TY - THES T1 - Heavy metals from phosphate fertilizers in maize-based food-feed energy systems A1 - Niño Savala,Andrea Giovanna Y1 - 2023/03/21 N2 - The problem of polluted agricultural lands with heavy metals due to anthropogenic activities, including applying phosphorous (P) fertilizers polluted with cadmium (Cd) and other metal such as uranium, has been extensively studied. Several reviews, including the one in the present dissertation, have elaborated this issue with often the same results: the application of P fertilizers with high Cd levels is strongly correlated to Cd accumulation in arable soil, which could imply environmental risks as well as health risks for humans and animals through the food chain. Therefore, these reviews have often the same conclusion: the application of low Cd-P fertilizers, either mineral, organic or recycled, is diminishing the risks of Cd pollution at the soil, crop and consumption level. However, globalization, trade politics, economy, dependency on Morocco mineral P fertilizers, and the finite stock in the raw material have challenged this possibility, especially in the European Union. Meanwhile, in China, polluted arable soils are related to other anthropogenic activities and type of fertilizers rather than Cd-polluted phosphate rock and mineral P fertilizers. At the farm level, other options to diminish Cd pollution in soil and crops, besides low Cd-P fertilizers, could consist of different fertilizer and crop management. These options were studied in this dissertation. A different P management, including different rate applications and placements, did not influence the total Cd concentration in silage maize grown in Germany, regardless of the developmental stage of the crop and the Cd levels in P fertilizer. Silage maize might take up Cd derived from P fertilizers under unpolluted soils, without high risks due to its high biomass production. However, significant changes in the labile Cd fraction were already visible after applying Cd-polluted P fertilizers at 150% of the required amount to the soil after only two growing seasons. Further research should be done to understand the correlations between the bioavailable metal fraction and the actual Cd uptake by silage maize, especially in unpolluted soils. This recommendation also follows the meta- analysis results presented in the second publication, which indicated a possible bias as most of the studies are performed under polluted conditions. Considering the results of the third and fourth publication, the Cd uptake by silage maize was strongly correlated to labile Zn in the soil and the Zn uptake at the early development stage after two field seasons. Placed P fertilizer had a significant and negative effect on the Zn uptake by young silage maize. Further research is needed to understand the behavior of Cd and Zn in the uptake process by maize under P fertilization in unpolluted soils. According to three of the four publications presented in this dissertation, the soil pH was the main soil characteristic influencing the bioavailability and the plant uptake of Cd under unpolluted conditions, regardless of the P treatment, the development stage, and the maizes intended use. However, the total Cd concentration in the soil was the dominant variable for the Cd concentration in maize grain when the soil was polluted with high Cd levels, which was the case in several experiments analyzed in the second publication. P fertilizers with average Cd contamination might enhance labile Cd accumulation in arable land and crops when applied to low biomass crops, such as wheat and legume crops. In this regard, crop management such as crop rotation in the central field experiment indicated that the wheat rotation induced a lower Cd accumulation in maize-soil systems, owing to wheat likely accumulating Cd at higher levels than other crops. The results presented in the second publication also indicated high Cd accumulation by the wheat crop: the wheat grain accumulated more Cd than the maize grain. Thus, potential hazards related to Cd accumulation in wheat grain should also be considered in wheat-maize systems. In conclusion, suitable crop rotations considering the crop-specific potential of Cd accumulation, efficient P management including soil P levels and nutrient use efficiency, and low Cd-P fertilizers remain the most viable options and the main challenge to avoid Cd accumulation in arable soils. KW - Mais KW - Phosphor KW - Schwermetall KW - Cadmium KW - Düngemittel CY - Hohenheim PB - Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim AD - Garbenstr. 15, 70593 Stuttgart UR - http://opus.uni-hohenheim.de/volltexte/2023/2123 ER -