Effects of irrigation and nitrogen,potassium fertilizer coupling on yield and quality of pitaya

【Objective】To systematically study the coupling effect of water and fertilizer on pitaya,and formulate suitable irrigation and fertilization plans,so as to provide technical basis for its high yield,high quality and sustainable development.【Method】With Hylocereus polyrhizus(Zihonglong)as the experimental material,field capacity,nitrogen application and potassium application as experimental factors,a three-factor and five-level quadratic regression general rotation combination design was adopted,and a total of 20 treatments were set to conduct a two-year(2018-2019)water and fertilizer coupling experiments on fixed plants. The annual yield and single fruit weight were counted,and the fruit soluble sugar, soluble protein and other quality indicators were measured in a comprehensive evaluation to investigate the effect of water,nitrogen and potassium on the yield and quality of H. polyrhizus. The frequency analysis method was used to optimize the mathematical model of yield and quality to obtain the irrigation and fertilization scheme under efficient production.【Result】Different treatments of water,nitrogen and potassium supply had a significant effect on fruit soluble protein, sugar-acid ratio and other quality indicators(P<0.05,the same below). Compared with other treatments,the pitaya under treatment 10(field water holding capacity 40%,N 300 kg/ha,K₂O 375 kg/ha)and treatment 15(field capacity 60%,N 300 kg/ha,K₂O 375 kg/ha)had higher protein content compared to that under other treatments. Treatment 4(field capacity 72%,N 122 kg/ha,K₂O 152 kg/ha),compared with other treatments,could reduce the titratable acid content,raise the ratio of sugar to acid,thus,improving the fruit flavor,at the same time it also reduced total phenolic content. Overall,the yield and comprehensive quality of the fruit increased first and then decreased with the increase of field water holding capacity,nitrogen and potassium supply. The effect of each factor on yield and comprehensive quality was in the order:Field capacity>nitrogen application>potassium application. There were differences in the interaction effects of water,nitrogen and potassium on the yield of H. polyrhizus. The interaction effect of field water holding capacity and nitrogen supply on yield was significant. When the field capacity was 52.43%-70.86%,N 215.17-511.00 kg/ha,K₂O 148.99-565.47 kg/ha,the yield could reach more than 22500 kg/ha;when the field water holding capacity was 48.25%-64.68%,N 247.89- 404.48 kg/ha,K₂O 247.30-581.51 kg/ha,the comprehensive quality score of dragon fruit was above 80 points.【Conclusion】The level of field capacity,nitrogen application and potassium application significantly affects the yield and quality indicators of H. polyrhizus. Appropriate irrigation and sufficient nitrogen and potassium supply can improve the fruit yield and quality,and increase its commerciality and economic benefits it could bring. Considering the effects of field capacity, nitrogen and potassium fertilizer supply on yield and quality,the irrigation and fertilization plan for efficient production of H. polyrhizus under drip irrigation is as follows:field capacity 52%-65%,N 247.89-404.48 kg/ha,K₂O 247.30-565.47 kg/ha. This optimized irrigation and fertilization plan can be used as a reference for the management of the water and fertilizer integration mode in the same fertility level of pitaya orchards.