Transformation of Podzolic and Leached Chernozems of the Central Russian Upland under Farm Use.
Pavel S. Shulga, Kursk State Agricultural Academy, appt.100,72\16,prospekt Karla Marxa, Kursk, Russia
In Russia chernozems cover about 9 % of the territory (60% of arable lands) and produce 80% of the Russian grain. Therefore it is important to study an influence of agricultural production on transformation of the major agrogenetical chernozems' propeties. The podzolic and leached virgin chernozems of the Central Russian Upland were compared with their analogues having different intensity of agricultural use (middle intensity with domination of grasses or grains in crop rotations and strong intensity with domination of industrial cultures in crop rotation). It is shown that long-term agricultural use of the soil has resulted in change of morphological, chemical, physico - chemical, physical and other soil properties. The arable chernozems have deeper carbonate level and the reduced ÑàÑÎ3 content. Structure formation process has changed essentially. Aggregation of fine units in large ones was replaced by condensation with the subsequent destruction. The structure factor has decreased in upper subsoil (from 8,1 up to 1, 7 for the podzolic chernozem; from 9,5 to 2,5 for the leached chernozem) with simultaneous reduction in stability of structural units (measured by ultrasound) in topsoil and subsoil horizons in 2 times. Micromorphological researches have discovered change of pore spaces quality (increase by more than 50 % of 0,1-0,3 mm pores with their forms simplification). Intensive agricultural use of soil has led to the greater loss of Ñà2 + from a soil absorbing complex of the podzolic chernozem in comparison with the leached chernozem, that had a considerable effect on soil colloids and soil agrophysical properties. Introduction of industrial crops in crop rotation has been accompanied by humus reduction and humus quality change. In the podzolic chernozem humic /fulvic acid ratio has changed from humic (1, 5) to fulvic-humic (1,3). No change of this characteristic has been found for the leached chernozem. For both types of chernozems decrease in Ca-bound fraction of humus acids has been found. The intensification of agricultural use of chernozems has affected the activity of soil enzymes in soil profiles. For the podzolic chernozems oxyde reductase activity was lower by 35% and hydrolytic activity – by 36% low as compared with the leached chernozem. Oxyde reductase /hydrolytic activity ratio in humus horizon was 1:10 for the podzolic chernozem and 1:0,15 for the leached chernozem. This fact is evidence of different processes of humus transformation of fresh plant material. The cellulosolytic activity under the strengthening of agricultural use was higher by 44% for the leached chernozem as compared with the podzolic chernozem. To determine a degradation threshold of chernozems it is necessary to pay attention to reduction in soil structure factor, change of pore's category and forms, decrease in humus' content, transformation of humus structure. Results of the experiments have showed, that use of phytomeliorational rotation of crops is necessary for elimination of negative properties of chernozems.