Abstract: The amounts of nitrogen, phosphorus and potassium applied and the ratio of legume to grass in mixed sowings are key factors affecting the yield and fertilizer use efficiency of mixed grassland. The forage yield and utilization efficiency of nitrogen, phosphorus and potassium under different application ratios of those nutrients were analyzed to provide a scientific basis to manage cultivation of mixed grass-legume grassland for high yield. Field experiments were conducted on mixed swards of alfalfa and smooth brome. The experiment comprised two row configurations (legume:grass inter-row pattern 2:2 and 1:2) and seven nitrogen, phosphorus and potassium combinations: N₂₈₀P₁₅₀K₀ (A₁), N₃₅₀P₁₀₀K₃₆₀ (A₂), N₁₄₀P₃₀₀K₃₀₀(A₃), N₄₂₀P₂₅₀K₁₂₀ (A₄), N₇₀P₅₀K₆₀ (A₅), N₂₁₀P₀K₂₄₀ (A₆) and N₀P₂₀₀K₁₈₀ (A₇), where subscripts after each element indicate the application rate as kg·ha^-1 N, P₂O₅, and K₂O, respectively. The highest value for annual total yield of mixed legume-grass forage (11.68 t DM·ha^-1) occurred in the A₂ treatment, and yield in this treatment was significantly higher than in other treatments (P<0.01). Alfalfa yield in the A₂ treatment was 8.60 t DM·ha^-1, and it was significantly higher than A₁, A₅, A₆ and A₇ treatments (P<0.01). Grass yield in the A₁ treatment was 3.80 t DM·ha^-1, and it was significantly higher than in other treatments (P<0.01). Yields of grass and grass-legume forage were lowest in the zero nitrogen treatment, A₇. The combined grass-legume yield was significantly related to the rate of N fertilizer. Both combined grass-legume yield and alfalfa yield displayed a N×K interaction (P<0.05). The NPK partial productivity, and uptake efficiency of grass, alfalfa and grass-legume forage all showed a downward trend with increase in NPK level, and the A₅ treatment was significantly superior to other treatments (P<0.01). The nitrogen utilization efficiency of alfalfa decreased significantly in the zero potassium (A₁) and low potassium (A₅) treatments, and the potassium utilization efficiency of grass, alfalfa and grass-legume forage decreased significantly in the zero phosphorus (A₆) and high phosphorus (A₃) treatments. The annual total yield of alfalfa and legume-grass forage in the 2:2 row configuration were significantly higher than in the 1:2 configuration, with extreme significance (P<0.01). Also, the partial productivity, uptake rate and uptake efficiency of alfalfa NPK, and partial productivity of NPK, N uptake rate and N uptake efficiency of grass-legume forage in the 2:2 row configuration mixture were significantly higher than in the 1:2 configuration with extreme significance (P<0.01), and the partial productivity, uptake amount and absorption efficiency of grass NPK were significantly lower in the 2:2 than in the 1:2 configuration with extreme significance (P<0.01). Considering forage yield and nutrient utilization efficiency, alfalfa-smooth brome mixed sowing in a 2:2 row configuration, and fertilizer application of 140 kg·ha^-1 N, 100 kg·ha^-1 P₂O₅, and 120 kg·ha^-1 K₂O can be recommended, based on these results.

Key words: alfalfa, smooth brome, mixed pastures, fertilization, forage yield, fertilizer use efficiency