Crop Rotation, Red Clover and Cropping History Influences Microbial Amino Sugars of a Clay Loam Soil

Monoculture and rotational cropping influences the quantity and composition of substrates returned to soil and subsequently the growth and activity of soil microorganisms, which in turn may affect the accumulation of microbial-derived amino sugars in soil. A crop rotation study was established in 2001 which includes the monoculture cropping treatments, corn (Zea mays L.), soybean (Glycine max L.), and winter wheat (WW; Triticum aestivum L.) with/without a red clover (RC; Trifolium pretense L.) cover crop as well as 2-, 3-, and 4-yr rotations using these four crops with each phase present each year (144 field plots). In this study, a subset of these treatments (56 field plots) was evaluated for the concentrations of glucosamine (GluN), galactosamine (GalN), and muramic acid (MurA) in a clay loam soil (mesic Typic Argiaquoll) in southwestern Ontario, Canada. Monoculture WW increased the total amino sugar concentrations by 17.4 and 21.3% relative to monoculture corn and monoculture soybean, respectively. Underseeding monoculture WW with RC increased the total amino sugar concentrations by 24.2 and 28% over monoculture corn and soybean, respectively. Whenever WW or WW underseeded to RC was the current or previous crop in a 2-yr rotation (soybean-WW; soybean-WW+RC) or a 3-yr rotation (corn-soybean-WW; corn-soybean-WW+RC), total and individual amino sugar levels were greater relative to rotations which did not include WW or WW+RC. The GluN/MurA ratio was not affected by the current or previous crop in the rotation. It was concluded that the concentrations of total and individual amino sugars in soil are affected by crop species (especially WW and RC) and cropping history.