Effects of chemical and physical grassland renovation on the temporal dynamics of organic carbon stocks and water-stable aggregate distribution in a sandy temperate grassland soil

Grassland renovation can be done physically by ploughing or chemically using herbicides, but information on influences of grassland renovation on soil structure is scarce. Our objective was to compare physically and chemically renovated grasslands and to quantify temporal variations of soil organic carbon (SOC) stocks, water-stable aggregates and SOC stored in different aggregate fractions. Soil samples were taken on a sandy soil before (T-0), 6 days (T-6_days), 2 (T-2_mo), 7 (T-7_mo) and 12 months (T-12_mo) after grassland renovation and in permanent grassland. Neither grassland renovation practice led to SOC losses in 0-10 cm after 12 months. The physical renovation led to an increase in microaggregates (53-250 mu m) in the surface soil between T-0 and T-6_days and to highest microaggregate concentrations in T-2_mo and T-7_mo. Therefore, ploughing seems to have direct negative effects on macroaggregates (10 mm-250 mu m) followed by indirect longer-lasting negative effects which were nullified after 1 year. Chemical renovation resulted in no different aggregate distribution than permanent grassland. Strong temporal variations in aggregate distribution were found especially for large macroaggregates with lowest concentrations in T-6_days and 6.7- to 10.2-fold higher concentrations in T-2_mo. A linear regression suggested that the soil gravimetric moisture content might have caused this observation.