Effect of the storage conditions of soil samples on carbon and nitrogen extractability

Concentrations of carbon and nitrogen extractable by 0.05 M K2SO4 (C-ext and N-ext, respectively) in 14 soils of different ecosystems vary from 16 to 205 and from 4 to 53 mg/kg, respectively. The portion of C-ext in soil organic matter is 0.06 to 0.38% of total carbon, and the portion of N-ext is 0.12-1.05% of total nitrogen. The storage of samples and their preparation to analysis differently affect the extractability of elements. The concentration of C-ext is less variable than the concentration of N-ext. An increase in C extractability (by 1.4-6.7 times) is a common feature of all soils under drying; at the following incubation of dried soils, the extractability of C decreases by 28-56%. The extractability of N increases not only under drying (by 1.5-7.1 times) and the following incubation of samples (by 25-60% to 2-3 times), but also under freezing of most soils and at the incubation of fresh and defrozen samples. A close direct correlation is observed between the initial water content of soil and the relative increase in C extractability under drying and N extractability under freezing and drying.