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 determini ng 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 dis tributions of diethyl ether-(DEE) and chloroform-(CHCl3) extractable lipids and gravimetric DEE/CHCl3 and CHCl3/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 Quebec. Diethyl ether and T EL were significantly (P less than or equal to 0.001) more abundant under p erennial than annual crops, indicating that the perennial crops were better suppliers of easily biodegradable organic matter. Chloroform-extractable l ipids remained relatively constant under both crop rotations, indicating th at soil biochemical inertness was relatively the same. Spatial and temporal distributions of these indicators of soil organic matter quality closely c orrelated with total organic C and clay contents. The DEE/CHCl3 and CHCl3/T EL ratios proposed for assessing organic matter quality were very sensitive (P less than or equal to 0.01) in detecting changes in SOM status resultin g from crop rotations and tillage practices.