Vladimir Ćirić

Changes in soil carbon stock under the wheat-based cropping systems at Vojvodina province of Serbia

ABSTRACT The aim of this study was to assess the changes in soil organic carbon (SOC) stock in relation to the carbon (C) input from nine wheat-based cropping systems and untilled grass. The SOC pool ranged from 32.1 to 49.4 Mg ha−1 at 0–20 cm and from 94 to 171 Mg ha−1 at 0–100 cm for the arable soil, while in untilled grassland, it was higher (54 and 185 Mg C ha−1, respectively). SOC stock was observed to be lower at the unfertilized 2-year rotation and higher at the 4-year rotation with manure and mineral fertilization. The study showed a winter wheat yield decrease of 176.8 kg ha−1 for a 1- Mg ha−1 SOC stock change in the 0–20-cm soil depth. The estimated C input for SOC stock maintenance was from 266 to 340 g C m−2 year−1 for winter wheat and rotations, respectively. Additional C input did not increase the SOC pool, suggesting that arable plots had a limited ability to increase SOC. These results provide guidance for the selection of management practices to improve C sequestration.

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.

Microbiological Activity in the Soil of Various Agricultural Crops in Organic Production

Summary The purpose of this study is to investigate the microbial activity and the number of different groups of microorganisms in the soil under organic agricultural systems. A range of analyses was conducted on soil samples taken from calcareous chernozem soils managed under organic (7 sites) and conventional agricultural systems (1 site). Laboratory measurements were performed in the Laboratory of Microbiology, Faculty of Agriculture, Novi Sad. The total number of bacteria, actinomycetes, fungi, aminoheterotrophs and azotobacters was determined using the dilution method. Soil dehydrogenase activity was measured spectrophotometrically. The greatest number of the Azotobacter sp. bacteria was recorded in the soil devoted to pumpkins (132.61 × 102) and in the soil devoted to apples (126.39 × 102). The greatest number of aminoheterotrophs (1786.05 × 106) and the total number of bacteria (1370.82 × 106) and actinomycetes (235.45 × 104) were determined in the soil devoted to carrots. Fungi were more abounded in the soil devoted to chard (36.82 × 104) than in the soil devoted to other plants. The research results show that the soil devoted to wheat in organic production indicated a greater number of aminoheterotrophs, total bacteria, actinomycetes and fungi, whereas only the number of Azotobacter sp. was greater in the soil devoted to wheat in the conventional agricultural system. The highest dehydrogenase activity level was determined in the soil devoted to radishes, whereas the lowest dehydrogenase activity level was determined in the soil devoted to apples.

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.