Quantifying morphological stage to predict the nutritive value in sulla (Hedysarum coronarium L.)

A precise prediction of quality of legumes in the field would enable harvests to be conducted at appropriate nutritive composition levels. Our objective was to predict the nutritive value of sulla (Hedysarum coronarium) with the codified morphological stage and weather parameters at two Mediterranean sites (Ancona and Sassari, Italy) in 1996, 1997 and 1998. Herbage samples were collected at progressive morphological stages, from vegetative stage to seed setting. Mean stage by weight (MSW), dry matter yield (DMY), leaf:stem ratio (L:S), crude protein concentration (CP), neutral detergent fibre (NDF), gross energy (GE), and organic matter digestibility (OMD) were determined. Forage characteristics were regressed on growing degree days (GDD) and MSW. The DMY ranged from 2 to more than 10 tonnes ha-1 from vegetative to seed set while L:S decreased from almost 5.6 to 0.2 and the CP from a maximum of 295 to a minimum of 107 g kg-1 dry matter (DM). The NDF ranged from200 to 616 g kg-1 DM and was best predicted by L:S and MSW. The GE was relatively constant across growth stages with a mean value of 18.0 MJ kg-1 DM. The OMD ranged from 398 to 846 g kg-1 organic matter (OM) and declined linearly with increasing MSW. The OMD decreased 32.6 g kg-1 OM per stage unit and followed similar trends for the two sites, with a lower level at the warmer site (Sassari). The MSW was a better predictor of sulla OMD than GDD, with a higher R2 (0.70 vs. 0.54) and a lower root mean square error.