Abstract: The effects of different amounts of nitrogen fertilizer, phosphate fertilizer and potassium fertilizers on mid-season rice yield in Yunxi county were studied by experiment on mid-season rice "3414" in representative fields of four different townships in Yunxi county. At the same time, the ternary quadratic and quadratic equation of one variable regression effects equations of nutrient application rate and mid-season rice yield were obtained, and the optimal fertilization amount of the rice in each field was predicted. The results showed the most critical factor affecting the yield of mid-season rice in the tested area was nitrogen, followed by phosphorus, which was the least affected by potassium. The average yield reduction without fertilizer was 39.1% compared with the more reasonable fertilization. It was preliminarily indicated that the yield of the experimental field without fertilizer in one season will be reduced to a large extent and crop yield is more dependent on fertilizer. The application of N 160~200 kg/hm², P₂O₅ 60~80 kg/hm², K₂O 40~60 kg/hm² were more reasonable fertilization in experimental field and representative fields.

Key words: middle-season rice, soil testing formula, fertilizer effect, recommended fertilization, "3414" test, Yunxi county