Regulation Of Irrigation,Nitrogen,Potassium And Their Coupling On Nutritional Physiology,Yield And Quality Of Pitaya

Hylocereus undulates Britt.is a fruit cultivated plant of Hylocereus in the cactus family.It is native to tropical and subtropical forests in Central America.Pitaya was introduced to China in the early 1990s.After planting,the scale of commercial cultivation has expanded rapidly,and it has been vigorously developed as a dominant fruit industry in Guangxi,Hainan,Guizhou and other provinces.Guizhou has a good ecological environment and distinctive mountain agriculture.Pitaya is one of the six top-quality fruits for the development of the fruit industry in Guizhou Province.This is also one of the main economic tree species for farmers in hot areas to adjust the agricultural industry structure,get rid of poverty and increase income.Based on the advantages of climate and geography,pitaya fruit from Guizhou tastes better,but most of the production areas have poor soil,severe seasonal drought,high production cost,low yield,and weak competitiveness.In order to improve the quality of pitaya products and the level of water and fertilizer management under the ecological environment of Guizhou,and promote the sustainable development of the industry,the author of this article first took the main variety(Hylocereus polyrhizus,"Zihonglong")in Guizhou as the object,and studied its water demand by monitoring the dynamic changes of annual main stem sap flow and drought-resistant growth,and carried out a long-term fixed-plant fertilizer effect experiment in typical producing areas to reveal the law of nitrogen and potassium demand for H.polyrhizus.Long-term water and fertilizer coupling experiments were carried out in the greenhouse to clarify the appropriate water and fertilizer plan for improving the yield and quality of H.polyrhizus.Secondly,according to the growth characteristics of pitaya,the suitable planting area in Guizhou was evaluated,and water and fertilizer management were divided.The main research results are as follows:1.Aiming at the characteristics of broken terrain and three-dimensional distribution in Guizhou Province,ArcGIS was used to superimpose the cultivated land unit in Guizhou Province and divided the growth restriction area to establish a suitable area unit for pitaya planting based on the plot unit.Delphi method was used to evaluate planting suitability based on low temperature limiting factors and caloric indicators.Guizhou has an area of 82,000 hm²suitable for pitaya planting,the areas of the most suitable area,low-risk area,and high-risk area are 31,100 hm²,17,600 hm²,and 33,300 hm²,which are distributed in Nanpan River,Beipan River,Hongshui River,Chishui River Basin,Duliu River Basin,and Zhangjiang-Dagou River Basin and Jinjiang River Basin have some suitable planting areas.The evaluation index system of water and fertilizer management zones in the suitable planting area of pitaya were established and evaluated.The Beipanjiang River Basin and the Nanpan River Basin have serious water deficits,and the development of water conservancy facilities such as the integrated drip irrigation system of water and fertilizer should be emphasized;The Hongshui River Basin has a mild to moderate deficit,and areas where conditions permit should meet the irrigation needs during the spring drought.The nutrient distribution of cultivated land in suitable areas is unbalanced,and the organic matter content is high overall,but the phosphorus and potassium nutrients are lacking.2.The drought-rewatering alternate pot experiment was used to carry out research on the response of H.polyrhizus to drought.The results showed that:Under long-term severe drought conditions that ordinary plants cannot tolerate,H.polyrhizus still had no seedling death,indicating that H.polyrhizus was extremely drought-resistant and could be planted in dry and hot southwestern valleys and limestone desert areas in long-term dry environments.The root system of H.polyrhizus only accounts for a very small part of the total biomass(?4.71%),indicating that the strong drought resistance of H.polyrhizus was closely related to the biological morphology,water retention and physiological metabolism of the above ground.Drought increased the nitrogen,phosphorus,and potassium content of plants,and suitable drought enhanced the activities of superoxide dismutase,peroxidase and catalase,which was beneficial to retain moisture,maintain health,and reduce harm,so that the increase in malondialdehyde and proline content is much lower than that of ordinary plants.Under drought conditions,the size and openness of stomata decrease,the absorption of nutrients increases,and the activity of antioxidant protection enzymes increases can be regarded as one of the physiological reasons for the strong drought resistance of H.polyrhizus.Light and moderate droughts generally have no significant effect on the growth of new branches and the dry weight of the above ground and underground parts;however,severe droughts inhibited the growth of new branches of H.polyrhizus,reduced the biomass,and may affect the yield and quality of the fruit.Therefore,it is necessary to strengthen water management to promote the growth of new branches in the process of H.polyrhizus cultivation.3.The packaged stem flow meter was uesd to determine the plant to carry out the monitoring of annual sap flow characteristics of H.polyrhizus in greenhouse.The results show that:The peak and total sap flow of H.polyrhizus stems in spring were significantly higher