Abstract
The purpose of this trial was to determine the influence of levels of nitrogen fertilization, stage of maturity and growth phase on chemical composition and feeding value of Italian ryegrass forage (Lollium multiforum Lum.). A high level of nitrogen was applied at a rate of 18 Kg. per 10 a at sowing time and 6 Kg. top-dressing after first cut forage was harvested and a low level of nitrogen was one-third of the high level on each occasion. The first cuttings were made at vegetative, boot, head and milk stages of growth respectively. The aftermath forage was harvested at head stage. The harvested forage was fed in fresh form to rabbit. (1) High level of N fertilization increased protein content in the first cut forage throughout all growing stages and in the aftermath forage received top-dressing N fertlizer, and digestibility of the crude protein also increased significantly (P<0.01 except p<0.05 at milk stage) when compared to low level of N fertilization, but this effect was lost in the aftermath forage untreated. High level of N fertilization had no effect on content of crude fiber and crude lignin at different growth stages. There was, however, a statistically significant (P<0.05) increase in digestibility of crude fiber due to this treatment at vegetative and boot stages. This treatment also significantly (p<0.05) increased digestibility of dry matter at vegetative and milk stages, while this effect on those of crude fiber and dry matter disappeared in aftermath forage. (2) A variation of digestibility of all constituents of high level of N fertilization with advanced stage of maturity was similar to that of low level of N fertilization, but the variation of digestibility of crude protein and crude fiber of high level of N fertilization. Digestibility of all constituents declined markedly at head stage in the first cut forage. Regardless of top-dressing of N fertilizer, digestibility of dry matter, nitrogen-free extract and crude fiber in aftermath forage was lower than that of the similar stage in first cut forage, but those of other constituents were as high as those in the first cut forage. (3) There was a highly significant increase in DCP and TDN content due to high level of N fertilization at all growing stages in first cut forage and in aftermath forage which received top-dressing of N fertilizer. Both contents decreased sharply from boot to head stages and then remained almost unchanged. (4) There was a highly significant increase (P<0.01) in DCP yield per 10 a due to high level of N fertilization at all growth stages in first cut forage and in aftermath forage which received top-dressing of Nfertilizer. This effect on TDN yield was also found significantly (p<0.05) at head stage and milk stage in first cut forage and in aftermath forage untreated. Yields of DCP and TDN per 10 a obtained from both levels of N fertilization were greatest at milk stage. (5) Crude protein content was highly correlated positively (r=0.994) with digestibile crude protein content.
