The influence of aerial environment, nitrogen supply, and ontogenetical changes on the chemical composition and digestibility of Panicum maximum Jacq. var. trichoglume Eyles

Abstract

The effect of aerial environment and nitrogensupply on the chemical composition and in vitvo digestibility of a tropical grass was studied by comparing plants of Panicum maximum var. tvichoglume grown in pots either outdoors or in an humidified glasshouse. Plants from the two environments were similar in their percentage content of protein and cell wall materials. Young tissue from the outdoor plants was more digestible than material from the glasshouse, but the digestibility of this material was nevertheless very high in all plants. Thus, it appears that the unusually high nitrogen percentages and digestibilities which have been recorded for tropical grasses in laboratory studies by comparison with field-grown material may not be directly associated with differences in the aerial environment. This point remains to be conclusively tested under precisely controlled conditions. Increase in nitrogen supply from low to moderate levels increased digestibility by 3-5 percentage units, and had a small positive effect on the percentage of total soluble carbohydrates. Very high nitrogen supply lowered the soluble carbohydrate content of the plant tops. There was an inverse relation between tissue nitrogen concentration and the content of cell wall material. The amount of cell wall material increased progressively from the earlier- to the later-formed leaves on a tiller. When compared at a similar age, later-formed leaves tended to be less digestible. This influence of leaf position on nutritive quality is very interesting and warrants further investigation.