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

Safety of food crops on land contaminated with trace elements

Contamination of agricultural soils with trace elements (TEs) through municipal and industrial wastes, atmospheric deposition and fertilisers is a matter of great global concern. Since TE accumulation in edible plant parts depends on soil characteristics, plant genotype and agricultural practices, those soil- and plant-specific options that restrict the entry of harmful TEs into the food chain to protect human and animal health are reviewed. Soil options such as in situ stabilisation of TEs in soils, changes in physicochemical parameters, fertiliser management, element interactions and agronomic practices reduce TE uptake by food crops. Furthermore, phytoremediation and solubilisation as alternative techniques to reduce TE concentrations in soils are also discussed. Among plant options, selection of species and cultivars, metabolic processes and microbial transformations in the rhizosphere can potentially affect TE uptake and distribution in plants. For this purpose, genetic variations are exploited to select cultivars with low uptake potential, especially low-cadmium accumulator wheat and rice cultivars. The microbial reduction of elements and transformations in the rhizosphere are other key players in the cycling of TEs that may offer the basis for a wide range of innovative biotechnological processes. It is thus concluded that appropriate combination of soil- and plant-specific options can minimise TE transfer to the food chain