Increased SOM preserves microbial biomass C and ATP in soils stored air-dry for more than 100 year.

Soil microbial biomass (biomass C), adenosine tri-phosphate (ATP), CO2 evolution and soil organic C were measured in freshly sampled arable and grassland soils and in air-dried soils, which had been stored for up to 103 years. After rewetting and incubating for 12 days, microbial biomass C in the archived NPK soils ranged from about 2 to 4 ATP mol g-1 biomass C, while it ranged from about 12 to 14 mol ATP g-1 biomass C in the archived Farmyard Manure treated ones. This latter value is essentially the same range (10 to 15 mol ATP g-1 biomass C) as that measured in freshly sampled soils. The antioxidant capacity of HS extracted from these soils was measured by the crocin method. Humic substances appear to possess remarkable antioxidant properties: the relative antioxidant efficiency of humic substances is of the same order of magnitude of that of unsaturated fatty acids (ascorbil palmitate) and oleoresins and about 100 times larger than that of antioxidant mixtures naturally contained in some foods. Humic acid extracted from the NPK and FYM soils have similar antioxidant power. The FYM soil contained a much larger proportion of humic substances in its SOM and more than three times the humic acid content of the NPK soil (2.81 versus 0.81 mg g-1 humic C).