| Sugar beet is an important sugar crop in China,and has strong tolerance to saline-alkali stress.Therefore,it is very important for sugar beet planting in saline-alkali land to develop and utilize salt-alkali land.Sugar beet has the greatest demand for nitrogen,and it has the characteristics of large amount of fertilizer demand,strong ability to absorb fertilizer and long time of absorption.It is found in recent years that biochar not only has obvious effect on soil physical and chemical properties improvement,but also has the function of slow-release fertilizer.Therefore,the effects of combined application of biochar and nitrogen fertilizer on the soil environment and growth of sugar beet under saline-alkali stress were studied.It not only benefits the improvement and development of saline-alkali land in the future,but also lays a foundation for further research on the interaction between biochar and fertilizer.In this experiment,the sugar beet variety KWS0143 was used as the test material.Carry out the pot planting test.Set up seven treatments,which were normal soil(CK),saline-alkali treatment(Alk),saline-alkali treatment plus biochar(N180),applying biochar under salt-alkali stress and reducing nitrogen fertilizer by 10%,20%,30%,40%(N162,N144,N126,N108).Among them,three treatments of CK,Alk and N180 were normal nitrogen application(180 kg/ha nitrogen application).Saline-alkali treatment with neutral and alkaline salts in a ratio of 2:1 to the soil.Make Na+ content 3g/kg.The ratio of alkaline salt Na2CO3 and Na HCO3 is 1:2;the ratio of neutral salt Na Cl and Na SO4 is 1:2.The application rate of biochar is3% of the dry weight of soil.After treatment,the soil alkalinity(ESP)was 32.6%,the salt content was 0.39g/kg,and the conductivity(EC)was 781?S/cm,p H 9.14.Research the combined application of biochar and nitrogen fertilizer on the basic physical and chemical properties,rhizosphere microorganism quantity,soil enzyme activity,soil available nitrogen content under saline-alkali,sugar beet seedling emergence rate,dry mass,photosynthetic characteristics,yield,sugar production and quality and key enzyme activity of nitrogen inorganic metabolism.The research results are as follows:(1)After adding biochar,the conductivity and bulk density of the saline-alkali soil were significantly decreased(p<0.05),soil porosity and available nitrogen content increasedsignificantly(p<0.05),but the soil p H did not change significantly.With the decrease of nitrogen application rate,the physical and chemical properties of soil did not change obviously,but the soil available nitrogen showed a decreasing trend.With the decrease of nitrogen fertilizer application,the number of bacteria and actinomycetes in soil decreased with the decrease of nitrogen application,while the number of fungi increased first and then decreased.There was no significant difference in the number of bacteria and fungi between the treatment without reduction in nitrogen fertilizer(N180)and the application of reducing nitrogen fertilizer 10%(N162).There was no significant difference in the number of actinomycetes between the application of reducing nitrogen fertilizer 10%(N162)and compared with the control(CK).Soil urease and invertase activity increased first and then decreased with the decrease of nitrogen application rate.The enzyme activity was the highest when the amount of nitrogen fertilizer was reduced by 10%(N162),and it was significantly higher than the treatment without reduction in nitrogen fertilizer(N180)or no significant difference between the two treatments.Catalase activity showed the opposite trend.The difference in phosphatase activity between the treatments to which the biochar was applied was not significant and the difference from the control(CK)was not significantly or significantly higher than the control(CK)treatment.Correlation analysis shows that the number of bacteria,the number of fungi,urease activity,and invertase activity are highly positively correlated with each other.The number of actinomycetes was only significantly positively correlated with catalase activity and negatively or significantly negatively correlated with the other three soil enzymes.The amount of catalase in the rhizosphere soil was significantly or very significantly negatively correlated with the number of bacteria,the number of fungi,urease and invertase activities.(2)The seedling rate of sugar beet under saline-alkali stress was significantly increased(p<0.05),but there was no significant difference among the treatments with different nitrogen rates.After applying biochar,the dry weight of leaves and roots of sugarbeet increased significantly(p<0.05),the amount of nitrogen applied decreased and the dry weight decreased,and the application rate of nitrogen fertilizer decreased by 20%(N144),which was still significantly higher than that of(Alk).(3)Under saline-alkali stress the chlorophyll content,Fv/Fm,Y(?),ETR,q L,photosynthetic rate,stomatal conductance and Ru BP carboxylase activity of sugar beet leaves were significantly increased(p<0.05),NPQ decreased significantly(p<0.05).Chlorophyll content,Fv/Fm,Y(?),ETR,q L,photosynthetic rate,stomatal conductance and Ru BP carboxylase activity decreased with the decrease of nitrogen application.There was no significant difference in chlorophyll content,Y(?)and photosynthetic rate between the treatment without reduction in nitrogen fertilizer(N180)and the application of reducing nitrogen fertilizer 10%(N162).There was no significant difference in Fv/Fm between the two treatments only in the mid-reproductive period.The leaf NR and GS showed a decreasing trend with the decrease of nitrogen application rate.The effect of nitrogenapplication rate on NR activity and GOGAT activity was significant at the early stage of sugar beet growth,but there was no significant effect on GS activity.The application of reducing nitrogen fertilizer 20%(N144)made the activity of GOGAT was significantly higher than that of control(CK),the activity of GS was not significantly different from the treatment without reduction in nitrogen fertilizer(N180).(4)After application of biochar by saline-alkali stress,the yield,sugar content and sugar yield of sugar beet increased significantly(p<0.05).And it decreased with the decrease of nitrogen fertilizer application rate.When the nitrogen application rate was reduced by 10%(N162),the difference between sugar beet root yield and sugar production was not significantly different from the treatment without reduction in nitrogen fertilizer(N180).The sugar content of beet roots was not significantly different from the treatment without reduction in nitrogen fertilizer(N180)when nitrogen application rate was reduced by 20%(N144).The harmful nitrogen in sugar beet tuber root decreased significantly after biochar was applied(p<0.05).The content of amino acid and protein increased at first and then decreased with the decrease of nitrogen application.The content of nitrate decreased with the decrease of nitrogen application rate,and betaine and nitrate showed the opposite trend.However,the contents of four kinds of harmful nitrogen in all treatments were significantly lower than those in saline-alkali treatment(p<0.05).The correlation analysis showed that the root yield,sugar content and sugar yield of sugar beet were very significant positive correlation with each other.There was a significant negative correlation between betaine content and yield,sugar content and sugar production.Combined with the yield,sugar yield and quality of sugar beet root,the application of biochar in saline-alkali soil could reduce the application of nitrogen fertilizer by 10%. |
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