Bulgarian Journal of Soil Science

3 - 10

Authors: Kostadinka Nedyalkova; Galina Petkova; Irena Atanassova

Data on microbiology of water repellent (hydrophobic) soils in Bulgaria are scarce. This work aimed to find out relations between microbiological indicators, hydrophobicity level and other soil properties in a Spolic Technosol. Samples from 0-10 cm and 10-20 cm soil depth of a fly ash reclaimed soil covered with tuft vegetation and located near Obruchiste area were collected. Main microbiological (basal respiration - BR, microbial biomass carbon content -Cmic, amount of main microbial groups –CFU), chemical (organic carbon, available N, P and K contents) and physical (hydrophobicity level, moisture, sand and clay contents) properties were determined. It was found that the Technosol was hydrophobic in most of the monitoring points. Half of the samples were severely or extremely hydrophobic (assessed by water-drop-penetration time) and the hydrophobicity level was higher in the subsurface layer. The Spolic Techosol under tuft vegetation was characterized with low numbers of heterotrophic bacteria, actinomycetes and oligotrophic microorganisms (1-40 x 102 CFU/g) at 0-20 cm depth. As a whole, low BR rate (0.51-5.43 mg CO2/g/ 24h) and low Cmic values (2.37-18.18 mg C/100g) were established for both layers. Weak relationships of microbial parameters with organic carbon, humic acid, fulvic acid and clay contents were noticed in this soil. Significant correlations of the amount of fungi and actinomycetes with available nutrient and moisture contents were found. In general, a trend of positive relationships of fungi, actinomycetes and cellulolytic microorganisms with soil hydrophobicity was established. The relative parts of fungi and actinomycetes increased in the hydrophobic samples comparing to non-hydrophobic ones. Microbial biomass carbon tended to increase with increasing the hydrophobicity level. Data pointed on close positive relationships of microbial parameters studied with the hydrophobicity in this Technosol. Our results add new information to the monitoring study of hydrophobic Technosols from Maritsa-Iztok coal-mining region (Bulgaria).

23 - 33

Authors: Zornitsa Popov;, Benoit Gabrielle; Bruno Leviel; Milena Kercheva

This paper reports on CERES-maize model stepwise calibration, modification and validation using independent data from specific experiments carried out in a chromic luvisol (Chelopechene), Sofia field,1997-1999. Laboratory based water conductivity curve WCC (eq.1) and water retention curve WRC (eq.2) are calibrated (step i) and adjusted to data measured in field (step ii) (Fig.1; Table 3). Field observations of water dynamics under maize hybrid Kn 509 relative to optimal nitrogen supply N200 (kg ha-1 ) and variable water stress (irrigated A1 plots/lysimeters №1 and №2) are used to modify the function of Root Water Absorption (eq.3) (step iii). The ability of calibrated biological module of CERES-NC-Maize model to make predictions without any further adjustments of parameters is tested against independent three-year dataset (1997-1999) collected in the same field (Chelopechene) but in lysimeter №1 (step iv). Observed water contents in the 1.30 m root zone PESW and soil layers SW (Figs.3a, 3b, 3c, 3d), actual crop water uptake (evapotranspiration ET) (Figs. 4 and 5) and water fluxes prove acceptable agreement with validated model outputs. Model predictions of crop growth and dry weights of maize are acceptably precise in most of the tested situations (Fig.6). The results support the use of tested CERES-NC model in prediction of aboveground dry matter, water balance and storage under maize on Chromic Luvisols in Sofia field

50 - 63

Authors: Vania Kachova

A field experiment was carried out with Acer platanoides L. saplings fertilized using organic fertilizer „Sapton‟ in different variants: control (K); variant 1 (V1) - low dose of “Siapton” (1ml); variant 2 (V2) - high dose of “Siapton” (50ml); variant 3 (V3) - high dose of „Siapton” and mineral fertilizer “Krystalone” and variant 4 (V4) - high dose of “Siapton” and organic fertilizer “Biohumus”. All fertilized variants show better growth in mean diameters (root collar diameter (D0) and breast height diameter (BHD)), average height and wood biomass accumulation with the exception of V1. The dose turns out to be definitive in relation with the fertilization effect. Good results are obtained by combining two organic fertilizers (V4) during the first two years of fertilization. Variant 3 (combination with mineral fertilizer), however, has a longer duration and is manifested in a long time after application of fertilization (especially in the third year after treatment) and is also recommended to be applied in practice. The increment of height is most pronounced in V4 (a combination of two organic fertilizers) for a longer period, too: an increment of 0.43 m versus 0.07 m for the control during the third year. This gives the reason to recommend organic fertilization in improving the growth characteristics of Norway maple for the needs of forestry and urban planning where good growth and accumulation of woody biomass is desired.