Submitted to: Soil & Tillage Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/11/2006
Publication Date: 6/1/2007
Citation: Wright, S.E., Green, V.S., Cavigelli, M.A. 2007. Glomalin in aggregate size classes from three different farming systems. Soil & Tillage Research. 94:546-549. Interpretive Summary: Farmers are keenly interested in contributions to sustainable agriculture that come from manageable microorganisms. Soil aggregation is a visible and important sign of a healthy soil. One group of beneficial fungi that associates with plant roots produces copious amounts of a glue-like compound, glomalin. Glomalin concentration in soils is linked to aggregate stability, and production of glomalin is negatively affected by tillage. To study glomalin concentrations in different sizes of aggregates, comparisons were made among treatments that had been managed by no-tillage (NT) for 18 years, minimum conventional tillage for seven years (CT) and extensive disturbance for organic (ORG) management for seven years. The NT plots had the highest concentrations of glomalin in all size fractions of aggregates compared with CT and ORG. No-till soil also had larger amounts of glomalin incorporated in large aggregates than CT and ORG treatments. Little difference was seen between CT and ORG even though ORG management requires greater disturbance than CT management. These results are useful to scientists studying controls on aggregate formation and to soil management practitioners and advisers.
Technical Abstract: Chisel tilled (CT) and more intensively tilled organic (ORG) farming systems were compared with a no-till (NT) system for the distribution of glomalin in whole soil and macroaggregate size fractions of greater than 2.00, 0.50-2.00, 0.21-0.50 mm, microaggregates 0.05-0.21 mm, and fine material less than 0.05 mm. Glomalin, the insoluble glycoprotein produced by arbuscular mycorrhizal (AM) fungi, was extracted from 1 g samples with 100 mM sodium pyrophosphate, pH 9.0, at 121 degrees C in three extraction cycles, and extracts were pooled and assayed for Bradford dye-reactive soil protein (BRSP). Nylon mesh from a culture of an AM fungus was examined microscopically to determine whether a glue-like nature of glomalin is photographically demonstrable in order to propose the role of glomalin in aggregates. Whole soil concentration of BRSP was greater in NT than CT or ORG (P = 0.01). Mean values for BRSP in the three macroaggregate size fractions of NT were greater than mean values for CT and ORG by 0.579 and 0.678 mg/g of aggregates, respectively. Concentrations of NT BRSP in the macroaggregate size classes were greater than in microaggregates (0.05-0.21 mm) (P = 0.02). Less BRSP in microaggregates with large surface areas, and photographs of deposition of glomalin on a solid surface, suggest that glomalin can be an internal component of microaggregates. Significant differences detected in aggregate size classes for NT may reflect the contribution of glomalin as mortar that binds microaggregates within larger aggregates. Distribution of BRSP among aggregate sizes showed greater amounts in NT macroaggregates compared with greater amounts in microaggregates in CT and ORG treatments.