Silva Balcanica, 20(Special issue 1)/2019 HUMIC SUBSTANCES, PHYSICOCHEMICAL PROPERTIES AND AGROCHEMICAL CHARACTERISTIC OF STRONGLY LEACHED CHERNOZEM FROM NORTHEASTERN BULGARIA Toma Shishkov1, Ekaterina Filcheva1, Margarita Nankova2, Milena Kercheva1, Emil Dimitrov1 1N. Poushkarov Institute of Soil Science, Agrotechnology and Plant Protection – Sofia 2Dobrudzha Agricultural Institute – General Toshevo Abstract This paper discusses interpretation of variables on study of organic matter, physicochemical properties and agrochemical characteristic of strongly leached chernozem, formed in the region of Kavarna in NE Bulgaria. The composition of organic matter is used as evidence of advanced and specific balance of soil processes in the steppe zone as well as biological activity. Total organic carbon (%) was recognizable even at the depth of profile. With regard to the agrochemical characteristic the study of the potential nitrogen-supplying capacity of the soil (nitrification capacity), was carried out to determine the capabilities of the particular site (plot) under optimal nitrification conditions, yield available nitrogen in nitrate form. For this reason, it was followed in dynamics (7th, 14th, 28th, 56th days). The highest value of mineralized nitrogen (an average of 29.67 NO3 mg/1000 g) was reached at 56th days of incubation period. Key words: organic matter, cation exchange capacity, chernozems, nitrogen, phosphorous INTRODUCTION The research site is located in Northeastern Bulgaria and covers the eastern part of Dobrudzha plateau in an area with a pronounced influence of the Black Sea on the climate. To the north it is bounded by the village of St. Nicholas, to the northeast by the village of Balgarevo, in the eastern part with the Black Sea and to the west by the village of Krupen. The unique feature of Dobrudzha coastline is the steppe areas. Geomorphologically, the area is in the eastern part of the Misesian platform, as a major morpho-structural unit, and according to physical geographic zoning it falls into Dobrudzha subregion of the Eastern Danube Plain. In hypsometric terms, the area is referred to the lowland up to 200 m a. s. l. The terrain has a undulating relief plain to plain-hilly, with prevailing slopes from 3o to 5o. In geological terms, this region of Dobrudzha plateau is built on the lower and the middle-Sarmatian sediments, made up of alternating sandy limestones and marls with the aquiferous flow that run through in them. The most common surface karst forms are known in the region as kayryatsi. They are located at the edge part of Dobrudzha plateau and raised up to 110 m heigh near Kavarna town. Among the old abrasive flat forms, the one most well-known is the Sarmatian-Pontic with an altitude of 230-250 m. 29 The survey area is refered to the temperate continental climate, which is formed under the direct influence of the Black Sea. The localclimate is determined by the influx of oceanic air from the northwest and northeast and continental air from the East European Plain. Relatively level terrain and its bare location facilitate the influx of humid, warm air in the spring, summer and autumn, as well as that of polar air in the winter. The Black Sea also exerts an influence over the region’s climate, particularly within 40–60 km from the coast. The small amount of rainfall and the wind with cold continental northern air masses during winter are typical for the region. There is wind during about 85–90% of all days which usually comes from the north or northeast. Winter seems harsh due to the constantly winding winds. The average wind speed is about twice higher than the average in the country. The wind speed in the area is the highest in winter and spring, when it reaches 6.5-8.0 m/sec and the lowest is in summer and autumn less than 5 m/sec. The average annual temperatures range from 11°C inland and to 11.8°C on the coast. The area is relatively cold for its geographic location, with average temperature of 0.8oC in January and 22.3oC in July. The annual temperature amplitude is 21.7-21.9°C. The coastal region of Southern Dobrudzha is the most arid part of Bulgaria, with the average annual rainfall is in the range of 411-480 mm. The maximum rainfall for the area is in autumn, the minimum in spring and summer. In hydrological terms, the area is poor on surface water, the sparse rivers are usually short and with low discharge. Zoning the territory referred it to into the Euxin province of the European broad- leaved forest region and the Lower Danube province of the Eurasian steppe and forest- steppe region (Bondev, 2002). The vegetation is characterized by the prevalence of grass species and scarce involvement of tree and shrub species. In the larger range, the plain terrains distributed on non-cultivated land are dominated by the vegetation, represented predominantly by xerothermic species – bulbous grass (Poa bulbosa L.), pastoral grass (Lolium perenne L.), Bermuda grass (Cydon dactylon L.), belichma (Dichantium ischaemum (L.) Roberty), sadda (Chrysopogon gryllus (L.) Trin.), wheat grass (Agrobyron cristatum), brome