Change of Functional Parameters and Contents of Humus in Buried and Fallow Soils.
Serafim N. Chukov, Alexander G. Ryumin, and Alexander S. Koposov. Saint-Petersburg State Univ, 7-9, Universitetskaya nab., Saint-Petersburg, Russia
By means of level-by-level sampling we have tried to study in detail the profile organization of the organic substance and the basic physical and chemical parameters of the soils. Such sampling enables to receive as reliable information about the organization of the soil profile as possible. All results of our research have been received by means studying of the soil profile within 5 cm layers. Usage of level-by-level sampling optimally is for soils with the powerful humus profile and noncontrast borders of genetic horizons. In this sense the soils in the forest-steppe zone (chernozems and grey wood soils) correspond to the conditions mentioned above. This methodological approach has helped us to receive new data. We have obtained data which mark out the top 5 cm layer in soils of the forest-steppe zone as an independent horizon, the main criteria being biochemical characteristics of organic substance and humic substances of this layer rather then morphological properties. We studied profile of virgin (control), plowed and fallow (30 years) chernozem in the Central-Chernozem reservation in Kursk region. On the territory of "Belogorie" reservation in Belgorod region we studied 2 objects of the grey wood soil with short age of burial (the age is 31 and 68 years) and took virgin grey wood soil as a control. The results of our research on of structure and properties changes of chernozems have shown essential transformation caused by anthropogenous factor. Long ploughing up leads essential dehulmification of the plowed soils on the depth up to 70 cm. This fact can be connected with the lack of root waste in the whole soil profile. The decreased content of the humus occurred in fallow chernozem as a residual effect of the 30 years-long agricultural use. The indirect estimation of the soil biological activity based on CO2 emission has shown its essential decrease in the ploughed up soil. In the sub plowed horizon the CO2 emission doesn't appear. This facty is connected with dramatic decrease biological processes in this densed horizon. In fallow soil the CO2 emission is increasing. Due to the level-by-level sampling in the virgin chernozem an essential decrease of humic substances biochemical activity was determined within the top layer of the profile (0–10 cm). This decrease is market by set of humic acids, the CO2 emission and concentration of free radicals in the humic acids preparations (according to ESR). The amount of organic carbon in the virgin grey wood soil shows, that its quantity exponentially decreases in deeper layers. At 25 cm depth its content is stabilized at 0,6–0,7 % level then its amount gradually comes closer to the initial level of the loess-like loam (about 0,1 %). After the soil is buried, the income of fresh organic matter decreases rapidly. It happens because of shift of the humus horizon beyond the root-inhabited layer. This fact as well as general decline of the soil formation potential leads to mineralization of the organic matter. The speed of mineralization is practically constant: 0.042% C per year in 31 years and 0.038% C per year in 68 years. In deeper layers the speed of mineralization is declining. So at the depth of 25-30 cm the amount of organic carbon is equal to one in virgin soils (0.6-0.7%). This process is accompanied by the essential decrease of the CO2 emission directly connected with the burial age. Decrease of the CO2 emission can be caused by reduction the accessible organic carbon pool and followed by decrease of the biological activity. According to ESR the maximum quantity of the soil organic matter active fractions occurs while in the humic-accumulative horizon of the virgin soil amount of the organic-mineral matrix is next to nothing. At burial there is an essential reduction of active fractions and "levelling" of their content through the whole structure. In organic substance of the burial soils the increase of free radicals specific concentration (on 1 % of carbon) is connected with the accumulation of aromatic fragments of humic substances while lacking of fresh fossils.