than those in other seasons.The sap flow rate in a single day showed a gradual increase in the first half of the night,and a relatively flat change in the second half of the night.The fluctuation was large from sunrise to sunset,and the single-day liquid flow was dominated by a single-peak curve.The daytime sap flow accounts for 49.60%-71.51%of the single-day sap flow.The total night sap flow was significantly positively correlated with the total daytime sap flow.The greater the daytime transpiration,the higher the nighttime sap flow.The proportion of night sap flow rate in spring was relatively lower than in other seasons.The peak value of liquid flow occurred more frequently from 10:00 to 13:00,while the valley value occurs more than 17:00to 20:00.As the temperature rose,the time of peak liquid flow gradually advanced.The H.polyrhizus sap flow rate was extremely significantly positively correlated with Total solar radiation(TSR),Photosynthetically Active Radiation(PAR)and other factors,and extremely significantly negatively correlated with Relative Humidity,Soil moisture,Soil temperature,and Vapor Pressure Deficit.Under high temperature or high light intensity,photosynthesis was inhibited.When TSR>550 W/m²,the stem flow rate started to be negatively correlated with TSR and PAR.4.In a typical growing area of H.polyrhizus,a three-year fixed-plant fertilization experiment was used to study the effects of different nitrogen and potassium levels on the nutrient distribution,yield and quality of H.polyrhizus.The nutrient accumulation of nitrogen,phosphorus and potassium in each organ of H.polyrhizus first increased and then decreased with the increase of nitrogen and potassium application;the nutrient content of vines,pulp and peel were all potassium>nitrogen>phosphorus.As the amount of fertilizer increased,the yield first rose and then fell,and with the passage of time,the fertilizer effect became more significant.Three consecutive years of fertilization treatments under medium and low fertility increased the yield by 3.26%-41.85%,10.19%-37.82%.Increasing the supply of nitrogen fertilizer could promote the accumulation of vitamin C content in the fruit and reduce the sugar-acid ratio of the fruit,and low-level potassium fertilizer was not conducive to the accumulation of sugar and acid content in the fruit.As the amount of potassium increased,the vitamin C and sugar-acid ratio of the fruit increased first and then decreased.There was a very significant positive correlation between the nitrogen,phosphorus,and potassium content in the pulp,and the titratable acid and vitamin C content were positively correlated with the nitrogen content of the vine and the nitrogen content of the pulp.5.The changes of chlorophyll fluorescence spectrum characteristics of H.polyrhizus stem in the fertilizer efficiency test area were analyzed.The proper application of nitrogen and potassium was beneficial to the operation of photosynthetic organs and the accumulation of photosynthetic producted.H.polyrhizus stems showed a typical OJIP curve of chlorophyll fluorescence rising kinetics similar to that of conventional plant leaves.The lack of nitrogen caused the relatively small PSI terminal electron acceptor pool of H.polyrhizus stems.The spectral curves of H.polyrhizus were similar to the leaf characteristics of green leafy plants.The sensitive areas of spectrum and chlorophyll content were mainly located in 730 nm and near-infrared region.After wavelet transform,the estimation accuracy of chlorophyll in H.polyrhizus stem was 0.678.Chlorophyll fluorescence parameters and hyperspectral can accurately monitor the nutrient status of H.polyrhizus.6.Adopting three-factor five-level quadratic regression universal rotating combination design of water,nitrogen,and potassium,and the research on the effect of water and fertilizer coupling on the yield and quality of H.polyrhizus for three consecutive years showed that:Water-nitrogen-potassium coupling had no significant effect on H.polyrhizus shape index,soluble solids,flavonoids and other indicators.The comprehensive analytic hierarchy process determined the weight order of H.polyrhizus quality indicators as follows:single fruit weight>soluble sugar>sugar-acid ratio>soluble protein>total phenol>titrated acid.The main factors affecting the yield and overall quality of H.polyrhizus were irrigation volume,followed by nitrogen and potash fertilizer consumption;The interactive effects of water,nitrogen and potassium relative to H.polyrhizus yield and quality were different.Considering the effects of water,nitrogen,and potassium on the yield and quality of H.polyrhizus,under drip irrigation conditions,the optimization plan for H.polyrhizus output exceeding 22 500 kg�hm^-2 and a comprehensive quality score of 80 points or more was as follows:Irrigation volume is 52.43%-64.68%,N 247.89-404.48 kg�hm^-2,K₂O 247.30-565.47 kg�hm^-2,for reference for management under the same fertility level H.polyrhizus orchard's water and fertilizer integration mode.In short,through this study,the characteristics of water and fertilizer requirements for pitaya in typical producing areas were clarified,fertilization schemes and water-fertilizer coupling schemes were formulated,and water and nutrient distribution characteristics in suitable areas for pitaya cultivation were quantified.This provides data support and reference for the formulation of a suitable irrigation and fertilization system and the rational allocation of limited water and fertilizer resources in the production area.