Effects of nitrogen fertilizer application on the quality of pitaya planted in calcareous soil in karst area

Effects of different nitrogen fertilizer application rates on fruit quality of pitaya under the condition of calcareous soil in karst area were discussed in order to investigate the effects of nitrogen fertilizer application level on fruit quality of pitaya under calcareous soil condition in karst area. The ‘Taiwan Dahong’ pitaya were used as the experiment material. Based on 0.216 kg of phosphorus (P) and 0.324 kg of potassium (K), four nitrogen (N) application levels (CK, T1, T2, T3) were setted. Twenty-one fruit quality indexes were determined, and the quality differences of pitaya with different N application levels (CK, T1, T2, T3) were compared. At the same time, eleven appearance quality indexes were comprehensively analyzed by principal component analysis. The results were as follows: (1) Compared with the control, N application could increase the contents of soluble sugar and soluble solids of fruit, reduce the contents of protein and dietary fiber, and the high nitrogen treatment (T3) was significantly different from other treatments. With the increase of N application, the contents of titratable acid and vitamin C of fruit increased firstly and then decreased, while the solid-acid ratio decreased firstly and then increased. T3 significantly increased the fruit vertical and horizontal diameters, fruit shape index and single fruit weight. (2) Compared with the control, N application treatment reduced the N content of pitaya fruit and increased the P content, and the N and P contents of each treatment were significantly different. The K content of fruit increased with the increase of N application. N application increased fruit boron (B) content and decreased fruit cuprum (Cu) content. The contents of manganese (Mn), ferrum (Fe), calcium (Ca) and magnesium (Mg) in different treatments were ranked as T3 > T1 > CK > T2. The content of zinc (Zn) decreased firstly and then increased with the increase of N application. (3) The principal component comprehensive evaluation score of the high N treatment was the highest, indicating that when selecting brown calcareous soil in Guilin karst area to grow pitaya, supplemented by a certain amount of P and K fertilizers, high N treatment was more conducive to improving the quality of pitaya. Therefore, in actual production, it is necessary to make appropriate adjustments according to the soil fertility status of the plantation.