Study On Nutrient Optimization Management Of Tarocco Blood Orange In The Three Gorges Reservoir Area Of Chongqing

Citrus is a highly economical crop,and citrus industry is one of the pillar industries in the Three Gorges Reservoir area of Chongqing,which has important economic value and social effects for the farmers?immigrants?in the reservoir area to get rid of poverty and increase income.The efficient and optimal management of citrus nutrients is one of the key topics in citrus cultivation research in recent years.In this paper,late ripening citrus—Tarocco blood orange in Wanzhou district of Chongqing city was taken as the research object,three different experiments including the chemical fertilizer?nitrogen,phosphorus,potassium?elimination reaction,different nitrogen level,chemical fertilizer?nitrogen,phosphorus,potassium?reduction and the application of organic fertilizer were carried out to systematicly study the changes in biomass,nutrient absorption,response of fruit yield and quality and soil physicochemical properties of Tarocco blood orange in order to provide data and theoretical support for the optimal nutrient management of Tarocco blood orange in the Three Gorges Reservoir area of Chongqing.The main results were as follows:1.Chemical fertilizer?nitrogen,phosphorus,potassium?elimination tests showed that compared with the control?OPT?,the biomass and nutrient absorption of the new shoots of the blood orange tree were significantly reduced,with the effects of nitrogen being the most,the decline ranged from 36.45%to 49.8%,and the degree of influence was nitrogen>phosphorus>potassium;The nutrient content of fruit had little response to the treatments,and the difference between treatments was not significant,while the amount of nutrient removal of fruit was opposite,the removal amount of nitrogen,phosphorus?P₂O₅?,potassium?K₂O?of fruit treated by OPT-N were the lowest,respectively 28.37 g·plant^-1,9.35 g·plant^-1,30.72 g·plant^-1,followed by OPT-K treatment,respectively 35.32 g·plant^-1,10.71 g·plant^-1,35.93 g·plant^-1;Both OPT-N and OPT-K treatments had greater influence on fruit yield,average weight,fruit size and peel thickness while OPT-P treatment affected the content of total soluble solids?TSS?and solid acid ratio?TSS/TA?more;The soil pH and organic matter content had a elevated trend after OPT-N treatment,yet the content of available nitrogen,phosphorus and potassium were decreased after different treatments,but still in the suitable range of citrus growth;Compared with the 2 times/year of the customary fertilization by farmers,the fertilization frequency was adjusted to 3 times/year,meanwhile the fertilizer ratio was applied according to the citrus nutritional characteristics,the fruit yield was increased by5.80%,and the TSS content,TSS/TA,vitamin C content were increased by 4.06%,15.19%,7.75%,respectively,at the same time,the content of soil available nitrogen and available phosphorus decreased appropriately,and both of available potassium content and the potential pollution risk of nitrogen and phosphorus in farmland decreased.2.Compared with no-nitrogen application,the biomass of the spring and autumn shoots of the blood orange tree and fruit yield were significantly increased,and the absorption of nitrogen,phosphorus and potassium of the spring shoots were also significantly increased,however,the absorption of phosphorus and potassium of the autumn shoots under N1 and N2 treatments were slightly lower than that of N0 treatment;The contents of nitrogen,phosphorus and potassium in the fruit were less different under different treatments,while the nutrient removals decreased significantly under high nitrogen?N4,N5?treatment;With the increase of nitrogen application,the content of soil organic matter had been decreasing while the available nitrogen and the available phosphorus content had been rising,the content of available potassium increased first and then decreased,reached the peak value at N3 treatment,which was 348.96 mg?kg^-1;The comprehensive analysis of nutrient,yield and quality,soil condition and environmental pollution risk showed that the annual pure nitrogen amount of one single tree's application on the 7-year-old Tarocco blood orange in the Three Gorges Reservoir area of Chongqing was suitable ranged from 0.63—0.86 kg,among which the influence of 0.69 kgN·plant^-1was best on yield and quality,and the yield increased average by 44%;Under high nitrogen?N4,N5?treatments,fruit yield,average weight,fruit size,TSS content,TSS/TA,vitamin C and anthocyanin content decreased while TA content and peel thickness increased,the leaching amount of nitrate nitrogen from surface layer?0—20 cm?to deep layer of soil was increased,and the accumulation of ammonium nitrogen in surface layer increased,which increased the potential risk of nitrogen pollution.Correlation analysis showed that the correlation coefficient between nitrogen content in autumn leaves and TA content was 0.493*,and with TSS/TA was-0.568*;the correlation coefficient between available nitrogen content and TA content was 0.635**,and with TSS/TA was-0.719**;At the same time,the nitrogen content in spring and autumn leaves and available nitrogen content had significantly influence on peel thickness,the correlation coefficients were0.568*,0.520*and 0.917**,respectively.3.The application of organic fertilizer had excellent results.On the basis of nitrogen,phosphorus and potassium optimized fertilization?OPT?,the biomass of the branches increased by 10.33%—26.59%,and the nutrient uptake capacity of the branches and fruits was enhanced after the increase of 5 kg of organic fertilizer?OPTa?in each tree.Compared with the FP treatment,the yield,average weight,fruit size increased by 8.30%,9.38%,6.16%,respectively,which increased by 2.36%,9.74%,5.91%respectively compared with the OPT treatment;The color of fruit surface was redder than OPT and FP treatments;After applying organic fertilizer,soil organic matter and available potassium content increased by 20.40%and 40.10%,respectively compared with the FP treatment,the content of available nitrogen and available phosphorus decreased by 21.53%and21.31%,respectively.OPTa treatment reduced the risk of nitrogen and phosphorus pollution under the premise of ensuring yield and quality.4.On the basis of OPTa treatment,the reduction of nitrogen,phosphorus and potassium fertilizer by 25%had no significant difference on all indexes except for the significant decrease of the nitrogen removal amount of fruit and the soil available potassium content;The TSS/TA ratio and color of fruit surface were better than that of OPTa treatment,and the fruit quality was improved;it also increased soil pH and the organic matter content,decreased soil bulk density,and the content of available nitrogen,available phosphorus,available potassium in soil were all within a suitable range of citrus growth.Taken together,it is feasible to reduce the amount of chemical fertilizer by 25%on the basis of adding 5 kg of commercial organic fertilizer to one single 7-year-old Tarocco blood orange tree in the Three Gorges Reservoir area of Chongqing.