prilagođeno pretraživanje po punom tekstu

ŠUMARSKI LIST 1-2/2020 str. 48     <-- 48 -->        PDF

while promoting other ecosystems servises (Nair and Garrity, 2012). Vital, productive, sustainable and adaptive ecosystems are formed (Mosquera-Losada et al., 2012), including on degraded lands (Brumec at al., 2013). The established agroforestry systems frequently mimic the natural systems, and in most cases an appropriate combination of tree, shrub and grass species with agricultural crops are observed. Nevertheless, the reducing competition and increasing complementarity and compatibility of species used in agroforestry remains the main challenge facing science and practice. Tree species and agricultural crops are being defined, which are well combined and complementary each other’s in structuring agroforestry systems. Poplar is such tree species particularly suitable for the construction of silvoarable and silvopastoral agroforestry systems (Fakirov, 1972; Vassev, 2013; Newman, 1997). It is a fast-growing species and provides accelerated growth especially on typical habitats such as riparian lands (Dobrev and Bodgakov, 1971; Zahariev et al., 1975). In Bulgaria the cultivation of agricultural crops between rows of young poplar trees has been practiced for a long time and successfully (Marinov et al., 2003). Between tree rows is grown: sunflower, cabbage, corn, pepper and eggplant; melon and squash, cauliflower, wheat, beans etc. (Yakimov et al., 2003). The accumulation of waste green organic mass from agricultural plants supports the development of young poplar saplings, and agrochemical care (hoeing, irrigation, fertilizing, etc.) has a beneficial effect on their growth and development (Yakimov et al., 2003). At the same time, improved biodiversity in agroforestry systems, along with increased biomass accumulation in the soil, leads to an improvement in soil quality and fertility (Silva et al., 2012; Nair and Garrity, 2012; Tsonkova et al., 2012).
The aim of this study is to investigate the growth of saplings of Populus sp. and the composition of soil organic matter in agroforestry systems established on typical habitats along the Danube.
The region of Vidin is in the Missian forest vegetation zone with moderate continental climate. It has low January temperatures, high July temperatures and annual precipitation sums of 500-600 mm. Along the river Danube there were established 3 sample plots (SPs) and one control (K) located in Vidin Forestry Estate – the most north-western part of Bulgaria. SP1 is near the village of Novo selo. It has an area of 3.4 ha, with altitude of 30 m, eastern exposure, flatly, and plantation of the “Agathe” poplar clone at the age of 2 years. In SP1 between poplar rows is planted corn. Next to this SP is located the SP2 with an area of 2.4 ha, altitude 30 m, northwestern exposure, flatly, plantation of “mnBL” clone, 10 years old. When the tree plantation was 2-3 ears old there were planted corn and water-melon. The other two SP are located near the town of Vidin in eastern direction near the petrol station “Fantige”. SP3 has an area of 3.7 ha, altitude of 40m, eastern exposure, flatly, and plantation of “Agathe”, 3 years old. The last year between tree rows there were corn crop. Next to this SP is located the control – SP4, where no agricultural crops were grown – without agroforestry. SP4 has an area of 1.1ha with eastern exposure, flatly and plantation of “Agathe”,”mnBL” and “I 214”, 10 years old. All SPs lies in the zone of Nature 2000 and located in the Danube River’s defensive line. The soils are alluvial (Alluvial Fluvisols) developed on loess.
Dendrometrical indicators were determined by in situ measurements. The mean diameter breast height (DBH) was determined by the arithmetic basal area – formula (1):
G=∑gi/ n - is arithmetic basal area in sample plot (m²);
∑gi – the sum of basal area of all trees in sample plot (m²);
n - is number of trees in sample plot.
The mean height (Hm) was calculated as the weighted average in terms of basal areas of Lorey’s formula (2):
(2)           Hm = (h1g1 + h2g2 + ……..+hngn) /                 (g1 + g2 + ………+gn) (m) = ∑ / ∑gn               
h 1,2n    – is a arithmetic height of each degrees of thicknes (m);
g1,2n      – the basal area of all trees according to the relevant degree of thickness (m²);
Caliperring of older plantations (SP2 and SP4) was made by programme product FET 1.11 (Demo) (Evangelov, 2012), through option “Sorting of whole standings” which uses mathematical model of adopted by practice tables of high-stem poplar (Nedyalkov et al., 2004)
Statistical processing with the software product Statistica 12 was performed.
For soil analyses an average sample of 5 soil samples were taken from the 0-5 cm soil layer. In determining the total carbon, we used the Thurin method, and for the determination of the total nitrogen, the Keldal method was applied (Donov et al., 1974). We studied the composition of humus in soils by Kononova-Belchikova method (1961) which comprises the following steps: total content of humic and fulvic acids with a mixed solution of 0.1N Na4P2O7 and 0.1M NaOH; free and bound to the sesquioxides (R2O3) with 0.1M NaOH; aggressive fulvic acids with 0.05M H2SO4. The soil-to-solution ratio is 1:20 for all three extracts.