Objective The aim was to clarify the effect of potassium (K) fertilizer application rate on celery cultivation and production in the southern mountainous areas of Ningxia, and to provide technical support for overcoming the problems of K fertilizer application rate and its environmental pollution, frequent celery diseases, and low economic benefits of farmers.

Method Taking ‘Queen’ celery as the test material, a field plot experiment was carried out with a single factor multi-level randomized block design. Five K fertilization levels of 0 kg hm⁻², 225 kg hm⁻², 450 kg hm⁻², 675 kg hm⁻² and 900 kg hm⁻² were set up (recorded as K0, K225, K450, K675 and K900 treatments, respectively). The soil nutrient content, celery yield, nutrient absorption quantity, root, stem and leaf distribution and K fertilizer utilization rate were measured, and the relationship between K fertilizer dosage and the above measurement indices was analyzed.

Result The results showed that the total K content in soil increased with the increase of P application rate, and the maximum was 21.78 g kg⁻¹ in K900 treatment. The highest K uptake per unit area and per plant of celery was 344.68 kg hm⁻² and 1.57 g plant⁻¹ in K675 treatment. The dry matter accumulation of celery changed significantly with the increase of K fertilizer application rate, but the K450 treatment was the highest, which was 64.17 g plant⁻¹. The utilization efficiency of K fertilizer was between 12.68% and 34.43%, with K225 treatment as the highest, reaching 34.43%. The K partial factor productivity and K agronomic efficiency of celery were also the highest in K225 treatment, which were 1006.43 kg kg⁻¹ and 128.95 kg kg⁻¹. When the amount of K fertilizer was more than 450 kg hm⁻², the apparent balance of soil K was surplus. The yields of celery in the five treatments were 201.33 t hm⁻², 223.00 t hm⁻², 233.33 t hm⁻², 228.33 t hm⁻² and 217.67 t hm⁻², respectively. The yield of each K fertilizer treatment was 8.15% - 15.90% higher than that of the control (K0), and the K450 treatment was the highest. Using the method of fitting the relationship curve between the amount of K fertilizer and the yield of celery, the yield of celery was the highest when the amount of K fertilizer was 524.59 kg hm⁻², and the economic benefit of K fertilizer was the best when the amount of K fertilizer was 478.11 kg hm⁻². The Vc content, soluble solids, crude fiber and nitrate content of celery were the highest in K900 treatment. The membership function method was used to evaluate the comprehensive quality, and the results showed that K450 treatment had the best effect on K fertilizer application.

Conclusion In order to improve the economic income of farmers in the mountainous area of southern Ningxia and reduce the adverse effects caused by excessive application of K fertilizer, the recommended amount of K fertilizer for celery planting is 455.12 - 592.50 kg hm⁻².