Szili-Kovacs, T., T. Tóth, M. Halassy and K. Torok. 2000. Restoration of sandy 
grasslands through the immobilization of soil nitrogen. 1. Laboratory incubation 
experiments. (Hung.) Agrokémia és Talajtan. 49:479-490. 

It is a presumption of many ecologists that the vegetation recovery of disturbed 
lands highly depends on the soil N-availability. High available-N inhibits 
expansion of natural vegetation while favourable for early-seral r-
strategists.Experiments were design to test the applicability of nitrogen 
immobilization as means of accelerating the recovery of endemic open sand 
grassland community (Festucetum vaginatae danubiale) on old-fields in the Great 
Hungarian Plain. Sucrose and oak sawdust as carbon sources were selected for 
field application to increase microbial N-immobilization. The quantity of C-
sources applied in the field was 700 kg C/ha/year. The sawdust was broadcasted 
only once (300 kg/ha) in early spring while sucrose 4-times (1300kg/ha) during 
the vegetation season.Three experimental sites were located along an elevation 
gradient parallel with an aridity and productivity gradient (R="meadow"; 
Bk="depression"; Bt="hummock"). The first one is the most wet, productive and 
organic-rich. Six replicate plots (10 by 10 metres) both for control and treated 
in one site have been assigned for field observations.Soil organic matter, 
microbial biomass-C, cellulose decomposition and inorganic-N were measured 
during the vegetation season in 1998. Soil organic matter, microbial biomass-C 
and decomposition rate changed from site to site in accordance with the
elevation gradient. We found significant increase in microbial biomass-C and
decrease in soil available-N on the treated plots in two sites (Bk and Bt). The
third site having the highest organic-C (R) did not shown significant
differences due to the carbon source addition. Cellulose decomposition rate was
significantly lower in treated plots only in Bk site which can be probably
attributed to the reduced soil mineral-N caused by microbial N-removal. The
average rate of cellulose decomposition was 27.1; 20.9; and 7.0 mg cellulose
per g cellulose per day for site R; Bk and Bt respectively during the vegetation
season. The plant communities did not shown any alteration due to the treatment
in the first year, however they markedly differed in the sites.