Spatial and Temporal Variability of Extractable Lipids as Influenced by Cropping History

Tillage and crop rotations may alter soil organic matter (SOM) content and quality. Organic matter content can be satisfactorily assessed by determining total organic matter and C content, but easily obtainable, reliable, and highly sensitive indicators of its quality are still lacking to assess its biological, chemical, and physical functions. The spatial and temporal distributions of diethyl ether–(DEE) and chloroform‐(CHCl 3 ) extractable lipids and gravimetric DEE/CHCl 3 and CHCl 3 /total extractable lipids (TEL) ratios were evaluated as indicators of organic matter quality in two soils of Agri‐Food Canada cropping system fields situated in Qu e ´ bec. Diethyl ether and TEL were significantly ( P ≤ 0.001) more abundant under perennial than annual crops, indicating that the perennial crops were better suppliers of easily biodegradable organic matter. Chloroform‐extractable lipids remained relatively constant under both crop rotations, indicating that soil biochemical inertness was relatively the same. Spatial and temporal distributions of these indicators of soil organic matter quality closely correlated with total organic C and clay contents. The DEE/CHCl 3 and CHCl 3 /TEL ratios proposed for assessing organic matter quality were very sensitive ( P ≤ 0.01) in detecting changes in SOM status resulting from crop rotations and tillage practices.