Relazioni tra stadio morfologico di sviluppo, produttività e qualità del foraggio della sulla in due ambienti collinari

Sulla is a short-lived Mediterranean perennial legume with remarkable growth in clay and calcareous soils. It is of great interest for pasture utilisation for its good nutritional value in early stages and bloat-safe characteristics and it may be interest for silage conservation due to its high spring yield and sugar content. The aim of this work was to study the evolution of yield and nutritional characteristics of forage during the first growth cycle and their relationships with the morphological stages in two environments. The field experiments were set up in Sassari (Sardinia) and Ancona (central Italy). In one year experiment, yield, DM content, water soluble carbohydrates (WSC), crude protein, NDF, ADF, ADL, and in vitro organic matter digestibility (OMD) were determined in the first growth cycle on cultivar Grimaldi in the two environments plus cv. Sparacia in Ancona. The morphological stage was evaluated and codified with an original scale here proposed based on the Kalu and Fick's scale (1981) for lucerne. The forage characteristics were regressed on the codified morphological stage and some weather data. The DM content was positively related to the codified stage, and resulted to be particularly low, ranging from 100 to 200 g kg -1, without any difference between cv. and sites (R2 adj. = 0.81). The WSC resulted to be dependent on the codified stage, N content in the plant and minimum temperature of the day before harvesting (R2 adj. = 0.87). The NDF ranged from 300 to 550 g (kg DM)-1 and was directly related to growing degree days (DD) and stage. The OMD, which is the most important determinant of the nutritive value, was inversely related to the stage and ranged from 758 to 533 g (kg OM)-1 as extreme values without difference between cv. in Ancona and in Sassari ranged at a lower level from 714 to 492 g (kg OM)-1. Analysing the pooled data of OMD over the sites and cv. the following regression equation was obtained: OMD = - 20.7 STAGE - 0.111 DD + 830 (R2 adj. = 0.90). These relationships indicate the potential usefulness of the numerical codification of the morphological stage adopted for defining the quality of Sulla. The stage, together with DD, resulted to be a promising predictor for the estimation of OMD of sulla forage.