S. Todorova*, K. Trendafilov, M. Almaliev
Department of Agro-chemistry and Soil Science, Faculty of Agronomy, Agricultural University, 12 Mendeleev, 4000 Plovdiv, Bulgaria
Abstract. The aim of our study was to investigate phosphorus fractions, their content and distribution in alluvial meadow soil after continuous fertilization. Our research was focused on a long-term field experiment with different variants of fertilization set in 1959 in the Experimental field of Agricultural University of Plovdiv. Since 2006 the fertilization has been discontinued. In 2011, we collected soil samples from two depths (0 – 30 and 30 – 40 cm) and from the following variants: variant 1 (control, without fertilization), variant 2 (N50P30K20), variant 3 (N25P15K0 + 6t/da manure), variant 4 (N50P0K20). The studied soil is characterized by relatively good natural phosphate regime. The amount of available phosphates determined by the Egner-Rheem method is high – average 16.76% of the total phosphorus. Over 50% of the mineral phosphates in the soil are in available (in varying degree) form. Relatively high is the amount of organic phosphates, which during the mineralization can also be involved in the plant nutrition. The amount of available phosphates (according to Egner-Rheem) is determined to the highest degree by the total phosphorus in soil, which in turn is highly correlated with the content of hardly soluble calcium phosphates.