Tuesday, 11 July 2006 - 8:35 AM

Self-Restoration of Post-Agrogenic Soils: Recent Process of Late Antropocene.

Dmitry I. Lyuri, Nina A. Karavaeva, Tatiana G. Nefedova, Boris D. Konyushkov, and Sergey V. Goryachkin. Institute of Geography, Russian Academy of Sciences, Staromonetny, 29, Moscow, Russia

Since 1950s in many countries an abandoning of arable lands takes place against a background of the total growth of agricultural lands area in the world. This process is related to both traditional (wars, economic and ecological crises) and new reasons induced by intensification of agriculture that makes the growth of arable areas not advantageous. Totally, an area of arable lands abandoned since 1950s is >1.2 mln. sq. km (USA – 0.33 mln., Europe – ca 0.3 mln.) and ca 0.7 mln of them are abandoned because of agriculture intensification. Now this phenomenon exists only in developed countries, however the anticipated intensification of agriculture in the whole world may turn it to be a global trend of Antropocene. That is why it is crucial to study soil processes taking place at post-agrogenic lands for their rational landuse and management. The area of post-agrogenic lands in European part of Russia is tremendous - 0.43 mln. sq. km and the process of natural soil restoration (self-restoration) was studied in different ecoregions of it. The post-agrogenic self-restoration of soils, its trends, stages and rates was investigated in boreal forests (in areas of Albeluvisols – ABs and Podzols – PZs), forest-steppes (Phaeozems – PHs and Chernozems – CHs) and arid grasslands (Calcisols – CLs and Solonetzes – SNs). The age of studied fallows was in the range of 1-200 years. The profile morphology, soil organic carbon (SOC) store in 0.5 m, contents of nutrients, pH, CEC and exchangeable cations were determined in post-agrogenic soils of different ages. In boreal soils SOC stores decrease after beginning of self-restoration both in ABs (9.6 -> 6.1 kg/sq.m) and PZs (6.8 -> 4.8) in first 30-50 years, however they reach parameters of natural soils at the age of ca 200 years because of litter horizons development. Simultaneously, other properties, such pH, content of nutrients, acidity are also restored. The PHs of fallows also lose SOC during first 10-20 years (6.6 -> 4.7 kg/sq.m). After 50-80 years of self-restoration they approach natural undisturbed PHs by the depth of mollic horizons, acidity, content of nutrients. The CHs restore their parameters in the shortest period – 30-40 years – granular structure, high porosity, low bulk density. Both PHs and CHs restore their profile quicker than post-agrogenic biocenoses do. However, SOC stores of post-agrogenic CH do not reach the stores of virgin ones (23.6 kg/sq.m) even after 60 years of self-restoration (18.5 kg/sq.m). So, the agricultural use of CHs results in loss of 20% of SOC into atmosphere. In CLs the self-restoration is the slowest one. After 30-50 years negative agrogenic features are remained in soil profiles – 20%-lower SOC stores in comparison with virgin CLs (3.9 <- 4.8 kg/sq.m), cloddy structure, high bulk density. Secondary carbonates are within upper 50 cm and toxic salts occur beneath 50-cm depth. In post-irrigation CLs SOC stores are only ca 2 kg/sq.m, 3-8% of Na in exchangeable cations and toxic soils are found in fallow soils. The 30-years process of self-restoration of SNs results in lower SOC stores than virgin analogues (3.0 <- 4.3), less Na content, deeper leaching of calcite and remnants of cloddy structure in upper horizon. Thus, post-agrogenic soils of different environment in process of self-restoration approach their natural analogues. However, rates and results of self-restoration are not similar in different climatic zones. The highest rates are in CHs (almost full restoration in 30-50 years, except SOC store). The PHs need 50-80 years for the basic restoration of their profiles. The accumulation of mull-humus and the restoration of granular structure are the most important processes in these two soils. Much less rates of self-restoration are characteristic for ABs and PZs – they need >150-200 years. And the SOC stores regeneration takes place because of litter accumulation. Probably, the lowest rates of self-restoration are in CLs and SNs. It is not clear yet, if the full restoration is possible in these soils. The common feature of post-agrogenic soils is inheritance of grayish color in former ploughed horizon – the “memory” of agrogenic stage of these soils' history. In the study of self-restoration of post-agrogenic soils the international cooperation is very important as different countries have a lot of post-agrogenic soils restorated after various in time and character types of landuse in diverse environmental conditions – only such broad experience let us to investigate and model this recent process of the Late Antropocene.

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