Effects Of Different Heat Preservation And Nitrogen Fertilizer Levels On Physiological Growth,Fruit Quality And Soil Microbial Biomass Of Pitaya

Hylocereus undatus is a major economic fruit in tropical and subtropical regions of China,and it has developed rapidly in Guangxi.Facility cultivation can avoid rainy weather disasters and low-temperature damage to dragon fruit,making it mature early or late,improving yield and quality.In tourism agriculture,it can also extend the fruiting time and supply period,and improve efficiency.However,the environmental factors of facility cultivation and the effects of fertilization on the growth,development,and fruit quality of pitaya are still unclear.In order to obtain a suitable growth environment and optimal fertilization plan for the cultivation of dragon fruit under facilities suitable for the climate and environmental conditions in Guilin.This experiment takes"Jindu No.1"pitaya as the experimental object.Based on observing the effects of different insulation conditions in winter on environmental factors and physiological indicators of pitaya,the effects of different nitrogen fertilizer levels（T₀,T₁,T₂,T₃,T₄were 0,100.5,124.5,150,175.5 kg/hm²）on the growth and development of protected pitaya,plant nitrogen,phosphorus,and potassium accumulation,fruit yield and quality,soil physicochemical indicators,and microbial biomass were studied by covering with dry grass.The research results are as follows:1.Influence of different insulation conditions on environmental factors and physiological indexes of Pitaya fruitContinuous 3 d observation showed that the temperature in the facility greenhouse rose quickly,the peak temperature was earlier,and the decrease was slower.The effective accumulated temperature during the day was higher than that in open cultivation.The light intensity reached the growth demand of pitaya fruit at around 10:00 AM.It is found that the peak temperature of the facility greenhouse is in July,the average annual daytime temperature is above 20℃,the average annual night temperature is above 13℃,the highest temperature can be adjusted 43℃,the lowest temperature 11.8℃,long-term in high temperature,high humidity environment and direct sunlight,prone to sunburn damage.The peak temperature of open-air cultivation is in August,with the average annual daytime temperature above 13℃,the average annual nighttime temperature at 6℃,the highest daytime temperature at 39℃and the lowest daytime temperature at 1℃.The results of physiological indexes showed that the electrical conductivity（REC）of branch culture of Pitaya had no obvious change with the decrease of temperature,ranging from 36%to 38%.Malondialdehyde（MDA）increased slowly in 43.11-280 nmol/mg prot,and superoxide dismutase（SOD）first decreased and then increased in 169.45-176.66 U/g.The REC of open-air cultivation increased gradually to48%-60%.MDA increased slowly and then increased in 395.56～619.82 nmol/mg prot.SOD ranges from 182.32 to 187.08 U/g;The REC,MDA and SOD of facility cultivation were lower than those of open cultivation.2.Effects of different nitrogen fertilizer levels on growth,yield and fruit quality of Pitaya cultivated in facilitiesDifferent nitrogen fertilizer levels could promote branch differentiation in different degrees in plant Pitaya fruit.During the growth stage,the accumulation of nutrient nitrogen,phosphorus and potassium increased gradually with the increase of nitrogen fertilizer level.After the fruiting stage,high nitrogen fertilizer level could inhibit flower bud differentiation.Branch differentiation and growth of T₄were more obvious,plant nutrient accumulation was more,and fruit yield increased first and then decreased.The average fruit weight of T₄was375.26 g,and the total yield of T₃was 559.85 kg.The yield of T₁,T₂,T₃and T₄was 12.13%,20.3%,55.61%and 12.78%higher than that of T₀,respectively.Fruit N,P and K contents increased with the increase of N fertilizer level,and T4 was the highest（12.64,2.59 and 17.65g/kg,respectively）.The fruit soluble solid and titratable acid rose first and then fell,and T3 of soluble solid was 18.43%.3.Effects of Different Fertilization Levels on the Physical and Chemical Properties and Microbial Mass of Huolongguo Soil in FacilitiesCompared with the control group,different levels of nitrogen fertilizer increased soil fertility in varying degrees,organic matter gradually increased,nitrate nitrogen gradually decreased,available phosphorus,available potassium,exchangeable calcium and magnesium first increased and then decreased,and p H remained in the neutral range.The use of dry grass to cover the hotpot of dragon fruit plants provided a living environment for microorganisms.In the experiment,the total amount of bacteria was greater than the total amount of fungi,but the difference between the groups was not significant.In summary,facility cultivation of dragon fruit can prevent frostbite by keeping the temperature above 11.8℃during the overwintering period.In the early stage of dragon fruit growth,the use of nitrogen fertilizer of 175.5 kg/hm²can promote the growth of new branches.In the middle stage,the application of foliar fertilizer KH₂PO₄can accelerate the maturity of branches.The use of dry grass to cover the hotpot of dragon fruit plants provided a living environment for microorganisms.In the experiment,the total amount of bacteria was greater than the total amount of fungi,but the difference between the groups was not significant.