T. Tõnutare1, K. Krebstein1 , A. Toomsoo1, L. Szajdak2, L. Soobik3 , M. Jürgens1 , R. Kõlli1
1) Estonian University of Life Sciences, Tartu, EE; 2) Institute for Agricultural and Forest Environment, Polish Academy of Sciences, Poznan, PL; 3) University of Tartu, College of Foreign Languages and Cultures, Department of English Studies, Tartu, EE


Phosphorus (P) is an essential nutrient for plant growth and therefore the content of plant available phosphorus (PAP) in soil has a critical importance in receiving high yields in modern agriculture. However, excessive amounts of PAP in soil can lead to the environmental risks from which the most common is the eutrophication of surface waters. Due to intensive agriculture the loss of P from agricultural soils to the ambient environment represents a major trend in the world. According to PAP contents the soils are divided into different P status (fertility) classes. For determination of the PAP content of soils a huge number of methods has been developed but mainly all of them are based on the extraction of P from the soil with a diluted inorganic salt solutions. Due to unequal extraction power each method has an individual and specific gradation. Depending on soil properties and kinds of cultivated plants, more than one gradation may exist per one (the same) method. During the decades, a large number of articles about the comparison of results of PAP, determined by different methods and their dependence on soil properties, have been published. The aim of this work was to compare the distribution of soils, analysed by different methods, according to PAP fertility classes, and find the factors which caused this distribution. Our specific aim was to establish (identify) the factors which have a decisive role in distribution of soils by fertility classes. The content of PAP in 140 agricultural soil samples by methods of ammonium acetate-lactate (AL), calcium acetate-lactate (CAL), double lactate (DL) and Mehlich 3 (M3) was determined. Using the existing gradations for each method the soils were divided into PAP classes by AL, CAL, DL and M3 methods, respectively. Statistical methods are used for establishing the role of soil physical (clay and sand content, texture) and chemical (pH, organic matter and calcium content) properties in distribution of soils by fertility classes. The obtained results will indicate the factors which will be the key determinants of differences in distribution of soils to fertility classes and help to eliminate the dissimilarities. It allows to diminish the risk of environmental pollution caused by the incorrect use of phosphatic fertilizers.

Keywords: soil phosphorus, methods of P analysis, soil fertility classes