Abstract: 【Objective】 Sudangrass and ryegrass rotation is a new type of cropping system in Jianghan Plain, which developed very fast in recent years. So it is essential to understand the optimum nutrient and water management measures in this new system.【Method】 Effect of NPK fertilizer on yield of forage grass, nutrition and water utilization under sudangrass and ryegrass rotation was studied through continuous pot experiments for three years. 【Result】 The results showed that NPK combination could obviously improve the yield of forage grass, and the total yield in the period of 2005-2006, 2006-2007, 2007-2008 was 1 690.0 g/pot, 2 091.3 g/pot, 1 770.7 g/pot, and yield in PK treatment (No N) was 700.7%, 1 256.9%, 856.3% lower than that of NPK treatment, and yield in NK treatment (No P) was 426.3%, 384.9%, 792.3% lower than that of NPK treatment, and yield for NP treatment were 15.9%, 4.4%, 10.6% lower than that of NPK treatment, respectively. NPK combination could improve nutrition uptake, and total N uptake in the period of 2005-2006, 2006-2007, 2007-2008 were 6.36 g/pot, 4.91 g/pot, 6.85 g/pot, and was 10.0 times, 14.8 times, 10.6 times higher than that of PK treatment, and was 3.7 times, 1.8 times, 5.1 times higher than that of NK treatment, respectively, but was similar to NP treatment. Total P uptake were 0.79 g/pot, 1.01 g/pot, 0.82 g/pot, and was 4.6 times, 6.8 times, 5.3 times higher than that of PK treatment, and was 2.4 times, 2.3 times, 2.9 times higher than that of NK treatment, respectively, but was similar to NP treatment. Total K uptake were 11.58 g/pot, 6.36 g/pot, 5.62 g/pot, and was 5.2 times, 8.4 times, 4.9 times higher than that of PK treatment, and 3.9 times, 2.3 times, 3.9 times higher than that of NK treatment, and were 80.9%, 57.4%, 200.5% higher than that of NP treatment, respectively. Water productivity in three years was 16.5 kg•m-3, 16.1 kg•m-3, 16.2 kg•m-3, and was 3.8 times, 5.4 times, 4.2 times higher than that of PK treatment, and was 2.3 times, 1.3 times, 2.6 times higher than that of NK treatment, and was 16.4%, 8.8%, 22.4% higher than that of NP treatment, respectively. In this rotation, soil pH degraded, but soil organic matter all upgraded. Soil total N in NP, NK, NPK treatments upgraded, but soil total N in PK was steady. Soil extractable P in NP, PK and NPK treatments upgraded obviously, and soil extractable P in NK increased slightly. Soil available K in NK and PK treatments upgraded obviously, but available K in NP and NPK degraded. 【Conclusion】 NPK combination increased yield of forage, improved nutrient uptake and soil fertility in sudangrass and ryegrass rotation system.

Key words: sudangrass and ryegrass rotation, N, P, K fertilizer, nutrient uptake, water productivity, soil nutrition