Soil Fertility in Response to Long-Term Fertilization under the Tobacco Monoculture System on Rendzic Leptosol in Bulgaria

The effect of long-term mineral and organic-mineral fertilization on selected soil properties (pH, total humus and N, available phosphorus, potassium, calcium, magnesium, iron and manganese content) was studied in a stationary trail with tobacco monocropping system. The trial was established on Rendzic Leptosols in 1966. Five treatments were selected for this study, including control without fertilization (Check), nitrogen + phosphorus (NP), nitrogen + potassium (NK), nitrogen + phosphorus + potassium (NPK) and nitrogen + phosphorus + potassium + manure (NPK + manure). Soil samples at a depth of 0–25 cm were collected from all studied plots every year (2014, 2015 and 2016). The results indicated that maintaining humus content at the initial level is not possible through yearly mineral fertilizer application. Long-term mineral phosphorus fertilization increased 5.5–5.7 times available P 2 O 5 in the soil compared to the initial level. The soil available K 2 O content in NK and NPK treatments increased, respectively, by 41.1% and 44.9% over the initial level. A remarkable increase in available phosphorus (25.5 times) and potassium (2.5 times) content in the soil compared with the initial level was found due to longterm NPK + manure fertilization. The NPK + manure treatment was found to be the most efficient management system in accumulating of total humus and N, available P 2 O 5 , K 2 O , Fe and Mn in a long-term fertilized Rendzic Leposol, under a tobacco monocropping system.