Abstract: 【Objective】 Under the background of turning crop to forage and adjustment of plantation structure, the study on yield gap of alfalfa, ryegrass and oat grass is crucial for revealing yield potential. It can also provide a scientific basis for making high yield and high efficiency forage management strategies. 【Method】 The publications were collected by searching China National Knowledge Infrastructure and Web of Science with the keywords of “Alfalfa yield, Fertilizer”, “Ryegrass yield, Fertilizer”, “Oat grass yield, Fertilizer”, “Forage planting technology”, “Alfalfa, Fertilizer, China”, “Alfalfa, Irrigation, China”. A total of 176 published literatures were collected, including 101 articles for alfalfa, 51 articles for ryegrass and 24 articles for oat grass. This study summarized the yield potential and yield gap for three major cultivated forage species in China. Meta-analysis method was implied to quantify the effect of fertilization, sowing rate and irrigation rate on yield of three main cultivated forage species. This paper made a preliminary illustration about the factors that affect yield gap and ways to close the yield gap. 【Result】 The yield potential was 24 t·hm^-2 for alfalfa, 26 t·hm^-2 for ryegrass and 22 t·hm^-2 for oat grass. The farmer’s average yield of alfalfa, ryegrass and oat grass was 28%, 63% and 41%, respectively, of the yield potential. The fertilizer application rate of nitrogen (N) and phosphorus (P₂O₅), sowing rate and irrigation rate significantly affected forage yield. The optimized N and P₂O₅ application rate was 52 and 141 kg·hm^-2 for alfalfa, 585 and 46 kg·hm^-2 for ryegrass. For oat grass, the optimal nitrogen fertilizer application rate was not clear, but within the total amount of 225 kg·hm^-2, oat grass yield increased linearly with the increasing of N application rate. The optimal P₂O₅ application rate was 128 kg·hm^-2 for oat grass. The optimized sowing rate was 20 kg·hm^-2 for alfalfa, 30 kg·hm^-2 for ryegrass and 180 kg·hm^-2 for oat grass. The optimized irrigation volume was 5 737 m³·hm^-2 for alfalfa.【Conclusion】There was still a huge potential to increase yield of alfalfa, ryegrass and oat grass. The yield gap of alfalfa, ryegrass and oat grass was 17, 10 and 13 t·hm^-2. Furthermore, reasonable fertilizer application rate, seeding rate and irrigation volume are important to cut yield gap. By optimizing the fertilizer application rate, the yield of alfalfa, ryegrass and oat grass could increase by 3.4, 1.5 and 4.2 t·hm^-2. Suitable sowing rate could increase the yield by 60% for alfalfa, 78% for oat grass, but it was not enough to improve the yield of ryegrass only by adjusting the sowing rate. Optimal irrigation volume could increase the alfalfa yield by 9.1 t·hm^-2.

Key words: alfalfa, ryegrass, oat grass, yield gap, fertilizer application, sowing, irrigation