Organic Carbon Origin and Stock in Cultivated and Grassland Soil of the Argentine Pampa

Abstract

A study was carried out in the Argentine Pampa. Plots under continuous maize and maize–wheat/soybean–soybean rotation were used. Three control plots on grassland with different undisturbed periods were also used. The objective was to show that C3 and C4 plants have a different effect on the quantity of carbon retained in the soil when different crop sequences are used. Total organic carbon was determined, and mass spectrometry techniques were used to assess the natural variation of the abundance of ¹³C and ¹²C to trace carbon fate in the soil. No differences were observed in the carbon stock at 90 cm deep across cultivated plots. Maize monoculture represented an important contribution to the soil organic matter when compared to the grassland areas, but the comparison through the initial δ¹³C from reference plots did not allow an assessment of the original soil carbon in the plot under rotation.