially according to soil treatment being the smallest decrease in HR management 35%. Both PLFA and NLFA profiles showed strong potential to discriminate between different land uses. In winter samples, some rare or unknown fatty acids were relevant for the discrimination of agricultural practices while NLFA 20:0 appears to be a good marker of HR soils despite season or location. The PLFA‐based taxonomic biomarkers for total bacteria, Gram‐negative bacteria and arbuscular mycorrhiza showed a significant trend NE>HR>LR in the winter sampling. HR management was also characterized by high levels of NLFA in winter samples as if high crop rotation improves lipids reserves in soil during winter more than in monocropping soil management. In conclusion, PLFA and particularly NLFA profiles appear to provide useful and complementary information to obtain a footprint of different soil use and managements, improving soil biochemistry characterization tools.

Crop rotation in no‐till soils modifies the soil fatty acids signature

“…Most fatty acids obtained in this study had been found previously when the same set of samples was analysed by the PLFA/NLFA method (Ferrari et al ., ). Nevertheless, there were several fatty acids in the WSFA profile that were not found in the previous analysis with the PLFA/NLFA method.…”

“…Several fatty acids were exclusively extracted with the WSFA approach, not being found in the PLFA/NLFA method applied to the same soil sample set (Ferrari et al ., ). Fernandez et al .…”

“…In this study, both agricultural sites were under no‐till, and no differences were found between them, though CR samples showed slightly larger WSFA values than MC samples in winter. Similar results were found when the same soil samples were analysed in terms of PLFA/NLFA profiles (Ferrari et al ., ).…”

“…More analytical details can be found in Ferrari et al . (). The concentration of each fatty acid identified by the MIDI software was assessed in relation to the 19:0 standard and expressed as nanomoles per gram of dry soil.…”

“…Fatty acids with the same retention time in the chromatogram are grouped as ‘ summed in feature ’. The fatty acids were classified into the following chemical groups: straight chain, branched, MUFA, PUFA, cyclic, methylated, hydroxyl and hydroxy branched and the mentioned ‘sum in feature’, plus a category of fatty acids from mixed chemical functions (‘mixed or others’) (Ferrari et al ., ).…”