Joint International Conference on Long-term Experiments ...

Fertilizers, liming materials and manure have a low nickel content, therefore, it is not
probable that they would cause serious nickel contamination (Simon, 1999).
In a low exterior concentration, nickel has a favourable effect on the germination
of plant germination and growth. Nickel has only one physiological function in plant
life: it has a role in building the urease enzyme and its functioning. For the functioning
of the enzyme, 6-8 Ni 2+ ions are necessary per molecule, therefore, it is an essential
element for plants (Láng, 1998).
Luckily, nickel content is so low in most soils, that no toxic effect should be
expected: the average Ni 2+ concentration in non-contaminated soils is between 5 and 50
mg kg -1 (Stefanovits et al., 1999). However, in case of its accumulation, it hinders
growth and can result in chlorosis or necrosis. It influences the uptake of ions with two
positive chargings, primarily that of iron and it hinders the translocation of iron into the
shoot. This has a disadvantageous effect on the water management of the plant and
results in an oxidative stress. The human health risks of nickel are significant, it was
proven that nickel accumulating in the human body has a primary carcinogenic effect.
In the 1950s, coating of seeds with heavy metal compounds was a common practice also
in Hungary. In large-scale companies, coating with NiCl2 solution was also used among
others against rust and smut diseases of wheat. The improper use of the remaining
solutions at the place of coating resulted in punctual contaminations (Csathó, 1994).
In recent decades, it became a general practice to use sewage for fertilization after
composting or directly. By the application of sewage, valuable nutrients are provided
for soils (Balláné and Filep, 2000).
However, large amounts of heavy metal can enter the soil with the application of
sewage, even if the concentration of toxic elements is under the official limit since high
volumes are applied. Although the amount of toxic elements that can be applied to the
soil is low: As 0,3; Cd 0,02; Cr and Cu 10-10; Hg 0,1; Mn 20; Ni 2; Pb and Zn 20-20
kg ha -1 , the danger of accidental overdosing and the fact that repeating applications
result in accumulation of pollutants in the soil should be considered.
A significant part of the contamination in the soil fortunately becomes immobile
and only a fraction of it enters the plants. The heavy metal binding capacity of the soils
varies greatly. It should also be considered that environmental and production factors
(e.g. nutrient supply, changes in soil pH, precipitation) can modify the mobility of
nutrient elements (Kincses et al., 2005) and pollutants.
All the above facts indicate that it is important to study the effects and interactions
of factors influencing nickel-uptake with special regards to plant yields.
MATERIALS AND METHODS
The objective of the experiment was to reveal the interactions between and direct effects
of nickel contamination and factors having a favourable effect on plant development
(fertilization, CaCO3 application).
For studying the interaction between nickel contamination, nitrogen supply and
CaCO3 application, a pot experiment was set up at the Department of Agricultural
Chemistry in May 2006. The advantage of the pot experiment is that several factors
(e.g. water supply) can be controlled and the same conditions can be ensured for all the
treatment combinations. In addition, the amount of nutrients, pollutants and CaCO3 are
164