Abstract
This experiment was conducted to clarify the effect of nitrogen fertilization on yield and in vitro dry matter digestibility (DMD) of fall-sown cereal crops for silage. Six-rowed barley, two-rowed barley, naked barley, wheat and rye were cultivated at various nitrogen levels for three years. One cultivar was used for each crop. In a fertile and well-drained field, herbage showed the ceiling yield in dry matter (DM) at about 15kg nitrogen application per 10 ares. In a drained paddy field after rice culture, the ceiling yield in DM would be obtained more than 17kg N/10a. Applied nitrogen decreased the proportion of stem and ear in DM yield and increased that of leaf. It did not change DMD of most of plant parts and whole plants or it slightly decreased DMD of them. The relation between applied nitrogen amount and DMD of a whole plant was parallel to the relation between applied nitrogen amount and DMD of stem, because stem was the largest of three parts of a plant. On the assumption that the digestibility of cellular content (CC) is constant, a change in DMD of each plant part by the nitrogen application was mainly attributed to a change in estimated digestibility of cell wall constituent (CWC) in each plant part. Nitrogen application did not consistently change the ratio of CC to CWC of plant parts except stem, and a change of the ratio in stem by applied nitrogen showed a little effect on a change in DMD of stem. A change in estimated cell wall digestibility of leaf and ear by applied nitrogen was correlated with a change in acid detergent lignin in CWC. Nitrogen application increased the digestible DM yield and this increase depended on that of DM yield. Ceiling yield of digestible DM was obtained at the same nitrogen level that gave the ceiling yield in DM. Five cultivars were not different from each other in the response of DM yield and DMD to nitrogen application.
