Abstract: The fixed-spot test progressed in the suburbs of Tianjin for four years.The results indicate that the effects on increasing yield of N P K fertilizers in the main types of soil and main crops are significant N and P fertilizers can be effectively applied in 80-90%cultivated area of the all suburbs while K fer-tilizer in 15%area.The effects on increasing yield of N P K have a signifi-cant negative correlation to the quantity of the quick effective nutrients in the soil,thus we can decide the critical value of the quick effective nutrients in the soil where chemical fertilizer is effectively applied.According to the result of poly-regression analysis and given attention to both yield and economical gains.In order to popularize,we may choose the best applying fertilizer plans for different yield level of main crops.

Key words: Nitrogenous fertiilizer, Phosphatic fertilizer, Potassium fertilizer, Ratinoal dose Tianjing