Nitrogen Effects On Yield And Forage Quality Of Annual Ryegrass

Field experiments were conducted in Nanjing Agricultural University from 1998 to 2000 to evaluate forage yield and quality of annual ryegrass (Lolium mult{florum Lam.) in response to nitrogen application rate and timing. In 1998- 1999, six N treatments were applied at three rates of 112.5, 225, 337.5kgN/hm2 and two timings of early & late. In 1999-2000, eigkit N treatments were applied at four rates of 112.5. 225, 337.5, 45OkgN/hm2 and two timings of early & late. The two timings had interval of two weeks. Four replications of randomized complete blocks were established in 1998-1999 field experiments, three replications in 1999-2000. A three-cut management system was used in both years, with interval of four weeks. The results of two-year experiments showed that nitrogen treatments increased plant height, leaf area per plant. Application of N increased tiller number and tillering duration before peak of tillering. Increasing the application rate of N increased dry weight per plant, with dry weight of early application larger than late one. Increasing the application rate of N increased partitioning percentage of leaves, and decreased that of stems. At early application rate of 45OkgN/hm2, annual ryegrass produced the highest fresh forage yield of 142738.89kg/hm2, dry forage yield of 21398.56kg/hm2. With the increasing application rate of N, the promotive effects on forage yield decreased. Increasing the application rate of N improved re-growth of annual ryegrass, increased plant height, dry weight per stem and tiller number. With the increasing application rate of N, the promotive effects decreased. There was significantly positive correlation between dry weight per plant and leaf area per plait. The linear regression equations could be expressed as: y=0.0052x-0.01 74 (r0.9604X 1998-1999); y=0.0053x+0.0 153 (r0.9323) (1999-2000). Increasing the application rate of N increased leaf area, chlorophyll, soluble protein and total nitrogen contents of functional leaves, increasing of leaf area, chlorophyll, soluble protein and total nitrogen contents of functional leaves could reflect enhancement of photosynthesis. Applica駉n of N decreased soluble sugar content of functional leaves, which had no detrimental effects on forage quality. There was significantly positive correlation between chlorophyll and total nitrogen content of functional leaves. The linear regression equations could be expressed as: y5.4278x+29.819 (r0.7096); y6.3207x+26.889 (r=0.8059); y=6.4306x+19.487(r=0.7389), for the second, third, fourth leaves from top, respectively. Increasing the application rate of N increased FW/DW ratio, but decreased stem/leaf ratio and thus increased water content and palatability of forage. With the increasing application rate of nitrogen, total N, crude protein (CP), protein- N, true protein, total non-protein N (NPN), amino acids and nitrate contents were increased. In 1998-1999, early application rate of 337.5kgNIhm2 produced the highest crude protein (CP) content of 19.34%. In 1999-2000, early application rate of 45OkgN/hni2 produced the highest crude protein (CP) content of 13.49%. Nitrate contents of three cuttings in 1999-2000 were below potentially toxic level 0.15% (DM basis). Nitrogen treatments did not have consistent effects on Ca, Mg, K and P contents of plant. If the availability of P. K, Ca, Mg was high in soil, nitrogen treatments might increase Ca, Mg, K and P contents of plant. Ca, Mg, K and P contents of plant in two years were...