SEASONAL-VARIATIONS OF THE LIGHT ORGANIC FRACTIONS IN SOILS UNDER DIFFERENT AGRICULTURAL MANAGEMENT-SYSTEMS

Annual dynamics of soil organic matter and seasonal evolution of total and light forms of carbon (CL) and nitrogen were studied for three series of soils in the humid Pampa of Argentina. Agricultural practice effects on the organic fraction of soil were also evaluated. Seasonal fluctuations in the light organic fractions of soils were confirmed, presenting each one of them its particular behaviour. In the Typic Argiudoll (Azul) and the Argiaguic Argialboll (Lujan) persistence of CL is related to low temperaure and moisture excess. Diferences between grasses and other crops are of small importance. In the Typic Hapludoll Pehvajo, soil texture and climatological conditions favour rapid mineralization. In this case, is very important that the maintenance of light carbon incorporation be made by pastures.