Variance Of Dry Matter Digestibility Among Lines And Its Response To Nitrogen Application In Italian Ryegrass

Italian ryegrass (Lolium multiflorum Lam.) is suitable for feeding many kinds of herbivores, and is one of the most important over-winter forages in middle and low region of Yangtze River of China. The yield of Italian ryegrass increased greatly with the advancement of planting techniques and increasing fertilizer application, but the digestibility of Italian ryegrass declined. It is a very important problem for forage breeding to resolve the contradiction between yield and digestibility, to increase the total digestible nutrition yield and the ratio of conversion forage to livestock products.The in vitro dry matter digestibility (IVDMD) and content of cell wall structural matter of different lines with different maturity (earliest, early, middle and late mature) at heading stage of Italian ryegrass were measured in a field experiment. The variance of IVDMD among different lines and its relationship to cell wall substance composition were studied. The relationship between IVDMD and total soluble sugar, crude protein, cellulose, hemicelluloses and lignin were also studied under different nitrogen rate application (0, 150 , 300 , 450, 600kgN/hm2). The results are as follows.1. The IVDMD of Italian ryegrass at heading stage range from 53.68% to 68.41%. Significant difference existed in IVDMD among different maturity types, that of earliest lines and early lines significant higher than that of late lines, and that of late lines significant higher than that of middle mature lines. Within same maturity, there is no significant difference in IVDMD among different lines except middle maturity lines.2. Among all the cell wall structural matter affecting digestibility of different maturities of Italian ryegrass, the correlation of cellulose content and IVDMD is most closely. The coefficient of variation of the ratio of total cellulose to undigested cellulose changes roughly, and resulted in changes of digestibility.3. With the increasing rate of nitrogen application, the yield of dry matter and digestible nutrient increased; The content of cellulose and lignin increased and this coincided to the decreasing of IVDMD; The content of crude protein increased, but the content of total soluble sugar decreased: The content of crude protein is positive correlation to the content of lignin. and the content of total soluble sugar is negativecorrelation to the content of lignin. It indicated that soluble sugar and crude protein affect digestibility mainly in undirected method by influencing the composition of cell wall substance. Nitrogen application at 300kgN/ hm2 reached the highest fertilizer return.6. The digestibility of dry matter and content of total digestible nutrient should both be considered when select parental materials for high IVDMD breeding. The selection should base on the results of several years due to the nature environments such as temperature affecting IVDMD greatly.