Thursday, 13 July 2006

Quantitative Assessment of Soil Forming Processes Rate in Soil Succession Chronosequences.

Ivan I. Vasenev, Russian State Agricultural University - MTAA, Ecology Department, Timiryazevskaya Ulitca, 49, Moscow, 127550, Russia

Soil successions are one of principal forms of soil century evolution in concrete landscapes at middle-term intervals. It would be useful to suggest formal definition “soil successions” as soil local middle-term (n*(10-100)years) sequences with evident trend of development and consecutive change of soil taxons. In side of short-term dynamic (n*10 ys) soil successions border with easy-reversible fluc-tuations and frequently incorporate their residual consequences. In scale of centu-ries-old evolution (n*(100-10000) ys) soil successions are separate parts of general evolutionary trajectory of pedogenesis. Soil successions characterized by mutual temporary disturbances of soils' relative balance with there local soil forming conditions. As a result soil forming processes' (SFP) current potentials and rates considerably rise. Soil succession combinations in time frequently determine principal features of concrete soil development. Their combinations in space - often define soil cover patterns formation in conditions of particular natural or anthropogenic-changed landscape. The quantitative analysis of soil successions requires logic allocation the «pure» (homogeneous) succession chronosequences. It is usually achieved by ad-dress decreasing of soils initial variation in their succession chronosequences due to inclusion in the analysis only soils with similar versions of contrasty quantified impacts and syngenetic influences, and due to reliable temporal dating of chronosequences. As a result soil casual spatial heterogeneity essentially reduces in researched succession stages and quantitative analysis of soil forming processes dominated in them is facilitated. In windthrow soil successions transformational and migration SFP are sharply made active: humus acid formation - up to 200 g/m2 per year, iron segregation - up to 1,8 kg/m2 per year, ñ illite-smectit transformation - up to 400 g/m2 per year, al-fe-humus migration and lessivage - up to 1,3 and 3 kg cm/ m2 per year. Eluvial horizons can go deep on 6-18 cm per 50-150 ys - depending on depth of initial impacts and on morphogenetic profile of background soil. In case of soil agrogenic successions SFPs' rates and potentials are deter-mined by provincial-genetic and lithological features of soils, their position in agrolandscape, kind and history of land-use, and used agrotechnologies. Mean annual rate of erosion varies within 1-30 mm/year, humus decreasing – 0,2-1,0 g/kg per year, des-aggregation – 1-25 g/kg per year, over-compacting – 0,01-0,06 g/cm3 per year, alkalinization – 5-18 Na+ mg/kg per year. The average rate of progradation SFPs is in 2-4 times lower than degradation ones. The carried out researches of technogenic soil successions have shown strong activization of metamorphic and migration SFPs in them. Over-compacting achieves 0,3 g/cm3 per year. Mean annual rate of humus decreasing and increasing varies from 0,2 up to 2,0 g/kg per year, acidification and alkalization – from 0,02 up to 0,5 dpH per year, salinity and alkalinization – from 10-50 up to 500 mg/kg per year, rind accumulation of iron – up to 1-3 kg/m2 per year. The received data essentially expand known ranges of SFPs rate «in situ». Succession analysis of modern evolution of anthropogenic-changed soils raises accuracy of quantitative assessments of dominant SFPs' rate and potential.

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