Nmin = Ntot min•[1-exp(-k•t)]
Nmin = N0 + Nnet min•[1-exp(-k•t)]
where Ntot min - total mineralizable nitrogen; N0 - initial mineral N (NH4+-N and NO3--N) in soil; k - mineralization rate constant; t - incubation time; Nnet min - net-mineralized nitrogen amount.
The part of mineralizable nitrogen from Ntotal content was 2.6-5.1% in gray forest soil from different ecosystems, decreasing in a following order: forest > grassland > nonfertilized agroecosystem. The Ntot min part in leached chernozem was only 1.4-1.9%, and the ratio Ntot min / Ntotal was almost the same both in fallow plot and in nonfertilized variant of crop rotation. The calculated ratio Ntot min / Ntotal shows that organic matter protectability and nitrogen sequestration ability of leached chernozem are 2-3 times higher, than of gray forest soil. This fact is the main reason of nitrogen "economical" consumption and continuous nitrogen keeping in chernozemic soils. The gray forest soil from natural ecosystems has the same nitrogen mineralizable pool, as leached chernozem in the fallow plot. In nonfertilized agroecosystems the higher nitrogen mineralizing ability is peculiar to the leached chernozem. On the other hand, the manure usage once per 5 years in dozes 25 and 50 t ga-1 separately or together with inorganic fertilizers leads to relatively small increasing of the mineralizable nitrogen in comparison with control (approximately at 1.1-1.5 time). The Ntot min amount in fertilized variants is less than an Ntot min amount in the fallow plot. The experimental and calculated Nnet min amount shows that the real increase of mineralizable nitrogen in leached chernozem take place only under manure application. The existing practice of organic fertilizers usage once per 5 years doesn't results in increasing of carbon- and nitrogen-stabilizing potentials of leached chernozem. Increasing of the N0 part in soil sampled from the organic-mineral sites and respective decreasing of net-mineralization are agree with modern concept. In accordance with this concept the nitrogen fertilizers reduce mineralization of humificated organic matter, and the deficient supply of leached chernozem by easily-mineralizable organic matter can be the cause of the mineralized and immobilizated nitrogen disbalance. In this case the Nmin pool produced by inorganic fertilizer application is short-stored and can be lost from soil. Acknowledgements: This work was supported by Russian Foundation for Basic Researches (Grant No. 04-04-48670) and Presidium of Russian Academy of Sciences (Program No. 13, Project No. 4.1).