Objective The aim was to explore a reasonable agricultural fertilization system in celery production, in order to reduce inorganic fertilizer application and increase efficiency in the continuous cropping of celery.

Method In this experiment, the ‘Queen’ variety of celery was used as the test material. Through the single-factor randomized block experiment design, the organic fertilizer was used to replace different amounts of chemical fertilizer as a factor, and the nitrogen in the organic fertilizer was used to replace the nitrogen in the chemical fertilizer. Five levels of 0%, 15%, 30%, 45%, and 60%, namely CK, OF15, OF30, OF45, and OF60 were used to determine the relevant indicators of celery growth, yield, quality, and test soil with different organic fertilizers. A suitable fertilization scheme was explored for celery cultivation in the mountainous area of southern Ningxia, and various soil problems caused by continuous cropping were solved.

Result The results showed that the plant height, stem diameter, and yield showed a trend of increasing first and then decreasing with the increase of the proportion of organic fertilizer instead of chemical fertilizer. The OF45 treatment had the best performance, which the plant height was up to 59.25 cm, the stem diameter was up to 12.38 cm, and the yield was increased by 46.75% - 77.35%. Under this condition, the quality of celery was also improved, but the difference in Vc, soluble protein, and crude fiber among the treatments was small, and the difference in nitrate among the treatments was large. The nitrate content in OF45 treatment was the lowest, which was 52.55 % lower than that of the control. The substitution of organic fertilizer for chemical fertilizer had little effect on the physical and chemical properties of different layers of soil in each treatment. Combined with the nutrient differences before and after planting, it was found that the application of organic fertilizer could effectively improve the total nitrogen, total phosphorus, organic matter, available nutrients in different soil layers. In addition, through the analysis of soil comprehensive fertility, it is concluded that the application of organic fertilizer had obvious nutrient improvement in deep soil, and the nutrient improvement in shallow soil was weak. The correlation coefficient between soil integrated fertility index (IFI) and total nitrogen, available nitrogen, total phosphorus, available phosphorus, available potassium, and organic matter indices reached more than 0.85, which was enough to illustrate the reliability of soil comprehensive fertility evaluation results.

Conclusion Combined application of organic fertilizer has a certain improvement effect on continuous cropping soil. Through the analysis of the measured data, combined with the results of the TOPSIS method evaluation and analysis, the proportion of nitrogen in the organic fertilizer to replace the nitrogen in the chemical fertilizer is controlled between 45% ~ 60%, which can effectively regulate the nutrients in the soil, and can maintain the normal fertilizer requirements of celery, and can also improve the yield of celery.