Change of available forms of nitrogen and phosphorus in alluvial-meadow soil, after longterm fertilization

S. Todorova, N. Simeonova, K. Trendafilov, V. Valcheva

Abstract. Our work is aimed at studying the natural potential of the soil to provide assimilated forms of nitrogen and phosphorus for plants, after cessation of 45-year mineral and organic-mineral fertilization. The object of our study is alluvial-meadow soil (Mollic fluvisol) in the region of Plovdiv (Bulgaria), on which in 1961 was set a trial with different rates of fertilization in conditions of five-field crop rotation (maize – wheat – forage pea – barley – alfalfa). Since 2006 the fertilization was discontinued, but crop rotation is still maintained. As a result of the study we found that the natural reserves of mobile forms nitrogen and especially phosphorus in the soil are not sufficient for normal growth and development of plants. It is necessary to import organic and mineral fertilizers, but the rates must be based on these natural reserves of nutrients in soil. In this way excessive use of fertilizers can be avoided (especially nitrogen fertilizers), the negative environmental effect will be minimized and the cost of production will be somewhat reduced.