Nitrogen, phosphorus and potassium fertilization promotes Zanthoxylum armatum ‘Hanyuan Putao Qingjiao’ flower bud differentiation in Sichuan, China

Chinese prickly ash is an ecologically and economically important tree species. In southwestern China, its yield is low due to severe fruit and flower drop related to the relatively low nutrient status of shoots and/or flowers caused by a lack of nutrient supply. Therefore, studies on flower bud differentiation are of great importance to improve the yield of Chinese prickly ash. An orthogonal experimental design was used to study the effects of N (urea, 97.8, 195.7 and 391.3 g/individual), P (superphosphate, 150, 300 and 600 g/individual) and K (potassium sulphate, 83.3, 166.7 and 333.3 g/individual) treatments on flower bud differentiation in 3-year-old Zanthoxylum armatum ‘Hanyuan Putao Qingjiao’ trees. The results showed that N, P and K fertilizer application significantly increased the flower bud differentiation rate, branch diameter and number, the soluble sugar content, the soluble protein content, the C/N ratio, the ABA content and the ABA/IAA ratio but decreased the GA content and IAA content in Chinese prickly ash. The flower bud differentiation rate was positively related to the soluble sugar content, soluble protein content, C/N ratio and ABA/IAA ratio ( p < 0.05) but negatively related to GA and IAA ( p < 0.05). A higher P content increased the accumulation of nutrients and ABA in the buds, thereby promoting the flower bud differentiation in Z. armatum ‘Hanyuan Putao Qingjiao’. From these results, the flower bud differentiation in Z. armatum ‘Hanyuan Putao Qingjiao’ requires appropriate N, P and K fertilizer ratios and amounts. Treatment 12 (N 2 P 3 K 1 ) significantly improved the absorption of nutrients in the buds and promoted the differentiation of flower buds.