| Water and nitrogen as important limiting factors affecting crop growth under highly intensive plant production conditions,are also research hotspot in recent years,scientific and reasonable irrigation and nitrogen regulation is of great significance to improve the water and nitrogen use efficiency and explore soil nitrogen supply potential in greenhouse.To study the relationships of greenhouse soil organic nitrogen fractions,soil-retained nitrogen pools(soil microbial biomass nitrogen,fixed ammonium,and soil-retained nitrogen),soil-soluble nitrogen pools(soil mineral nitrogen,soluble organic nitrogen and total soluble nitrogen)and tomato yield and qulity under irrigation and nitrogen fertilization regulations,the tomato field experiment with mulch-film drip irrigation was conducted with different nitrogen application rate(low nitrogen,N1,75 kg N·ha-1;medium nitrogen,N2,300 kg N·ha-1;high nitrogen,N3,525 kg N·ha-1)and irrigation lower limit(high irrigation amount,W1,25 k Pa;medium irrigation amount,W2,35 k Pa;low irrigation amount,W3,45 k Pa).The main findings are as follows:(1)Soil organic nitrogen was main in the form of acidolyzable nitrogen(AHN)in greenhouse.Apart from few soil layers,effects of irrigation and nitrogen fertilization and their interactions on the greenhouse soil total nitrogen(Ntotal),soil organic nitrogen fractions,soilsoluble nitrogen pools(soil mineral nitrogen,soluble organic nitrogen and total soluble nitrogen)and soil-retained nitrogen pools(soil microbial biomass nitrogen,fixed ammonium,and soilretained nitrogen)were extremely significant(P<0.01).(2)In general,the contents of greenhouse soil organic nitrogen fractions,soil-soluble nitrogen pools(soil mineral nitrogen,soluble organic nitrogen and total soluble nitrogen)and soil-retained nitrogen pools(soil microbial biomass nitrogen,fixed ammonium,and soil-retained nitrogen)decreased with the increase of soil depths.(3)On the whole,the order of the contents and distribution proportions of greenhouse soil organic nitrogen fractions to total acidolyzable nitrogen was acidolyzable amino acid nitrogen(AAN)/ acidolyzable ammonia nitrogen(AN)> acidolyzable unknown nitrogen(UN)> acidolyzable amino sugar nitrogen(ASN).AAN and AN were the most important forms of soil organic nitrogen fractions in greenhouse soils.And AAN had a very significant positive correlation with AN,ASN,AHN,non-acidolyzable nitrogen(NHN),soil organic carbon(SOC)and Ntotal(P<0.01).(4)Fixed ammonium(FA)was the main component of soil-retained nitrogen pools in greenhouse soil,and soil mineral nitrogen(SMN)was the main component of soil-soluble nitrogen pools in greenhouse soil.The results of correlation analysis showed that soil-retained nitrogen(SRN)was significantly correlated with AN,ASN,Ntotal and soil microbial biomass nitrogen(SMBN),meanwhile,extremely correlated with FA.And the results of regression analysis showed that there was a very significant positive correlation between SMBN and AN,AAN,and there was a significant positive correlation with ASN in greenhouse soil,meanwhile,FA was positively correlated with AN and AAN in greenhouse soil.Ntotal,SOC and nitrate nitrogen(NO3--N)were the best variables for explaining the changes of soil organic nitrogen fractions as affected by irrigation and nitrogen fertilization.There was a highly significant positive correlation between SMN,NO3--N and AN,meanwhile,a significant positive correlation with AHN.Ammonium nitrogen(NH4+-N)was very significantly positively correlated with AN and AHN.However,there was no significant correlation between soil soluble organic nitrogen(SON)and soil organic nitrogen fractions in greenhouse soil.(5)The single effects of irrigation and nitrogen fertilization on tomato yield and its composition reached extremely significant levels,but the interactions just reached a significant level.Except that irrigation had a significant effect on soluble sugar content in tomato fruit,the effects of irrigation and nitrogen fertilization and their interactions on tomato quality indices(soluble sugar,organic acid,sugar-acid ratio,vitamin C and nitrate)were extremely significant.The correlations between tomato quality index and soil organic nitrogen fractions generally were not significant.In summary,greenhouse soil organic nitrogen fractions are closely related to soil-soluble nitrogen pools and soil-retained nitrogen pools under different irrigation and nitrogen regulations.AAN,AN,SMN and FA could be used as indicators of soil nitrogen supply capacity in greenhouse soil.Considering from the view of improving soil nitrogen supply capacity,it was concluded that the best schedule to be used in greenhouse were the W2N2 treatment(35 k Pa and 300 kg N·ha-1).But considering from the view of water-saving and nitrogen reduction,W2N1 treatment(35k Pa-75 kg N·ha-1)could be used as the optimizing schedule in greenhouse. |
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