Effects of nitrogen fertilization on the cadmium concentration in winter wheat grain

The thesis summarizes and discusses results from field studies on the effects of nitrogen (N) fertilization on cadmium (Cd) concentration in winter wheat (Triticum aestivum L.). It also deals with Cd and N uptake and distribution in shoots as related to stage of development. Furthermore, the possibility to predict the grain Cd concentration at harvest from the Cd concentration in the shoot at earlier stages of development was investigated. The studies were conducted in the major wheat-growing districts in southern and central Sweden. It was shown that N fertilization caused an increase in Cd concentration in winter wheat grain, independent of site and cultivar. For an N application rate of 145 kg N ha-1 (Swedish norm) an increase of 30 kg (to increase grain protein content) would increase the grain Cd concentration by 6-14%. There were no significant effects of N application strategies such as earlier application and split rates on grain Cd concentration. The amounts of Cd and N in wheat shoots increased with time during the entire study period, from stem elongation to maturity. Nitrogen appeared to be redistributed to the ear/grain as soon as the ear emerged, whereas for Cd such redistribution only occurred close to maturity. There was a general correlation between Cd concentration in shoots and Cd concentration in mature grain. The correlation was strongest at ear formation, about two months before harvest. However, some deviations from the general pattern related to specific sites and cultivars make further inves-tigations necessary before prediction of the Cd concentration in harvested grain becomes practicable