Long term flux measurements are needed to improve our understanding of the carbon
balance of
arable lands. The objective of our study was to determine the seasonal dynamics of
carbon cycling
in a Hungarian cropland and to examine the effect of crop rotation on net ecosystem
exchange of
CO2 (NEE), furthermore to assess the influences of C outputs and inputs derived from
lateral fluxes
on soil organic carbon (SOC) stock. In this study we update the results presented
in our poster of
last year’s conference (EGU21-10977).
The experiment began in 2017 and crop rotation of the measured field consisted of
winter wheat
(2017-2018 and 2019-2020), rapeseed (2018), sorghum (2019) and sunflower (2021). CO2
fluxes
and annual net ecosystem exchange (NEE) of CO2 were measured by a field-scale eddy
covariance
(EC) station at a Central Hungarian cropland site. Both vertical and lateral C fluxes
were taken into
account when calculating the net ecosystem carbon budget (NECB).
As presented in our previous study the largest sink activity was observed in the sorghum
season
(-277 g C m-2 from sowing to harvest). The cropland acted as a source of CO2 during
the rapeseed
season (140 g C m-2) due to incomplete germination caused by extreme autumnal drought.
We found that during the study period both meteorological variables and lateral carbon
fluxes
such as C inputs derived from seed and crop residues and outputs (harvest) had significant
influence on the C dynamics. The higher temperatures and precipitation amount that
characterised the fall of 2019 caused large differences in NEE dynamics for winter
wheat when
compared to 2017. The impact of climatic factors could be seen in the sunflower period
since lack
of precipitation in 2021 led to remarkably low carbon uptake.
Fallow periods in total covered a relatively long period of time (approximately 1
year out of the 4
year long study period). These fallow periods had a significant effect on NECB values
due to
immense C loss. During the four years of our experiment cumulative NEE was -222 g
C m-2 and
NECB was 726 g C m-2 as carbon loss during fallow periods (437 g C m-2 in total) and
carbon export
through harvest (964 g C m-2 in total) counterbalanced the crop’s CO2 uptake.
We can conclude that while this Hungarian cropland was a sink of carbon it could not
maintain the
soil organic carbon content as it was not able to sequester enough carbon to do so.
Cover plants
and crop residue retention could be a solution to reduce the risk of soil carbon stock
depletion but
further studies are needed in the field of soil management practices.
