Ljiljana Nešić

The sensitivity of water extractable soil organic carbon fractions to land use in three soil types

ABSTRACT Soil organic carbon (SOC) has a high impact on the sustainability of ecosystems, global environmental processes, soil quality and agriculture. Long-term tillage usually leads to SOC depletion. The purpose of this study was to determine the impact of different land uses on water extractable organic carbon (WEOC) fractions and to evaluate the interaction between the WEOC fractions and other soil properties. Using an extraction procedure at 20°C and 80°C, two fractions were obtained: a cold water extractable organic carbon (CWEOC) and a hot water extractable organic carbon (HWEOC). The results suggest that there is a significant impact from different land uses on WEOC. A lower relative contribution of WEOC in SOC and a lower concentration of labile WEOC fractions are contained in arable soil compared to forestlands. Chernozem soil was characterized by a lower relative contribution of WEOC to the SOC and thus higher SOC stability in contrast to Solonetz and Vertisol soils. Both CWEOC and HWEOC are highly associated with SOC in the silt and clay fraction (<53 µm) and were slightly associated with SOC in the macroaggregate classes. The WEOC fractions were highly and positively correlated with the SOC and mean weight diameter.

TOTAL AND HOT-WATER EXTRACTABLE CARBON RELATIONSHIP IN CHERNOZEM SOIL UNDER DIFFERENT CROPPING SYSTEMS AND LAND USE

A study was conducted to determine the hot water extractable organic carbon (HWOC) in 9 arable and 3 non arable soil samples on Haplic Chernozem. The hot water extractable carbon represents assimilative component of the total organic matter (OM) that could contain readily available nutrients for plant growth. The obtained fraction of organic carbon (C) makes up only a small percentage of the soil OM and directly reflects the changes in the rhizosphere. This labile fraction of the organic matter was separated by hot water extraction at 80°C. In our study the HWOC content in different samples ranged from 125 mg g-1 to 226 mg g-1. On the plots that are under native vegetation, higher values were determined (316 mg g-1 to 388 mg g-1). Whereas samples from arable soils were lower in HWOC. It was found that this extraction method can be successfully used to explain the dynamics of the soil OM. Soil samples with lower content of the total OM had lower HWOC content, indicating that the preservation of the OM depends on the renewal of its labile fractions.

Aggregate stability and sealing risk of solonetz under different land use regimes

Solonetz is a type of alkaline soil which covers about 3.75% of the Province of Vojvodina, Serbia. In order to investigate the potential implementation of efficient agricultural production on this soil, we investigated the stability of structural aggregates and sealing risk (crusting hazard) in the surface layer (0-20 cm) of solonetz exposed to different land use. Four classes of stable aggregates (8000-2000, 2000-250, 250-53 and <53 μm) were obtained and the risk of sealing was calculated. The results show relatively stable structure in the surface layer of the investigated solonetz soils, but also a high risk of sealing. Solonetz under native vegetation showed higher aggregate stability and lower risk of sealing compared to solonetz exposed to long term tillage. Such soils can be recommended for establishing protective forests or cultivation of shallow rooted plants under condition that appropriate chemical properties of the surface horizon are monitored and cultivation practices against risk of sealing are implemented. Also further interdisciplinary study of these alkaline soils is recommended bearing in mind its high prevalence and variability of their properties.