Maintaining or enhancing the stock of soil organic carbon (SOC) is a key factor in sustaining the soil
resources of the world. The objective of this research was to study the effect of different farming systems
(conventional farming with mineral fertilizers and crop specific fertilization vs. organic farming with
organic fertilizers (catch crops and composted manure)) under the same 5-crop rotation (red clover,
winter wheat, pea, potato, barley undersown with red clover) system on the SOC stock and the stability of
SOC. The second aim was to quantify plant C inputs to the soil and to identify the relationship between C
sequestration rate and C input. Data presented in this paper concerned the
first rotation during 2008–
2012. The main factors were farming systems: conventional and organic. Four conventional farming
systems differed in the mineral nitrogen application rates used. In two organic farming systems catch
crops were used with or without composted solid cattle manure. The SOC stock was determined before
experiment establishment and after the
first rotation. The C input into the soil was calculated based on
the main product yield. The stock of SOC increased (2.57 Mg ha1 y1) considerably after the
first rotation
only in the organic farming systems, where the total C inputs were 1368 kg C ha1 y1 higher compared to
the average C inputs in conventional systems. The mineral N rate did not influence the C-input but it had
an effect on the properties and mineralisation of soil organic matter. The stable C fraction of SOC
proportion increased in the system in which the highest rate of mineral N (20–150 kg N ha1y1
depending on crop) was used and its proportion in the soil was comparable with the results obtained
from organic farming systems. Thus, the intensive management with high N rates may benefit to a
formation of more stabile SOC if the crop rotation used is properly elaborated.