grass (Bromus commutatus), and other dry-resistant grass species, including steppe elements such as feather grass (Stipa lessingiana), wheat grass (Agropyrum brandzae), corncrake (Astra galus cornutus Pall.), (Jurinea albicaulis ssp. kilaea), cornflower (Centaurea salonitana Vis.), and others (Kitanov, Penev, 1980). The legumes occupy about 20% of the grassland and include mainly annual or heather species such as Astragalus hamosus, Medicago minima, Vicia sativa, Vicia peregrina, and the most well-represented perennials are a common star (Lotus corniculatus), Medicago lupulina, M. falcata, and Melilotus officinalis. There are separate forest-protection belts on chernozems dominated by oak (Quercus cerris L.), mixed with rust colored oak (Quercus pedunculifloraeL.), summer oak (Quercus robur L.), maple (Acer campestre L.), (Carpinus orientalis) and flowering ash (Fraxinus ornus), and communities of Christ’s thorn (Paliurus spina-Christi) and common smoke-tree (Cotinus coggygria Scop.) Along the gullies and drylands, there are some forms of elm Ulmus minor, Fraxinus oxycarpae, Quercus pedunculifloraeL. and willows Salix alba, S. fragilis. The natural forest ecosystems occupy local areas and fields of protection, dominated by the mixed deciduous forests. 30 In the area among Balgarevo village, Cape Kaliakra and Eni Kulak takes place the last and best preserved steppe habitats in Bulgaria. They are result from the combination of specific relief, soils and climatic conditions. Most of the plants belong to the xerothermic type formations similar to the Crimean peninsula. MATERIALS AND METHODS Soil organic carbon content was determined by modified Turin’s method (Filcheva, Tsadilas, 2002; Filcheva, 2015) (dichromate digestion at 125oC, 45 min, in presence of Ag2SO4 and (NH4)2SO4 FeSO4 6H2O titration, phenyl anthranilyc acid as indicator). According to the method of Ganev, Arsova (1980) the total acidity is determined by the solutions of 1.0 N sodium acetate and 0.2 N potassium maleinate at pH 8.25, the value with maximum saturation of soil colloids with strong alkaline bases. Agrochemical characteristic was carried out on the territory of AGROSPECTOR LTD in the region of Kavarna. The analytical data for the mobile and total forms of the basic macroelements as well as the mineralization capacity of the soil was carried out in the Laboratory of Agrochemistry and physical characteristics of the soil at Dobrudzha Agricultural Institute, General Toshevo. Soil samples were prepared according to the requirements of each specific analysis, as follows: • Soil pH was determined in water and salt suspension of 1 N KCl (Palaveev, Totev, 1979). • The sum of the mineral nitrogen forms in soil was determined by extraction with 1% K2SO4 (mg/1000 g soil). • The identification of 3NO -N in the filtrate was done using the disulphophenol method; and ammonium nitrate was determined by the phenol method (Agrochemical methods for soil investigation, 1975). • The potential nitrogen supplying ability of soil was determined through incubation under constant temperature of 30oC at 60% humidity from its total moisture absorption capacity in order to develop optimal conditions for nitrification. The incubation was done in thermostat to investigate its dynamics at the 14th, 28th and 56th days. The samples were analyzed to determine the amount of nitrate nitrogen in 1% K2SO4 extract. The ability of NO3-N to form intensive yellow coloration when interacting with disulphurphenolic acid [C6H3OH(HSO3)2] in alkaline media was used (Agrochemical methods for soil investigation, 1975). • Available phosphorus and the exchangeable potassium were determined by AL-method (modification of Ivanov, 1984). Phosphorus available to plants (mg P2O5/100 g soil) was determined colourimetrically, and the amount of exchangeable potassium (mg C2O/100 g soil) through flame photometry. • The total nitrogen content in soil (mg/100 g) was determined by the method of Kjeldahl after wet burning with concentrated H2SO4 diluted in distilled water at ratio 1:10, followed by distillation of nitrogen in Parnas-Wagner distillation apparatus. 31 • Total phosphorus content (%) was determined according to Bone method (Agro chemical methods for soil investigation, 1975). • The mathematical analysis of the obtained results was made by means of the software SPSS 16.0 (2007). Mean was separated by Least Significant Difference test (LSD) and the post-hoc analyses were presented through the Waller-Duncan’s Multiple Range Test (DMRT (Р < 0.05). The location of soil is nearby Krupen village, municipality of Kavarna, with coordinates N 43o34’22.43’’ E 28o14’45.59’’ and elevation 173 m. Relief is plane to undulating, parent materials are loess deposits. Soil moisture and temperature regime is mesic-xeric. Soil classification is as follows: the Bulgarian classification (1976): Strongly leached chernozem, none eroded and slightly eroded; according to the WRB (2015): Endocalcic Phaeozem (Pachic, Profundihumic, Siltic); according to the Soil Taxonomy USDA (2014): Pachic Haploxerolls; according to the FAO (1990): Haplic Chernozem.