Content of magnesium and heavy metals fractions in selected natural fertilisers

Our objective has been to determine the total content of magnesium, iron, chromium and zinc, as well as the heavy metal fractions in selected natural fertilisers, such as swine and bovine manure and poultry litter from laying hens and broilers. The total content of the metals was determined by the ICP-AES method following dry mineralisation in a muffle furnace at 450°C and dissolving the ash in HCl (1:1). Fractions of Fe, Zn and Cr were isolated by the 3-step sequential fractionation method proposed by the Community Bureau of Reference (BCR). This study has shown that the analysed organic materials had different content of the determined metals. The largest amount of Mg was found in litter from laying hens and the largest amounts of Fe, Cr and Zn were in litter from broiler chickens. The smallest amount of Mg was found in swine manure, Fe and Cr were the least abundant in litter from laying hens, and the lowest Zn content was in bovine manure. The content of these four heavy metals was significantly differentiated by the origin of fertiliser. The exchangeable fraction F1 had the smallest share in the total Fe content among all the fertilisers. As for chromium, this fraction made the smallest contribution to the total Cr content in litter from laying hens and broilers while the reducible fraction F2 was the smallest part of the total content in both types of manure. Fraction F1 of zinc was the smallest in the total content in swine and bovine manure and while the oxidisable fraction F3 made up the smallest share in the total content of this metal in litter from broilers.