Extractable Soil Lipids and Microbial Activity as Affected by Bt and Non Bt Maize Grown on a Silty Clay Loam Soil

Abstract

Pyrolysis‐gas (Py‐GC) chromatography was used to characterize extractable lipids from Bt and non‐Bt maize shoots and soils collected at time of harvesting. Py‐GC‐MS (mass spectrometry) showed that the concentrations of total alkenes identified in non‐Bt shoots and soils were 47.9 and 21.3% higher than in Bt maize shoots and soils, respectively. N‐alkanes identified were of similar orders of magnitude in Bt and non‐Bt maize shoots, but were 28.6% higher in Bt than in non‐Bt soils. Bt maize shoots contained 29.7% more n‐fatty acids than non‐Bt maize shoots, whereas the concentrations of n‐fatty acids in Bt soils were twice as high as those in non‐Bt soils. Concentrations of unsaturated fatty acids in Bt maize shoots were 22.1% higher than those in non‐Bt maize shoots, while concentrations of unsaturated fatty acids were 22.5% higher in non‐Bt than in Bt soils. The cumulative CO₂–C evolved from soils under Bt and non‐Bt crops was 30.5% lower under Bt as compared to non‐Bt crops, whereas when maize shoots were added to Bt and non‐Bt soils, the decrease in CO₂–C evolved were 16.5 and 23.6%, respectively. Our data showed that the cultivation of Bt maize significantly increased the saturated to unsaturated lipid ratios in soils which appeared to negatively affect microbial activity.

Keywords:

• Bt maize
• Soil lipids
• Microbial activity
• Soil respiration
• Soil organic matter