Nitrogen mineralization potential of alluvial meadow soil after long-term fertilization

V. Valcheva*, 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 this study was to investigate the nitrogen mineralization potential of 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-Plovdiv. Since 2006 the fertilization has been discontinued. In 2010 and 2011, we collected soil samples from depth 0 – 30cm and from the following variants: 1 – control, 2 – N50P30K20, 3 – N25P15K0 + 6 t/da manure, 4 – N50P0K20. In accordance with relatively high content of total nitrogen, the nitrogen mineralization potential of the soil is high. The maximum amount of nitrogen, susceptible to mineralization at optimum temperature and humidity ranges from 233.21 to 350.90 mg N/kg soil. The proportion of potentially mineralizable nitrogen from the total nitrogen in soil is low – average 17%. The reason for this is the humic type of soil organic matter. Also in its composition dominated black humic acids, which are bonded with Ca and resistant to decomposition. Sufficient amount of clay particles and micropores provide physical protection of organic matter from microbial activity. The mean value of mineralization rate constant (k), 0.041, denotes that at optimal conditions the mineralizable N fraction is released at an average rate of 4,1% per week, based on the quantity of mineralizable N remaining after each succeeding week of incubation.