Concentration of trace metals in winter wheat and spring barley as a result of digestate, cattle slurry, and mineral fertilizer application.

Concentration of trace metals (TMs) is one of the most crucial factors determining the quality of cereal grains. The aim of this study was to evaluate the effect of digestate, manure, and NPK fertilization on TM concentration in grains and straw of two cereal crops-winter wheat (WW) and spring barley (SB)-and TM transfer from soil to plants. The experiment was carried out between 2012 and 2016. Every year, the same treatment was used on each plot: control (without fertilization), digestate, digestate + straw, cattle slurry, and mineral NPK fertilization. In general, fertilization increased the concentration of TMs that belong to the micronutrient group (Zn, Cu, Fe), particularly after application of digestate and cattle slurry. At the same time, fertilization, regardless of the fertilizer type, led to an increase in Cd concentration in the grain of WW in comparison with the control. Despite the increase in Cd and micronutrient content as a result of fertilization, the concentration of elements remained below the applicable standards. Among TMs, only Pb content exceeded the European Union limits. The increased concentration of Pb was, however, an effect of other factors, rather than fertilization. The results clearly indicated that the biogas digestate from anaerobic codigestion of cattle slurry and agricultural residue could be utilized as fertilizer in agricultural applications without a risk of contaminating the food chain with TMs.