Effetti dell’intensità di utilizzazione sulla produttività, composizione della fitomassa e azotofissazione della sulla (Hedysarum coronarium L.)

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 contro I species were tested: Lolillm hybridum, Cicorillm inthybus and Phalaris
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-I).
The nitrogen fixation assessed by the NB method was underestimated when Phalaris aqllatica was used as controi species,
while nitrogen fixation was not affected by the control species using the NA method. The resu1ts show that soi! () 15N in the experimental site was sufficient for the application of NA method. The () 15N of
sulla cultivated in a soi! 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 Iegume crop. The dynamics of the morphoogical stage of
deveIopment, of the Ieaf to stem ratio and of the total nitrogen of the aboveground phytomass influenced the reliabiIity of the
control species using the NB method.