Effects Of Soil Species And Nitrogen Application On Yield,Quality And Nitrogen Efficiency Of Sweet Potato

In order to explore the effects of nitrogen application on the growth of sweet potato,photosynthetic and physiological characteristics of stem and leaf,storage root yield and quality,and nitrogen efficiency of different soil species,the most suitable planting species for high yield and high quality cultivation of sweet potato and the scientific management method of nitrogen fertilizer were obtained.Sweet potato varieties Yu Shu198 was used as materials in this experiment.In this experiment,five soil species were set up,which were Calcium purple soil（S1）,Calcareous brown soil（S2）,Calcium purple stone bone soil（S3）,Lime brown purple sand soil（S4）and Calcareous yellow soil（S5）.In this experiment,four nitrogen application levels were set,namely 0（N0）,5（N1）,10（N2）and 15（N3）kg N/667m².The indexes of agronomic characters,leaf photosynthetic physiology and so on were measured in the growth period of sweet potato.It was found that soil species,nitrogen application amount and their interaction effects had significant effects on the growth of sweet potato,photosynthetic physiological characteristics of stem and leaf,storage root yield and quality,and nitrogen efficiency.The main results were as follows:1.The effects on the growth of sweet potatoThe aboveground fresh weight,LAI,root length,projected area,surface area and volume of S2 were all the largest,but the R/T value was the smallest.The average root diameter and root activity were the largest in S5,but the other physical growth indexes and R/T value were the worst.The aboveground biomass of S1 was second only to that of S2,and the R/T value was the largest.S1 is more conducive to the coordination of the abovemention and underground part of the growth of the relationship,promoting the transport of organic matter to the underground part.Nitrogen application significantly increased branch number,longest vine length,overground fresh weight,LAI and root growth of sweet potato.The maximum R/T value was easily obtained at 5 kg N/667m²for Calcium purple soil.In the other four planting species,there was no significant difference in R/T value of each nitrogen application level.2.The effects on the sweet potato stem leaf photosynthetic physiological characteristicNet photosynthetic rate（Pn）,stomatal conductance（Gs）,intercellular CO₂concentration（Ci）,chlorophyll a content,chlorophyll b content,total chlorophyll content,nitrate reductase（NR）and glutamine synthetase（Gs）were all the largest in S1.The photosynthetic capacity and nitrogen metabolism capacity of S1 were the strongest,which was more conducive to promoting the absorption and utilization of organic matter and nitrogen fertilizer.The photosynthetic index,NR and GS activity of S5 were the worst.The other three were somewhere in between.Nitrogen application significantly increased the content of Pn,Gs,Ci,Tr,chlorophyll a,chlorophyll b and total chlorophyll in sweet potato leaves.At the same time,the physiological activities of NR and GS of leaves were also significantly improved,but excessive nitrogen application would lead to a decrease in NR activity of leaves.When different soil species obtained the highest photosynthetic capacity,chlorophyll content and nitrogen metabolism related enzyme activity,the corresponding nitrogen application amount was different.Considering comprehensively,the nitrogen application rate of Calcium purple soil,Calcareous brown soil,Calcium purple stone bone soil,Lime brown purple sand soil and Calcareous yellow soil were 5 kg N/667m²,10 kg N/667m²,10 kg N/667m²,15 kg N/667m² and 5 kg N/667m²,the net photosynthetic rate and chlorophyll content of sweet potato leaves were better,which was more conducive to improving the photosynthetic capacity of the leaves.3.The effect on storage root yieldS1 had the largest yield of fresh potatoes per plant,which was significantly higher than the other four planted soil species.S5 had the lowest yield of fresh potatoes per plant.The yield of fresh potatoes of the other three planted soil species was somewhere in between.Nitrogen application significantly increased the yield of sweet potatoes per plant.The different nitrogen application rates of different planting soils to obtain the best yield of fresh potato per plant were different.Considering comprehensively,the nitrogen application rate of Calcium purple soil,Calcareous brown soil,Calcium purple stone bone soil,Lime brown purple sand soil and Calcareous yellow soil were 5 kg N/667m²,15 kg N/667m²,10 kg N/667m²,15 kg N/667m² and 5 kg N/667m²,the sweet potato yield per plant was the best.4.The effect on the quality of sweet potatoThe root tuber quality was different in different soil types.S3 had the highest root dry rate,starch rate and reducing sugar.S2 had the highest crude protein content.The soluble sugar content in roots of S2,S4 and S5 was relatively high,and the difference was not significant.S4 had the highest soluble protein content in roots.Nitrogen application significantly increased root dry rate,starch rate,soluble protein,and significantly reduced the content of reducing sugar in root.The crude protein content of roots showed an increasing trend and then decreasing trend with the increase of nitrogen application.The nitrogen application rates corresponding to the highest dry matter and starch content obtained by different soil specieswere different.Considering comprehensively,the nitrogen application rates of Calcium purple soil,Calcareous brown soil,Calcium purple stone bone soil,Lime brown purple sand soil and Calcareous yellow soil were 10 kg N/667m²,10 kg N/667m²,15 kg N/667m²,10 kg N/667m² and 5 kg N/667m²,which was more conducive to the accumulation of root dry matter and starch.Then Calcareous yellow soil was more conducive to high yields,and the better the accumulation of root dry matter and starch.5.The effect on nitrogen efficiencyS1 had the highest nitrogen fertilizer agronomic efficiency and nitrogen fertilizer contribution rate,and its nitrogen fertilizer agronomic efficiency was significantly higher than that of the other four planted soil species.The nitrogen fertilizer contribution rate was not significantly different from S3.S5 has the smallest agronomic efficiency of nitrogen fertilizer and contribution rate of nitrogen fertilizer.The agronomic efficiency of nitrogen fertilizer was not significantly different from that of S2,S3 and S4,and the contribution rate of nitrogen fertilizer was not significantly different from that of S2.With the increased of nitrogen application,the partial productivity of root nitrogen fertilizer and the agronomic efficiency of nitrogen fertilizer both showed a decreasing trend,and the N1 level was the best.The nitrogen application rate corresponding to the best nitrogen efficiency of different planting soils was different.Considering comprehensively,Calcium purple soil,Calcium purple stone bone soil,Lime brown purple sand soil and Calcareous yellow soil were respectively 5kg N/667m² and 10 kg N/667m²,15 kg N/667m² and 5 kg N/667m² sweet potato tuber root nitrogen fertilizer agronomic efficiency and nitrogen fertilizer contribution rate performance was better.The nitrogen efficiency of Calcareous brown soil between the different nitrogen application levels of nitrogen efficiency was not significant.6.Correlation analysis showed thatThe yield of sweet potato per plant was significantly positively correlated with Gs of leaves and partial productivity of tuberous nitrogen fertilizer（r=0.45*,0.58*）,and significantly positively correlated with agronomic efficiency of tuberous nitrogen fertilizer and contribution rate of tuberous nitrogen fertilizer（r=0.73**,0.89**）.The number of sweet potato per plant was positively correlated with the contribution rate of root nitrogen fertilizer（r=0.59*）.There was a significant positive correlation between the number of commercial potato per plant and the agronomic efficiency of Pn,Gs and root nitrogen fertilizer（r=0.46*,0.44*,0.50*）,and the contribution rate of root nitrogen fertilizer（r=0.69**）.