Epsilon Archive for Student Projects

Abstract

Eutrophication of the Baltic Sea is a serious problem. A major contributing factor is diffuse losses of phosphorus (P) from agricultural land in surrounding countries. In order to estimate P losses, environmental monitoring of small agriculture-dominated catchments is being carried out in most of these countries. Evaluation of the risk of P leaching to waters is usually based on chemical tests originally developed to quantify the amount of soil P available for plant production. The tests are performed in different ways in the different countries and a number of different extraction agents are in use. The ammonium lactate method (P-AL) is used in Sweden and Lithuania, the double lactate method (P-DL) in Latvia and Poland, the Mehlich 3 method (P-M3) in Estonia and the Olsen method (P-Olsen) in Denmark.

A total of 99 soil samples from five agricultural catchments and two field trials in the Baltic States and Sweden were extracted according to the four methods listed above. The amount of P was then quantified either colorimetrically or by inductively coupled plasma (ICP) spectrometry in accordance with the practices of the respective country. The amount of P determined by ICP spectrometry was nearly always (in 98% of cases) higher than that determined colorimetrically, with an average difference of 19% in plant-available P. The amount of P extracted by the four methods increased in the order Olsen-P < P-DL ≤ P-M3 < P-AL, with Olsen-P values being on average only 24% of P-AL values. The different active agents used in the four methods differ in their efficiency in desorbing and releasing P from minerals and organic compounds.

In the Baltic Sea area, neither a P adsorption index (PSI) or the amounts of P in relation to aluminium (Al-AL) and iron (Fe-AL) in the acidic AL extract is suggested to be a general good predictor of soil capacity to adsorb P or release dissolved reactive P (DRP) to water, based on the results from the limited number of sites in the present study.