Effetti dell'intensità di utilizzazione sulla produzione foraggera e sull'azotofissazione della sulla

Objectives of this research were (I) to quantify nitrogen fixation under field conditions of sweetvetch in relation to the cutting
intensity; (II) to evaluate the effect of the control species on the reliability of the estimate of nitrogen fixation, using the
nitrogen balance method (NB); (III) to verify the possibility of application of the natural abundance method (NA) in the environmental
conditions of the experimental site.Two cutting intensities were compared: intensive (2 early cuts in spring and 1 autumn cut) and extensive (1 cut in spring
+ possible cleaning cut in summer). Three control species were tested:Lolium hybridum, Cicorium inthybusandPhalaris
aquatica.The intensive cutting regime showed higher levels of nitrogen fixation in the above ground phytomass compared to those
achievabie through extensive utilization (about 300 vs. 235 kg N ha-1).The nitrogen fixation assessed by the NB method was underestimated when Phalaris aquatica was used as control species,
while nitrogen fixation was not affected by the control species using the NA method.The results show that soil δ15N in the experimental site was sufficient for the application of NA method. The δ15N of
sulla cultivated in a soil without combined nitrogen was obtained indirect1y (B = -2,4) by assuming that the percentage of nitrogen
fixation on total nitrogen of sulla is never higher than 95%. Further investigations are required to verify this parameter and
to evaluate the fate of fixed nitrogen in the following crop after a legume crop. The dynamics of the morphological stage of
deveIopment, of the leaf to stem ratio and of the total nitrogen of the aboveground phytomass influenced the reliability of the
control species using the NB method.