Är kolrika jordar en källa till fosforläckage? : en sammanställning av data från 130 åkerjordar

Abstract: Phosphorus (P) is an essential nutrient but a surplus could lead to eutrophication. Furthermore, the minerals used to produce the mineral phosphate is a non renewable resource. There are in other words several reasons to reduce the leakage of P and the agriculture is one important area to attend. The aim of this work has been to investigate if carbon-rich arable soils content contain more P than arable soils with low carbon content. Moreover it has been calculated if the carbon-rich soils could pose a risk of P leakage by comparing their delivery of P with the plant uptake. The work has consisted of compiling the results from former gathered and analysed soil samples of 130 Swedish arable soils. The fractions of P considered are water soluble P (Pw), ammonium lactate-extractable P (P-AL), hydrochloric acid-soluble P (P-HCl), organic ammonium lactate-extractable P (Porg-AL) and inorganic ammonium lactate-extractable P (Porg-HCl). The P-AL and P-HCl has been analysed both with colorimetric method, which detects the inorganic fraction and ICP, which detects the inorganic as well as the organic fraction. The diference between these values has given the value of Porg-AL and Porg-HCl, respectively. The results show that there is a strong correlation between Pw and P-AL, which implies the possibility to make a realicstic estimation of the amount of P in the soil solution by measuring the P-AL fraction. With the colorimetric method it is also shown not to exist any relation between P and the carbon content, whilst there with the ICP method exists a relation. This suggests that for carbon-rich soils, the colorimetric method could give an defective perception of the P content. It may therefore be advisable to consider other methods for such soils. The majority of the soils investigated present a risk of P leakage. The carbon-rich soils often contain the highest concentration of P, however the soils with low carbon content contain the highest amounts of P. That indicates that the soils with low carbon content might pose a greater risk of leakage. Nevertheless, carbon-rich soils contain more organic carbon, which is a more mobile form of P and therefore is more easily transported to aquatic ecosystems. Based on this work it is difficult to conclude which kind of soil presents the greatest risk of leakage since the leakage is the result of many different processes taking part in complex systems.