Forage quality and quantified morphological stage relationships in Italian ryegrass during the spring growth cycle. I. Stage codification, yield and ensilability characteristics

BACKGROUND. Italian ryegrass is of great interest due to its high yield and high potential nutritional value in the early stages. Its diffusion has been greatly favoured by the recent development of the wilted silage technique. The study of phenological stage and herbage quality relationships would be valuable for the crop management and is a good basis for set up a method for predicting forage quality.
METHODS. A trial was conducted in the western Po Valley (Italy) from 1991 to 1993 on stands of Italian ryegrass cv. Barmultra (4n), seeded in the first days of October. The herbage samples were collected at progressive morphological stages, ranging from early stem elongation to full flowering. The stage was evaluated and codified with a new method which is here proposed. The yield and ensilability characteristics were regressed on the codified stage and certain environmental factors.
RESULTS. The leaf/stem ratio and the plant component evolution resulted to be highly correlated to the codified stage. The dry matter (DM) yield was already high in early elongation with around 5.0 t ha-1 which is sufficient for silage harvesting. The DM content at cutting resulted to be directly correlated to the codified stage and was lower in the N fertilised crops. The water soluble carbohydrates decreased with increasing stages with different trends, influenced by the thermic conditions of the year. The buffering capacity was not correlated to the stage, and showed the highest values in the coldest year.
CONCLUSIONS. The stage codification system here proposed is a precise quantitative method to specify the morphological development of Italian ryegrass. For ensiling purposes the only unfavourable characteristic of the cv. Barmultra is the too low DM content which causes the prewilting process to last long.